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2010


Microscopic and spectroscopic techniques for the study of paper supports and textile used in the binding of hispano-arabic manuscripts from Al-Andalus: A transition model in the 15th century


Espejo, T; Duran, A; Lopez-Montes, A; Blanc, R
Journal of Cultural Heritage, 11 (2010) 50-58

ABSTRACT ▼

This work focuses on the study of paper and textiles used in the binding of a series of manuscripts that share some specific characteristics that lead us to speculate on the possibility of a transitional codicological typology from the Arabic to the Christian book in Al-Andalus during the 15th century. The books we analyzed belong to the collection of the Historical Archive of Malaga, the Archive of Sacromonte Abbey, in Granada, the School of Arabic Studies and the Library of P.P. Escolapios, also in Granada. Paper physical study was performed by microscopic and spectroscopic techniques. A routine and objective method, Fourier Transform Infrared (FTIR) spectroscopy, was employed and proved to be a useful technique for the characterization of cellulosic fibres, main component of paper from the boards and the envelope flap pasteboards, and the fabric lining from the cover. The results of our research will help us to date, identify and study the evolution of the techniques, proving that the materials and innovations of the Italian paper manufacturing processes were perfectly known in the south of modern day Spain, before the Christian Reconquest.


Enero, 2010 | DOI: 10.1016/j.culher.2009.01.007

The Multistep Nature of the Kaolinite Dehydroxylation: Kinetics and Mechanism


Ortega, A; Macias, M; Gotor, FJ
Journal of the American Ceramic Society, 93 (2010) 197-203
Reactividad de Sólidos - Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT ▼

The thermal dehydroxylation of kaolinite has been reexamined using small sample weights, a homogeneous particle size distribution and high-vacuum conditions in order to reduce the influences of heat and mass-transfer phenomena. The controlled rate thermal analysis (CRTA) technique, which was specially developed to minimize the pressure and temperature gradients through the sample, was employed to carry out meaningful kinetic experiments. Two advanced isoconversional methods, the Vyazovkin and the Galwey methods, were used complementarily to determine the dependence of the activation energy on the degree of conversion. For this purpose, the Vyazovkin method has been adapted to CRTA experiments. It was demonstrated that there are at least two different stages, revealing the multistep nature of this reaction. The activation energy for the first step, which is assigned to nucleation and the growth of nuclei, decreases from 100 to 75 kJ/mol. The second stage corresponds to a diffusion process and the activation energy rises to 120 kJ/mol because of the metakaolinite formation, which closes the interlamellar channels and leaves isolated patches of kaolinite from which the water escapes with difficulty.


Enero, 2010 | DOI: 10.1111/j.1551-2916.2009.03328.x

Determination of the decay rate constant for hepatocytes immobilized in alginate microcapsules


Leal-Egana, A; Diaz-Cuenca, A; Bader, A
Journal of Micoencapsulation, 27 (2010) 86-93
Materiales para Bioingeniería y Regeneración Tisular

ABSTRACT ▼

Primary mouse hepatocytes (between 10-250 cells per capsule) were immobilized within 1.0% w/v alginate microbeads. The textural properties of the alginate matrix were characterized and a full protocol based upon the measurement of the initial rate of Resazurin reduction was studied and standardized. Using this method, the decay rate constant (K-d = 0.45 +/- 0.01 days(-1)) and the time in which the cell viability decreases in half (VI50 = 37 +/- 0.7 h) have been measured. The method was compared with the analysis of cell vitality using Calcein A/M and Ethidium Homodimer I. Differences between the two methods were found in the viability profile due to the significant presence of double stained cells along the culture time. According to the author's knowledge, this is the first report of a systematic study and determination of the K-d value for immobilized hepatocytes, incorporating a wide range of cell concentrations within the alginate matrix.


Enero, 2010 | DOI: 10.3109/02652040903050550

Conformal Growth of Organic Luminescent Planar Defects within Artificial Opals


Aparicio, FJ; Lozano, G; Blaszczyk-Lezak, I; Barranco, A; Miguez, H
Chemistry of Materials, 22 (2010) 379-385
Materiales Ópticos Multifuncionales - Nanotecnología en Superficies y Plasma

ABSTRACT ▼

Herein, we present the result of combining, for the first time, the techniques of colloidal self-assembly and plasma-enhanced chemical vapor deposition to create a novel, high-quality, purely Organic active photonic crystal structure of controlled optical properties. We show a fast. reliable, and accurate procedure to introduce two-dimensional luminescent organic defect layers within artificial polystyrene opals via a versatile room-temperature remote plasma deposition process. This method is gentle enough to allow highly coil formal growth on polystyrene microspheres without altering their morphology or the ordered arrangement that they form. The luminescent organic layer behaves both as all optical dopant, causing the opening of transmission windows within the forbidden frequency interval of the lattice, and as an optically active material, whose emission call be tailored by the photonic environment.


Enero, 2010 | DOI: 10.1021/cm902819x

Chemical and electronic characterization of cobalt in a lanthanum perovskite. Effects of strontium substitution


Hueso, JL; Holgado, JP; Pereniguez, R; Mun, S; Salmeron, M; Caballero, A
Journal of Solid State Chemistry, 183 (2010) 27-32
Materiales y Procesos Catalíticos de Interés Ambiental y Energético

ABSTRACT ▼

Two different cobaltites, LaCoO3 and La0.5Sr0.5CoO3-delta, have been prepared and characterized by means of high energy Co K-edge and low energy O K-edge X-ray absorption spectroscopy (XAS). Even though half of the La(III) is substituted by Sr(II), little or no changes call be detected in the formal oxidation state of cobalt atoms. The presence of strontium cations induces two main effects in the chemical and electronic state of the perovskite. The charge balance with Sr(II) species is reached by the formation of oxygen vacancies throughout the network, which explains the well-known increase in the reactivity of this Substituted perovskite. O K-edge XAS experiments show that the Sr(II) species induce the transitions of d electrons of cobalt cations from low to high Spill Configuration. We propose that this change in Spill Multiplicity is induced by two cooperative effects: the oxygen vacancies. creating five coordinated cobalt atoms, and the bigger size of Sr(II) cations, aligning the Co-O-Co atoms, and favoring the overlapping of pi-symmetry cobalt and oxygen orbitals, reducing the splitting energy of e(g) and t(2g) levels.


Enero, 2010 | DOI: 10.1016/j.jssc.2009.10.008

Supported nickel catalysts with a controlled molecular architecture for the catalytic reformation of methane


Hufschmidt, D; Bobadilla, LF; Romero-Sarria, F; Centeno, MA; Odriozola, JA; Montes, M; Falabella, E
Catalysis Today, 149 (2010) 394-400
Química de Superficies y Catálisis

ABSTRACT ▼

In this work a lanthanum and nickel catalyst having perovskite structure, grown on a gamma-alumina carrier, is being presented. The structure of the catalyst was confirmed by XRD. The behaviour of this material under the conditions of steam reforming has been studied and the influence of the temperature, the space velocity and the steam/carbon ratio on the conversion of methane and the product distribution in the process was determined. In all cases at higher temperatures conversions of more than 90% and high selectivities were achieved. The experiments to determine the stability of the catalyst demonstrated that no deactivation in experimental runs of more than 17h occurred. Additionally a study of the catalyst after the reaction showed that only lowly structured carbonaceous species were formed on the catalyst surface, which is not expected to inhibit strongly the initial catalytic activity.


Enero, 2010 | DOI: 10.1016/j.cattod.2009.06.002

Synthesis and characterization of a LaNiO3 perovskite as precursor for methane reforming reactions catalysts


Pereñiguez, R; Gonzalez-DelaCruz, VM; Holgado, JP; Caballero, A
Applied Catalysis B-Environmental, 93 (2010) 346-353
Materiales y Procesos Catalíticos de Interés Ambiental y Energético

ABSTRACT ▼

The objective of the present work has been the study of the physicochemical and catalytic properties of a Ni/La2O3 catalyst obtained by reduction of a lanthanum nickelite, LaNiO3, with perovskite structure. The perovskite, obtained by means of a spray pyrolysis method, provides a Ni/La2O3 system active in different methane reforming reactions. The catalyst was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), X-Ray photoemission spectroscopy (XPS), temperature-programmed reduction and oxidation (TPR, TPO) and catalytic activity tests. Although not evidenced by XRD data, XAS and TPR measurements show the presence of an amorphous NiO phase in the original sample, together with the crystalline LaNiO3 phase. Upon reoxidation treatment of the reduced Ni/La2O3 catalyst, the LaNiO3 structure is partly recovered which provides a convenient way to regenerate a waste catalyst (reoxidation and new reduction in hydrogen). The catalyst is active in several reactions of methane with oxygen, water and CO2, showing a remarkable stability specially under dry reforming of methane (DRM) reaction conditions. This quite great catalytic performance has been explained by the high resistance of the nickel particles to be oxidized, as detected by in situ XAS. In the presence of water, as in steam reforming of methane (SRM) reaction conditions, these metallic particles are gradually oxidized, which explains the linear decreasing of the catalytic performance observed for the SRM reaction.


Enero, 2010 | DOI: 10.1016/j.apcatb.2009.09.040



2009


Characterization of illuminated manuscripts by laboratory-made portable XRD and micro-XRD systems


Duran, A; Perez-Rodriguez, JL; Espejo, T; Franquelo, ML; Castaing, J; Walter, P
Analytical and Bioanalytical Chemistry, 395 (2009) 1997-2004

ABSTRACT ▼

Illuminated Arabic manuscripts have been studied, employing two laboratory-made X-ray diffraction (XRD) systems developed recently in the C2RMF laboratory. The validity of the µ-XRD and XRD portable systems for the study of this type of artworks has been demonstrated. A common observation in all the analyses is the presence of calcite and rutile; also, hematite, goethite, cinnabar, brass, anatase and barite were detected in the various colours. Differences between the results obtained by both techniques due to acquisition mode are discussed. In addition, other techniques such as X-ray fluorescence (XRF) and micro-Raman were used for the complete characterization of the manuscripts.


Diciembre, 2009 | DOI: 10.1007/s00216-009-2992-5

Study of metallic components of historical organ pipes using synchrotron radiation X-ray microfluorescence imaging and grazing incidence X-ray diffraction


Herrera, LK; Justo, A; Munoz-Paez, A; Sans, JA; Martinez-Criado, G
Analytical and Bioanalytical Chemistry, 395 (2009) 1969-1975

ABSTRACT ▼

A comparative study of the composition and microstructure of two different brass alloys from reed pipes, one from a Spanish baroque organ and the other from a modern one, was carried out. This study allowed us to determine the procedure followed to produce the brass used to make ancient reed pipes. Moreover the distribution and correlation of lead and other trace elements present into the main component of the brass, the copper and zinc phases, of the historical tongues and shallots were established. This chemical composition was compared with that of a tongue from a twentieth-century organ. The whole study was accomplished using a combination of laboratory and synchrotron radiation techniques. X-ray fluorescence was the technique used to obtain elemental and chemical imaging of the main phases and the trace elements at a sub-micrometer scale.


Diciembre, 2009 | DOI: 10.1007/s00216-009-3075-3

Reversibility of La and Lu sorption onto smectites: Implications for the design of engineered barriers in deep geological repositories


Galunin, E; Alba, MD; Aviles, MA; Santos, MJ; Vidal, M
Journal of Hazardous Materials, 172 (2009) 1198-1205
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT ▼

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.


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

Thermogravimetric and in situ SEM characterisation of the oxidation phenomena of protective nanocomposite nitride films deposited on steel


Mege-Revil, A; Steyer, P; Thollet, G; Chiriac, R; Sigala, C; Sanchez-Lopez, JC; Esnouf, C
Surface and Interface Analysis, 204 (2009) 893-901
Materiales Nanoestructurados y Microestructura

ABSTRACT ▼

The lifetime of TiN coatings is often limited by its poor resistance to high temperatures. For an optimized addition of silicon, both mechanical and physico-chemical properties are enhanced, owing to the formation of a nanocomposite structure. In this study, pure Ti and TiSi (80/20) targets were arc-evaporated to produce hard, single-layered coatings. Magnetron sputtered SiNx films were also synthesized for a comparison purpose. The nanocomposite structure was determined by XRD and TEM, and its efficiency regarding the mechanical properties was confirmed by nanohardness measurements. Through thermogravimetric experiments it is shown that in isothermal and dynamic conditions, the chemical stability inherent to SiNx controls the oxidation behaviour of TiSiN. However, in thermal cycling conditions TiSiN withstand efficiently temperature variations whereas SiNx does not. The aim of this study is to understand the role of SiNx on the oxidation of the TiSiN nanocomposite film. For this purpose, an in situ approach of the oxidation phenomena is detailed, based on experiments performed in an environmental scanning electron microscope (ESEM) operating in controlled pressure mode up to 1000 °C. ESEM, used in real-time oxidative conditions, has been proved to be an efficient tool to characterise the mechanism of degradation. The successive steps of the attack throughout the in situ oxidation process are as follow: oxidation first initiates at coating defects (open pores and droplets), then spreads to the whole surface. The whole flaking of the film that is observed at the microscopic scale during the cooling step proves the poor thermal fatigue resistance of SiNx. This strong propensity to cracking is explained on the basis of thermo-mechanical considerations. The nanocomposite structure thus combines the chemical stability inherent to the SiNx matrix with the beneficial thermo-mechanical properties associated to TiN nanograins.


Diciembre, 2009 | DOI: 10.1016/j.surfcoat.2009.06.040

Metal carbide/amorphous C-based nanocomposite coatings for tribological applications


Sanchez-Lopez, JC; Martinez-Martinez, D; Abad, MD; Fernandez, A
Surface and Coatings Technology, 204 (2009) 947-954
Materiales Nanoestructurados y Microestructura

ABSTRACT ▼

This paper tries to assess the factors governing the tribological behaviour of different nanocomposites films composed by metallic carbides (MeC) mixed with amorphous carbon (a-C). Different series of MeC/a-C coatings (with Me: Ti(B) and W) were prepared by magnetron sputtering technique varying the power applied to the graphite target in order to tailor the carbon content into the films. A deep investigation of the chemical and structural features at the nano-scale is carried out by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron energy-loss spectroscopy (EELS) and Raman spectroscopy techniques in order to establish correlations with the tribological properties measured by a pin-on-disk tribometer in ambient air. The analysis of the counterfaces by Raman confocal microscopy after the friction tests is used to follow the chemical phenomena occurring at the contact area responsible of the observed friction behaviour. The importance of determining the fraction of C atoms in the amorphous phase (xa-C) is highlighted as a key-parameter to control the tribological properties. A comparative analysis of the mechanical and tribological performance of the three systems (TiC/a-C, WC/a-C, TiBC/a-C) is done and conclusions are obtained concerning the friction and wear mechanism involved.


Diciembre, 2009 | DOI: 10.1016/j.surfcoat.2009.05.038

The hydrothermal conversion of kaolinite to kalsilite: Influence of time, temperature, and pH


Becerro, AI; Escudero, A; Mantovani, M
American Mineralogist, 94 (2009) 11-12
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT ▼

Kalsilite (the low-temperature form of KAlSiO4) is used as the precursor of leucite, an important component in porcelain-fused-to-metal and ceramic-restoration systems, and it has also been proposed as a high-thermal expansion ceramic for bonding to metals. The present study reports the hydrothermal synthesis and characterization of pure kalsilite from kaolinite in subcritical conditions, as well as the characterization of the intermediate products by means of XRD, 29Si and 27Al MAS NMR, IR, SEM, and TEM. Effects of time, temperature, and pH on the reaction products are analyzed. The experimental data indicate that pure kalsilite is obtained after hydrothermal treatment of kaolinite at 300 °C for 12 h in 0.5 M KOH solution. Longer reaction times increase the crystallinity of the structure, whereas lower reaction times give rise to the metastable ABW-type KAlSiO4 polymorph. Lower temperatures are not sufficient to produce kalsilite, but zeolite W is obtained instead as the unique reaction product. Finally, the pH of the aqueous solution in contact with kaolinite is an important parameter for the synthesis of kalsilite, which must be ≥13.70.


Noviembre, 2009 | DOI: 10.2138/am.2009.3284

Self-Assembling of Er2O3-TiO2 Mixed Oxide Nanoplatelets by a Template-Free Solvothermal Route


Julian-Lopez, B; Martos, M; Ulldemolins, N; Odriozola, JA; Cordoncillo, E; Escribano, P
Chemistry-A European Journal, 15 (2009) 12426-12434
Química de Superficies y Catálisis

ABSTRACT ▼

An easy solvothermal route has been developed to synthesize the first mesoporous Er2O3-TiO2 mixed oxide spherical particles composed of crystalline nanoplatelets, with high surface area and narrow pore size distribution. This synthetic strategy allows the preparation of materials at low temperature with interesting textural properties without the use of surfactants, as well as the control of particle size and shape. TEM and Raman analysis confirm the formation of nanocrystalline Er2O 3-TiO2 mixed oxide. Mesoscopic ordered porosity is reached through the thermal decomposition of organic moieties during the synthetic process, thus leading to a template-free methodology that can be extended to other nanostructured materials. High specific surface areas (up to 313 m 2g-1) and narrow pore size distributions are achieved in comparison to the micrometric material synthesized by the traditional sol-gel route. This study opens new perspectives in the development, by solvothermal methodologies, of multifunctional materials for advanced applications by improving the classical pyrochlore properties (magnetization, heat capacity, catalysis, conductivity, etc.). In particular, since catalytic reactions take place on the surface of catalysts, the high surface area of these materials makes them promising candidates for catalysts. Furthermore, their spherical morphology makes them appropriate for advanced technologies in, for instance, ceramic inkjet printers.


Noviembre, 2009 | DOI: 10.1002/chem.200901423

Advanced combined application of μ-X-ray diffraction/μ-X-ray fluorescence with conventional techniques for the identification of pictorial materials from Baroque Andalusia paintings


Herrera, LK; Montalbani, S; Chiavari, G; Cotte, M; Sole, VA; Bueno, J; Duran, A; Justo, A; Perez-Rodriguez, JL
Talanta, 80 (2009) 71-83

ABSTRACT ▼

The process of investigating paintings includes the identification of materials to solve technical and historical art questions, to aid in the deduction of the original appearance, and in the establishment of the chemical and physical conditions for adequate restoration and conservation. In particular, we have focused on the identification of several samples taken from six famous canvases painted by Pedro Atanasio Bocanegra, who created a very special collection depicting the life of San Ignacio, which is located in the church of San Justo y Pastor of Granada, Spain. The characterization of the inorganic and organic compounds of the textiles, preparation layers, and pictorial layers have been carried out using an XRD diffractometer, SEM observations, EDX spectrometry, FT-IR spectrometry (both in reflection and transmission mode), pyrolysis/gas chromatography/mass spectrometry and synchrotron-based μ-X-ray techniques. In this work, the advantages over conventional X-ray diffraction of using combined synchrotron-based μ-X-ray diffraction and μ-X-ray fluorescence in the identification of multi-layer paintings is demonstrated.


Noviembre, 2009 | DOI: 10.1016/j.talanta.2009.06.032

Methane steam reforming in a microchannel reactor for GTL intensification: A computational fluid dynamics simulation study


Arzamendia, G; Dieguez, PM; Montes, M; Odriozola, JA; Sousa-Aguiar, EF; Gandia, LM
Chemical Engineering Journal, 154 (2009) 168-173
Química de Superficies y Catálisis

ABSTRACT ▼

The integration of the steam reforming and combustion of methane in a catalytic microchannel reactor has been simulated by computational fluid dynamics (CFD). Two models including 4 or 20 square microchannels of 20 mm of length and 0.7 mm of side have been developed. It has been assumed that a thin and homogeneous layer of an appropriate catalyst has been uniformly deposited onto the channels walls. The kinetics of the steam reforming of methane (SRM), water-gas shift (WGS) and methane combustion in air have been incorporated into the models. This has allowed simulating the effect of the gas streams space velocities, catalyst load, steam-to-carbon (S/C) ratio and flow arrangement on the microreformer performance. The results obtained illustrate the potential of microreactors for process intensification: complete combustion of methane is achieved at gas hourly space velocities (GHSV) as high as 130,000 h−1. As concerns the SRM, methane conversions above 97% can be obtained at high GHSV of 30,000 h−1 and temperatures of 900–950 °C. Under these conditions selectivity for syngas is controlled by the WGS equilibrium.


Noviembre, 2009 | DOI: 10.1016/j.cej.2009.01.035

Hybrid catalytic-DBD plasma reactor for the production of hydrogen and preferential CO oxidation (CO-PROX) at reduced temperatures


Rico, VJ; Hueso, JL; Cotrino, J; Gallardo, V; Sarmiento, B; Brey, JJ; Gonzalez-Elipe, AR
Chemical Communications, 41 (2009) 6192-6194
Nanotecnología en Superficies y Plasma

ABSTRACT ▼

Dielectric Barrier Discharges (DBD) operated at atmospheric pressure and working at reduced temperatures (T < 115 °C) and a copper–manganese oxide catalyst are combined for the direct decomposition and the steam reforming of methanol (SRM) for hydrogen production and for the preferential oxidation of CO (CO-PROX)


Noviembre, 2009 | DOI: 10.1039/b909488a

Characterization of sepiolite-gel-based formulations for controlled release of pesticides


Maqueda, C; Partal, P; Villaverde, J; Perez-Rodriguez, JL
Applied Clay Science, 46 (2009) 289-295

ABSTRACT ▼

Novel controlled release formulations (CRFs) were developed for reducing leaching of herbicides and contamination of groundwater. The herbicide metribuzin (MTB) was entrapped within a sepiolite-gel matrix using a novel and ultrasound-based technique. Different sepiolite/herbicide matrices (either as a gel or as a powder after freeze-drying) were prepared with pesticide loading between 28.6 and 9.1%. The release of MTB from the control released formulations into water was retarded when compared with commercial formulation (CF), except in the case of the sepiolite-gel-based formulations with lower amounts of sepiolite. The rheological properties and microstructure of these formulations were examined in detail. FTIR spectra showed that there was no evidence of herbicide inside the sepiolite tunnels. The SEM micrograph of the sepiolite-gel-based formulations showed the fibrous morphology typical of sepiolite and no separate particles of MTB were found. However, the chemical analysis by EDX confirmed the presence of S, N, and C, which were attributed to MTB, together with the fibers of sepiolite. Rheological characterization indicated that samples containing MTB develops a microstructure, which is irrespective of concentration above 1 mass % sepiolite. There was a good agreement between the microstructure characteristics and MTB release behavior.


Noviembre, 2009 | DOI: 10.1016/j.clay.2009.08.019

Synthesis and characterization of a plant cutin mimetic polymer


Heredia-Guerrero, JA; Heredia, A; Garcia-Segura, R; Benitez, JJ
Polymer, 50 (2009) 5633-5637
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT ▼

A mimetic polymer of plant cutin have been synthesized from 9,10,16-trihydroxyhexadecanoic (aleuritic) acid through a low temperature polycondensation reaction. Reaction conditions (solvent, catalyst, temperature, etc…) were studied and modified to optimize yield and product characteristics. The resulting polyaleurate polymer was characterized by Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD) and solid state 13C-Cross Polarization/Magic Angle Spinning Nuclear Magnetic Resonance (13C-CP/MAS NMR). Mechanical and hydrodynamic properties were also investigated. In the average, the product obtained is physically and chemically very similar to plant cutin (a hydrophobic polyester). However, a more detailed analysis of results reveals that polyaleurate framework is more rigid than natural cutin and with additional larger short-range ordered domains. Also, the synthetic polymer displays slightly different mechanical properties with respect to natural cutin. Additional hydrogen bonding within the framework of polyaleurate is considered to be responsible for such experimental observations.


Noviembre, 2009 | DOI: 10.1016/j.polymer.2009.10.018

Bonding Structure and Mechanical Properties of Ti-B-C Coatings


Abad, MD; Caceres, D; Pogozhev, YS; Shtansky, DV; Sanchez-Lopez, JC
Plasma Processes and Polymers, 6 (2009) S107-S112
Materiales Nanoestructurados y Microestructura

ABSTRACT ▼

Nanocomposite coatings combining hard phases (TiB2, TiC) with an amorphous carbon (a-C) were developed to provide a good compromise between mechanical and tribological properties for M2 steels used in a wide variety of applications such as cutting tools, bearings and gear mechanisms. A combined d.c.-pulsed and r.f.-magnetron deposition process was used to deposit nanocomposite TiBC/a-C coatings with a variable content of carbon matrix phase. Chemical composition was determined by electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy (TEM) revealed that the coatings microstructure is rather amorphous with small nanocrystals of TiC and/or TiB2 (not possible to differentiate by diffraction techniques). Investigation of the chemical bonding environment by XPS and EELS allows us to confirm the presence of titanium-boron and titanium-carbon bonds together with free a-C. Coatings exhibited hardness values (H) of 25–29 GPa, effective Young modulus (E*) of 310–350 GPa, H/E* ratios over 0.080 and resistance to plastic deformation (H3/E*2) from 0.15 to 0.20. Tribological properties of the coatings were characterized by a pin-on-disk tribometer using steel and WC balls at high contact stresses (1.1 and 1.4 GPa respectively). Friction coefficients were reduced from 0.6 to 0.2 by increasing the content of free carbon without reduction of the hardness (around 28 GPa), by self-lubricant effects. The tribo-mechanical data are revised according to the phase composition and chemical bonding inside the nanocomposites.


Noviembre, 2009 | DOI: 10.1002/ppap.200930403

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