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Ingeniería de Cerámicas para Medioambientes Agresivos

Broad objectives:
Development of a new generation of advanced ceramics that can withstand extreme environments, The effective immobilization of the industrial wastes
Specific objectives:
Develop processing routes for silicon carbide-based ceramics to customize its properties aimed to specific application such as resistive elements, high temp./ abrasion resistant parts, medical implants
Specific advantages
Pioneer laboratory at international scale in the development of bioinspired SiC-based ceramics and tailoring of its properties, Strong expertise in the study of mechanical behaviour and microstructure in ceramics and the study of lamellar silicates and functional mesoporous materials, Strong industrial interaction as driving force of the research orientation

Catedráticos
Nombre Teléfono email web
Castro Arroyo, Miguel Angel 954 48 95 46 macastro@us.es sisius
Jiménez Melendo, Manuel 954 55 97 36 melendo@us.es sisius
Malet Maenner, María del Pilar 954 48 95 27 malet@us.es sisius
Martínez Fernández, Julián 954 55 28 94 martinez@us.es sisius
Ramírez de Arellano-López, Antonio 954 55 97 32 aral@us.es sisius
Científicos Titulares
Nombre Teléfono email web
Alba Carranza, María Dolores 954 48 95 46 alba@icmse.csic.es mdol
Benítez Jiménez, José Jesús 954 48 95 51 benitez@icmse.csic.es
Profesores Titulares
Nombre Teléfono email web
Bravo León, Alfonso 954 55 09 37 albravo@us.es sisius
Clauss Klamp, Caroline Maria 954 55 09 41 clauss@us.es sisius
Investigadores/Doctores Contratados
Nombre Teléfono email web
Cruz Carrillo, Miguel Antonio 954 48 95 00 + ext. 90 92 14 miguel.cruz@icmse.csic.es
Pavón González, Esperanza epavon@icmse.csic.es
Ramírez Rico, Joaquín jrr@us.es sisius
Becarios Predoctorales
Nombre Teléfono email web
Cabezas Rodríguez, Rafael rcabezasrodriguez@gmail.com
Orihuela Espina, María del Pilar
Osuna Barroso, Francisco Javier 954 48 95 00 + ext. 90 92 14 francisco.osuna@icmse.csic.es
Personal Contratado
Nombre Teléfono email web
Gómez Martín, Aurora agomez28@us.es

Nuevo concepto de caldera de biomasa basada en materiales biocerámicos y combustión porosa para operación eficiente con residuos



Investigador Principal: Joaquín Ramírez Rico
Periodo: 30-12-2016 / 29-12-2019
Organismo Financiador: Ministerio de Economía y Competitividad
Código: MAT2016-76526-R
Componentes: Julián Martínez Fernández, Manuel Jiménez Melendo

Resumen [+]

En la Unión Europea se generan anualmente más de cinco toneladas de residuos por personas, siendo aproximadamente el 60% de esta cantidad materia orgánica. La tecnología de las calderas de biomasa actuales no permiten el uso de estos residuos funcionando con altos valores de eficiencia, bajas emisiones y alta fiabilidadad de operación, siendo especialmente relevante en calderas de pequeño tamaño.

El principal objetivo de este proyecto es desarrollar un nuevo concepto de tecnología para calderas de biomasa doméstica capaz de operar con gran variedad de mezclas de biomasas y residuos agrícolas.  Para ello se aprovecharán las sinergias de la integración de investigadores del: i) Grupo Maquinas y Motores Térmicos, GMTS, especialistas en combustión, calderas y máquinas térmicas ii) Grupo Materiales Biomiméticos y Multifuncionales, MBM, especialistas en la obtención de cerámicos porosos bioderivados, así como en caracterización físico-química y microestructural. El proyecto se completa con la colaboración de empresas en la evaluación de la tecnología y su aplicabilidad industrial En la Unión Europea se generan anualmente más de cinco toneladas de residuos por personas, siendo aproximadamente el 60% de esta cantidad materia orgánica. La tecnología de las calderas de biomasa actuales no permiten el uso de estos residuos funcionando con altos valores de eficiencia, bajas emisiones y alta fiabilidadad de operación, siendo especialmente relevante en calderas de pequeño tamaño.

El principal objetivo de este proyecto es desarrollar un nuevo concepto de tecnología para calderas de biomasa doméstica capaz de operar con gran variedad de mezclas de biomasas y residuos agrícolas.  Para ello se aprovecharán las sinergias de la integración de investigadores del: i) Grupo Maquinas y Motores Térmicos, GMTS, especialistas en combustión, calderas y máquinas térmicas ii) Grupo Materiales Biomiméticos y Multifuncionales, MBM, especialistas en la obtención de cerámicos porosos bioderivados, así como en caracterización físico-química y microestructural. El proyecto se completa con la colaboración de empresas en la evaluación de la tecnología y su aplicabilidad industrial

El proyecto se basa en la innovadora integración de material biocerámico microporoso en las cámaras de combustión de calderas de biomasa de modo que actúen con diferentes funciones: combustor microporoso, filtro de partículas y recuperador de calor. Estas funcionalidades  pueden ser simultáneas, en función de la región del flujo en que se encuentren y el rango de temperaturas de esa región. Este material biocerámico es desarrollado a partir de precursores vegetales para obtener elementos de Carburo de Silicio (SiC). Para ello se usan materiales locales sin tratar, produciendo elementos hechos a medida con propiedades microestructurales adecuadas para trabajar con altas temperaturas. Así, productos con geometrias complejas pueden ser obtenidos con relativamente bajo coste comparados con otros materiales con características macánicas y químicas similares. La integración de componentes basados en estos materiales posibilita nuevos diseños de calderas de biomasa con un alto control de la combustión, las temperaturas y la emisión de partículas. El nuevo diseño evita la sinterización y fusión de las cenizas, actuando en la formación y evolución de contaminantes, inhibiendo los mecanismos de producción de dioxinas y activando la completa oxidación del monóxido de carbono (CO) y soots. El nuevo concepto permitirá la operación con una importante varieda de mezclas biomasa/ residuos agrícolas con bajas emisiones aun cuando el combustible pesente un alto contenido de cenizas, resolviendo el principal reto para el desarrollo del uso residuos agrícolas en calderas de biomasa (especialmente las de menor tamaño). El desarrollo de esta tecnología permitirá ampliar los recursos de la Unión Europea para calefacción de uso doméstico. En la actualidad este uso supone un 30% del consumo energético total en la misma. La propuesta incluye el estudio de los procesos básicos de combustión, flujos, fabricación a medida de las matrices de materiales biocerámicos, así como estudio y desarrollo de prototipos de componentes y del sistema final. Estos serán estudiados a nivel de ensayos de laboratorio con residuos agrícolas, forestales y de la industria olivarera.


Bases genéticas de la composición y propiedades biofísicas de la cutícula del fruto del tomate. Aprovechamiento de la variabilidad natural



Investigador Principal: Fafael Fernández Muñoz (IHSM)
Periodo: 01-01-2016 / 31-12-2018
Organismo Financiador: Ministerio de Economía y Competitividad
Código: AGL2015-65246-R
Componentes: José Jesús Benítez, Fernando Gallardo Alba (UMA), Antonio Heredia Bayona (IHSM)

Resumen [+]

La producción de frutos de gran calidad y valor añadido es uno de los retos importantes de la agricultura. La cutícula que cubre el exterior de las células epidérmicas juega un papel crucial en la calidad del fruto de tomate, concretamente en su apariencia externa (color, brillo, textura, uniformidad), en el origen y desarrollo de fisiopatías de gran importancia económica como el agrietado, además de en el mantenimiento del estado hídrico de los frutos durante la postcosecha. En proyectos anteriores (AGL2006-12494, AGL2009-12134 y AGL2012-32613), de los que éste puede considerarse una continuación, se puso de manifiesto el importante papel que juega la cutícula en el agrietado y cómo cambios en las propiedades biomecánicas de la misma repercuten en la incidencia de esta fisiopatía. De igual manera, el estudio de los flavonoides presentes en la cutícula que le proporcionan su especial coloración en estadios maduros permitió identificar el papel que éstos juegan como reguladores de la síntesis de cutícula y en su permeabilidad al agua. En este proyecto se empleará una población de líneas recombinantes puras (RIL) y una población de líneas de introgresión (IL) de un cruzamiento S. lycopersicum x S. pimpinellifolium para la validación e identificación de QTLs y genes candidatos involucrados en la deposición de los distintos componentes de la cutícula (ceras, cutina, flavonoides, polisacáridos) y la localización de QTLs/regiones genómicas asociadas a otros caracteres de cutícula como el grosor y densidad que hasta el momento no han sido estudiados. Este abordaje multidisciplinar, que incluye el análisis biofísico de las cutículas, permitirá el diseño de variedades de fruto de tomate con propiedades biomecánicas e hidrodinámicas que reduzcan la incidencia del agrietado, que mantengan el estatus hídrico del fruto durante la postcosecha y que eviten caracteres gustativos de la piel poco deseables para el consumidor. Finalmente, se estudiará una colección de entradas de todas las especies silvestres de tomate que ahondará en el conocimiento de cómo ha evolucionado la cutícula y sus componentes en el taxon Lycopersicon. Este análisis evolutivo permitirá la identificación de diferentes tipos morfológicos de cutículas y de diversas combinaciones de sus componentes que serán útiles para el aumento de la variabilidad disponible en los futuros programas de mejora genética para la obtención de variedades de tomate de calidad. 


Tratamiento sostenible de residuos industriales: Materiales adsorbentes de diseño y bionanocomposites en la inmovilization de metales pesados y productos de fision



Investigador Principal: Maria Dolores Alba Carranza
Periodo: 01-01-2016 / 31-12-2018
Organismo Financiador: Ministerio de Economía y Competitividad
Código: MAT2015-63929-R
Componentes: Miguel Angel Castro Arroyo, Ana Carmen Perdigón Aller, María del Mar Orta Cuevas

Resumen [+]

El Proyecto de investigación que se presenta aborda la exigencia tecnológica y medioambiental de desarrollar metodologías avanzadas para la eliminación de agentes contaminantes. El interés y los esfuerzos encaminados al desarrollo de nuevas tecnologías orientadas a tratamientos más eficientes en la inmovilización y revalorización de los residuos peligrosos es creciente en los planes de I+D+i. El objetivo central del proyecto se basa en el diseño de una estrategia de funcionalización de silicatos laminares de alta carga expansibles y en la síntesis de bionanocomposites a partir de ellos para conseguir una actividad eficaz respecto de la inmovilización de residuos tóxicos y peligrosos, catiónicos y aniónicos. Este objetivo es un cambio cualitativo en el trabajo que se viene desarrollando en el diseño de sistemas modelos adsorbentes con aplicaciones medioambientales de clara repercusión en la mejora de la calidad de vida de la población y conservación del medioambiente, ya que la funcionalización de diseño de los silicatos sintéticos permitirá la adsorción de un amplio abanico de adsorbentes en estado de oxidación aniónico-catiónico. La finalidad y objetivos del proyecto se centran en la Focus Area WASTE de H2020 y esta Focus Area se desarrolla dentro del reto 2 y 5 de H2020 y dentro del Reto 5 y 3 de los Planes Estatales de Investigación.

El proyecto ha despertado el interés de diversas empresas observadoras, EPOs, (ENRESA  y la Agencia de la Energía y para la Sostenibilidad del Ayuntamiento de Sevilla ) impulsando la colaboración público-privada. Por tanto, la investigación desarrollada auna los principios básicos de la estrategia estatal de Ciencia y Tecnología: Poner la I+D+I al servicio de la ciudadanía, del bienestar social y de un desarrollo sostenible, hacer de la I+D+I un factor de mejora de la competitividad empresarial (transferencia de los resultados al sector privado, ver interes de los EPOs) y reconocer y promover la I+D como un elemento esencial para la generación de nuevos conocimientos de excelencia.

La viabilidad de la propuesta se garantiza porque el equipo de investigación, EI, por un lado, ha desarrollado con éxito la síntesis de silicatos laminares hidratables de alta carga, a través de un método novedoso que permite ajustar la carga deseada para el material, y, por otro, ha conseguido exitosamente su organofuncionalización (patente ES2362597B1). Además, ha desarrollado la metodología necesaria para el correcto progreso de este proyecto, en estrecha colaboración con otros Grupos de investigación internacionales de reconocido prestigio (e.g. CNRS-Universidad de Lille, Universidad de Cambridge...). Además el EI ha demostrado que potencia la agrupación de las capacidades y competencias científico-técnicas esenciales para abordar esta propuesta de marcado caracter transversal.

 


Estudio del mecanismo de adsorción de contaminantes aniónicos peligrosos por aluminosilicatos de diseño



Investigador Principal: Esperanza Pavón González
Periodo: 01-02-2015 / 28-02-2017
Organismo Financiador: Junta de Andalucía
Código: TAHUB-082. Programa Talent HUB
Componentes:

Resumen [+]

El desarrollo científico, tecnológico e industrial en la últimas décadas del siglo pasado ha causado un incremento en la contaminación del medio ambiente. Debido a ello, la comunidad internacional reconoce la necesidad de desarrollar nuevas tecnologías y estrategias para el control de la contaminación. El objective principal de este Proyecto cumple con este propósito: el diseño de silicatos laminares expansibles de alta carga y su posterior modificación superficial para que se conviertan en materiales adecuados para la retención e inmobilización de contaminantes tóxicos aniónicos.
La metodología del Proyecto se basas en la síntesis de micas de alta carga expansibles con sustituciones isomórficas de Si+4 por Al+3 y con una densidad de carga en el rango de las micas frágiles pero con una capacidad de intercambio e hinchamiento inusuales en estos materiales. Para potenciar su capacidad de adsorción, la superficie de estos materiales se funcionalizará con magnetica por un lado y con la inclusion de cationes de alquilamonio, por otro.
Además, se establecerá un protocolo de inmobilizacion de productos aniónicos altamente tóxicos como son AsO42-, SO42-, en función de la estructura y la funcionalización de las micas de alta carga expansibles. Más tarde, la aplicabilidad de estas reacciones de adsorción se comprobará en suelos reales contaminados de Chile y España.


Desarrollo de procesos de combustión catalítica de hidrógeno y estudio de su integración en dispositivos para aplicaciones portátiles



Investigador Principal: Asunción Fernández Camacho
Periodo: 16-05-2014 / 15-05-2016
Organismo Financiador: Junta de Andalucía
Código: P12-TEp-862
Componentes: Julián Martínez, Gisela Arzac, Dirk Hufschmidt, Joaquín Ramírez, M.Carmen Vera, Vanda Godinho, Lionel Cervera, T.Cristina Rojas, Olga Montes, Mariana Paladini, Jaime Caballero-Hernández

Resumen [+]

El hidrógeno como vector de transporte y almacenamiento de energía es un candidato muy atractivo en el contexto de un mayor uso de las energías renovables y limpias. La producción y el uso de la energía basada en la tecnología del hidrógeno es de especial relevancia en pequeña escala para aplicaciones portátiles (y potencialmente escalable para aplicaciones estacionarias). En el presente proyecto se abordará el estudio del proceso de combustión catalítica o controlada de hidrógeno en los distintos aspectos que puedan conducir a una configuración final integrada con un sistema de generación de H2 en aplicaciones portátiles. Para ello se aprovecharán las sinergias integrando investigadores de dos grupos del PAI: i) Del grupo TEP217, especialistas en almacenamiento y generación de hidrógeno en sistemas basados en hidruros metálicos, hidruros complejos y composites de hidruros reactivos; así como en el uso de catalizadores y aditivos para controlar y mejorar las cinéticas de estos procesos. ii) Del grupo FQM342, especialistas en la obtención de cerámicos porosos de alto interés como soportes de catalizadores en entornos agresivos de combustión. Además la colaboración se completa con la participación de la empresa Abengoa Hidrógeno S.A. que participa en calidad de subcontratada como especialistas en sistemas de producción y almacenamiento de hidrógeno.
En particular se trabajará en este proyecto en las siguientes líneas de actuación:
1.- Desarrollo de catalizadores y soportes para la combustión controlada. Típicamente cerámicas porosas biomórficas de carburo de silicio y catalizadores clásicos tipo metal noble y nuevos catalizadores de bajo coste a desarrollar en el proyecto.
2.- Desarrollo de los reactores necesarios para el estudio de la combustión controlada. Típicamente para flujos de hidrógeno de unos pocos ml/min y para la escala de un generador de H2 ya disponible de 0.5 a 1.5 L/min.
3.- Acoplamiento al sistema de combustión controlada de los sistemas portátiles de generación de hidrógeno que hemos desarrollado en proyectos anteriores.
4.- Aplicación de la tecnología de pulverización catódica de una manera exploratoria en este proyecto para depositar los catalizadores de combustión catalítica en sustratos porosos.
5.- Caracterización microestructural y química de los soportes y catalizadores en la nanoescala para seguir los procedimientos de síntesis y evolución en operación.
 


Estudio de la inmovilización de metales pesados por micas de alta carga sintéticas organofuncionalizadas: pruebas a escala de laboratorio



Investigador Principal: María Dolores Alba Carranza
Periodo: 16-05-2014 / 16-02-2019
Organismo Financiador: Junta de Andalucía
Código: P12-FQM-567
Componentes:

Resumen [+]

El tema central del proyecto aborda la exigencia tecnológica mediambiental de desarrollar metodologías avanzadas para la eliminación de agentes contaminantes. El interés y los esfuerzos encaminados al desarrollo de nuevas tecnologías orientadas a tratamientos más eficientes en la inmovilización y revalorización de los residuos peligrosos es crecientes en los planes de I + D + i de los últimos años. Es en este escenario donde debe encuadrarse el presente proyecto y en concreto en el marco de la gestión de cationes de metales pesados, tema de elevado interés social en la presente década.

Desde la segunda mitad del siglo XX la Humanidad se ha enfrentado a un enorme desarrollo científico y tecnológico que es el responsable de un incremento de la contaminación mediambiental. Como ejemplo podemos mencionar dos problemas que en la actualidad son motivos de preocupación y actuación de la Junta de Andalucía: contaminación de los litorales andaluces y las aguas residuales urbanas. Por tanto, estamos ante un problema complejo en el que los agentes contaminantes son variados, las fuentes de procedencia son diversas y las vías o rutas seguidas por los distintos contaminantes, frecuentemente, escapan al control necesario para evitar efectos indeseados sobre el entorno natural y urbano. Es por ello, que se demanda una investigación a nivel básico y aplicado de los mecanismos necesarios para la inmovilización de dichos cationes nocivos.

Los objetivos y alcance de este proyecto se basan en los avances llevados a cabos por otros grupos de investigación de la gestión de estos tipos de contaminantes y en los últimos resultados de la investigación llevada a cabo por el equipo de investigación que han permitido el diseño de silicatos laminares expansibles de alta carga con especiales propiedades como precursores para la retención de residuos nocivos. Por tanto, se propone en este proyecto la organofuncionalización de dichas micas sintéticas con grupos tioles o con cationes de alquilamonio de longitud de cadena variable y la evaluación de su capacidad de adsorción y retención irreversible de metales pesados.


Filtros Bio-cerámicos para partículas en motores diesel



Investigador Principal: Julián Martínez Fernández / Ricado Chacartegui
Periodo: 01-01-2014 / 31-12-2016
Organismo Financiador: Ministerio de Economía y Competitividad
Código: MAT2013-41233-R (Programa Retos)
Componentes: José Antonio Becerra Villanueva, Alfonso Bravo León, Manuel Jiménez Melendo, Antonio Ramírez de Arellano López, Joaquín Ramirez Rico, Francisco Varela Feria

Resumen [+]

La importancia del control de las emisiones de partículas en  motores diésel es fundamental dados el  volumen global  de los mismos y el impacto medioambiental y económico asociado. Los sistemas de control de partículas basados en modificaciones del proceso de combustión en el motor no son suficientes para alcanzar las exigencias normativas actuales, y menos las futuras, y por tanto necesariamente hay que emplear sistemas de postratamiento como los filtros. Existe un amplio margen de mejora de los mismos tanto en fiabilidad, control de la degradación de prestaciones, durabilidad, operación multicombustible y reducción de costes.

En el presente proyecto se abordará el desarrollo y fabricación de un filtro de partículas regenerativo en motores diésel que mejore las especificaciones de los sistemas actuales, basado en una nueva generación de materiales cerámicos bioderivados, y que integre sistemas para la combustión de partículas. Para ello se aprovecharán las sinergias integrando investigadores del: i) Grupo Maquinas y Motores Térmicos, GMTS, especialistas en motores de combustión interna ii) Grupo Materiales Biomiméticos y Multifuncionales, MBM, especialistas en la obtención de cerámicos porosos bioderivados, así como en caracterización físico-química y microestructural. El proyecto se completa con la colaboración de empresas en la evaluación de la tecnología y su aplicabilidad industrial.

Se trabajará en las siguientes líneas:

-Determinación de rutas de procesado para el desarrollo de elementos filtrantes con propiedades físico‐químicas idóneas, en base a los conocimientos previos en materiales bioderivados y nuevas tecnologías relativas al uso de geles de SiO2.
-Determinación de catalizadores idóneos y sistemas para su deposición.
-Fabricación de los elementos filtrantes constituidos de soporte poroso más catalizador.
-Caracterización exhaustiva de las propiedades microstructurales y físico-químicas de interés para la aplicación.
-Desarrollo de sistemas de activación para la regeneración del filtro.
-Diseño y fabricación de los filtros con geometría idónea y dimensiones prototipo.
-Diseño de la unidad piloto y estudio de la integración y operación sobre el motor de referencia.
-Diseño final del filtro para su instalación industrial.

Estudios previos desarrollados por MBM en estos materiales bioderivados han demostrado su potencialidad como elementos filtrantes de gas a altas temperaturas en plantas de gasificación de carbón, lo que avala el éxito de este proyecto, que abordará las mejoras necesarias para desarrollar la tecnología en las condiciones de combustión de los motores diésel, bajo condiciones dinámicas en vehículos y filtros regenerativos.

Una reducción de contaminantes en las emisiones de los motores diésel tendría un gran impacto medioambiental, para la salud y económico, debido a los cerca de 100 millones de vehículos diésel circulando en Europa y una industria vinculada con más de 2 millones de empleos directos y tendencia creciente en el mercado. Este proyecto aborda el Reto Social 3 del Horizonte 2020, Energía segura, limpia y eficiente. Además el uso de materiales biocerámicos permite la sustitución de los elementos metálicos empleados en la actualidad, por lo que también se alinea  con el Reto Social 5 del Horizonte 2020 en la búsqueda de alternativas a las materias primas esenciales en aplicaciones ya existentes reduciendo la dependencia de importaciones y sostenibilidad de las aplicaciones.


Obtención de bioplásticos tipo polihidroxialcanoato (PHA) de cadena larga a partir de desechos de epidermis de frutos comerciales



Investigador Principal: José Jesús Benítez Jiménez
Periodo: 16-05-2013 / 15-05-2015
Organismo Financiador: Junta de Andalucía
Código: P11-TEP-7418 (Proyecto de Excelencia)
Componentes: Antonio Heredia Bayona, Miguel Angel San Miguel Barrera, Jaime Oviedo López, J. Alejandro Heredia Guerrero, Santiago Domínguez Meister, Daniel Aguilera Puerto, Francisco Javier Navas Martos, José Manuel de la Torre Ramírez

Resumen [+]

El presente proyecto de investigación tiene por objeto el estudio de la viabilidad de la implementación de un proceso a escala planta piloto que permita obtener un material bioplástico a partir de una materia prima asequible y de bajo coste como son los desechos de pieles (epidermis) de frutos. La oportunidad de la propuesta parte de proponer un nuevo tipo de material polimérico completamente inocuo, biodegradable y ecológico como sustituto de plásticos tradicionales obtenidos a partir del petróleo que conllevan un serio problema medioambiental, tanto en su producción industrial como en su posterior desecho. Por otro lado, el concepto de sostenibilidad medioambiental se extiende no sólo a la biodegradabilidad del producto final y al bajo impacto del proceso de producción propuesto, también a su obtención a partir de un recurso vegetal que no se retrae de la cadena alimenticia animal y humana, como es el caso de los bioplásticos que se vienen fabricando actualmente a partir de maíz o patata. Por otro lado, y en nuestro ámbito territorial andaluz, la materia prima es especialmente accesible dado el volumen de la actividad agroalimentaria. En este mismo sentido, el nuevo bioplástico podría paliar un importante problema de eliminación de residuos plásticos en explotaciones agrarias ya que se concibe como plenamente compostable y, por tanto, capaz de generar biomasa asimilable por la siguiente generación de plantas. El producto propuesto viene, además, a completar la gama de polihidroxialcanoatos (PHA) a los miembros de la serie obtenidos a partir de polihidroxiácidos de cadena larga. Las propiedades singulares de esta nueva familia puede ser un buen complemento de los ya conocidos y podría dar lugar a aplicaciones novedosas y de mayor valor añadido.


Inmovilización de cationes en un espacio confinado de alta densidad de carga: gestión de residuos peligrosos



Investigador Principal: María Dolores Alba Carranza
Periodo: 01-01-2011 / 31-12-2013
Organismo Financiador: Ministerio de Ciencia e Innovación
Código: CTQ2010-14874/BQU
Componentes: Miguel Angel Castro Arroyo, Maria del Mar Orta Cuevas, Mery Carolina Pazos Zarama, Said ElMrabet, Esperanza Pavón González, Maria Villa Alfageme, Santiago Medina Carrasco, Ana Isabel Becerro Nieto, Alberto José Fernández Carrión

Resumen [+]

El tema central del Proyecto aborda la exigencia tecnológica medioambiental de desa-rrollar metodologías avanzadas para la eliminación de agentes contaminantes. El interés y los esfuerzos encaminados al desarrollo de nuevas tecnologías orientadas a tratamientos más eficientes en la inmovilización y revalorización de los residuos peligrosos es crecientes en los planes de I + D + i de los últimos años. Es en este escenario donde debe encuadrarse la presente propuesta, circunscrita en dos hallazgos básicos experimentales: el diseño de silicatos laminares expansibles de alta carga con una distribución controlada de sus centros activos que le confieren especiales propiedades como precursores para el diseño de materiales eficaces en cuanto a la retención de residuos nocivos y radiactivos, y la obtención de fases disilicatos insolubles en condiciones suaves, apropiadas para la inmovilización de dichas especies. Dicho objetivo representa un cambio cualitativo en el trabajo que se viene desarrollando en cuanto a su aplicación a residuos radioactivos y tóxicos reales, de una parte, y en cuanto a la aplicación de la metodología desarrollada en sistemas modelos a silicatos de utilidad, de otra. Los objetivos se adecuan, en general, a las líneas prioritarias de Investigación básica de Química, en concreto en el área de Química Inorgánica (Química del Estado Sólido) y Química Medioambiental, pero a pesar de su carácter básico posee un carácter aplicado que se adecua a diversas líneas de investigación de Química Orientada y ha despertado el interés de diversas empresas observadoras (ENRESA, BEFESA y ALQUIMIA). Estos objetivos requieren el desarrollo de técnicas de análisis sofisticado como la Resonancia magnética Nuclear de Sólido, la Difracción de Rayos-X bajo atmósfera controlada o espectroscopia gamma de bajo recuento, teniendo en cuenta el objetivo particular de dicha área de usar la tecnología instrumental y experimental para el estudio de materiales, satisfaciendo además el objetivo O2.5 (Potenciar la disponibilidad de infraestructuras de uso interdisciplinar y de uso compartido por los distintos agentes del sistema) del plan nacional de I+D+i 2008-2011. La viabilidad de la propuesta se garantiza, en primer lugar, porque el EI ha publicado recientemente la síntesis de silicatos laminares hidratables de alta carga, donde describe un método a partir del cual se puede ajustar la carga deseada para el material; en segundo lugar, el EI posee una dilatada experiencia en el diseño de mecanismos de síntesis de silicatos, como se demuestra por los numerosos artículos publicados en esta área durante la última década y finalmente, el EI ha desarrollado metodología necesaria para el desarrollo de este experimento en colaboración con otros Grupos con los que mantiene una estrecha colaboración científica.


Bioener: Aplicación de tecnologías biomiméticas a sistemas energéticos



Investigador Principal: Julián Martínez Fernández
Periodo: 01-01-2010 / 31-12-2012
Organismo Financiador: Junta de Andalucía
Código: P09-TEP-5152 (Proyecto de Excelencia)
Componentes: Manuel Jiménez Melendo, Antonio De Arellano-López, Alfonso Bravo León, F.M. Varela Feria

Resumen [+]

Los avances tecnológicos han permitido diversificar y optimizar la producción de ener-gía, lo que ha conducido al mismo tiempo, a desarrollar nuevas vías de almacenamiento de la misma. En particular, a medida que se diversifican los métodos de producción energética, es necesario desarrollar nuevos materiales para almacenamiento de energía, para su uso en dispositivos de consumo y transporte. Esto es especialmente importante para países que, como España, llevan años aumentando la presencia de las renovables en su carta de tecnologías de producción eléctrica y son actualmente líderes mundiales del sector. El Plan de Fomento de las Energías Renovables 2000-2010 tiene como objetivo para este año generar hasta el 30% de las necesidades de consumo energético nacionales a partir de energías renovables, mientras que en algunas comunidades autónomas la cuota de renovables supone ya más del 75% del consumo anual. La progresiva penetración de las renovables debe ir necesariamente acompañada del desarrollo de nuevas tecnologías de distribución y almacenamiento energético, teniendo en cuenta que la potencia suministrada por las renovables es intermitente y variable, al depender las condiciones meteorológicas. Otra estrategia a corto plazo para reducir la dependencia de los combustibles fósiles es la mejora de la eficiencia los sistemas de generación de energía convencionales mediante el aumento de las temperaturas de operación, por ejemplo en turbinas de combustión de gas. El desarrollo de nuevos materiales para aplicaciones de alta temperatura ha ido tradicionalmente ligado a la demanda de mayores eficiencias. De entre ellos, los materiales cerámicos se postulan como candidatos para aplicaciones en entornos químicamente agresivos a temperaturas superiores a los 1000ºC. Carburos y nitruros en particular, con su elevado punto de fusión y excelentes propiedades termomecánicas, están siendo extensamente estudiados en la actualidad para este tipo de aplicaciones. Los cerámicos porosos también son de gran interés en aplicaciones energéticas, como intercambiadores de calor o sistemas de filtrado de gas de síntesis, entre otros. De las líneas de investigación en nuevos materiales para almacenamiento energético, el desarrollo de nuevos sistemas de almacenamiento electroquímico tendrá un gran impacto a corto plazo, especialmente en el consumidor final: el desarrollo de baterías y condensadores electroquímicos de alta capacidad es clave para la viabilidad de tecnologías que, como los vehículos eléctricos, deberán implantarse en un corto plazo para reducir nuestra dependencia de los combustibles fósiles. Es por esta razón que los materiales para almacenamiento electroquímico han recibido gran atención de la comunidad científica y constituyen uno de los grandes retos tecnológicos actuales. El carburo de silicio biomórfico (bioSiC) es un material cerámico obtenido por infiltra-ción reactiva de preformas de carbono obtenidas mediante pirólisis de precursores vegetales. El precursor, generalmente madera, se mecaniza en bruto y se carboniza mediante un proceso de pirólisis en atmósfera controlada a alta temperatura, obteniéndose un material de carbono macroporoso (bioC) cuya microestructura es similar a la del precursor vegetal. Este precursor se mecaniza hasta una forma cercana al producto final y se infiltra reactivamente con silicio líquido o gaseoso para obtener un material de SiC/Si que presenta unas excelentes propiedades termomecánicas, con una microestructura que mimetiza la microestructura de la madera original. Es posible seleccionar las propiedades del material resultante mediante la elección adecuada del precursor. El silicio residual puede eliminarse para obtener un material de SiC macroporoso. Es posible, por último, reinfiltrar el bioSiC poroso con otros materiales, por ejemplo metales para obtener cermets bioSiC/Al o bioSiC/Cu. La posibilidad de producir materiales de carbono macroporosos con nanoporosidad controlada es interesante para su uso en aplicaciones electroquímicas, puesto que es posible infiltrar o recubrir los macroporos con una fase secundaria que proporcione funcionalidad adicional, por ejemplo en pilas de litio con arquitectura tridimensional o en supercondensadores oxido/carbono. En este sentido, el desarrollo de nuevos carbonos con porosidad y/o estructura controlada puede abrir una puerta hacia nuevas arquitecturas y diseños de dispositivo capaces de almacenar mayores densidades de energía. La mayoría de materiales nanoporosos de carbono utilizados en la actualidad se obtie-nen mediante la activación de carbones obtenidos por pirólisis de precursores orgánicos sintéticos, aunque en los últimos años el carbono obtenido a partir de carburos ha sido objeto de gran interés. Es posible, mediante el tratamiento a alta temperatura de carburos metálicos en una atmósfera clorada, obtener carbonos nanoporosos de alta pureza que resultan idóneos para aplicaciones electroquímicas. En este sentido ya se ha demostrado la posibilidad de obtener carbono nanoporoso a partir de carburos obtenidos por infiltración reactiva de precursores vegetales. El objetivo de este proyecto es doble: por un lado, se estudiará en detalle el procedi-miento de obtención de materiales de carbono a partir de precursores vegetales, prestando atención a la posibilidad de introducir distintos gases (CO2, vapor de agua) durante el proceso de pirólisis para obtener carbones activos con nanoporosidad para su uso en sistemas de almacenamiento electroquímico. Se estudiará además el efecto de la temperatura de pirólisis en el grado de cristalinidad, nanoporosidad, tamaño de cristal y estructura del carbono resultante, y se explorará la posibilidad de promover la cristalización del carbono mediante el uso de distintos catalizadores. Se caracterizará la microestructura de los materiales resultantes, así como sus propiedades físicas y termo-mecánicas.


Microestructura y deformación plástica a alta temperatura de óxidos eutécticos basados en Al2O3. Superplasticidad



Investigador Principal: Manuel Jiménez Melendo
Periodo: 01-01-2010 / 31-12-2012
Organismo Financiador: Ministerio de Ciencia y Tecnología
Código: MAT2009-13979-C03-01
Componentes: Julián Martínez Fernández, Antonio Ramírez De Arellano-López, Alfonso Bravo León, Caroline Clauss Klamp, F.M. Varela Feria, C. Vaquero Aguilar

Resumen [+]

Se pretende desarrollar óxidos eutécticos binarios y ternarios basados en la alúmina –en concreto, Al2O3/ZrO2, Al2O3/Y3Al5O12(YAG), Al2O3/ZrO2/YAG y Al2O3/SiO2/ZrO2, con la circona estabilizada con diferentes contenidos de Y2O3– con microestructuras controladas en el intervalo micro- a nanométrico, para su empleo en aplicaciones estructurales y térmicas de sistemas de generación y conversión más eficientes de la energía: soportes para pilas de combustible, reactores químicos, reactores enfriados por gas de alta temperatura, barreras térmicas sobre superaleaciones metálicas en turbinas y motores, etc. Entre las altas prestaciones de estos materiales caben destacar: elevado punto de fu-sión, baja densidad, conductividad térmica, escasa reactividad química incluso a alta tempera-tura, y excelentes propiedades mecánicas tanto a bajas como a elevadas temperaturas: resis-tencia mecánica cercana a 5 GPa a temperatura ambiente, resistencia a la fluencia, al desgaste y a la erosión. Pero lo más novedoso y potencialmente interesante de estos materiales es su comportamiento superplástico, en microestructuras nanométricas, recientemente descubierto por el equipo investigador solicitante.Estos materiales se producirán por técnicas de procesamiento asistido por láser en tres configuraciones distintas: masivos, recubrimientos planos (capas individuales sobre soportes cerámicos y metálicos) y multicapas. En particular, para esta última configuración se diseñarán estructuras con campos de tensiones residuales favorables para unas prestaciones mecánicas y térmicas óptimas en función de las diferentes aplicaciones requeridas. Estas tensiones residuales se investigarán mediante técnicas de espectroscopía Raman y piezoespectroscopía, y se compararán con los resultados de simulaciones numéricas. Por otra parte, las técnicas de tratamiento por láser se emplearán también para alterar la microestructura de los recubrimientos cerámicos convencionales depositados por proyección térmica sobre las superaleaciones metálicas en componentes de motores así como para mecanizar los materiales producidos con objeto de conferirles una determinada geometría funcional, o con el fin de modificar su superficie de forma que mejore el comportamiento frente al desgaste. Uno de los objetivos fundamentales de este proyecto será estudiar materiales con fases nanométricas que posibiliten un comportamiento superplástico a altas temperaturas (que contrasta con la extraordinaria resistencia a la deformación de los materiales con fases micrométricas), de forma que abra la posibilidad de la unión y el conformado fácil con forma casi final de piezas complejas, recuperando su resistencia característica tras tratamientos térmicos. Las propiedades mecánicas (resistencia a compresión y a flexión, módulo de elastici-dad, dureza, tenacidad a fractura y desgaste) de los materiales se evaluarán desde temperatura ambiente hasta 1950 K mediante diferentes técnicas en aire, así como en otras atmósferas para determinar su influencia en el comportamiento mecánico o la degradación del material. Una parte complementaria, pero fundamental, del proyecto es la caracterización es-tructural y microestructural de los materiales fabricados, así como su evolución con los ensa-yos mecánicos. De esta forma se podrán establecer las relaciones entre el comportamiento mecánico observado (propiedades necesarias para el diseño ingenieril) y sus parámetros microestructurales característicos. Con esta finalidad, se utilizarán técnicas de microscopía óptica convencional y confocal, electrónica con microanálisis y difracción, de fuerzas atómicas, así como difracción con textura por rayos X. Del análisis de los resultados de los ensayos termo-mecánicos y de la caracterización microestructural se pretende llegar al entendimiento básico de la relación entre microestruc-tura y propiedades. Esto permitirá retroalimentar el proceso de producción de los materiales eutécticos, para lograr microestructuras específicas para las diferentes aplicaciones con pro-piedades macroscópicas optimizadas.


Materiales compuestos de matriz cerámica y fase de baja dimensionalidad orientados a la gestión de residuos



Investigador Principal: Miguel Angel Castro Arroyo
Periodo: 01-10-2007 / 30-09-2010
Organismo Financiador: Ministerio de Educación y Ciencia
Código: CTQ2007-63297
Componentes: Alba, M.D., Alvero, R., Becerro, A.I., Chain, P., Escudero, A., Naranjo, M., Trillo, J.M.

Resumen [+]

El objetivo central del Proyecto es la obtención de materiales compuestos a partir de silicatos laminares de alta carga expansibles particularmente diseñados conteniendo fases de baja dimensionalidad con actividad eficaz respecto de la retención e inmovilización de residuos tóxicos y peligrosos. El aspecto esencialmente innovador surge, de una parte, de la confluencia de los estudios que el E.I. venía realizando con investigadores de la Universidad de Cambridge (Reino Unido) con los resultados del último proyecto nacional desarrollado. De otra, de la acción de reunificación de los investigadores que participan en un proyecto único, de carácter multidisciplinar, en la frontera de la química básica de los silicatos con la gestión de residuos e interpretación del fenómeno de subducción en el manto inferior de la Tierra. La hipótesis según la cual la eficacia en la eliminación de contaminantes tóxicos y radioactivos por aluminosilicatos laminares viene controlada por la disposición estructural y por la composición de las fases de baja dimensionalidad originada durante los tratamientos se ha elaborado a partir de los resultados obtenidos por el E.I. en la última década de trabajo. La metodología prevista no se limita a la síntesis de los materiales compuestos y a su caracterización, pues incorpora una medida del potencial que representarían en el tratamiento de residuos, esencialmente basados en algunos contaminantes orgánicos y cationes pesados, tóxicos y radiactivos. El desarrollo del proyecto incidirá sobre las relaciones del E.I. con los Grupos de la Universidad de Bayreuth (Alemania) y Cambridge (Reino Unido), las cuales han conducido a numerosas publicaciones conjuntas, antecedentes de la presente solicitud. El carácter multidisciplinar del proyecto junto con el marcado carácter académico y docente, se considera avales de la elevada capacidad formativa del Proyecto.


Inertización de residuos tóxicos y radioactivos en una matriz de silicatos



Investigador Principal: Miguel Angel Castro Arroyo
Periodo: 28-2-2007 / 1-3- 2010
Organismo Financiador: Junta de Andalucía
Código: P06-FQM-02179
Componentes: Alba, M.D., Alvero, R., Becerro, A.I., Chain, P., Escudero, A., Naranjo, M., Pavón, E., Trillo, J.

Resumen [+]

El presente Proyecto pretende emplear silicatos laminares expansibles de alta carga, diseñados bajo procedimientos que permitan controlar la cantidad y distribución de los centros tetraédricos activos, en un conjunto de tratamientos químicos suaves, en contacto con elementos tóxicos seleccionados, en colaboración con las empresas BEFESA y ENRESA, que permitan su encapsulamiento e inmovilización posterior. Durante la realización del mismo se plantea, en un primer período, analizar el efecto que las variables experimentales involucradas en el procedimiento de síntesis ejercen sobre la distribución de los centros activos de los materiales. En un segundo período, los precursores obtenidos se tratarán bajo condiciones hidrotermales, en condiciones subcríticas, con disoluciones conteniendo elementos tóxicos y radioactivos cuidadosamente seleccionados. Finalmente, se estimará el grado de retención de los elementos en las nuevas fases obtenidas. El Equipo Investigador (E.I.) responsable de la realización del Proyecto incorporará una metodología experimental desarrollada recientemente en su seno que incluye el empleo combinado de técnicas tales como la Resonancia Magnética Nuclear de Sólidos, la Difracción, y la Fluorescencia y Microfluorescencia de Rayos X, que suministrarán información acerca tanto del orden a largo alcance como del entorno local de los centros activos de los residuos, responsables de su peligrosidad. Ello deberá suministrar información directa, no disponible en la actualidad, acerca del mecanismo final de fijación, piedra angular del Proyecto. Los Resultados esperados aportarán, desde el punto de vista de la investigación desarrollada, información básica útil acerca de los mecanismos de interacción de iones metálicos con la red de silicatos laminares expansibles y su relación con el ordenamiento local de los átomos constituyente de éstos y, en segundo lugar, un conocimiento útil, de carácter aplicado, que permita desarrollar nuevos procedimientos adecuados de encapsulamiento de residuos industriales, en conexión con las colaboraciones actualmente desarrolladas con empresas del sector, lo cual marca el carácter innovador del mismo.


Nuevos procesos de bio-ceramización aplicables a estructuras vegetales jerarquizadas



Investigador Principal: Julián Martínez Fernández
Periodo: 01-10-2006 / 30-09-2010
Organismo Financiador: Unión Europea
Código: STRP 033277 TEM-PLANT
Componentes: Ramírez de Arellano-López, A., Jiménez, M., Marrero, M., Clauss, M., Bravo, A., Quispe, J.J.

Resumen [+]

El Proyecto TEM PLANT se centra en el desarrollo y aplicación de procesos avanzados para transformar estructuras jerarquizadas vegetales en dispositivos biomédicos innovadores con comportamientos anisotrópicos inteligentes y características biomédicas avanzadas, diseñadas para la sustitución de huesos y ligamentos. Las bioestructuras naturales normalmente poseen propiedades superiores a sus análogos sintéticamente fabricados con iguales composiciones de fase, ya que están sumamente organizadas desde las escalas molecular, a la nano, micro y macroscópica, siempre de una forma jerarquizada, con unas arquitecturas complejas pero extremadamente funcionales capaces de adaptarse constantemente a los cambios mecánicos necesarios. El proyecto TEM-PLANT combina la biología, química, ciencia de materiales, nanotecnología y tecnologías de producción, en nuevos y complejos procesos de transformación que originen materiales para implantes óseos o sustitutos de ligamentos. Partiendo de la materia prima vegetal adecuadamente seleccionada, se originarán precursores carbonosos, sobre los cuales se realizará procesos de infiltración en fase líquida o vapor de silicio y calcio, electroforesis y mineralización/deposición superficial, produciendo estructuras cerámicas inertes/reabsorbibles de carburo de silicio/apatita.

Los experimentos de implantación in vivo demuestran la excelente biocompatibilidad de este nuevo material, y cómo es colonizado por el tejido óseo anfitrión debido a su porosidad jerárquicamente interconectada única. Este proyecto desarrollará materiales ligeros y resistentes para la sustitución de huesos con una estructura-morfología adecuada para una funcionalidad mecánica óptima, lo que abriría las puertas a una amplia nueva generación de aplicaciones biomédicas.


2017


Titulo: High-temperature thermal conductivity of biomorphic SiC/Si ceramics
Autores: Ramirez-Rico, J.; Singh, M.; Zhu, D.; Martinez-Fernandez, J.
Revista: Journal of Materials Science, 52 (2017) 10038-10046
resumen | texto completo


Thermal conductivity of biomorphic SiC/Si, a silicon carbide + silicon containing two phase material, was evaluated using the laser steady-state heat flux method. These materials were processed via silicon melt infiltration of wood-derived carbon scaffolds. In this approach, heat flux was measured through the thickness when one side of the specimen was heated with a 10.6-A mu m CO2 laser. A thin mullite layer was applied to the heated surface to ensure absorption and minimize reflection losses, as well as to ensure a consistent emissivity to facilitate radiative loss corrections. The influence of the mullite layer was accounted for in the thermal conductivity calculations. The effect of microstructure and composition (inherited from the wood carbonaceous performs) on measured conductivity was evaluated. To establish a baseline for comparison, a dense, commercially available sintered SiC ceramic was also evaluated. It was observed that at a given temperature, thermal conductivity falls between that of single-crystal silicon and fine-grained polycrystalline SiC and can be rationalized in terms of the SiC volume fraction in biomorphic SiC/Si material.

Septiembre, 2017 | DOI: 10.1007/s10853-017-1199-y

Titulo: New insights into surface-functionalized swelling high charged micas: Their adsorption performance for non-ionic organic pollutants
Autores: Pazos, MC; Castro, MA; Cota, A; Osuna, FJ; Pavon, E; Alba, MD
Revista: Journal of Industrial and Engineering Chemistry, 52 (2017) 179-186
resumen | texto completo


The major components of the wastewater from the petroleum refineries are benzene, toluene and phenol and one of the techniques applied to the treatment of effluents is sorption using organo-functionalized clay. The materials exploited in the present study are a family of surface-functionalized synthetic micas and their sorption capacities for non-ionic organic pollutants are analyzed. The organo-functionalization of their surface provides them the capacity to sorb effectively non-ionic pollutants in the interface. Their adsorption performance is a function of the alkylamonium properties such as the chain length, the mass fraction and the organization of the organic cation in the interlayer space of the micas.

Agosto, 2017 | DOI: 10.1016/j.jiec.2017.03.042

Titulo: Cs+ immobilization by designed micaceous adsorbent under subcritical conditions
Autores: Osuna, FJ; Cota, A; Pavon, E; Pazos, MC; Alba, MD
Revista: Applied Clay Science, 143 (2017) 293-299
resumen | texto completo


The adsorption of Cs+ by clay minerals is a complicate process, being cation exchange and frayed-edge sites the major mechanisms that govern it. However, environmental variables have a significant impact on the process. In this work, the influence of the temperature and time in the cesium adsorption capacity of Na-Mica-n (n = 2 and 4) have been explored under subcritical conditions. Those synthetic micas were able to immobilize cations Cs+ combining adsorption at nonspecific sites, at specific sites and chemical reaction. The distribution constant of Cs+ was larger in the Na-Mica-2 denoting a higher concentration of specific adsorption sites when layer charge decreased.

Julio, 2017 | DOI: 10.1016/j.clay.2017.03.041

Titulo: Failure mode and effect analysis of a large scale thin-film CIGS photovoltaic module
Autores: Delgado-Sanchez, JM; Sanchez-Cortezon, E; Lopez-Lopez, C; Aninat, R; Alba, MD
Revista: Engireering failure analysis, 76 (2017) 55-60
resumen | texto completo


The efficiency of thin-film CIGS based cells at the laboratory scale is now getting closer to conventional Silicon technologies. As a consequence, the long-term stability of CIGS is now one of the main challenges left to address in order to assess its potential as an alternative for photovoltaic plants. This paper reports an overview of the critical risks for the commercial viability of the CIGS thin-film technology. The key causes of the potential failures of this technology are determined through the Failure Mode Analysis and Effects (FMEA) methodology. To validate the results obtained from the FMEA, aging tests and outdoor monitoring were also carried out. Based on the results obtained, we argue that the encapsulation material is the main cause of degradation in CIGS modules. 

Junio, 2017 | DOI: 10.1016/j.engfailanal.2017.02.004

Titulo: Features of electrical properties of BE-C(Fe) biocarbons carbonized in the presence of an Fe-containing catalyst
Autores: Popov, VV; Orlova, TS; Gutierrez-Pardo, A; Ramirez-Rico, J
Revista: Physics of the Solid State
resumen | texto completo


The effect of partial graphitization on electrical and galvanomagnetic properties of BE-C(Fe) biomorphic carbons produced by beech wood carbonization at temperatures of 850-1600A degrees C in the presence of an iron-containing catalyst is studied. The use of an Fe catalyst at D cent (carb) ae<yen> 1000A degrees C leads to the formation of nanoscale graphite-phase inclusions; its total volume and nanocrystallite sizes increase with D cent (carb). The data on the carrier concentration and mobility are obtained. It was shown that partially graphitized BE-C(Fe) carbons with D cent (carb) ae<yen> 1000A degrees C in the conductivity type and magnetoresistance features relate to highly disordered metal systems whose conductivity can be described taking into account the contribution of quantum corrections, mainly the correction caused by the electron-electron interaction. It is shown that nonmonotonic dependences of the Hall constant R on the magnetic field are characteristic of BE-C(Fe) samples with 1000 ae<currency> D cent (carb) < 1600A degrees C, which is most probably caused by the contribution of various carrier groups, i.e., electrons and holes. In BE-C(Fe) samples with D cent (carb) = 1600A degrees C, the Hall coefficient corresponds to the metal state, which is associated with conducting medium homogenization resulting from the formation of a significant graphite phase volume.

Abril, 2017 | DOI: 10.1134/S1063783417040205

Titulo: Precision and accuracy of stress measurement with a portable X-ray machine using an area detector
Autores: Lee, SY; Ling, JJ; Wang, SH; Ramirez-Rico, J
Revista: Journal of Applied Crystallography, 50 (2017) 131-144
resumen | texto completo


The use of portable X-ray stress analyzers, which utilize an area detector along with the newly adopted 'cos alpha' or full-ring fitting method, has recently attracted increasing interest. In laboratory conditions, these measurements are fast, convenient and precise because they employ a single-exposure technique that does not require sample rotation. In addition, the effects of grain size and orientation can be evaluated from the Debye ring recorded on the area detector prior to data analysis. The accuracy of the measured stress, however, has been questioned because in most cases just a single reflection is analyzed and the sample-to-detector distances are relatively short. This article presents a comprehensive analysis of the uncertainty associated with a state-of-the-art commercial portable X-ray device. Annealed ferrite reference powders were used to quantify the instrument precision, and the accuracy of the stress measurement was tested by in situ tensile loading on 1018 carbon steel and 6061 aluminium alloy bar samples. The results show that the precision and accuracy are sensitive to the instrument (or sample) tilt angle (0) as well as to the selected hkl reflection of the sample. The instrument, sample and data analysis methods all affect the overall uncertainty, and each contribution is described for this specific portable X-ray system. Finally, on the basis of the conclusions reached, desirable measurement/analysis protocols for accurate stress assessments are also presented.

Febrero, 2017 | DOI: 10.1107/S1600576716018914

Titulo: Front contact optimization of industrial scale CIGS solar cells for low solar concentration using 2D physical modeling
Autores: Delgado-Sanchez, JM; Lopez-Gonzalez, JM; Orpella, A; Sanchez-Cortezon, E; Alba, MD; Lopez-Lopez, C; Alcubilla, R
Revista: Renewable Energy, 101 (2017) 90-95
resumen | texto completo


Cu(In,Ga)Se-2 (CIGS) technology is one of the best absorber materials with record efficiencies among photovoltaic thin-film technologies (22.3% at lab scale and 16% at large commercial module). Although research on this material was originally motivated by low-cost, glass-glass applications focusing to fixed photovoltaic structures, the high efficiency values make CIGS an interesting alternative for low concentration systems. In this paper a 2D model for Cu(In,Ga)Se-2 (CIGS) solar cells under low solar concentration is described and contrasted with experimental data. Using simulation, the effect of front electric contact design parameters: finger width, finger separation, and number of buses are analyzed for solar concentrations from 1 up to 10 suns. Efficiency maps allowing front contact grid optimization are shown and analyzed for each concentration factor (Cx), assessing the viability of CIGS solar cells for low concentration applications, where commercial CIGS solar cells may exhibit 35% of electrical power increases with proper front grid optimization under low concentration respect to conventional grid design. 

Enero, 2017 | DOI: 10.1016/j.renene.2016.08.046

Titulo: Insolubilization and thermal stabilization of a long-chain polyester by noncatalyzed melt-polycondensation synthesis in air
Autores: Benitez, JJ; Heredia-Guerrero, JA; Cruz-Carrillo, MA; Barthel, MJ; Knicker, HE; Heredia, A
Revista: Journal of Applied Polymer Science, 134 (2017) 1 art 44350
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Self-standing films of poly(-hydroxyl hexadecanoic acid) [poly(-OHC16)] have been prepared by noncatalyzed melt-polycondensation in air at 150, 175, and 200 degrees C. Poly(-OHC16)s obtained are characterized as polyesters by infrared spectroscopy (FT-IR) and solid state magic angle spinning C-13 nuclear magnetic resonance (C-13 MAS-NMR). Structurally, poly(-OHC16)s are quite crystalline as revealed by wide angle X-ray diffraction (WAXD). The presence of oxygen in the reaction atmosphere causes a mild oxidation in the form of peroxyester species, tentatively at the interphase between poly(-OHC16) crystallites, and the structure amorphization. The interfacial peroxyester phase ends up in the encapsulation of the polyester grains and provides a barrier towards the action of solvents. Thermal stabilization and insolubility resulting from the synthesis conditions used are interesting features to prepare solvent and heat resistant poly(-OHC16) coatings. Thus, a few microns thick poly(-OHC16) layer has been fabricated on aluminum foil and its resistivity towards a chloroform:methanol (1:1, v:v) mixture has been confirmed.

Diciembre, 2016 | DOI: 10.1002/app.44350

2016


Titulo: Microstructure, elastic, and inelastic properties of biomorphic carbons carbonized using a Fe-containing catalyst
Autores: Orlova, TS; Kardashev, BK; Smirnov, BI; Gutierrez-Pardo, A; Ramirez-Rico, J
Revista: Physics of the Solid State, 58 (2016) 2481-2487
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The microstructure and amplitude dependences of the Young’s modulus E and internal friction (logarithmic decrement δ), and microplastic properties of biocarbon matrices BE-C(Fe) obtained by beech tree carbonization at temperatures Tcarb = 850–1600°C in the presence of an iron-containing catalyst are studied. By X-ray diffraction analysis and transmission electron microscopy, it is shown that the use of Fe-catalyst during carbonization with Tcarb ≥ 1000°C leads to the appearance of a bulk graphite phase in the form of nanoscale bulk graphite inclusions in a quasi-amorphous matrix, whose volume fraction and size increase with Tcarb. The correlation of the obtained dependences E(Тcarb) and δ(Tcarb) with microstructure evolution with increasing Тcarb is revealed. It is found that E is mainly defined by a crystalline phase fraction in the amorphous matrix, i.e., a nanocrystalline phase at Тcarb < 1150°C and a bulk graphite phase at Tcarb > 1300°C. Maximum values E = 10–12 GPa are achieved for samples with Тcarb ≈ 1150 and 1600°C. It is shown that the microplasticity manifest itself only in biocarbons with Tcarb ≥ 1300°C (upon reaching a significant volume of the graphite phase); in this case, the conditional microyield stress decreases with increasing total volume of introduced mesoporosity (free surface area).

Noviembre, 2016 | DOI: 10.1134/S1063783416120234

Titulo: Manganese Dioxide Supported on Porous Biomorphic Carbons as Hybrid Materials for Energy Storage Devices
Autores: Gutierrez-Pardo, A; Lacroix, B; Martinez-Fernandez, J; Ramirez-Rico, J
Revista: ACS Applied Materials & Interfaces, 8 (2016) 30890-30898
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A facile and low-cost method has been employed to fabricate MnO2/C hybrid materials for use as binder-free electrodes for supercapacitor applications. Biocarbon monoliths were obtained through pyrolysis of beech wood, replicating the microstructure of the cellulosic precursor, and serve as 3D porous and conductive scaffolds for the direct growth of MnO, nanosheets by a solution method. Evaluation of the experimental results indicates that a homogeneous and uniform composite material made of a carbon matrix exhibiting ordered hierarchical porosity and MnO, nanosheets with a layered nanocrystalline structure is obtained. The tuning of the MnO2 content and crystallite size via the concentration of KMnO4 used as impregnation solution allows to obtain composites that exhibit enhanced electrochemical behavior, achieving a capacitance of 592 F g(-1) in electrodes containing 3 wt % MnO2 with an excellent cyclic stability. The electrode materials were characterized before and after electrochemical testing.

Octubre, 2016 | DOI: 10.1021/acsami.6b09361

Titulo: Thermal conductivity of porous biomorphic SiC derived from wood precursors
Autores: Gomez-Martin, A; Orihuela, MP; Ramirez-Rico, J; Chacartegui, R; Martinez-Fernandez, J
Revista: Ceramics International, 42 (2016) 16220-16229
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Biomorphic SiC is a SiC/Si composite made by the reactive infiltration of molten silicon by capillarity into a carbon preform from high-temperature pyrolysis of a wood porous precursor. When excess silicon is removed, a hierarchically porous SiC material with highly interconnected porosity is obtained. By choosing different wood precursors, different pore size distributions can be obtained thus tailoring the resulting properties. 

We study the thermal conductivity of porous biomorphic SiC from five different precursors, including a recycled wood product, in order to determine the microstructure-conductivity correlation. Here, we remove the excess of silicon by a high temperature capillary extraction-evaporation method. We used the laser flash technique to measure thermal diffusivity in the range similar to 300 K to 973 K, in order to determine the thermal conductivity. Thermal conductivities in the range 4-88 W/m K were achieved. The temperature, porosity, pore shape and orientation, and the treatment used to remove the remaining silicon all have a significant impact in the resulting thermal conductivity. We explain this influence in a first approximation in terms of a geometrical model.

Octubre, 2016 | DOI: 10.1016/j.ceramint.2016.07.151

Titulo: Enhancement of dielectric barrier layer properties by sol-gel and PECVD stacks
Autores: Lopez-Lopez, C; Menendez, MF; Menendez, LA; Menendez, A; Sanchez, P; Alba, MD; Sanchez-Cortezon, E; Delgado-Sanchez, JM
Revista: Surface and Coatings Technology, 305 (2016) 36-40
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Thin-film PV modules grown on flexible, light weight, thermally stable and low cost substrates such as stainless steel foil, are an attractive product for solar market applications. When metal foils are used as substrate, it is essential to deposit a dielectric barrier layer to isolate electrically and chemically the thin-film solar cells from the substrate. In this work, SiOx stacks deposited on ‘rough’ stainless steel by a combination of a new sol-gel formulation and a Plasma Enhanced Chemical Vapor Deposition (PECVD) deposition step are reported as a suitable dielectric barrier layer candidate. Using these SiOx multilayers, a smooth and homogeneous film was achieved. X-ray diffraction (XRD) analysis showed that back contact of the solar cell (based on Molybdenum) is not affected by the presence of the barrier layer. Moreover, according to X-ray photoelectron spectroscopy (XPS) and Secondary Ion Mass Spectrometry (SIMS) measurements, this approach led to excellent barrier layer properties against the diffusion of impurities from the stainless steel. A complete electrical characterization of these dielectric barrier layers was also carried out showing good electrical insulation.

Octubre, 2016 | DOI: 10.1016/j.surfcoat.2016.07.085

Titulo: Permeability and mechanical integrity of porous biomorphic SiC ceramics for application as hot-gas filters
Autores: Gomez-Martin, A.; Orihuela, M. P.; Becerra, J. A.; Martinez-Fernandez, J.; Ramirez-Rico, J.
Revista: Materials & Design, 107 (2016) 450-460
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Biomorphic SiC is a biotemplated material fabricated by Si melt-infiltration of carbon preforms from wood pyrolysis. In this work, porous bioSiC ceramics from five different wood precursors, with porosities between 45 and 72% were studied for their feasibility in filtering applications.

Gas permeability and mechanical stability were investigated as a function of the microstructure of the starting wood precursor. Air-permeation performance at room temperature was measured for a range of flow rates, and the permeability constants were assessed by fitting of Forchheimer's equation to the experimental data. Darcian permeabilities were achieved in the range 10− 11–10− 12 m2, while inertial terms were in the range 10− 7–10− 8 m, showing a correlation with the average pore size and orientation of the larger channels. Regarding the mechanical stability, maximum compressive strength values were reached in the range of 3–115 MPa.

These results improve our understanding of the ways in which the microstructure influences permeability and mechanical robustness, enabling the device requirements to be tailored by selecting the wood precursor. It was also shown that these materials are promising for hot-gas filtering applications.

Septiembre, 2016 | DOI: 10.1016/j.matdes.2016.06.060

Titulo: Monolithic supports based on biomorphic SiC for the catalytic combustion of hydrogen
Autores: Arzac, G. M.; Ramirez-Rico, J.; Gutierrez-Pardo, A.; Jimenez de Haro, M. C.; Hufschmidt, D.; Martinez-Fernandez, J.; Fernandez, A.
Revista: RSC Advances, 6 (2016) 66373-66384
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Catalytic hydrogen combustion was studied with H-2/air mixtures in conditions that simulate the H-2 concentration of the exhaust gases from fuel cells (3-4% v/v H-2 in air). Pt-impregnated monoliths based on porous biomorphic SiC (bio-SiC) substrates were employed for the first time for this reaction. Capillary forces were exploited for the incipient impregnation of supports with H2PtCl6 solutions. Freeze drying permitted us to obtain a homogeneous distribution of the active phase reducing accumulation at the monolith's outer shell. The supports and catalysts were characterized from a structural and thermal point of view. Catalytic tests were performed in a homemade reactor fed with up to 1000 ml min(-1) H-2/air mixtures and a diffusional regime (non-isothermal) was achieved in the selected conditions. Catalyst loading was tested in the range of 0.25-1.5 wt% Pt and 100% conversion was achieved in all cases. Temperatures were recorded at different points of the monoliths during the reaction showing anisotropic thermal behavior for selected bio-SiC substrates. These effects are of interest for heat management applications and were explained in correlation with thermal conductivity measurements performed on the supports. Pt-impregnated monoliths were also tested in less than 100% conversion conditions (1% v/v H-2 in air) and in powder form in kinetic conditions for comparative purposes.

Agosto, 2016 | DOI: 10.1039/c6ra09127j

Titulo: Electrochemical Energy Storage Applications of CVD Grown Niobium Oxide Thin Films
Autores: Fiz, Raquel; Appel, Linus; Gutierrez-Pardo, Antonio; Ramirez-Rico, Joaquin; Mathur, Sanjay
Revista: ACS Applied Materials & Interfaces, 8 (2016) 21423–21430
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We report here on the controlled synthesis, characterization, and electrochemical properties of different polymorphs of niobium pentoxide grown by CVD of new single-source precursors. Nb2O5 films deposited at different temperatures showed systematic phase evolution from low-temperature tetragonal (TT-Nb2O5, T-Nb2O5) to high temperature monoclinic modifications (H–Nb2O5). Optimization of the precursor flux and substrate temperature enabled phase-selective growth of Nb2O5 nanorods and films on conductive mesoporous biomorphic carbon matrices (BioC). Nb2O5 thin films deposited on monolithic BioC scaffolds produced composite materials integrating the high surface area and conductivity of the carbonaceous matrix with the intrinsically high capacitance of nanostructured niobium oxide. Heterojunctions in Nb2O5/BioC composites were found to be beneficial in electrochemical capacitance. Electrochemical characterization of Nb2O5/BioC composites showed that small amounts of Nb2O5 (as low as 5%) in conjunction with BioCarbon resulted in a 7-fold increase in the electrode capacitance, from 15 to 104 F g–1, while imparting good cycling stability, making these materials ideally suited for electrochemical energy storage applications.

Julio, 2016 | DOI: 10.1021/acsami.6b03945

Titulo: Thermal conductivity of Fe graphitized wood derived carbon
Autores: Ramirez-Rico, J; Gutierrez-Pardo, A; Martinez-Fernandez, J; Popov, VV; Orlova, TS
Revista: Materials & Design, 99 (2016) 528-534
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Graphitic porous carbon materials from pyrolysis of wood precursors were obtained by means of a nanosized Fe catalyst, and their microstructure and electrical and thermal transport properties investigated. Thermal and electrical conductivity of graphitized carbon materials increase with the pyrolysis temperature, indicating a relationship between the degree of graphitization and thus in crystallite size with transport properties in the resulting carbon scaffolds. Evaluation of the experimental results indicate that thermal conductivity is mainly through phonons and increases with the temperature in Fe-catalyzed carbons suggesting that the mean free path of phonons in the material is small and defect scattering dominates over phonon-phonon interactions in the range from room temperature to 800 °C.

Mayo, 2016 | DOI: 10.1016/j.matdes.2016.03.070

Titulo: Biological strategy for the fabrication of highly ordered aragonite helices: the microstructure of the cavolinioidean gastropods
Autores: Checa, AG; Macias-Sanchez, E; Ramirez-Rico, J
Revista: Scientific Reports, 6 (2016) article number 25989
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The Cavolinioidea are planktonic gastropods which construct their shells with the so-called aragonitic helical fibrous microstructure, consisting of a highly ordered arrangement of helically coiled interlocking continuous crystalline aragonite fibres. Our study reveals that, despite the high and continuous degree of interlocking between fibres, every fibre has a differentiated organic-rich thin external band, which is never invaded by neighbouring fibres. In this way, fibres avoid extinction. These intra-fibre organic-rich bands appear on the growth surface of the shell as minuscule elevations, which have to be secreted differentially by the outer mantle cells. We propose that, as the shell thickens during mineralization, fibre secretion proceeds by a mechanism of contact recognition and displacement of the tips along circular trajectories by the cells of the outer mantle surface. Given the sizes of the tips, this mechanism has to operate at the subcellular level. Accordingly, the fabrication of the helical microstructure is under strict biological control. This mechanism of fibre-by-fibre fabrication by the mantle cells is unlike that any other shell microstructure.

Mayo, 2016 | DOI: 10.1038/srep25989

Titulo: Stress measurement using area detectors: a theoretical and experimental comparison of different methods in ferritic steel using a portable X-ray apparatus
Autores: Ramirez-Rico, J; Lee, SY; Ling, JJ; Noyan, IC
Revista: Journal of Materials Science, 51 (2016) 5343-5355
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Using area detectors for stress determination by diffraction methods in a single exposure greatly simplifies the measurement process and permits the design of portable systems without complex sample cradles or moving parts. An additional advantage is the ability to see the entire or a large fraction of the Debye ring and thus determine texture and grain size effects before analysis. The two methods most commonly used to obtain stress from a single Debye ring are the so-called cosαcos⁡αand full-ring fitting methods, which employ least-squares procedures to determine the stress from the distortion of a Debye ring by probing a set of scattering vector simultaneously. The widely applied sin2ψsin2⁡ψ method, in contrast, requires sample rotations to probe a different subset of scattering vector orientations. In this paper, we first present a description of the different methods under the same formalism and using a unified set of coordinates that are suited to area detectors normal to the incident beam, highlighting the similarities and differences between them. We further characterize these methods by means of in situ measurements in carbon steel tube samples, using a portable detector in reflection geometry. We show that, in the absence of plastic flow, the different methods yield basically the same results and are equivalent. An analysis of possible sources of errors and their impact in the final stress values is also presented.

Mayo, 2016 | DOI: 10.1007/s10853-016-9837-3

Titulo: Biodegradable polyester films from renewable aleuritic acid: surface modifications induced by melt-polycondensation in air
Autores: Benitez, JJ; Heredia-Guerrero, JA; de Vargas-Parody, MI; Cruz-Carrillo, MA; Morales-Florez, V; de la Rosa-Fox, N; Heredia, A
Revista: Journal of Physics D-Applied Physics, 49 (2016) 175601
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Good water barrier properties and biocompatibility of long-chain biopolyesters like cutin and suberin have inspired the design of synthetic mimetic materials. Most of these biopolymers are made from esterified mid-chain functionalized.-long chain hydroxyacids. Aleuritic (9,10,16-trihydroxypalmitic) acid is such a polyhydroxylated fatty acid and is also the major constituent of natural lac resin, a relatively abundant and renewable resource. Insoluble and thermostable films have been prepared from aleuritic acid by melt-condensation polymerization in air without catalysts, an easy and attractive procedure for large scale production. Intended to be used as a protective coating, the barrier's performance is expected to be conditioned by physical and chemical modifications induced by oxygen on the air-exposed side. Hence, the chemical composition, texture, mechanical behavior, hydrophobicity, chemical resistance and biodegradation of the film surface have been studied by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), atomic force microscopy (AFM), nanoindentation and water contact angle (WCA). It has been demonstrated that the occurrence of side oxidation reactions conditions the surface physical and chemical properties of these polyhydroxyester films. Additionally, the addition of palmitic acid to reduce the presence of hydrophilic free hydroxyl groups was found to have a strong influence on these parameters.

Abril, 2016 | DOI: 10.1088/0022-3727/49/17/175601

Titulo: Strength and microplasticity of biocarbons prepared by carbonization in the presence of a catalyst
Autores: Shpeizman, VV; Orlova, TS; Smirnov, BI; Gutierrez-Pardo, A; Ramirez-Rico, J
Revista: Physics of the Solid State, 58 (2016) 703-710
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The microdeformation has been investigated under uniaxial compression of beech-derived biocarbons partially graphitized during carbonization in the presence of a Ni- or Fe-containing catalyst. The strength and ultimate fracture strain have been determined at different temperatures of carbonization of the samples in the absence or in the presence of a catalyst. It has been shown using high-precision interferometry that the deformation of biocarbon samples under uniaxial loading occurs through jumps (in magnitude and rate of deformation) with axial displacements in the nanometer and micrometer ranges. The use of a catalyst leads to a decrease in the size of nanometer-scale jumps and in the number of micrometer-scale jumps. The standard deviations of the strain rate on loading steps from the smooth average dependence of the strain rate on the displacement have been calculated for micrometer-scale jumps. A similar characteristic for nanometer- scale jumps has been determined from the distortion of the shape of beats in the primary interferogram. It has been shown that the variation in the standard deviation of the strain rate with a change in the carbonization temperature is similar to the corresponding dependence of the ultimate fracture strain.

Marzo, 2016 | DOI: 10.1134/S1063783416040223

Titulo: Active metal brazing of silicon nitride ceramics using a Cu-based alloy and refractory metal interlayers
Autores: Fernandez, JM; Asthana, R; Singh, M; Valera, FM
Revista: Ceramics International, 42 (2016) 5447-5454
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Silicon nitride/silicon nitride joints with refractory metal (W and Mo) interlayers were vacuum brazed using an active braze, Cu-ABA (Cu-3Si-2Al-2.25Ti, wt%), and two interlayer arrangements in a double-lap offset configuration: Si3N4/Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si3N4 and Si3N4/Cu-ABA /Si3N4. Titanium segregated at the Si3N4/Cu-ABA and Mo/Cu-ABA interfaces, but not at the W/Cu-ABA interface. The room-temperature compression-shear strength values of Si3N4/Cu-ABA/Si3N4 and Si3N4/Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si3N4 joints were 118 +/- 24 MPa and 22 +/- 5 MPa, respectively. Elevated-temperature compression tests showed that Si3N4/Cu-ABA/Si3N4 joints had strength of 31 +/- 6 MPa at 1023 K and 17 +/- 3 MPa at 1073 K. Likewise, Si3N4/Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si3N4 joints had strength of 19 +/- 4 MPa at 1023 K and 13 +/- 3 MPa at 1073 K. Knoop microhardness profiles revealed hardness gradients across the joints. The effect of joint microstructure and test configuration on the mechanical behavior is discussed.

Febrero, 2016 | DOI: 10.1016/j.ceramint.2015.12.087

Titulo: Influence of temperature and time on the Eu3+ reaction with synthetic Na-Mica-n (n=2 and 4)
Autores: Garcia-Jimenez, MJ; Cota, A; Osuna, FJ; Pavon, E; Alba, MD
Revista: Chemical Engineering Journal, 284 (2016) 1174-1183
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Bentonite is accepted as the best clay material for the engineered barrier of Deep Geological Repositories (DGRs). The performance of clay as the main component of the engineered barrier in the DGR has been intensively studied and the structure of the selected clay mineral play a crucial role. In this sense, a new family of synthetic swelling silicates, Na-Mica-n, with tuned layer charge (n) values between 2.0 and 4.0 per unit cell has recently been synthesized and a general synthetic method has been reported. These swelling high-charge micas could be highly valuable for the decontamination of harmful cations. The ability of these micas to immobilize Eu3+ under subcritical conditions has been probed. The adsorption was in both non-specific sites (cation exchange mechanism) and specific sites (chemical reaction or surface defects adsorption). Moreover, its adsorption capacity, under the same conditions is higher than in saponite and far superior to the bentonites. 

Diciembre, 2015 | DOI: 10.1016/j.cej.2015.09.077

Titulo: Thermal conductivity of partially graphitized biocarbon obtained by carbonization of medium-density fiberboard in the presence of a Ni-based catalyst
Autores: Orlova, TS; Parfen'eva, LS; Smirnov, BI; Gutierrez-Pardo, A; Ramirez-Rico, J
Revista: Physics of the Solid State, 58 (2016) 208-214
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The thermal conductivity k and resistivity rho of biocarbon matrices, prepared by carbonizing medium-density fiberboard at T (carb) = 850 and 1500A degrees C in the presence of a Ni-based catalyst (samples MDF-C( Ni)) and without a catalyst (samples MDF-C), have been measured for the first time in the temperature range of 5-300 K. X-ray diffraction analysis has revealed that the bulk graphite phase arises only at T (carb) = 1500A degrees C. It has been shown that the temperature dependences of the thermal conductivity of samples MDFC- 850 and MDF-C-850(Ni) in the range of 80-300 K are to each other and follow the law of k(T) similar to T (1.65), but the use of the Ni-catalyst leads to an increase in the thermal conductivity by a factor of approximately 1.5, due to the formation of a greater fraction of the nanocrystalline phase in the presence of the Ni-catalyst at T (carb) = 850A degrees C. In biocarbon MDF-C-1500 prepared without a catalyst, the dependence is k(T) similar to T (1.65), and it is controlled by the nanocrystalline phase. In MDF-C-1500(Ni), the bulk graphite phase formed increases the thermal conductivity by a factor of 1.5-2 compared to the thermal conductivity of MDF-C-1500 in the entire temperature range of 5-300 K; k(T = 300 K) reaches the values of similar to 10 W m(-1) K-1, characteristic of biocarbon obtained without a catalyst only at high temperatures of T (carb) = 2400A degrees C. It has been shown that MDF-C-1500(Ni) in the temperature range of 40aEuro'300 K is characterized by the dependence, k(T) similar to T (1.3), which can be described in terms of the model of partially graphitized biocarbon as a composite of an amorphous matrix with spherical inclusions of the graphite phase.

Diciembre, 2015 | DOI: 10.1134/S1063783416010236

2015


Titulo: Impact of hydrothermal treatment of FEBEX and MX80 bentonites in water, HNO3 and Lu(NO3)(3) media: Implications for radioactive waste control
Autores: Osuna, FJ; Chain, P; Cota, A; Pavon, E; Alba, MD
Revista: Applied Clay Science, 118 (2015) 48-55
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Engineered barriers of deep geological repositories (DGR) are commonly constructed with bentonite. FEBEX and MX80 bentonites have been selected by different countries as reference materials for the sealing of repositories; however, their chemical reactivity with high-level long-lived radioactive wastes (HLRW) under subcritical conditions had not been explored before. The hydrothermal stability in neutral and acid media and chemical reactivity in contact with an actinide analogous compound were both studied. The long-range and short-range structural changes were analyzed by X-ray diffraction, nuclear magnetic resonance and scanning electron microscopy. Both bentonites have exhibited a good stability in neutral and acid media and have generated a new phase immobilizing the actinide analogous compound. The extent of the chemical reaction is higher in MX80 bentonite than in FEBEX bentonite. 

Noviembre, 2015 | DOI: 10.1016/j.clay.2015.08.036

Titulo: Specific features of the electrical properties in partially graphitized porous biocarbons of beech wood
Autores: Popov, VV; Orlova, TS; Gutierrez-Pardo, A; Ramirez-Rico, J
Revista: Physics of the solid state, 57 (2015) 1746-1751
resumen | texto completo


The electrical and galvanomagnetic properties of partially graphitized highly porous bioC(Ni) biocarbon matrices produced by pyrolysis (carbonization) of beech wood at temperatures T (carb) = 850-1600A degrees C in the presence of a Ni-containing catalyst have been studied in comparison with their microstructural features. The temperature dependences of the resistivity, the magnetoresistance, and the Hall coefficient have been measured in the temperature range of 4.2-300 K in magnetic fields to 28 kOe. It has been shown that an additional graphite phase introduction into samples with T (carb) a parts per thousand yen 1000A degrees C results in an increase in the carrier mobility by a factor of 2-3, whereas the carrier (hole) concentration remains within similar to 10(20) cm(-3), as in biocarbons obtained without catalyst. An analysis of experimental data has demonstrated that the features of the conductivity and magnetoresistance of these samples are described by quantum corrections related to their structural features, i.e., the formation of a globular graphite phase of nano- and submicrometer sizes in the amorphous matrix. The quantum corrections to the conductivity decrease with increasing carbonization temperature, which indicates an increase in the degree of structure ordering and is in good agreement with microstructural data.

Agosto, 2015 | DOI: 10.1134/S1063783415090280

Titulo: Viability of adding gypsum and calcite for remediation of metal-contaminated soil: laboratory and pilot plant scales
Autores: Gonzalez-Nunez, R; Alba, MD; Vidal, M; Rigol, A
Revista: International Journal of Environmental Science and Technology, 12 (2015) 2697-2710
resumen | texto completo


The effect of adding waste materials (gypsum and calcite) for the remediation of a soil contaminated by pyritic minerals was examined. Materials were characterised in terms of their acid neutralisation capacity (ANC), sorption capacity and structural components. Their effect on the contaminant leaching in soil + material mixtures over a wide range of pH was also evaluated. Results at laboratory and pilot plant scales were compared to account for the potential variability in the material efficiency when applied at larger scale. The use of gypsum permitted its valorisation, although calcite was a more effective amendment because its addition led to a greater increase in the pH and acid neutralisation capacity, and thus in the sorption capacity in the resulting soil + material mixture. In the same way, when the combination of gypsum + calcite was added to the soil, it led to an increase in the pH from 2.5 to 6.9 and in the ANC from −86 to 1,513 meq/kg. As a result, the concentration of extractable heavy metals and As was reduced, and they were successfully immobilised both at laboratory and at pilot plant scales. Thus, the use of these materials induced a significant reduction in the contaminant mobility and permitted the valorisation of waste materials.

Julio, 2015 | DOI: 10.1007/s13762-014-0671-3

Titulo: Uranium immobilization by FEBEX bentonite and steel barriers in hydrothermal conditions
Autores: Villa-Alfageme, M; Hurtado, S; El Mrabet, S; Pazos, MC; Castro, MA; Alba, MD
Revista: Chemical Engineering Journal, 269 (2015) 279-287
resumen | texto completo


FEBEX clay is considered a reference material in engineered barriers for safe storage of nuclear waste and uranium is a minor component of high-level radioactive waste (HLRW) and a main component of the spent nuclear fuel (SNF). Here, the kinetics of reaction of uranium with FEBEX was investigated in addition to the uranium immobilisation ability and the structural analysis of the reaction products. Hydrothermal treatments were accomplished with UO22+ and tetravalent actinide simulator ZrO2+, also present in HLRW. The quantification of the reaction was performed through gamma spectrometry of uranium. Two mechanisms for UO22+ retention by FEBEX were detected: adsorption and formation of stable and insoluble new phases. The structural analyses performed using ZrO2+, confirmed the uranium adsorption and the presence of new phases, ZrO2 and Zr(SiO4), that emphasise the existence of a chemical reaction with the bentonite. The analysis of the velocity of reaction uranium-clay minerals revealed temperature dependence. An exponential fitting suggested that the removal of uranium from solution at temperatures over 200 °C could be completed in less than a year. For lower temperatures, several years are needed. Milliequivalents of UO22+ immobilised by the clay depended on temperature and time and were over cation exchange capacity (CEC) of FEBEX even at 100 °C (reaching 600% of CEC). The reaction with steel, also temperature dependent, was finally analysed. At 200 °C 40–70% of uranium reacted with steel. But only 30–15% reacted at 300 °C and 100 °C. The reactions provide a stable immobilisation mechanism for uranium even when its sorption and swelling capacities fail. Our experiments will be of particular interest for very deep borehole disposals were higher temperatures and pressures are expected.

Mayo, 2015 | DOI: 10.1016/j.cej.2015.01.134

Titulo: Self-Assembling of Tetradecylammonium Chain on Swelling High Charge Micas (Na-Mica-3 and Na-Mica-2): Effect of Alkylammonium Concentration and Mica Layer Charge
Autores: Pazos, MC; Cota, A; Osuna, FJ; Pavon, E; Alba, MD
Revista: Langmuir, 31 (2015) 4394-4401
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A family of tetradecylammonium micas is synthesized using synthetic swelling micas with high layer charge (NanSi8-nAln,Mg6F4O20 center dot XH2O, where n = 2 and 3) exchanged with tetradecylammonium cations. The molecular arrangement of the surfactant is,elucidated on the basis of XRD patterns and DTA. The ordering conformation of the surfactant molecules into the interlayer space of Micas is investigated by IR/FT, C-13, Al-27, and Si-29 MAS NMR. The structural arrangement of the tetradecylammonium cation in the interlayer space of high-charge micas is more sensitive to the effect of the mica layer charge at high concentration. The surfactant arrangement is found to follow the bilayer-paraffin model for all values of layer charge and surfactant concentration. However, at initial concentration below the mica CEC, a lateral monolayer is also observed. The amount of ordered conformation all-trans is directly proportional to the layer charge and surfactant concentration.

Marzo, 2015 | DOI: 10.1021/acs.langmuir.5b00224

Titulo: Pectin-Lipid Self-Assembly: Influence on the Formation of Polyhydroxy Fatty Acids Nanoparticles
Autores: Guzman-Puyol, Susana; Jesus Benitez, Jose; Dominguez, Eva; Bayer, Ilker Sefik; Cingolani, Roberto; Athanassiou, Athanassia; Heredia, Antonio; Heredia-Guerrero, Jose Alejandro
Revista: Plos One, 10 (2015) e0124639
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Nanoparticles, named cutinsomes, have been prepared from aleuritic (9,10,16-trihidroxipalmitic) acid and tomato fruit cutin monomers (a mixture of mainly 9(10), 16-dihydroxypalmitic acid (85%, w/w) and 16-hydroxyhexadecanoic acid (7.5%, w/w)) with pectin in aqueous solution. The process of formation of the nanoparticles of aleuritic acid plus pectin has been monitored by UV-Vis spectrophotometry, while their chemical and morphological characterization was analyzed by ATR-FTIR, TEM, and non-contact AFM. The structure of these nanoparticles can be described as a lipid core with a pectin shell. Pectin facilitated the formation of nanoparticles, by inducing their aggregation in branched chains and favoring the condensation between lipid monomers. Also, pectin determined the self-assembly of cutinsomes on highly ordered pyrolytic graphite (HOPG) surfaces, causing their opening and forming interconnected structures. In the case of cutin monomers, the nanoparticles are fused, and the condensation of the hydroxy fatty acids is strongly affected by the presence of the polysaccharide. The interaction of pectin with polyhydroxylated fatty acids could be related to an initial step in the formation of the plant biopolyester cutin.

Marzo, 2015 | DOI: 10.1371/journal.pone.0124639

Titulo: Effect of catalytic graphitization on the electrochemical behavior of wood derived carbons for use in supercapacitors
Autores: Gutierrez-Pardo, A; Ramirez-Rico, J; Cabezas-Rodriguez, R; Martinez-Fernandez, J
Revista: Journal of Power Sources, 278 (2015) 18-26
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Porous graphitic carbons were successfully obtained from wood precursors through pyrolysis using a transition metal as catalyst. Once the catalyst is removed, the resulting material mimics the microstructure of the wood and presents high surface area, open and interconnected porosity and large pore volume, high crystallinity and good electrical conductivity, making these carbons interesting for electrochemical devices. Carbons obtained were studied as electrodes for supercapacitors in half cell experiments, obtaining high capacitance values in a basic media (up to 133 F g−1 at current densities of 20 mA g−1 and 35 F g−1 at current densities of 1 A g−1). Long-cycling experiments showed excellent stability of the electrodes with no reduction of the initial capacitance values after 1000 cycles in voltammetry.

Febrero, 2015 | DOI: 10.1016/j.jpowsour.2014.12.030

Titulo: Synthesis temperature effect on Na-Mica-4 crystallinity and heteroatom distribution
Autores: Naranjo, M; Castro, MA; Cota, A; Osuna, FJ; Pavon, E; Alba, MD
Revista: Microporous and Mesoporous Materials, 204 (2015) 282-288
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The discovery of swelling brittle mica, Na-Mica-4, has been one of the most significant advances in the pursuit for a material with high ion-exchange capacity. For technical applications, the control of the phase evolution during the synthesis is crucial. The main aim of this study was to investigate the effect of Na-Mica-4 synthesis temperature on the crystalline phase evolution, Si–Al distribution in the tetrahedral sheet, the Al occupancy between tetrahedral and octahedral sites and their effects on the interlayer space composition. The synthesis temperature range between 600 °C and 900 °C was explored. At low temperature (600 °C), the precursors were transformed in a low-charged swelling 2:1 phyllosilicate, saponite type, which was progressively aluminum enriched with temperature. The high-charged swelling mica was completely formed at 700 °C, although a minor anhydrous contribution remained up to 850 °C. Up to 800 °C, silicates and fluorides secondary phases were detected as a minor contribution.

Febrero, 2015 | DOI: 10.1016/j.micromeso.2014.11.026

Titulo: Sliding wear resistance of sintered SiC-fiber bonded ceramics
Autores: Vera, MC; Ramirez-Rico, J; Martinez-Fernandez, J; Singh, M
Revista: International Journal of Refractory Metals & Hard Materials, 49 (2015) 232-239
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Advanced SiC-based ceramics and fiber reinforced composites are interesting materials for a wide variety of applications involving sliding wear conditions because of their excellent thermomechanical properties. The microstructure and wear resistance of sintered SiC fiber bonded ceramics (SA Tyrannohex) were studied. The material is composed of SiC-fibers in two orientations, with polygonal cross sections and cores having higher carbon content than their surroundings, as observed with SEM. A thin layer of C exists between the fibers. This layer has been found to be a turbostratic-layered structure oriented parallel to the fiber surface. XRD shows that the material is highly crystalline and composed mostly of β-SiC. Unlubricated wear behavior of the SA-Tyrannohex material when sliding against a Si3N4 ball in air at room temperature was evaluated. Experiments were performed using a pin on disk apparatus, under different normal loads of 2, 5 and 10 N at sliding speeds of 25, 50, 100 mm/s. A decrease of the friction coefficient with load was found due to the presence of the turbostratic carbon layer between the fibers. Wear rates of the order of 100 mm3/MJ were obtained, independently of sliding speed. Microfracture of the fibers is the main wear mechanism.

Febrero, 2015 | DOI: 10.1016/j.ijrmhm.2014.06.020

Titulo: Sliding wear resistance of biomorphic SiC ceramics
Autores: Vera, MC; Ramirez-Rico, J; Martinez-Fernandez, J; Singh, M
Revista: International Journal of Refractory Metals & Hard Materials, 49 (2015) 327-333
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Biomorphic SiC ceramics were fabricated from four different wood precursors and their Knoop hardness and sliding wear resistance when sliding against a Si3N4 ball in air were studied. Tribological experiments were performed using a pin on disk apparatus, under normal loads of 2 and 5 N, at a sliding speed of 100 mm/s. The effects of specimen porosity and microstructure on measured wear were evaluated. A commercial sintered silicon carbide ceramic was also tested for comparison. Small differences in friction coefficient comparable to monolithic SiC ceramics were obtained. Several concurrent wear mechanisms are taking place: microfracture, plastic deformation in the Si phase and oxidation of the Si and/or SiC phase. The presence of an oxide tribolayer was assessed using fluorescence microscopy. Wear rates were found to scale with SiC content and depend on residual porosity in the composite.

Febrero, 2015 | DOI: 10.1016/j.ijrmhm.2014.07.004

Titulo: Microstructure, elastic and inelastic properties of partially graphitized biomorphic carbons
Autores: Orlova, TS; Kardashev, BK; Smirnov, BI; Gutierrez-Pardo, A; Ramirez-Rico, J; Martinez-Fernandez, J
Revista: Physics of the Solid State, 57 (2015) 586-591
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The microstructural characteristics and amplitude dependences of the Young's modulus E and internal friction (logarithmic decrement delta) of biocarbon matrices prepared by beech wood carbonization at temperatures T (carb) = 850-1600A degrees C in the presence of a nickel-containing catalyst have been studied. Using X-ray diffraction and electron microscopy, it has been shown that the use of a nickel catalyst during carbonization results in a partial graphitization of biocarbons at T (carb) a parts per thousand yen 1000A degrees C: the graphite phase is formed as 50- to 100-nm globules at T (carb) = 1000A degrees C and as 0.5- to 3.0-mu m globules at T (carb) = 1600A degrees C. It has been found that the measured dependences E(T (carb)) and delta(T (carb)) contain three characteristic ranges of variations in the Young's modulus and logarithmic decrement with a change in the carbonization temperature: E increases and delta decreases in the ranges T (carb) < 1000A degrees C and T (carb) > 1300A degrees C; in the range 1000 < T (carb) < 1300A degrees C, E sharply decreases and delta increases. The observed behavior of E(T (carb)) and delta(T (carb)) for biocarbons carbonized in the presence of nickel correlates with the evolution of their microstructure. The largest values of E are obtained for samples with T (carb) = 1000 and 1600A degrees C. However, the samples with T (carb) = 1600A degrees C exhibit a higher susceptibility to microplasticity due to the presence of a globular graphite phase that is significantly larger in size and total volume.

Febrero, 2015 | DOI: 10.1134/S106378341503018X

Titulo: Polyester Films Obtained by Noncatalyzed Melt-Condensation Polymerization of Aleuritic (9,10,16-Trihydroxyhexadecanoic) Acid in Air
Autores: Benitez, JJ; Heredia-Guerrero, JA; Guzman-Puyol, S; Dominguez, E; Heredia, A
Revista: Journal of Applied Polymer, 132 (2015) Art. 41328
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To mimic nontoxic and fully biodegradable biopolymers like the plant cutin, polyester films from a natural occurring fatty polyhydroxyacid like aleuritic (9,10,16-trihydroxyhexadecanoic) acid have been prepared by noncatalyzed melt-polycondensation at moderate temperature (150 degrees C) directly in air. The course of the reaction has been followed by infrared spectroscopy, C-13 magic angle spinning nuclear magnetic resonance spectroscopy, differential scanning calorimetry and X-ray diffraction and well differentiated stages are observed. First, a high conversion esterification reaction leads to an amorphous rubbery, infusible, and insoluble material whose structure is made out of ester linkages mostly involving primary hydroxyls and partially branched by minor esterification with secondary ones. Following the esterification stage, the cleavage of vicinal secondary hydroxyls and further oxidation to carboxylic acid is observed at the near surface region of films. New carboxylic groups created also undergo esterification and generate cross-linking points within the polymer structure. Additionally, and despite the harsh preparation conditions used, very little additional side reaction like peroxidation and dehydration are observed. Results demonstrate the feasibility of polyester films fabrication from a reference fatty polyhydroxyacid like aleuritic acid by noncatalyzed melt-polycondensation directly in air. The methodology can potentially be extended to similar natural occurring hydroxyacids to obtain films and coatings to be used, for instance, as nontoxic and biodegradable food packaging material.

Diciembre, 2014 | DOI: 10.1002/app.41328

Titulo: Long-Chain Polyhydroxyesters from Natural Occurring Aleuritic Acid as Potential Material for Food Packaging
Autores: Benitez, JJ; Heredia-Guerrero, JA; Guzman-Puyol, S; Dominguez, E; Heredia, A
Revista: Soft Materials, 13 (2015) 5-11
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Fatty polyhydroxyesters (C≥16) are present in nature as barrier polymers like cutin in some protective tissues of higher plants. The mimicry of these biopolymers is regarded as a strategy to design nontoxic and fully biodegradable food packaging films and coatings. To obtain cutin inspired materials we have used a natural occurring polyhydroxylated monomer like aleuritic (9,10,16-trihydroxypalmitic) acid and a direct and scalable synthesis route consisting in the noncatalyzed melt-condensation polymerization in air. To reduce the number of hydroxyl groups and to increase hydrophobicity, palmitic acid has been used as a capping agent. Aleuritic-palmitic polyhydroxyesteres films have been obtained and characterized.

Diciembre, 2014 | DOI: 10.1080/1539445X.2014.993476

2014


Titulo: Ceramic Barrier Layers for Flexible Thin Film Solar Cells on Metallic Substrates: A Laboratory Scale Study for Process Optimization and Barrier Layer Properties
Autores: Delgado-Sanchez, JM; Guilera, N; Francesch, L; Alba, MD; Lopez, L; Sanchez, E
Revista: ACS Applied Materials & Interfaces, 6 (2014) 18543-18549
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Flexible thin film solar cells are an alternative to both utility-scale and building integrated photovoltaic installations. The fabrication of these devices over electrically conducting low-cost foils requires the deposition of dielectric barrier layers to flatten the substrate surface, provide electrical isolation between the substrate and the device, and avoid the diffusion of metal impurities during the relatively high temperatures required to deposit the rest of the solar cell device layers. The typical roughness of low-cost stainless-steel foils is in the hundred-nanometer range, which is comparable or larger than the thin film layers comprising the device and this may result in electrical shunts that decrease solar cell performance. This manuscript assesses the properties of different single-layer and bilayer structures containing ceramics inks formulations based on Al2O3, AlN, or Si3N4 nanoparticles and deposited over stainless-steel foils using a rotogravure printing process. The best control of the substrate roughness was achieved for bilayers of Al2O3 or AlN with mixed particle size, which reduced the roughness and prevented the diffusion of metals impurities but AlN bilayers exhibited as well the best electrical insulation properties.

Octubre, 2014 | DOI: 10.1021/am504923z

Titulo: Enhanced activity of clays and its crucial role for the activity in ethylene polymerization
Autores: Camejo-Abreu, C; Tabernero, V; Alba, MD; Cuenca, T; Terreros, P
Revista: Journal of Molecular Catalysis A-Chemical, 393 (2014) 96-104
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This paper presents a study of the effects of different treatments on the polymerization activity of modified clays as cocatalysts. To achieve this goal, an intercalating cation was introduced into two smectites and these clays were then modified with trimethyl aluminium. The results for ethylene polymerization, when a zirconocene complex was used as catalyst, and the structure analysis, allow us to obtain interesting deductions about the generation mode of the active species. All active materials employed as support activators presented aluminium in a pentahedral environment together with acidic hydrogen atoms. These two features were detected only after TMA treatment and they seem to be crucial elements in active cocatalyst generation. Moreover, a material without structural aluminium displayed the best activity pointing to the new aluminium species generated in the solid matrix as the determining factor for the activity. We proposed a synergic effect between Lewis acid aluminium centres and acidic Bronsted protons that generate the SiOHAl groups that activate the zirconium compound.

Octubre, 2014 | DOI: 10.1016/j.molcata.2014.05.030

Titulo: Quantification and comparison of the reaction properties of FEBEX and MX-80 clays with saponite: Europium immobilisers under subcritical conditions
Autores: Villa-Alfageme, M; Hurtado, S; Castro, MA; El Mrabet, S; Orta, MM; Pazos, MC; Alba, MD
Revista: Applied Clay Science, 101 (2014) 10-15
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The evaluation of the retention mechanisms in FEBEX and MX-80 bentonites, selected as reference materials to construct engineered barriers, carries major implications in the safe storage of immobilisation capacity through a recently discovered chemical retention mechanism and the structural analysis of the reaction products. Hydrothermal treatments were accomplished with immobilisation capacity through a recently discovered chemical retention mechanism and the structural analysis of the reaction products. Hydrothermal treatments were accomplished with Eu(NO3)3 (151Eu and 153Eu, with 52.2% 153Eu) and spiked with radioactive 152Eu for the quantification of the reactions. Results were compared with saponite as the reference smectite. The strong dependence of the reaction parameters with temperature and time was quantified and the reaction velocity was evaluated. The velocity follows these trends: 240 days are needed for the total retention of europium for temperatures over 200 °C; below 150 °C, significantly longer reaction times, on the order of three years, are required to complete the reaction. Clays do not influence velocity rates, but the retention capacity of bentonites remains lower than for saponite. At 300 °C, the milliequivalents retained by the three clays are consistently over CEC. The structural analyses reveal not only adsorption of europium but also the presence of Eu(OH)3 precipitation and Eu2SiO3 confirming the existence of a chemical reaction.

Octubre, 2014 | DOI: 10.1016/j.clay.2014.08.012

Titulo: Characterization of porous graphitic monoliths from pyrolyzed wood
Autores: Gutierrez-Pardo, A; Ramirez-Rico, J; de Arellano-Lopez, AR; Martinez-Fernandez, J
Revista: Journal of Materials Science, 49 (2014) 7688-7696
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Porous graphitic carbons were obtained from wood precursors using Ni as a graphitization catalyst during pyrolysis. The structure of the resulting material retains that of the original wood precursors with highly aligned, hierarchical porosity. Thermal characterization was performed by means of thermogravimetry and differential scanning calorimetry, and the onset temperature for graphitization was determined to be similar to 900 A degrees C. Structural and microstructural characterization was performed by means of electron microscopy, electron and x-ray diffraction, and Raman spectroscopy. The effect of maximum pyrolysis temperature on the degree of graphitization was assessed. No significant temperature effect was detected by means of Raman scattering in the range of 1000-1400 A degrees C, but at temperatures over the melting point of the catalyst, the formation of graphite grains with long-range order was detected.

Octubre, 2014 | DOI: 0.1007/s10853-014-8477-8

Titulo: Direct evidence of Lowenstein's rule violation in swelling high-charge micas
Autores: Pavon, E; Osuna, FJ; Alba, MD; Delevoye, L
Revista: Chemical Communications, 53 (2014) 6984-6986
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The structure of high-charged micas, Na-n-micas (n = 2 and 4), a family of synthetic silicates with a wide range of applications, was investigated through the use of 17O solid-state NMR at natural abundance in order to preserve quantitative spectral information. The use of a very high-field and highly sensitive probehead, together with 17O NMR literature data allowed for the detection of an isolated signal at 26 ppm, assigned partially to AlOAl, as evidence of the violation of Lowenstein's rule for Na-4-mica.

Junio, 2014 | DOI: 10.1039/C4CC01632G

Titulo: Biomimetic polymers of plant cutin: an approach from molecular modeling
Autores: San-Miguel, MA; Oviedo, J; Heredia-Guerrero, JA; Heredia, A; Benitez, JJ
Revista: Journal of Molecular Modeling, 20 (2014) 2329
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Biomimetics of materials is based on adopting and reproducing a model in nature with a well-defined functionality optimized through evolution. An example is barrier polymers that protect living tissues from the environment. The protecting layer of fruits, leaves, and non-lignified stems is the plant cuticle. The cuticle is a complex system in which the cutin is the main component. Cutin is a biopolyester made of polyhydroxylated carboxylic acids of 16 and 18 carbon atoms. The biosynthesis of cutin in plants is not well understood yet, but a direct chemical route involving the self-assembly of either molecules or molecular aggregates has been proposed. In this work, we present a combined study using experimental and simulation techniques on self-assembled layers of monomers selectively functionalized with hydroxyl groups. Our results demonstrate that the number and position of the hydroxyl groups are critical for the interaction between single molecules and the further rearrangement. Also, the presence of lateral hydroxyl groups reinforces lateral interactions and favors the bi-dimensional growth (2D), while terminal hydroxyl groups facilitate the formation of a second layer caused by head–tail interactions. The balance of 2D/3D growth is fundamental for the plant to create a protecting layer both large enough in 2D and thick enough in 3D.

Junio, 2014 | DOI: 10.1007/s00894-014-2329-y

Titulo: Infrared and Raman spectroscopic features of plant cuticles: a review
Autores: Heredia-Guerrero, JA; Benitez, JJ; Dominguez, E; Bayer, IS; Cingolani, R; Athanassiou, A; Heredia, A
Revista: Frontiers in Plant Science, 25 (2014)
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The cuticle is one of the most important plant barriers. It is an external and continuous lipid membrane that covers the surface of epidermal cells and whose main function is to prevent the massive loss of water. The spectroscopic characterization of the plant cuticle and its components (cutin, cutan, waxes, polysaccharides and phenolics) by infrared and Raman spectroscopies has provided significant advances in the knowledge of the functional groups present in the cuticular matrix and on their structural role, interaction and macromolecular arrangement. Additionally, these spectroscopies have been used in the study of cuticle interaction with exogenous molecules, degradation, distribution of components within the cuticle matrix, changes during growth and development and characterization of fossil plants.

Mayo, 2014 | DOI: 10.3389/fpls.2014.00305

Titulo: Influence of the synthesis parameter on the interlayer and framework structure of lamellar octadecyltrimethylammonium kanemite
Autores: Corredor, JI; Cota, A; Pavon, E; Osuna, FJ; Alba, MD
Revista: Applied Clay Science, 95 (2014) 9-17
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Inorganic–organic nanostructures, used as host materials for selective adsorption of functional molecules and as mesostructured material precursors, can be constructed by the interlayer modification of inorganic layered materials with surfactants. The formation mechanism is mainly determined by the surfactant assemblies in the 2D limited space. In this paper, a detailed structural analysis of the lamellar mesophases prepared from kanemite, a lamellar silicate, and octadecyltrimethylammonium (ODTMA) under various conditions was reported. The adsorbed amount of ODTMA and the long and short range structural orders were explored by TGA, XRD, IR/FT and MAS NMR spectroscopies. The results revealed that ODTMA molecules were efficiently intercalated in the interlayer space of kanemite and, in all synthesis conditions, an ordered lamellar structure was obtained. The ODTMA adsorption in kanemite caused changes not only in the interlayer space but also in the silicate framework, where five-member rings were formed. The characteristics of the final products were influenced by the synthesis conditions, although the separation mode, filtration or centrifugation, was not relevant. Therefore, the adsorption conditions of ODTMA in kanemite will contribute to the design of novel layered materials with potential environmental and technological use.

Mayo, 2014 | DOI: 10.1016/j.clay.2014.02.030

Titulo: Biomechanical properties of the tomato (Solanum lycopersicum) fruit cuticle during development are modulated by changes in the relative amounts of its components
Autores: Espana, L; Heredia-Guerrero, JA; Segado, P; Benitez, JJ; Heredia, A; Dominguez, E
Revista: New Phytologist, 202 (3) (2014) 790-802
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Keywords:
attenuated total reflectance–Fourier transform infrared (ATR-FTIR);biomechanics;cuticle;cutin;flavonoids;tomato (Solanum lycopersicum) fruit


Summary

- In this study, growth-dependent changes in the mechanical properties of the tomato (Solanum lycopersicum) cuticle during fruit development were investigated in two cultivars with different patterns of cuticle growth and accumulation.

- The mechanical properties were determined in uniaxial tensile tests using strips of isolated cuticles. Changes in the functional groups of the cuticle chemical components were analysed by attenuated total reflectance–Fourier transform infrared (ATR-FTIR).

- The early stages of fruit growth are characterized by an elastic cuticle, and viscoelastic behaviour only appeared at the beginning of cell enlargement. Changes in the cutin:polysaccharide ratio during development affected the strength required to achieve viscoelastic deformation. The increase in stiffness and decrease in extensibility during ripening, related to flavonoid accumulation, were accompanied by an increase in cutin depolymerization as a result of a reduction in the overall number of ester bonds.

- Quantitative changes in cuticle components influence the elastic/viscoelastic behaviour of the cuticle. The cutin:polysaccharide ratio modulates the stress required to permanently deform the cuticle and allow cell enlargement. Flavonoids stiffen the elastic phase and reduce permanent viscoelastic deformation. Ripening is accompanied by a chemical cleavage of cutin ester bonds. An infrared (IR) band related to phenolic accumulation can be used to monitor changes in the cutin esterification index.

Abril, 2014 | DOI: 10.1111/nph.12727

Titulo: Thermal conductivity at the amorphous-nanocrystalline phase transition in beech wood biocarbon
Autores: Parfen'eva, LS; Orlova, TS; Smirnov, BI; Smirnov, IA; Misiorek, H; Jezowski, A; Ramirez-Rico, J
Revista: Physica of the Solid State, 56 (2014) 1071-1080
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High-porosity samples of beech wood biocarbon (BE-C) were prepared by pyrolysis at carbonization temperatures T carb = 650, 1300, and 1600°C, and their resistivity ρ and thermal conductivity κ were studied in the 5–300 and 80–300 K temperature intervals. The experimental results obtained were evaluated by invoking X-ray diffraction data and information on the temperature dependences ρ(T) and κ(T) for BE-C samples prepared at T carb = 800, 1000, and 2400°C, which were collected by the authors earlier. An analysis of the κ(T carb) behavior led to the conclusion that the samples under study undergo an amorphous-nanocrystalline phase transition in the interval 800°C < T carb < 1000°C. Evaluation of the electronic component of the thermal conductivity revealed that the Lorentz number of the sample prepared at T carb = 2400°C exceeds by far the classical Sommerfeld value, which is characteristic of metals and highly degenerate semiconductors.

Abril, 2014 | DOI: 10.1134/S1063783414050229

Titulo: Effect of clays and metal containers in retaining Sm3+ and ZrO2+ and the process of reversibility
Autores: El Mrabet, S; Castro, MA; Hurtado, S; Orta, MM; Pazos, MC; Villa-Alfageme, M; Alba, MD
Revista: American Mineralogist, 99 (4) (2014) 696-703
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Knowledge and understanding about radionuclides retention processes on the materials composing the engineered barrier (clay mineral and metallic container waste) are required to ensure the safety and the long-term performance of radioactive waste disposal. Therefore, the present study focuses on the competitiveness of clay and the metallic container in the process of adsorption/desorption of the radionuclides simulators of Am3+ and UO22+. For this purpose, a comparative study of the interaction of samarium (chosen as chemical analog for trivalent americium) and zirconyl (as simulator of uranyl and tetravalent actinides) with both FEBEX bentonite and metallic container, under subcritical conditions, was carried out. The results revealed that the AISI-316L steel container, chemical composition detailed in Table 1, immobilized the high-radioactive waste (HRW), even during the corrosion process. The ZrO2+ was irreversibly adsorbed on the minireactor surface. In the case of samarium SEM/EDX analysis revealed the formation of an insoluble phase of samarium silicate on the container surface. There was no evidence of samarium diffusion through the metallic container. Samarium remained adsorbed by the container also after desorption experiment with water. Therefore, steel canister is actively involved in the HRW immobilization.

Marzo, 2014 | DOI: 10.2138/am.2014.4665

Titulo: A new route of synthesis of Na-Mica-4 from sodalite
Autores: Naranjo, M; Castro, MA; Cota, A; Pavon, E; Pazos, MC; Alba, MD
Revista: Microporous and Mesoporous Materials, 188 (2014) 176-180
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Synthesis of Na-Mica-4 has been achieved by a “mix and calcine” method using sodalite and magnesium fluoride as the only precursors. Previous research found sodalite as a key intermediate reaction product in the formation of Na-Mica-4 when the NaCl melt method was employed. Similarities in structure, chemical composition and cation distribution in products using the proposed method and the NaCl melt method are described and suggest that Na-Mica-4 is a very stable product. The use of sodalite as precursor provokes microporous formation in the final mica. The absence of excess Na leads to a lower particle size and to the presence of less impurity in the calcined product. Different sodalites could be used in the synthesis of different Na-Mica-4 with presumably different physicochemical properties.

Febrero, 2014 | DOI: 10.1016/j.micromeso.2013.12.004

Titulo: Effect of carbonization temperature on the microplasticity of wood-derived biocarbon
Autores: Shpeizman, VV; Orlova, TS; Kardashev, BK; Smirnov, BI; Gutierrez-Pardo, A; Ramirez-Rico, J
Revista: Physics of the Solid State, 56 (2014) 538-545
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The uniaxial compression strength under stepped loading and the 325-nm-stepped deformation rate of biocarbon samples obtained by carbonization of beech wood at different temperatures in the 600–1600°C range have been measured using high-precision interferometry. It has been shown that the strength depends on the content of nanocrystalline phase in biocarbon. The magnitude of deformation jumps at micro- and nanometer levels and their variation with a change in the structure of the material and loading time have been determined. For micro- and nanometer-scale jumps, standard deviations of the differences between the experimentally measured deformation rate at loading steps and its magnitude at the smoothed fitting curve have been calculated, and the correlation of the error with the deformation prior to destruction has been shown. The results obtained have been compared with the previously published data on measurements of the elastic properties and internal friction of these materials.

Febrero, 2014 | DOI: 10.1134/S1063783414030305

Titulo: New Bio-Ceramization Processes Applied to Vegetable Hierarchical Structures for Bone Regeneration: An Experimental Model in Sheep
Autores: Filardo, G; Kon, E; Tampieri, A; Cabezas-Rodriguez, R; Di Martino, A; Fini, M; Giavaresi, G; Lelli, M; Martinez-Fernandez, J; Martini, L; Ramirez-Rico, J; Salamanna, F; Sandri, M; Sprio, S; Marcacci, M
Revista: Tissue Engineering Part A, 20 (2014) 763-773
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Bone loss is still a major problem in orthopedics. The purpose of this experimental study is to evaluate the safety and regenerative potential of a new scaffold based on a bio-ceramization process for bone regeneration in long diaphyseal defects in a sheep model. The scaffold was obtained by transformation of wood pieces into porous biomorphic silicon carbide (BioSiC®). The process enabled the maintenance of the original wood microstructure, thus exhibiting hierarchically organized porosity and high mechanical strength. To improve cell adhesion and osseointegration, the external surface of the hollow cylinder was made more bioactive by electrodeposition of a uniform layer of collagen fibers that were mineralized with biomimetic hydroxyapatite, whereas the internal part was filled with a bio-hybrid HA/collagen composite. The final scaffold was then implanted in the metatarsus of 15 crossbred (Merinos-Sarda) adult sheep, divided into 3 groups: scaffold alone, scaffold with platelet-rich plasma (PRP) augmentation, and scaffold with bone marrow stromal cells (BMSCs) added during implantation. Radiological analysis was performed at 4, 8, 12 weeks, and 4 months, when animals were sacrificed for the final radiological, histological, and histomorphometric evaluation. In all tested treatments, these analyses highlighted the presence of newly formed bone at the bone scaffolds' interface. Although a lack of substantial effect of PRP was demonstrated, the scaffold+BMSC augmentation showed the highest value of bone-to-implant contact and new bone growth inside the scaffold. The findings of this study suggest the potential of bio-ceramization processes applied to vegetable hierarchical structures for the production of wood-derived bone scaffolds, and document a suitable augmentation procedure in enhancing bone regeneration, particularly when combined with BMSCs.

Enero, 2014 | DOI: 10.1089/ten.tea.2013.0108

Titulo: Interaction of Hydrated Cations with Mica-n (n = 2, 3 and 4) Surface
Autores: Pavon, E; Castro, MA; Cota, A; Osuna, FJ; Pazos, MC; Alba, MD
Revista: Journal of Physical Chemistry C, 118 (2014) 2115-2121
resumen | texto completo


High charged swelling micas, with layer charge between 2 and 4, have been found to readily swell with water, and complete cation exchange (CEC) can be achieved. Because of their high CEC, applications like radioactive cation fixation or removal of heavy metal cations from wastewater were proposed. Their applicability can be controlled by the location of the interlayer cation in a confined space with a high electric field. In synthetic brittle micas, the interlayer cation has a low water coordination number; therefore, their coordination sphere would be completed by the basal oxygen of the tetrahedral layer as inner-sphere complexes (ISC). However, no direct evidence of these complexes formation in brittle micas has been reported yet. In this contribution, we mainly focus on the understanding the mechanisms that provoke the formation of ISC in high charge swelling micas, Mica-n. A whole series of cations (X) were used to explore the influence of the charge and size of the interlayer cation. Three brittle swelling micas, Mica-n (n = 4, 3 and 2), were selected in order to analyze the influence of the layer charge in the formation of ISC. The contribution of the ISC has been analyzed thorough the evolution of the 060 reflection and the changes in the short-range order of the tetrahedral cations will be followed 29Si and 27Al MAS NMR. The results showed that ISC was favored in X-Mica-4 and that provoked a high distortion angle between the Si–Al tetrahedra. When the content of aluminum decreases, the electrostatic forces between the layers are relaxed, and the hydrated cations did not interact so strongly with the tetrahedral sheet, having the opportunity to complete their hydration sphere.

Diciembre, 2013 | DOI: 10.1021/jp4110695

Titulo: Competitive effect of the metallic canister and clay barrier on the sorption of Eu3+ under subcritical conditions
Autores: El Mrabet, S; Castro, MA; Hurtado, S; Orta, MM; Pazos, MC; Villa-Alfageme, M; Alba, MD
Revista: Applied Geochemistry, 40 (2014) 25-31
resumen | texto completo


An in depth knowledge and understanding of high activity radionuclide (HLRW) immobilization processes on the materials composing the engineered barrier (clay and metallic canister) is required to ensure the safety and the long-term performance of radioactive waste disposal procedures. Therefore, the aim of this study was to understand the mechanisms involved in the retention of Eu3+ by two components of the multibarrier system, the bentonite barrier and the canister. As such, a comparative study of the interaction of trivalent Eu3+, used to simulate trivalent actinides, with both bentonite and a metallic canister has been undertaken in this work. To this end, we designed a minireactor into which the bentonite was introduced and compacted. The minireactor-bentonite system was then submitted to a hydrothermal reaction with a 7.9 × 10−2 M solution of Eu3+ at 300 °C for 4.5 days. SEM and XRD results revealed that both bentonite and the container were involved in the immobilization of europium by the formation of insoluble europium silicate phases. The presence of europium silicate adsorbed on the surface of the metallic canister indicates the competitive effect of both components of the engineered barrier (bentonite and metallic canister) in HLRW immobilization. These results suggested that the canister could play a role in the HLRW immobilization even during its corrosion process.

Diciembre, 2013 | DOI: j.apgeochem.2013.10.014

2013


Titulo: Modeling Macro-Sized, High Aspect Ratio Through-Hole Filling by Multi-Component Additive-Assisted Copper Electrodeposition
Autores: Childers, AS; Johnson, MT; Ramirez-Rico, J; Faber, KT
Revista: Journal of the Electrochemical Society, 160 (2013) D3093-D3102
resumen | texto completo


A multi-element, time-dependent model is used to examine additive-assisted copper electroplating in macro-channels. This model is an adaptation of the work of Akolkar and Landau [J. Electrochem. Soc., 156, D351 (2009)], used to describe plating in micro-vias for integrated circuits. Using their method for describing species movement in the channel, the model has been expanded to include transport and adsorption limitations of the inhibitor and accelerator, as well as the copper ions in solution. The model is used to investigate copper plating as an infiltration method across many size scales and aspect ratios. Biomorphic graphite scaffolds produced from wood are used as a representative system and the results of a two-additive bath are used to characterize the behavior of the additives and determine the effectiveness of the plating. The results indicate that at macro-scales, channel dimensions play an increasingly important role in dictating the behavior of additive-assisted plating. Because additive systems are designed to establish differential surface coverage within the channel, the success of which is determined by the additive's rates of diffusion and adsorption, certain size scale/aspect ratio combinations preclude such coverage. A guide for sample geometries that may be successfully infiltrated with a two-additive bath is provided.

Noviembre, 2013 | DOI: 10.1149/2.018312jes

Titulo: Thermal conductivity of wood-derived graphite and copper–graphite composites produced via electrodeposition
Autores: Johnson, MT; Childers, AS; Ramirez-Rico, J; Wang, H; Faber, KT
Revista: Composites Part A: Applied Science and Manufaturing, 63 (2013) 182-189
resumen | texto completo


The thermal conductivity of wood-derived graphite and graphite/copper composites was studied both experimentally and using finite element analysis. The unique, naturally-derived, anisotropic porosity inherent to wood-derived carbon makes standard porosity-based approximations for thermal conductivity poor estimators. For this reason, a finite element technique which uses sample microstructure as model input was utilized to determine the conductivity of the carbon phase independent of porosity. Similar modeling techniques were also applied to carbon/copper composite microstructures and predicted conductivities compared well to those determined via experiment.

Septiembre, 2013 | DOI: 10.1016/j.compositesa.2013.06.009

Titulo: Structure-mediated transition in the behavior of elastic and inelastic properties of beach tree bio-carbon
Autores: Kardashev, BK; Orlova, TS; Smirnov, BI; Gutierrez, A; Ramirez-Rico, J
Revista: Physics of the Solid State, 55 (2013) 1884-1891
resumen | texto completo


Microstructural characteristics and amplitude dependences of the Young modulus E and of internal friction (logarithmic decrement δ) of bio-carbon matrices prepared from beech tree wood at different carbonization temperatures T carb ranging from 600 to 1600°C have been studied. The dependences E(T carb) and δ(T carb) thus obtained revealed two linear regions of increase of the Young modulus and of decrease of the decrement with increasing carbonization temperature, namely, ΔE ∼ AΔT carb and Δδ ∼ BΔT carb, with A ≈ 13.4 MPa/K and B ≈ −2.2 × 10−6 K−1 for T carb < 1000°C and A ≈ 2.5 MPa/K and B ≈ −3.0 × 10−7 K−1 for T carb > 1000°C. The transition observed in the behavior of E(T carb) and δ(T carb) at T carb = 900–1000°C can be assigned to a change of sample microstructure, more specifically, a change in the ratio of the fractions of the amorphous matrix and of the nanocrystalline phase. For T carb < 1000°C, the elastic properties are governed primarily by the amorphous matrix, whereas for T carb > 1000°C the nanocrystalline phase plays the dominant part. The structurally induced transition in the behavior of the elastic and microplastic characteristics at a temperature close to 1000°C correlates with the variation of the physical properties, such as electrical conductivity, thermal conductivity, and thermopower, reported in the literature.

Agosto, 2013 | DOI: 10.1134/S1063783413090151

Titulo: Monolayer arrangement of fatty hydroxystearic acids on graphite: Influence of hydroxyl groups
Autores: Medina, S; Benitez, JJ; Castro, MA; Cerrillos, C; Millan, C; Alba, MD
Revista: Thin Solid Films, 539 (2013) 194-200
resumen | texto completo


Previous studies have indicated that long-chain linear carboxylic acids form commensurate packed crystalline monolayers on graphite even at temperatures above their melting point. This study examines the effect on the monolayer formation and structure of adding one or more secondary hydroxyl, functional groups to the stearic acid skeleton (namely, 12-hydroxystearic and 9,10-dihydroxystearic acid). Moreover, a comparative study of the monolayer formation on recompressed and monocrystalline graphite has been performed through X-ray diffraction (XRD) and Scanning Tunneling Microscopy (STM), respectively. The Differential Scanning Calorimetry (DSC) and XRD data were used to confirm the formation of solid monolayers and XRD data have provided a detailed structural analysis of the monolayers in good correspondence with obtained STM images. DSC and XRD have demonstrated that, in stearic acid and 12-hydroxystearic acid adsorbed onto graphite, the monolayer melted at a higher temperature than the bulk form of the carboxylic acid. However, no difference was observed between the melting point of the monolayer and the bulk form for 9,10-dihydroxystearic acid adsorbed onto graphite. STM results indicated that all acids on the surface have a rectangular p2 monolayer structure, whose lattice parameters were uniaxially commensurate on the a-axis. This structure does not correlate with the initial structure of the pure compounds after dissolving, but it is conditioned to favor a) hydrogen bond formation between the carboxylic groups and b) formation of hydrogen bonds between secondary hydroxyl groups, if spatially permissible. Therefore, the presence of hydroxyl functional groups affects the secondary structure and behavior of stearic acid in the monolayer.

Junio, 2013 | DOI: 10.1016/j.tsf.2013.05.053

Titulo: Evaluation of rare earth on layered silicates under subcritical conditions: Effect of the framework and interlayer space composition
Autores: Chain, P; Cota, A; El Mrabet, S; Pavon, E; Pazos, MC; Alba, MD
Revista: Chemical Geology, 347 (2013) 208-216
resumen | texto completo


Clay-based minerals are considered to be an important component in backfill barriers due to both their ability to seal and adsorb radioactive waste and to interact chemically with it under subcritical conditions. Herein, we describe a systematic study of the properties of layered silicates that could affect their hydrothermal reactivity, namely type of layers, octahedral occupancy, origin and total amount of the layer charge, and nature of the interlayer cation. The silicates studied were selected on the basis of their different characteristics associated with these properties and were treated hydrothermally at 300 °C for 48 h in a 7.3 · 10− 2 M Lu(NO3)3 · 3.6H2O solution. The final products were analyzed by X-ray diffraction and solid-state NMR spectroscopy. All the layered silicates studied were found to be able to generate a Lu2Si2O7 phase after hydrothermal treatment under subcritical conditions, thereby confirming the participation of a chemical mechanism of the clay barrier generating phases being stables with temperature and pH conditions. However, the extent of this reaction depends to a large extent on the physicochemical properties of the framework and the interlayer space composition, such as the presence or absence of an octahedral sheet, the degree of occupancy of this sheet, and the origin and total layer charge. Therefore, this study allows tuning the clay mineral framework characteristic that favors the rare earth cations (as trivalent actinide simulator) immobilization.

Mayo, 2013 | DOI: 10.1016/j.chemgeo.2013.03.006

Titulo: Solution Properties of the System ZrSiO4–HfSiO4: A Computational and Experimental Study
Autores: Cota, Agustin; Burton, Benjamin P.; Chain, Pablo; Pavon, Esperanza; Alba, Maria D.
Revista: Journal of Physical Chemistry C, 117 (2013) 10013-10019
resumen | texto completo


ZrSiO4 and HfSiO4 are of considerable interest because of their low thermal expansions, thermal conductivities, and the optical properties of HfSiO4. In addition, silicate phases of both are studied as model radioactive waste disposal materials. Previous first principles calculations reported near ideal mixing in the Zr1–xHfxSiO4 system, with a very weak propensity for phase separation. Density functional theory (DFT)/cluster-expansion first principles calculations presented in this work indicate near ideal mixing with a very weak propensity for ordering. Zr1–xHfxSiO4 samples (x = 0, 0.25, 0.5, 0.75, and 1.0) were synthesized from intimate stoichiometric mixtures of constituent-oxides and annealing at 1823 K for 20 days in a platinum crucible. Samples were characterized by X-ray diffraction (XRD; Rietveld analysis) and 29Si MAS NMR. The XRD data exhibited a pronounced negative deviation from Vegard’s law in the excess volume of mixing, and the 29Si MAS NMR spectra also suggest nonideal mixing. Given the very weak energetics that favor cation ordering, it is clear that there must be some other cause(s) for the observed deviations from ideal mixing behavior.

Abril, 2013 | DOI: 10.1021/jp401539g

Titulo: Synthesis and characterization of kanemite from fluoride-containing media: Influence of the alkali cation
Autores: Corredor, JI; Cota, A; Pavon, E; Alba, MD
Revista: American Mineralogist, 98 (2013) 1000-1007
resumen | texto completo


Kanemite belongs to the group of naturally occurring sodium silicate minerals that was first found in Kanem, at the edge of the Lake Chad, and has been synthesized in different ways from NaOH-SiO2 mixtures and used as precursor for the design of microporous and mesoporous materials. The fluoride route to the synthesis of microporous materials is based on the substitution of OH− anions by fluoride anions, which may subsequently also play a mineralizing role, and gives rise to materials with higher hydrophobicity and thermal and hydrothermal stability. Moreover, F− plays an important role in the incorporation of framework heteroatoms, thereby affecting the activity of the final material. The aim of this study was to synthesize fluorokanemite using different synthetic routes and different F− source. The final product was characterized by a combination of methods that provided information regarding the incorporation of fluorine into the framework and the short- and long-range structural order of the fluorosilicate. Kanemite with water content close to ideal was obtained in all cases. The washing process was found to have no effect in the long- or short-range structural order of the layer framework, although it did affect the structure of the cation in the interlayer space of kanemite. The mineralizing agent therefore appears to be the key to the synthesis. Furthermore, it governs the resulting kanemite structure by controlling the formation of hydrogen bonds in the framework, and therefore the degree of lamellar structure condensation.

Abril, 2013 | DOI: 10.2138/am.2013.4372

Titulo: Joining and interface characterization of in situ reinforced silicon nitride
Autores: Asthana, R; Singh, M; Martinez-Fernandez, J
Revista: Journal of Alloys and Compounds, 552 (2013) 137-145
resumen | texto completo


Copper-base active metal interlayers were used to bond in situ reinforced silicon nitride (Honeywell AS800) at 1317 K for 5 and 30 min in vacuum. The joints were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron back scattered diffraction (EBSD), and transmission electron microscopy (TEM). A Ti-rich interaction zone (∼3.0–3.5 μm thick) formed at the Si3N4/braze interface. This reaction layer grew toward the inner part of the joint with a featureless microstructure, creating a strong bond. Regions of a Ti-rich phase were frequently found next to the reaction layer but surrounded by the Cu alloy. Extensive Ti and Si enrichments were noted at the interface but there was no evidence of interfacial segregation of Y, La, and Sr (from Y2O3, La2O3 and SrO, added as sintering aids). The reaction layer thickness and composition did not change when brazing time increased from 5 min to 30 min suggesting rapid growth kinetics in the early stages of reaction. The joints were crack-free and showed features associated with plastic deformation, which indicated that the metal interlayer accommodated strain associated with CTE mismatch. The inner part of the joint consisted of highly textured large grains of the braze alloy.

Febrero, 2013 | DOI: 10.1016/j.jallcom.2012.09.104

Titulo: Hydration properties of synthetic high-charge micas saturated with different cations: An experimental approach
Autores: Pavon, E; Castro, MA; Naranjo, M; Orta, MM; Pazos, MC; Alba, MD
Revista: American Mineralogist, 98 (2013) 394-400
resumen | texto completo


An understanding of the interaction mechanisms between exchangeable cations and layered silicates is of interest from both a basic and an applied point of view. Among 2:1 phyllosilicates, a new family of swelling high-charge synthetic micas has been shown to be potentially useful as decontaminant. However, the location of the interlayer cations, their acidity and the water structure in the interlayer space of these silicates are still unknown. The aim of this paper was therefore to study the hydration state of the interlayer cations in the interlayer space of high-charge expandable micas and to evaluate the effect that this hydration has on the swelling and acidity behavior of these new materials. To achieve these objectives, three synthetic micas with different charge density total layer charges (ranging between 2 and 4 per unit cell) and with five interlayer cations (Na+, Li+, K+, Mg2+, and Al3+) were synthesized and their hydration state, interlayer space, and acidity analyzed by DTA/TG, XRD, and 1H MAS NMR spectroscopy. The results showed that the hydration state depends on both the layer charge and the nature of the interlayer cation. A high participation of the inner-sphere complexes in the highly charged confined space has been inferred and proposed to induce Brønsted acidity in the solid.

Febrero, 2013 | DOI: 10.2138/​am.2013.4217

Titulo: Heat capacity of Bio-SiC and SiC/Si ecoceramics prepared from white eucalyptus, beech, and sapele tree wood
Autores: Smirnov, IA; Smirnov, BI; Orlova, TS; Wlosewicz, D; Hackemer, A; Misiorek, H; Mucha, J; Jezowski, A; Ramirez-Rico, J; Martinez-Fernandez, J
Revista: Physics of the Solid State, 55 (2013) 454-460
resumen | texto completo


This paper reports on measurement of the heat capacity at constant pressure C p of silicon bio-carbide prepared within the 5–300 K temperature interval from beech tree wood (bio-SiC(BE)), and within 80–300 K, from tree wood of sapele (bio-SiC(SA)), as well as SiC/Si ecoceramics of beech, sapele, and white eucalyptus wood. It has been shown that in bio-SiC(BE) the measured heat capacity contains a significant contribution of surface heat capacity, whose magnitude decreases with increasing temperature. Of the ecoceramics, only SiC/Si(SA) characterized by a high enough porosity has revealed a small contribution to the heat capacity coming from its surface component. The experimental results obtained are discussed.

Enero, 2013 | DOI: 10.1134/S1063783413020285

Titulo: Thermopower of Bio-SiC and SiC/Si ecoceramics prepared from sapele tree wood
Autores: Smirnov, IA; Smirnov, BI; Orlova, TS; Sulkovski, C; Misiorek, H; Muha, J; Jezowski, A; Ramirez-Rico, J; Martinez-Fernandez, J
Revista: Physics of the Solid State, 55 (2013) 54-59
resumen | texto completo


The thermopower coefficients of bio-SiC and SiC/Si ecoceramics prepared from sapele tree wood have been measured in the temperature interval 5–300 K. The measurements have been performed both along and perpendicular to empty (bio-SiC), as well as empty and partially silicon-filled (SiC/Si) channels in the samples. In bio-SiC, a contribution to thermopower associated with electron drag by phonons has been shown to exist within the temperature interval 5–200 (250) K. No such effect is realized in SiC/Si. This is assumed to derive from the presence in this material of heavily doped silicon embedded in SiC channels and the dominant part it plays in the behavior of the thermopower of this ceramics. The results obtained for the thermopower are compared with the available data for bio-SiC prepared from white eucalyptus tree wood and heavily doped bismuth.

Diciembre, 2012 | DOI: 10.1134/S1063783413010307

2012


Titulo: Microstructural and high-temperature mechanical characteristics of nickel oxide/zirconia composites for solid oxide fuel cells
Autores: Oliva-Ramirez, M.; Huaman-Mamani, F. A.; Jimenez-Melendo, M.
Revista: Fuel Processing Technology, 103 (2012) 45-50
resumen | texto completo


NiO/8YSZ (8 mol% Y 2O 3-stabilized ZrO 2) composites with different NiO contents (10, 20 and 40 mol%) have been fabricated by a conventional route of mechanical mixing of NiO and 8YSZ powders and sintering at 1500 °C for 10 h in air. The resulting microstructures have been characterized by electron microscopy. In 10 and 20 mol% NiO/8YSZ, the composite is formed by isolated NiO particles surrounded by zirconia matrix grains; this phase is interconnected in the 40 mol% NiO/8YSZ composite. Mechanical tests at constant strain rate and at constant load were conducted on these materials at temperatures of up to 1350 °C. Different behaviors were found depending on the percolation of the NiO phase. Microstructural observations after deformation are essential to understand the overall mechanical behavior of the composites.

Octubre, 2012 | DOI: 10.1016/j.fuproc.2011.09.013

Titulo: Effect of ytterbium doping on the microstructure and plastic deformation of BaCeO3 perovskite oxide
Autores: Jimenez-Melendo, M; Vaquero-Aguilar, C; Huaman-Mamani, FA
Revista: Fuel Processing Technology, 103 (2012) 146-150
resumen | texto completo


Trivalent cation-doped barium cerate perovskites are attractive materials for clean-energy applications, in particular solid oxide fuel cells, due to their singular proton conductivity in wet environments. Furthermore, these devices operate at high temperatures, where creep and other deformation processes determine the lifetime and overall performance. In this work, the structural and microstructural characteristics of undoped and ytterbium-doped (1 to 10 at.%) BaCeO 3 polycrystals produced by solid state reaction have been investigated. A single orthorhombic perovskite phase was found after sintering in air at 1500 °C for 10 h. The microstructure shows a complex evolution with doping: the average grain size firstly decreases with increasing Yb content up to 5 at.%, and then increases with further Yb additions. The high-temperature mechanical properties have been studied in compression between 1100 and 1250 °C in air at constant initial strain rate. The creep strength increases with increasing Yb content. Extended steady states of deformation were attained at lower strain rates and higher temperatures when increasing doping amount.

Octubre, 2012 | DOI: 10.1016/j.fuproc.2011.10.005

Titulo: Creep strength of nickel oxide/zirconia composites under different environmental atmospheres
Autores: M. Jiménez-Melendo; F.A. Huamán-Mamani
Revista: Solid State Ionics, 225 (2012) 471-475
resumen | texto completo


NiO/8YSZ (8 mol% Y2O3-stabilized cubic ZrO2) and NiO/3YTZP (3 mol% Y2O3-stabilized tetragonal ZrO2) composites with different NiO contents have been fabricated by a conventional route of mechanical mixing of NiO and zirconia powders and sintering at 1500 °C for 10 h in air. The resulting microstructures have been characterized by electron microscopy. The composites show a duplex microstructure formed by equiaxed grains of NiO and ZrO2, without any intermediate phase. Compressive mechanical tests at constant strain rate were carried out at temperatures between 1150 and 1350 °C under different environments: air, inert (Ar) and reducing (5% H2/95% Ar) atmospheres. The overall creep behavior of the composites is essentially controlled by the zirconia matrix, due to the softness of the NiO phase in the experimental conditions used in this study. The creep strength is not affected by oxygen partial pressure. However, a large decrease in creep resistance under reducing conditions was observed in samples submitted to in situ redox cycling.

Septiembre, 2012 | DOI: 10.1016/j.ssi.2012.02.011

Titulo: High-temperature plastic deformation mechanisms of ytterbium-doped barium cerate proton conductor
Autores: M. Jiménez-Melendo
Revista: Solid State Ionics, 225 (2012) 286-290
resumen | texto completo


The enhanced proton conductivity exhibited by trivalent cation-doped barium cerate perovskites makes these materials excellent candidates for electrochemical applications, in particular as electrolytes for solid oxide fuel cells. These devices operate at elevated temperatures, where creep and other deformation processes influence the overall efficiency and lifetime. In this work, the high-temperature plastic deformation mechanisms of fine-grained 5 at.% Yb-doped BaCeO3 polycrystals produced by conventional solid-state reaction has been investigated by means of compressive tests at constant load between 1150 and 1250 °C in air. The creep curves show an unusual sigmoidal behavior, followed by extended steady states of deformation. Grain boundary sliding is the main deformation mechanism, characterized by a stress exponent n of 2, as found in other fine-grained superplastic ceramics and metals.

Septiembre, 2012 | DOI: 10.1016/j.ssi.2012.03.031

Titulo: Electrical resistivity and thermal conductivity of SiC/Si ecoceramics prepared from sapele wood biocarbon
Autores: Parfen'eva, LS; Orlova, TS; Smirnov, BI; Smirnov, IA; Misiorek, H; Mucha, J; Jezowski, A; Pardo, AG; Rico, JR
Revista: Physics of the Solid State, 54 (2012) 2132-2141
resumen | texto completo


Samples of β-SiC/Si ecoceramics with a silicon concentration of ∼21 vol % have been prepared using a series of consecutive procedures (carbonization of sapele wood biocarbon, synthesis of high-porosity biocarbon with channel-type pores, infiltration of molten silicon into empty channels of the biocarbon, formation of β-SiC, and retention of residual silicon in channels of β-SiC). The electrical resistivity ρ and thermal conductivity κ of the β-SiC/Si ecoceramic samples have been measured in the temperature range 5–300 K. The values of ρ Si chan(T) and κ Si chan(T) have been determined for silicon Sichan located in β-SiC channels of the synthesized β-SiC/Si ecoceramics. Based on the performed analysis of the obtained results, the concentration of charge carriers (holes) in Sichan has been estimated as p ∼ 1019 cm−3. The factors that can be responsible for such a high value of p have been discussed. The prospects for practical application of β-SiC/Si ecoceramics have been considered.

Septiembre, 2012 | DOI: 10.1134/S1063783412100289

Titulo: Microstructure and high-temperature mechanical behavior of melt-growth Al2O3/Er3Al5O12/ZrO2 ternary eutectic composites
Autores: Huaman-Mamani, FA; Jimenez-Melendo, M; Mesa, MC; Oliete, PB
Revista: Journal of Alloys and Compounds, 536 (2012) S527-S531
resumen | texto completo


The microstructural and high-temperature mechanical characteristics of directionally solidified rods of Al2O3–Er3Al5O12–ZrO2 ternary eutectic oxides processed by the laser-heated floating zone method at different growth rates have been investigated. The eutectic microstructure displayed an entangled three-dimensional network of Al2O3 and Er3Al5O12 phases of similar sizes, elongated along the growth direction; the minority zirconia phase formed small fibers into the alumina phase. The interphase spacing is reduced with increasing solidification rate, changing about 2 μm down to 200 nm. These microstructural features are essentially the same exhibited by Al2O3–Y3Al5O12–ZrO2 composites processed by the same technique. Compressive deformation tests performed at 1400 °C at constant strain rate showed that the creep resistance decreased when increasing the growth rate due to the refinement of the microstructure.

Agosto, 2012 | DOI: 10.1016/j.jallcom.2012.01.105

Titulo: High-temperature mechanical characteristics of NiO/3YTZP composites
Autores: Jimenez-Melendo, M; Oliva-Ramirez, M; Huaman-Mamani, FA
Revista: Journal of Alloys and Compounds, 536 (2012) S472-S476
resumen | texto completo


NiO/3YTZP (3 mol% Y2O3-stabilized tetragonal ZrO2) composites with 40 mol% NiO (26 vol% NiO) have been fabricated by mechanical mixing of NiO and 3YTZP powders and sintering at 1500 °C for 10 h in air. The resulting microstructures have been characterized by electron microscopy. Compressive mechanical tests at constant strain rate were conducted on these materials at temperatures between 1150 and 1350 °C in air. The σ–ɛ curves display extended secondary creep regimes without signals of macroscopic failure. The composite creep behavior is characterized by a stress exponent n = 2 and an activation energy for flow Q = 490 kJ/mol. The overall creep behavior of the composites is essentially controlled by the zirconia matrix, due to the softness of the NiO phase in the experimental conditions used in this study.

Agosto, 2012 | DOI: 10.1016/j.jallcom.2011.11.040

Titulo: Effects of the presence of Fe(0) on the sorption of lanthanum and lutetium mixtures in smectites
Autores: Galunin, E; Alba, MD; Santos, MJ; Vidal, M
Revista: Applied Clay Science, 65-66 (2012) 162-172
resumen | texto completo


The sorption of La and Lu mixtures was examined in two bentonites after incubation for three months at 20 and 80 °C with Fe(0), as a laboratory approach to evaluate the effects of waste canister corrosion in a deep repository on the performance of clay engineered barriers. The sorption/desorption parameters were determined from batch tests in two ionic media: deionized water and, to consider the additional effect of cement leachates, 0.02 mol L− 1 Ca.

Results from XRD analyses showed the formation of crystalline FeO(OH), goethite, in a few samples and the degradation of the bentonites due to Fe(0) oxidation during incubation. Moreover, the EDX spectra showed that the lanthanides were sorbed primarily at smectite sites, although sorption onto goethite was also observed, whereas Fe(0) particles did not contribute to lanthanide sorption. The formation of goethite could explain the high Kd values measured in a few scenarios (e.g., those with single solutions or mixtures with the lowest initial concentration of the competitive lanthanide in which high affinity sites governed sorption), with up to 3-fold increases over the values obtained without Fe incubation. However, at higher lanthanide concentration, Kd values decreased or remained constant compared to the samples without Fe incubation, which could be explained by bentonite degradation. In the Ca medium, as much as 5 times lower Kd values were obtained, because of the competitive effect of the Ca ions, especially for Lu in the MX80 bentonite. This indicated that the small number of high affinity sites had been diminished.

The sorption data were satisfactorily fitted to a two-solute Langmuir model. In addition, Kd values correlated well with desorption data, which showed that the larger the decrease in Kd, the larger the increase in sorption reversibility. It is suggested that corrosion products from the metal canister might compromise the long-term radionuclide retention of the clay-engineered barriers.

Agosto, 2012 | DOI: 10.1016/j.clay.2012.06.011

Titulo: Thermal conductivity of high-porosity heavily doped biomorphic silicon carbide prepared from sapele wood biocarbon
Autores: Parfen'eva, LS; Orlova, TS; Smirnov, BI; Smirnov, IA; Misiorek, H; Mucha, J; Jezowski, A; Cabezas-Rodriguez, R; Ramirez-Rico, J
Revista: Physics of the Solid State, 54 (2012) 1732-1739
resumen | texto completo


The electrical resistivity and thermal conductivity of high-porosity (~52 vol %, channel-type pores) bio-SiC samples prepared from sapele wood biocarbon templates have been measured in the temperature range 5-300 K. An analysis has been made of the obtained results in comparison with the data for bio-SiC samples based on beech and eucalyptus, as well as for polycrystalline β-SiC. The conclusion has been drawn that the electrical resistivity and thermal conductivity of bio-SiC samples based on natural wood are typical of heavily doped polycrystalline β-SiC.

Julio, 2012 | DOI: 10.1134/S1063783412080240

Titulo: Biomimetic mineralization of calcium phosphate on a functionalized porous silicon carbide biomaterial
Autores: Dey, A; van den Hoogen, CJ; Rosso, M; Lousberg, N; Hendrix, MMRM; Friedrich, H; Ramirez-Rico, J; Zuilhof, H; de With, G; Sommerdijk, NAJM
Revista: ChemPlusChem, 77 (2012) 694-699
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Porous biomorphic silicon carbide (bioSiC) is a structurally realistic, high-strength, and biocompatible material which is promising for application in load-bearing implants. The deposition of an osteoconductive coating is essential for further improvement of its integration with the surrounding tissue. A new strategy towards biomimetic calcium phosphate coatings on bioSiC is described. X-ray photoelectron spectroscopy (XPS) analysis shows that using 10-undecenoic acid methyl ester a covalently bound monolayer can be synthesized on the surface of the bioSiC. After hydrolysis it exposes carboxylic acid groups that promote the selective nucleation and growth of a very well-defined crystalline layer of calcium phosphate. The resulting calcium phosphate coating is characterized by X-ray diffraction and electron microscopy techniques. Further, ion beam imaging is employed to quantify the mineral deposition meanwhile, three-dimensional dual-beam imaging (FIB/SEM) is used to visualize the bioSiC/mineral interface. The monolayer is show to actively induce the nucleation of a well-defined and highly crystalline mixed octacalcium phosphate/hydroxyapatite (OCP/HAP) coating on implantable bioSiC substrates with complex geometry. The mild biomimetic procedure, in principle, allows for the inclusion of bioactive compounds that aid in tissue regeneration. Moreover, the mixed OCP/HAP phase will have a higher solubility compared to HAP, which, in combination with its porous structure, is expected to render the coating more reabsorbable than standard HAP coatings.

Julio, 2012 | DOI: http://onlinelibrary.wiley.com/doi/10.1002/cplu.201200118/full

Titulo: Synthetic high-charge organomica: Effect of the layer charge and alkyl chain length on the structure of the adsorbed surfactants
Autores: Pazos, MC; Castro, MA; Orta, MM; Pavon, E; Rios, JSV; Alba, MD
Revista: Langmuir, 28 (2012) 7325-7332
resumen | texto completo


A family of organomicas was synthesized using synthetic swelling micas with high layer charge (NanSi8-nAlnMg6F4O20 center dot XH2O, where n = 2, 3, and 4) exchanged with dodecylammonium and octadecylammonium cations. The molecular arrangement of the surfactant was elucidated on the basis on XRD patterns and DTA. The ordering conformation of the surfactant molecules into the interlayer space of micas was investigated by C-13, Al-27, and Si-29 MAS NMR The arrangement of alkylammonium ions in these high-charge synthetic micas depends on the combined effects of the layer charge of the mica and the chain length of the cation. In the organomicas with dodecylammonium, a transition from a parallel layer to a bilayer-paraffin arrangement is observed when the layer charge of the mica increases. However, when octadecylammonium is the interlayer cation, the molecular arrangement of the surfactant was found to follow the bilayer-paraffin model for all values of layer charge. The amount of ordered conformation all-trans is directly proportional of layer charge.

Abril, 2012 | DOI: 10.1021/la300153e

Titulo: Remediation of metal-contaminated soils with the addition of materials - Part II: Leaching tests to evaluate the efficiency of materials in the remediation of contaminated soils
Autores: Gonzalez-Nunez, R; Alba, MD; Orta, MM; Vidal, M; Rigol, A
Revista: Chemosphere, 87 (2012) 829-837
resumen | texto completo


The effect of the addition of materials on the leaching pattern of As and metals (Cu, Zn, Ni, Pb, and Cd) in two contaminated soils was investigated. The examined materials included bentonites, silicates and industrial wastes, such as sugar foam, fly ashes and a material originated from the zeolitization of fly ash. Soil + material mixtures were prepared at 10% doses. Changes in the acid neutralization capacity, crystalline phases and contaminant leaching over a wide range of pHs were examined by using pHstat leaching tests. Sugar foam, the zeolitic material and MX-80 bentonite produced the greatest decrease in the leaching of pollutants due to an increase in the pH and/or the sorption capacity in the resulting mixture. This finding suggests that soil remediation may be a feasible option for the reuse of non-hazardous wastes.

Abril, 2012 | DOI: 10.1016/j.chemosphere.2012.01.015

Titulo: Interfacial characterization of silicon nitride/silicon nitride joints brazed using Cu-base active metal interlayers
Autores: Singh, M; Fernandez, JM; Asthana, R; Rico, JR
Revista: Ceramics Intenational, 38 (2012) 2793-2802
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Silicon nitride/silicon nitride joints were vacuum brazed at 1317 K for 5 min and 30 min using ductile Cu-base active metal interlayers. The joints were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron back scattered diffraction (EBSD), and transmission electron microscopy (TEM). An inhomogeneous Ti-rich reaction layer (similar to 2-3 mu m thick) formed in 5 min at the Si3N4/braze interface. The inhomogeneity disappeared after brazing for 30 min and was replaced with a compact and featureless reaction zone. TEM studies revealed fine grains in the reaction layer, and larger grains in the inner part of the joint interfaces. The joints were crack-free and presented features associated with plastic deformation, which indicated accommodation of strain associated with CTE mismatch. Electron Backscatter diffraction (EBSD) revealed a highly textured braze alloy interlayer and its crystallographic orientation was determined. The formation of additional phases at the joint interface during brazing is discussed.

Abril, 2012 | DOI: 10.1016/j.ceramint.2011.11.050

Titulo: Residual stresses in Al2O3-ZrO 2 (3mol.% Y2O3) directionally solidified eutectic ceramics as a function of temperature
Autores: Ramirez-Rico, J; Martinez-Fernandez, J; Pena, JI; Singh, D; Routbort, J
Revista: Materials Science and Engineering A, 541 (2012) 61-66
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Directionally solidified eutectics are in situ composites grown from the melt. Due to the differences in the thermoelastic properties of the different phases present in the material, these composites often exhibit residual stresses that can affect their mechanical properties. In this work we use neutron diffraction to investigate residual stresses in Al 2O 3-ZrO 2 eutectic composites as a function of temperature, for samples processed at two different growth rates, 10mm/h and 750mm/h. Our results show that the stress-free temperature is in the range of 1200±200°C. We explain the experimental observations based on the thermoelastic properties of the phases in the material and confirm our measurements using a simple, self-consistent model.

Marzo, 2012 | DOI: 10.1016/j.msea.2012.02.001

Titulo: Effect of oxidation on the compressive strength of sintered SiC-fiber bonded ceramics
Autores: Ramirez-Rico, J; Martinez-Fernandez, J; Singh, M
Revista: Materials Science and Engineering A, 534 (2012) 394-399
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The compressive strength of SiC-fiber bonded ceramics obtained from hot-pressed amorphous Si-Al-C-O fibers and its degradation by high temperature exposure to an oxidizing environment was studied. Compressive strength was measured at room temperature as a function of strain rate, orientation, and oxidation temperature. Weight loss was monitored as a function of exposure time in atmospheric air at temperatures ranging from 800 to 1600°C, for times ranging from 0.5 to 5. h. Room-temperature compressive strength had a moderate decrease after exposures at 800°C associated to carbon burnout; increased for exposures in the range 1000-1500°C due to a defect-blunting action of the silica scale; and decreased significantly at 1600°C due to extensive surface recession.

Enero, 2012 | DOI: 10.1016/j.msea.2011.11.085

2011


Titulo: Remediation of metal-contaminated soils with the addition of materials – Part I: Characterization and viability studies for the selection of non-hazardous waste materials and silicates
Autores: R. González-Núñez, M.D. Alba, M.M. Orta, M. Vidal, A. Rigol
Revista: Chemosphere, 85 (2011) 1511-1517
resumen | texto completo


Contamination episodes in soils require interventions to attenuate their impact. These actions are often based on the addition of materials to increase contaminant retention in the soil and to dilute the contaminant concentration. Here, non-hazardous wastes (such as sugar foam, fly ash and a material produced by the zeolitization of fly ash) and silicates (including bentonites) were tested and fully characterized in the laboratory to select suitable materials for remediating metal-contaminated soils. Data from X-ray fluorescence (XRF), N2 adsorption/desorption isotherms, X-ray diffraction (XRD) and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM–EDX) analyses revealed the chemical composition, specific surface area and the phases appearing in the materials. A pH titration test allowed the calculation of their acid neutralization capacity (ANC). The metal sorption and desorption capacities of the waste materials and silicates were also estimated. Sugar foam, fly ash and the zeolitic material were the best candidate materials. Sugar foam was selected because of its high ANC (17 000 meq kg−1), and the others were selected because of their larger distribution coefficients and lower sorption reversibilities than those predicted in the contaminated soils.

Octubre, 2011 | DOI: 10.1016/j.chemosphere.2011.09.042

Titulo: Application of the solid state NMR to the study of the alcohol/alkane mixtures adsorption onto graphite
Autores: María D. Alba, Miguel A. Castro, Stuart M. Clarke, Santiago Medina, Loic Messe, Carmen Millán
Revista: Solid State Nuclear Magnetic Resonance, 40 (2011) 138-143
resumen | texto completo


The mixing of molecules adsorbed from solution to different interfaces has both industrial and academic relevance and the mixing behaviour at the interface is a key to understanding for example, that the surface tension of a mixture of two surfactants is lower than either of the two pure materials and many other effects. In this paper, we report, for the first time, the application of Solid State NMR to the study of alkane/alcohol mixtures, in a range of relative size ratio between 0 and 0.35, adsorbed onto graphite at high, multilayer coverage. Moreover, this paper evaluated, for the first time, the utility of the combined used of 1H and 2H NMR for: (i) determining the surface composition and (ii) making a theoretical approach to the sorption isotherm. A variety of preferential adsorption behaviour is reported. Preferential adsorption of the longer molecule (decane vs. heptanol) from a mixture has been observed. However, if both components are of similar length, the alcohol is preferentially adsorbed (heptanol vs. octane and octanol vs. octane). Finally, a linear relation between the relative size ratio and the amount of alcohol at monolayer coverage is observed.

Octubre, 2011 | DOI: 10.1016/j.ssnmr.2011.11.002

Titulo: Structure, Electrical Resistivity, and Thermal Conductivity of Beech Wood Biocarbon Produced at Carbonization Temperatures below 1000 degrees C
Autores: Parfen'eva, LS; Orlova, TS; Kartenko, NF; Smirnov, BI; Smirnov, IA; Misiorek, H; Jezowski, A; Muha, J; Vera, MC
Revista: Physics of the Solid State, 53 (2011) 2398-2407
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This paper reports on measurements of the thermal conductivity. and the electrical resistivity. in the temperature range 5-300 K, and, at 300 K, on X-ray diffraction studies of high-porosity (with a channel pore volume fraction of similar to 47 vol %) of the beech wood biocarbon prepared by pyrolysis (carbonization) of tree wood in an argon flow at the carbonization temperature T(carb) = 800 degrees C. It has been shown that the biocarbon template of the samples studied represents essentially a nanocomposite made up of amorphous carbon and nanocrystallites-"graphite fragments" and graphene layers. The sizes of the nanocrystallites forming these nanocomposites have been determined. The dependences rho(T) and kappa(T) have been measured for the samples cut along and perpendicular to the tree growth direction, thus permitting determination of the magnitude of the anisotropy of these parameters. The dependences rho(T) and kappa(T), which have been obtained for beech biocarbon samples prepared at T(carb) = 800 degrees C, are compared with the data amassed by us earlier for samples fabricated at T(carb) = 1000 and 2400 degrees C. The magnitude and temperature dependence of the phonon thermal conductivity of the nanocomposite making up the beech biocarbon template at T(carb) = 800 degrees C have been found.

Octubre, 2011 | DOI: 10.1134/S1063783411110230

Titulo: Evolution of Phases and Al–Si Distribution during Na-4-Mica Synthesis
Autores: María D. Alba, Miguel A. Castro, Moisés Naranjo, M. Mar Orta, Esperanza Pavón, and M. Carolina Pazos
Revista: Journal of Physical Chemistry C, 2011, 115 (41), pp 20084–20090
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Na-4-mica, a highly charged fluorophlogopite, has recently attracted much attention because of its unique combination of high charge (four charges per unit cell) and its swelling and cation-exchange properties. The ability to improve the properties of this mica depends on gaining knowledge about its phase evolution during the calcination process. For the synthesis, the stoichiometric powder mixture (4SiO 2/2Al 2O 3/6MgF 2/8NaCl) was heated to 900 °C for 0-600 h. The obtained solids were characterized by X-ray fluorescence (XRF); X-ray diffraction (XRD); scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) analysis; 29Si, 27Al, and 23Na magic-angle-spinning MAS NMR spectroscopy; and thermogravimetric/differential thermal analysis (TG/DTA). The results showed that the precursors are rapidly (t < 3 h) transformed into sodalite, Al 6Na 8(SiO 4) 6Cl 2, and a 2:1 phyllosilicate. For t = 7.5 h, the amount of 2:1 phyllosilicate increased as a result of the decomposition of sodalite, with a progressive incorporation of aluminum in the 2:1 phyllosilicate being observed. For t = 7.5 h, synthesis of Na-4-mica was considered to be complete, as the material remained essentially unaltered for the next 15 h. For t = 30 h, the mica started to decompose, and for very long reaction times (t ≥ 300 h), only forsterite and a carnegierite phase were present.

Septiembre, 2011 | DOI: 10.1021/jp207408h

Titulo: The effect of polymorphic structure on the structural and chemical stability of yttrium disilicates
Autores: Evgeny Galunin, Miquel Vidal and María D. Alba
Revista: American Mineralogist, 96 (2011) 1512-1520
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Under pressure and temperature conditions like those found in deep geological repositories (DGRs), rare-earth cations may react with silicates to form rare-earth disilicates. This study establishes the stability range of yttrium disilicates in response to changes in pH. The α, β, γ, and δ polymorphs of Y2Si2O7 were synthesized by the sol-gel process at temperatures between 1100 and 1650 °C and subjected to pHstat leaching tests. By measuring the Y and Si leaching rates and monitoring the transformation of the crystalline and amorphous phases, we showed that yttrium disilicates were stable at pH > 5. At pH < 5, the pH stability sequence was consistent with the temperature-dependent stabilities of Y2Si2O7 phases, with the δ polymorph showing the lowest leaching rates. Because rare-earth compounds can be used as a proxy for analogous actinide hosts, the results of this study can be used to predict the performance of engineered barriers in DGR.

Septiembre, 2011 | DOI: 10.2138/​am.2011.3659

Titulo: Structural elucidation of Β-(Y,Sc)2Si2O 7: Combined use of 89Y MAS NMR and powder diffraction
Autores: Allix, M., Alba, M.D., Florian, P., Fernandez-Carrion, A.J., Suchomel, M.R., Escudero, A., Suard, E., Becerro, A.I.
Revista: Journal of Applied Crystallography, 44 (2011) 846-852
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Although the structures of pure Sc2Si2O7 and &#914;-Y2Si 2O7 have been described in the literature using the C2/m space group, 29Si magic angle spinning (MAS) NMR measurements of the intermediate members of the Sc2Si2O7-&#914;- Y2Si2O7 system indicate a lowering of the symmetry to the C2 space group. Indeed, these compositions exhibit a unique Si crystallographic site and an Si-O-Si angle lower than 180°, incompatible with the C2/m space group. C2 is the only possible alternative. Space group Cm can be discarded with regard to its two different Si sites per unit cell. Moreover, 89Y MAS NMR data have revealed the existence of two different Y sites in the structure of the intermediate members of the Sc 2Si2O7-&#914;-Y2Si2O 7 system, confirming the lowering of the symmetry to the C2 space group. The viability of the C2 model has therefore been tested and confirmed by refinement of synchrotron and neutron powder diffraction data for the different members of the system. The structural evolutions across the Sc 2Si2O7-&#914;-Y2Si2O 7 system are discussed.

Julio, 2011 | DOI: 10.1107/S0021889811021303

Titulo: Formation of organo-highly charged mica
Autores: Alba, M.D. , Castro, M.A., Orta, M.M., Pavón, E., Pazos, M.C., Valencia Rios, J.S.
Revista: Langmuir, 16 (2011) 9711-9718
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The interlayer space of the highly charged synthetic Na-Mica-4 can be modified by ion-exchange reactions involving the exchange of inorganic Na + cations by surfactant molecules, which results in the formation of an organophilic interlayer space. The swelling and structural properties of this highly charged mica upon intercalation with n-alkylammonium (RNH 3) + cations with varying alkyl chain lengths (R = C12, C14, C16, and C18) have been reported. The stability, fine structure, and evolution of gaseous species from alkylammonium Mica-4 are investigated in detail by conventional thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), in situ X-ray diffraction (XRD), and solid-state nuclear magnetic resonance (MAS NMR) techniques. The results clearly show the total adsorption of n-alkylammonium cations in the interlayer space which expands as needed to accommodate intercalated surfactants. The surfactant packing is quite ordered at room temperature, mainly involving a paraffin-type bilayer with an all-trans conformation, in agreement with the high density of the organic compounds in the interlayer space. At temperatures above 160 °C, the surfactant molecules undergo a transformation that leads to a liquid-like conformation, which results in a more disordered phase and expansion of the interlayer space.

Julio, 2011 | DOI: 10.1021/la200942u

Titulo: Electrical properties of biomorphic SiC ceramics and SiC/Si composites fabricated from medium density fiberboard
Autores: T.S. Orlova, V.V. Popov, J. Quispe Cancapa, D. Hernández Maldonado, E. Enrique Magarino, F.M. Varela Feria, A. Ramírez de Arellano, J. Martínez Fernández
Revista: Journal of the European Ceramic Society, 31 (2011) 1317-1323
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A study has been made of the dependences of the electrical resistivity and the Hall coefficient on the temperature in the range 1.8–1300 K and on magnetic fields of up to 28 kOe for the biomorphic SiC/Si (MDF-SiC/Si) composite and biomorphic porous SiC (MDF-SiC) based upon artificial cellulosic precursor (MDF – medium density fiberboards). It has been shown that electric transport in MDF-SiC is effected by carriers of n-type with a high concentration of ∼1020 cm−3 and a low mobility of ∼0.4 cm2 V−1 s−1. The specific features in the conductivity of MDF-SiC are explained by quantum effects arising in disordered systems and requiring quantum corrections to conductivity. The TEM studies confirmed the presence of disordering structural features (nanocrystalline regions) in MDF-SiC. The conductivity of MDF-SiC/Si composite originates primarily from Si component in the temperature range 1.8–500 K and since ∼500 to 600 K the contribution of MDF-SiC matrix becomes dominant.

Mayo, 2011 | DOI: 10.1016/j.jeurceramsoc.2010.06.015

Titulo: High-temperature mechanical behavior of polycrystalline yttrium-doped barium cerate perovskite
Autores: Vaquero-Aguilar, C; Lopez-Robledo, MJ; Martinez-Fernandez, J; Real, C; Jimenez-Melendo, M
Revista: Journal of the European Ceramic Society, 31 (2011) 1333-1338
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The high-temperature mechanical properties of the mixed ionic-electronic conductor perovskite BaCe0.95Y0.05O3−δ with average grain size of 0.40 μm have been studied in compression between 1100 and 1300 °C in air at different initial strain rates. The true stress–true strain curves display an initial stress drop, followed by an extended steady-state stage. As the temperature decreases and/or the strain rate increases, there is a transition to a damage-tolerant strain-softening stage and eventually to catastrophic failure. Analysis of mechanical and microstructural data revealed that grain boundary sliding is the primary deformation mechanism. The strength drop has been correlated with the growth of ultrafine grains during deformation, already present at grain boundaries and triple grain junctions in the as-fabricated material.

Mayo, 2011 | DOI: 10.1016/j.jeurceramsoc.2010.05.023

Titulo: Microstructural and mechanical evaluation of a Cu-based active braze alloy to join silicon nitride ceramics
Autores: Singh, M; Asthana, R; Varela, FM; Martinez-Fernandez, J
Revista: Journal of the European Ceramic Society, 31 (2011) 1309-1316
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Self-joining of St. Gobain Si3N4 (NT-154) using a ductile Cu–Al–Si–Ti active braze (Cu-ABA) was demonstrated. A reaction zone (∼2.5–3.5 μm thick) developed at the interface after 30 min brazing at 1317 K. The interface was enriched in Ti and Si. The room temperature compressive shear strengths of Si3N4/Si3N4 and Inconel/Inconel joints (the latter created to access baseline data for use with the proposed Si3N4/Inconel joints) were 140 ± 49 MPa and 207 ± 12 MPa, respectively. High-temperature shear tests were performed at 1023 K and 1073 K, and the strength of the Si3N4/Si3N4 and Inconel/Inconel joints were determined. The joints were metallurgically well-bonded for temperatures above 2/3 of the braze solidus. Scanning and transmission electron microscopy studies revealed a fine grain microstructure in the reaction layer, and large grains in the inner part of the joint with interfaces being crack-free. The observed formation of Ti5Si3 and AlN at the joint interface during brazing is discussed.

Mayo, 2011 | DOI: 10.1016/j.jeurceramsoc.2010.07.022

Titulo: Microstructural and mechanical evaluation of porous biomorphic silicon carbide for high temperature filtering applications
Autores: Bautista, MA; Cancapa, JQ; Fernandez, JM; Rodriguez, MA; Singh, M
Revista: Journal of the European Ceramic Society, 31 (2011) 1325-1332
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Biomorphic SiC (bioSiC) is a low cost SiC/Si composite obtained by melt infiltration of carbon preforms obtained from the pyrolysis of cellulose precursors. The porosity and pore size distribution of bioSiC can be tailored for specific applications by adequate selection of the wood precursor. Natural and artificial industrial woods were explored as possible bioSiC precursors. Silicon was removed by chemical etching. Relevant microstructural parameters such as pore size distribution, total porosity, and permeability were characterized. Since the filtration process involves large pressure gradients along the material at high temperatures, mechanical properties of porous bioSiC from the different precursors were evaluated at room temperature and 800 °C. The feasibility of porous bioSiC as a filtration material for high temperature gasification processes is discussed in terms of these properties. MDF-bioSiC is shown to be a promising material for such applications because of its good mechanical properties, interconnected porosity, pore sizes, and permeability.

Mayo, 2011 | DOI: 10.1016/j.jeurceramsoc.2010.06.014

Titulo: Interaction of Eu-isotopes with saponite as a component of the engineered barrier
Autores: María D. Alba, Miguel A. Castro, P. Chaín, Santiago Hurtado, M. Mar Orta, M. Carolina Pazos and María Villa
Revista: Applied Clay Science, 52 (2011) 253-257
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Bentonite is accepted as the best clay material in the engineered barrier of deep geological repositories (DGRs) for radioactive waste disposal. In recent years, the interactions between a wide range of rare-earth (REE) cations and smectites have been studied. A combined study of stable europium and radioactive isotopes is reported here. Saponite was subjected to hydrothermal reactions with stable and radioactive (152Eu) europium ions under subcritical conditions. The structural changes of saponite were evaluated by XRD and SEM. The effect of temperature and reaction time on the changes was quantified by measuring 152Eu through gamma spectrometry. The reaction between europium and saponite was a first-order reaction. The presence of Eu in the precipitate in an amount much higher than the cation exchange capacity of saponite confirmed participation of chemical reactions or surface adsorption in the europium immobilization, even at temperatures as low as 150 °C. The reaction rate constant indicated that an 8- to 9-month period was needed for the completion, without significant changes, of the europium/saponite chemical reaction under the subcritical conditions of 200 °C and 350 °C.

Abril, 2011 | DOI: 10.1016/j.clay.2011.02.027

Titulo: Stability of Rare-Earth Disilicates: Ionic Radius Effect
Autores: Galunin, E; Alba, MD; Vidal, M
Revista: Journal of the American Ceramic Society, 94 (2011) 1568–1574
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Rare-earth (RE) disilicates, of general formula RE2Si 2O7, are one of the products of the chemical reaction between RE (elements), which are actinide simulators, and the silicates used in the engineered barrier systems of deep geological repositories (DGPs). The aim of this paper is to establish the stability range of the disilicate phase as function of the nature of the RE (RE=Sc, Lu, or Y) and examine whether this phase would permit RE leaching under experimental conditions simulating those of the DGP. The &#946;-polymorphs of the RE disilicates were synthesized by the sol-gel method and subsequently submitted to a pHstat leaching test. The rates of RE and Si leaching were measured and the transformation of the crystalline and amorphous phases was examined by X-ray powder diffraction and nuclear magnetic resonance techniques. The results indicate that the disilicate phases were stable within a wide range of pH, their stability being related to the hydrated ratio of the RE. Disilicate stability increased with the ionic radius of the RE. As a result, the Sc disilicate was stable throughout the pH range tested, whereas Y and Lu disilicate leaching was only observed at pH<4. Thus, it was confirmed that the formation of the disilicate phases could contribute to the confinement of radioactive wastes in engineered barriers.

Abril, 2011 | DOI: 10.1111/j.1551-2916.2010.04272.x

Titulo: Bulk and Adsorbed Monolayer Phase Behavior of Binary Mixtures of Undecanoic Acid and Undecylamine: Catanionic Monolayers
Autores: Sun, C; Bojdys, MJ; Clarke, SM; Harper, LD; Jefferson, A; Castro, MA; Medina, S
Revista: Langmuir, 27 (2011) 3626-3637
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Differential scanning calorimetry (DSC) and X-ray powder diffraction (PXRD) have been used to determine the phase behavior of the binary mixtures of undecanoic acid (A) and undecylamine (B) in the bulk. In addition, we report DSC data that indicates very similar behavior for the solid monolayers of these materials adsorbed on the surface of graphite. The two species are found to form a series of stoichiometric complexes of the type AB, A2B, and A 3B on the acid rich side of the phase diagram. Interestingly, no similar series of complexes is evident on the amine rich side. As a result of this complexation, the solid monolayers of the binary mixtures exhibit a very pronounced enhancement in stability relative to the pure adsorbates.

Marzo, 2011 | DOI: 10.1021/la1048198

Titulo: Blocking of grain reorientation in self-doped alumina materials
Autores: Suarez, M; Fernandez, A; Menendez, JL; Ramirez-Rico, J; Torrecillas, R
Revista: Scripta Materialia, 64 (2011) 517-520
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Alumina nanoparticles 10-20 nm in diameter were nucleated on alumina particles, 150 nm average diameter, by a colloidal route followed by calcination. It is shown that after sintering, the final grain size is up to 20% smaller due to the addition of the alumina nanoparticles. Electron backscattered diffraction analysis shows that whereas a correlation in the relative crystalline orientations between neighbouring grains exists in the pure materials, the addition of alumina nanoparticles results in a random crystalline orientation.

Febrero, 2011 | DOI: 10.1016/j.scriptamat.2010.11.031

Titulo: Monolayer structures of alkyl aldehydes: Odd-membered homologues
Autores: Phillips, TK; Clarke, SM; Bhinde, T; Castro, MA; Millan, C; Medina, S
Revista: Thin Solid Films, 519 (2011) 3123-3127
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Crystalline monolayers of three aldehydes with an odd number of carbon atoms in the alkyl chain (C7, C9 and C11) at low coverages are observed by a combination of X-ray and neutron diffraction. Analysis of the diffraction data is discussed and possible monolayer crystal structures are proposed; although unique structures could not be ascertained for all molecules. We conclude that the structures are flat on the surface, with the molecules lying in the plane of the layer. The C11 homologue is determined to have a plane group of either p2, pgb or pgg, and for the C7 homologue the p2 plane group is preferred.

Febrero, 2011 | DOI: 10.1016/j.tsf.2010.12.084

Titulo: Examination of competitive lanthanide sorption onto smectites and its significance in the management of radioactive waste
Autores: Galunin, E; Alba, MD; Santos, MJ; Abrao, T; Vidal, M
Revista: Journal of Hazardous Materials, 186 (2011) 1930-1941
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The competitive effect of La and Lu (analogues of radionuclides appearing in radioactive waste) in the sorption in four smectites was examined. Sorption and desorption distribution coefficients (Kd; Kd,des), and desorption rates (Rdes) were determined from batch tests in two media: deionized water and, to consider the influence of cement leachates, 0.02molL-1 Ca. The competitive effect was lower when high-affinity sites were available, as in the water medium at the lowest range of initial lanthanide concentration, with high Kd for La and for Lu (5-63×104Lkg-1). Lower Kd was measured at higher initial concentrations and in the Ca medium, where Lu showed a stronger competitive effect. This was confirmed by fitting the sorption data to a two-solute Langmuir isotherm. The desorption data indicated that sorption was virtually irreversible for the scenarios with high sorption, with an excellent correlation between Kd and Kd,des (R2 around 0.9 for the two lanthanides). Assuming that radioactive waste is a mixture of radionuclides, and that Ca ions will be provided by the cement leachates, this would reduce the retention capacity of clay engineered barriers.

Enero, 2011 | DOI: 10.1016/j.jhazmat.2010.12.098

2010


Titulo: Bioactivation of biomorphous silicon carbide bone implants
Autores: Will J, Hoppe A, Muller FA, Raya CT, Fernandez JM, Greil P
Revista: Acta Biomaterialia, 6 (2010) 448-4494
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Wood-derived silicon carbide (SiC) offers a specific biomorphous microstructure similar to the cellular pore microstructure of bone. Compared with bioactive ceramics such as calcium phosphate, however, silicon carbide is considered not to induce spontaneous interface bonding to living bone. Bioactivation by chemical treatment of biomorphous silicon carbide was investigated in order to accelerate osseointegration and improve bone bonding ability. Biomorphous SiC was processed from sipo (Entrandrophragma utile) wood by heating in an inert atmosphere and infiltrating the resulting carbon replica with liquid silicon melt at 1450 °C. After removing excess silicon by leaching in HF/HNO3 the biomorphous preform consisted of &#946;-SiC with a small amount (approximately 6 wt.%) of unreacted carbon. The preform was again leached in HCl/HNO3 and finally exposed to CaCl2 solution. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared analyses proved that oxidation of the residual carbon at the surface induced formation of carboxyl [COO-] groups, which triggered adsorption of Ca2+, as confirmed by XPS and inductively coupled plasma optical emission spectroscopy measurements. A local increase in Ca2+ concentration stimulated in vitro precipitation of Ca5(PO 4)3OH (HAP) on the silicon carbide preform surface during exposure to simulated body fluid, which indicates a significantly increased bone bonding activity compared with SiC.

Noviembre, 2010 | DOI: 10.1016/j.actbio.2010.06.036

Titulo: Sc-45 Spectroscopy of Solids: Interpretation of Quadrupole Interaction Parameters and Chemical Shifts
Autores: Alba, MD; Chain, P; Florian, P; Massiot, D
Revista: Journal of Physical Chemistry C, 114 (2010) 12125-12132
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The aims of the present study is to describe for the first time the Sc-45 MAS NMR spectra of X-2-Sc2SiO5 and C-Sc2Si2O7, to combine the spectroscopic information with the structures published from diffraction data, and to propose a rational interpretation of the chemical shifts and quadrupolar parameters. For that purposed, we have correlated the experimental quadrupole coupling parameters of Sc-45 determined for a number of scandium compounds to those found by a simple electrostatic calculation and we have found that the isotropic chemical shift of the Sc-45 is linearly correlated to the shift parameter, calculated by bond-valence theory. We also show that a simple point charge calculation can approximate the electric field gradient to a sufficiently good approximation that it provides a valuable mean to assign the NMR spectra.

Junio, 2010 | DOI: 10.1021/jp1036525

Titulo: Application of Micro-X-ray Fluorescence Analysis for the Characterization of Industrial Wastes
Autores: Alba, MD; Aparicio, P; Benitez, JM; Castro, MA; Diaz, M; Orta, MM
Revista: Industrial & Engineering Chemistry Research, 49 (2010) 2348-2352
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The issue of how to improve product quality and product yield in a short period of time is becoming more critical in many industries. Thus, shorter delay times between laboratory analysis and process correction are important in process control. Elimination of sample handling and operator Manipulation is desirable. The present article proposes micro-X-ray fluorescence (mu XRF) as an economical control method for industrial product quality with a minimum time cost. Samples from different industrial processes have been chosen and analyzed by XRF and mu XRF, The results show that the two techniques give similar results and that mu XRF allows the waste to be classified and is able to detect problems in the production process.

Febrero, 2010 | DOI: 10.1021/ie901716w

Titulo: Lanthanide sorption on smectitic clays in presence of cement leachates
Autores: Galunin, E; Alba, MD; Santos, MJ; Abrao, T; Vidal, M
Revista: Geochimica et Cosmochimica Acta, 74 (2010) 862-875
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Due to their potential retention capacity, clay minerals have been proposed for use in the engineered barriers for the storage of high-level radioactive actinides in deep geological waste repositories. However, there is still a lack of data on the sorption of actinides in clays in conditions simulating those of the repositories. The present article examines the sorption of two lanthanides (actinide analogues) in a set of smectitic clays (FEBEX bentonite, MX80 bentonite, hectorite, saponite, Otay montmorillonite, and Texas montmorillonite). Distribution coefficients (K-d) were determined in two media: water and 0.02 mol L-1 Ca, the latter representing the cement leachates that may modify the chemical composition of the water in contact with the clay. The K-d values of the lanthanides used in the experiments (La and Lu) varied greatly (25-50 000 L kg(-1)) depending on the ionic medium (higher values in water than in the Ca medium), the initial lanthanide concentration (up to three orders of magnitude decrease inversely with lanthanide concentration), and the examined clay (up to one order of magnitude for the same lanthanide and sorption medium). Freundlich and Langmuir isotherms were used to fit sorption data to allow comparison of the sorption parameters among smectites. The model based on the two-site Langmuir isotherms provided the best fit of the sorption data, confirming the existence of sorption sites with different binding energies. The sites with higher sorption affinity were about 6% of the total sorption capacity in the water medium, and up to 17% in the Ca medium, although in this latter site sorption selectivity was lower. The wide range of K-d values obtained regarding the factors examined indicated that the retention properties of the clays should also be considered when selecting a suitable clay for engineered barriers.

Enero, 2010 | DOI: 10.1016/j.gca.2009.11.003

2009


Titulo: Reversibility of La and Lu sorption onto smectites: Implications for the design of engineered barriers in deep geological repositories
Autores: Galunin, E; Alba, MD; Aviles, MA; Santos, MJ; Vidal, M
Revista: Journal of Hazardous Materials, 172 (2009) 1198-1205
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The sorption reversibility of La and Lu (considered as actinide analogues) onto a set of smectites (bentonite FEBEX; hectorite, HEC; MX80; saponite, SAP; Otay montmorillonite, SCa-3; and Texas montmorillonite, STx-1) was studied to estimate actinide retention by smectites that are candidates for use as engineered barriers in deep geological repositories. The sorption distribution coefficients (K d) and the reversibility parameters (desorption distribution coefficients (K d,des), adjusted distribution coefficients (K d,adj), and desorption rates (R des)) were determined from batch tests in two ionic media: deionized water and Ca 0.02 mol L -1. The latter simulates possible conditions due to the presence of concrete leachates. The results varied greatly depending on the ionic medium, the lanthanide concentration and the clay structure. The high values of K d,des obtained (up to 1.1 × 10 5 and 9.2 × 10 4 L kg -1 for La and Lu in water, and 2.8 × 10 4 and 4.1 × 10 4 L kg -1 for La and Lu in the Ca medium) indicate the suitability of the tested smectites for lanthanide (and therefore, actinide) retention. Based on all the data, SCa-3, HEC and FEBEX clays are considered the best choices for water environments, whereas in Ca environments the suitable clays depended on the lanthanide considered.

Noviembre, 2009 | DOI: 10.1016/j.jhazmat.2009.07.124

Titulo: Rare-earth disilicate formation under Deep Geological Repository approach conditions
Autores: Alba, MD; Chain, P; Orta, MM
Revista: Applied Clay Science, 46 (2009) 63-68
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The Deep Geological Repository (DGR) concept involves the placement of long-lived radioactive waste in rooms excavated deep. The major responsibility of the disposal safety falls on the Engineered Barrier System (EBS). The main constituent of EBS is bentonite that prevents the release of radiactive nuclei by physical and chemical mechanisms. The physical mechanism is expected to fault with the weathering of the bentonite while the chemical mechanisms have been only proved at 300 °C. It is the aim of this paper to explore the feasibility of the chemical mechanism at temperatures closer to the DGP conditions and to shed light on the mechanism of transformation of the argillaceous materials of the EBS in rare-earth disilicate phases. Saponite was submitted to hydrothermal reaction at 175 °C and 150 °C with different solutions of REE3+ cations (REE = Sc, Lu, Y, Sm, Nd and La). The products were analyzed by XRD, NMR and electron microscopy. At conditions close to the DGP, the saponite was able to form rare-earth silicates. The formation of the disilicate phase, as final product, needs a set of stages and oxyorthosilicate as precursor.

Agosto, 2009 | DOI: 10.1016/j.clay.2009.07.012

Titulo: Stability of phyllosilicates in Ca(OH)2 solution: Influence of layer nature, octahedral occupation, presence of tetrahedral Al and degree of crystallinity
Autores: Mantovani, M; Escudero, A; Alba, MD; Becerro, AI
Revista: Applied Geochemistry, 24 (2009) 1251-1260
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This paper presents the results of a comprehensive investigation of the interaction of layered silicates with Ca(OH)2 in hydrothermal conditions. The study is intended to evaluate the stability of the clay buffer in radioactive waste repositories, at the intermediate stages of concrete leaching, when the pH is controlled by the dissolution of portlandite. The influence of layer nature, octahedral occupation, presence of tetrahedral Al and degree of crystallinity will be assessed by analysing the behaviour of a set of well-selected phyllosilicates and using the combined capabilities of 29Si and 27Al MAS-NMR spectroscopy, powder X-ray diffraction and SEM/EDX. The results show that the main factor affecting the stability of the clay is the octahedral occupation, so that trioctahedral phyllosilicates are much more stable than dioctahedral ones. The nature and expandability of the layer does not seem to much influence the stability of the clay, so that a 2:1 expandable phyllosilicate shows the same stability as a chemically analogous 1:1 non-expandable phyllosilicate. However other factors like the poor crystallinity of the starting material or the presence of Al in the tetrahedral sheet of trioctahedral phyllosilicates weaken the clay structure in alkaline conditions and favour the transformation towards other phases.

Junio, 2009 | DOI: 10.1016/j.apgeochem.2009.03.012

Titulo: Preferential Adsorption from Binary Mixtures on Graphite: The n-Decane−n-Heptan-1-ol System
Autores: Alba, MD; Castro, MA; Clarke, S; Medina, S; Messe, L; Millan, C; Orta, MM; Perdigon, AC
Revista: Journal of Physical Chemistry C, 113 (2009) 3176-3180
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The competitive adsorption of n-decane and n-heptan-1-ol adsorbed from the binary liquid mixture onto graphite has been studied using differential scanning calorimetry, incoherent quasielastic neutron scattering, and 1H and 2H nuclear magnetic resonance. A solid monolayer is identified at all bulk solution compositions with a melting temperature that varies with bulk composition in a manner resembling the bulk behavior. Incoherent elastic neutron scattering, IQNS, and nuclear magnetic resonance, NMR, data indicate that decane is preferentially adsorbed onto the surface over most of the composition range, heptanol being the principal surface component only at very high heptanol concentrations. NMR is proved, for the first time, to be an efficient tool to provide independent information on each component of the system.

Enero, 2009 | DOI: 10.1021/jp8072014

Titulo: Synthesis of MCM-22 zeolites of different Si/Al ratio and their structural, morphological and textural characterisation
Autores: Delitala, C; Alba, MD; Becerro, AI; Delpiano, D; Meloni, D; Musu, E; Ferino, I
Revista: Microporous and Mesoporous Materials, 118 (2009) 1-10
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MCM-22 zeolites with Si/Al in the 9–46 range were synthesised in rotating autoclave and characterised by X-ray diffraction, 1H, 29Si and 27Al magic angle spinning nuclear magnetic resonance, scanning electron microscopy and nitrogen physisorption. For the Si/Al = 21, 30 and 46 samples both X-ray diffraction and scanning electron microscopy revealed the crystallisation of pure MCM-22. Besides the latter, crystals of ferrierite also formed during the synthesis of the Si/Al = 9 sample. Based on the 1H MAS NMR spectra of dehydrated samples, the different proton species present on the MCM-22 samples were determined and quantified. Information about the incorporation of Al ions into the zeolite framework, as well as on the preferential crystallographic sites occupied in dependence on the Si/Al ratio of the sample, was obtained by 27Al MAS NMR spectroscopy. From 29Si MAS NMR spectra, differences in the degree of crystallinity of the samples were assessed, the results being in agreement with the diffraction data. Nitrogen physisorption runs revealed the microporous nature of the adsorbents, with a supermicropore to ultramicropore volume ratio in good agreement, for the best crystallised samples, with the porous structure with supercages and sinusoidal channels of the ideal MCM-22 crystal.

Enero, 2009 | DOI: 10.1016/j.micromeso.2008.07.047

Titulo: Liquid-phase thiophene adsorption on MCM-22 zeolites. Acidity, adsorption behaviour and nature of the adsorbed products
Autores: Delitala, C; Cadoni, E; Delpiano, D; Meloni, D; Alba, MD; Becerro, AI; Ferino, I
Revista: Microporous and Mesoporous Materials, 118 (2009) 11-20
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The liquid-phase adsorption of thiophene from thiophene/iso-octane solutions has been investigated in batch conditions at room temperature and atmospheric pressure on MCM-22 zeolites with Si/Al in the 9–46 range. Thiophene adsorption was found to occur in two steps whatever the Si/Al ratio of the adsorbent. The presence of ferrierite besides the MCM-22 phase caused a significant loss of the adsorption performance. For pure MCM-22 samples, the Si/Al ratio influenced the adsorption performance. Based on the acid properties of the samples, investigated by adsorption microcalorimetry of ammonia, the adsorption features were interpreted by assuming that positively charged species were originated during the first step; these species underwent successive reaction with weakly adsorbed species formed in the second step, leading to heavy molecular weight organosulphur compounds. Direct evidence for the occurrence of reactive adsorption of thiophene involving its transformation into heavy molecular weight organosulphur compounds was obtained by GC/MS investigation of the nature of the adsorbed material recovered after the adsorption experiments. The peculiar structure of MCM-22 zeolites made possible the formation of long-sized organosulphur compounds. Due to the mechanism by which thiophene is transformed (i.e. progressive addition of other thiophene molecules), the size of the resulting products was found to depend also on the concentration of the weakly adsorbed thiophene molecules able to interact with those already activated through protonation.

Enero, 2009 | DOI: 10.1016/j.micromeso.2008.08.008

Titulo: Synthesis, Rietveld Analysis, and Solid State Nuclear Magnetic Resonance of X2-Sc2SiO5
Autores: Alba, MD; Chain, P; Gonzalez-Carrascosa, T
Revista: Journal of the American Ceramic Society, 92 (2009) 487-490
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Compounds containing rare earths are of increasing technological interest especially because of their unique mechanical, magnetic, electrical, and optical properties. Among them, rare earth oxyorthosilicates are attractive scintillators for γ- and X-ray spectroscopy and detection. However, there are many structural aspects of those compounds that are not clear. In this research, the structure parameters for Sc2Si2O5, X2-polymorph, have been refined from powder X-ray diffraction (XRD) data and the 29Si MAS NMR spectrum is reported for the first time. X2-Sc2SiO5 polymorph was synthesized by the sol–gel method and characterized by XRD and 29Si MAS NMR. The XRD pattern was indexed in a monoclinic unit cell with space group I2/c; the resulting unit cell parameters were a=9.9674(2) Å, b=6.4264(9) Å, c=12.0636(2) Å, and β=103.938(1)°. The 29Si MAS NMR spectrum showed a unique signal at −79.5 ppm, compatible with the unique Si crystallographic site in the unit cell. Finally, the band valence method has been applied to the calculation of a “shift parameter,” which is correlated with the NMR chemical shift.

Enero, 2009 | DOI: 10.1111/j.1551-2916.2008.02877.x

Titulo: Phase separation of carboxylic acids on graphite surface at submonolayer regime
Autores: Alba, MD; Bickerstaffe, AK; Castro, MA; Clarke, SM; Medina, S; Millan, C; Orta, MM; Pavon, E; Perdigon, AC
Revista: The European Physical Journal Special Topics, 167 (2009) 151-156
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Mixing behaviour of solid crystalline monolayers adsorbed onto graphite from different mixtures of undecanoic and dodecanoic acids at submonolayer coverage has been investigated. X-ray diffraction measurements have been collected from a variety of compositions as a function of temperature. An extensive phase separation is found for all the compositions – the scattering patterns characteristic of the pure material crystalline structures being preserved across the entire composition range. The temperature dependence of the monolayer melting points and their depression is also clearly indicative of separation of the two surface components, in clear contrast to that expected if the two carboxylic acids mixed ideally in the monolayer.

Enero, 2009 | DOI: 10.1140/epjst/e2009-00951-6



José María Delgado Sánchez
Estrategia de Optimización de Dispositivos Fotovoltaicos de Lámina Delgada desde la Microestructura a la Macroestructura

Director/es: María Dolores Alba Carranza
Universidad de Sevilla
Miércoles, 18 Febrero, 2015




Moisés Naranjo Muñoz
Síntesis y reactividad de silicatos laminares de alta carga

Director/es: Miguel Angel Castro Arroyo
Universidad de Sevilla
Viernes, 25 Junio, 2010




Pablo Chain Villar
Síntesis hidrotermal de disilicatos de tierras raras a partir de silicatos laminares. Un mecanismo inmovilizador de residuos radioactivos de alta actividad

Director/es: María Dolores Alba Carranza
Universidad de Sevilla
Martes, 18 Diciembre, 2007




Alberto Escudero Belmonte
Síntesis y caracterización estructural de sistemas binarios de disilicatos de tierras raras

Director/es: Ana Isabel Becerro Nieto
Universidad de Sevilla
Lunes, 9 Julio, 2007


Nuevo material nanoestructurado adsorbente de contaminantes orgánicos del agua

El Instituto de Ciencia de Materiales de Sevilla (CSIC) y la Universidad de Sevilla han patentado un nuevo material basado en una mica sintética, único por sus propiedades organofílicas (capacidad de atraer a las moléculas orgánicas). Esto hace al material muy interesante en aplicaciones para el tratamiento de aguas residuales ya que es capaz de eliminar una amplia gama de contaminantes orgánicos y, por tanto, una gran parte de los residuos que contaminan las aguas. Adicionalmente, el proceso se puede optimizar para cada uno de los residuos específicos normalmente presentes en el agua. Ello posibilita que esta innovadora tecnología contribuya al cumplimiento de las leyes ambientales más estrictas.

Se buscan socios industriales para la licencia de la patente.

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