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2010


Hydraulic structures of the Roman Mithraeum house in Augusta emerita, Spain


Robador, MD; Perez-Rodriguez, JL; Duran, A
Journal of Archaeological Science, 37 (2010) 2426-2432

ABSTRACT

This paper deals with some of the hydraulic structures of Augusta Emerita (Merida, Spain), specifically those found in the Mithraeum House. In particular, we describe and characterise the hydraulic mortars and coatings of the viridarium water channel. The recipient of the channel was covered with two hydraulic mortars and a finishing coating. Hydrated lime was used as binder. Calcite grains with different morphology have been observed in the mortars studied. The siliceous aggregate was composed of quartz, mica and feldspars. Ceramic fragments, which were added to the mortar to improve its hydraulic properties, were composed of quartz, mica, iron oxides, anorthite and an amorphous phase; aluminium-iron silicates were used as raw materials for their manufacture. We discuss the interactions between the hydrated lime and the surface of the ceramics in the mortars.


Octubre, 2010 | DOI: 10.1016/j.jas.2010.05.003

Superplasticity in nanocrystalline ceramics: pure grain boundary phenomena or not?


Dominguez-Rodriguez, A; Gomez-Garcia, D; Castillo-Rodriguez, M; Zapata-Solvas, E; Chaim, R
International Journal of Materials Research, 101 (2010) 1215-1221
Propiedades Mecánicas de Sólidos

ABSTRACT

Superplasticity in ceramics has been the subject of intense research activity for the last two decades. Quite recently, the fabrication of fully dense nanocrystalline oxides with grain size below 100 nm enabled examination of their superplastic behaviour. This work presents a critical analysis of the plasticity of two important nanostructured oxide systems: MgO and yttria tetragonal zirconia polycrystals. A thorough comparison of their plastic deformation reveals that nano-structuring may be a necessary, but not a sufficient condition for superplasticity in ceramics as commonly assumed. Instead, the changes in the chemical composition and the transport properties, through the bulk and at grain boundaries, versus temperature and grain size can induce a rich variety of mechanical responses.


Octubre, 2010 | DOI: 10.3139/146.110401

Photocatalytic degradation of phenolic compounds with new TiO2 catalysts


Araña, J; Dona-Rodriguez, JM; Portillo-Carrizo, D; Fernandez-Rodriguez, C; Perez-Pena, J; Diaz, OG; Navio, JA; Macias, M
Applied Catalysis B-Environmental, 100 (2010) 346-354
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

New TiO2 catalysts have been synthesised by means of a sol-gel method in which aggregates have been selected before thermal treatment. Sieving and calcination temperature have been proved to be key factors in obtaining catalysts with greater photoactivity than that of Degussa P-25. These new catalysts have been characterized by means of transmission electron microscopy (TEM), BET surface area, diffuse reflectance spectroscopy (DRS). UV-vis spectroscopy, Fourier transformed infrared (FTIR) and X-ray diffraction (XRD). The different parameters studied were compared to those obtained from two commercial catalysts (Degussa P-25 and Hombikat-UV100). The photocatalytic efficiency of the new catalysts was evaluated by the degradation of various phenolic compounds using UV light (maximum around 365 nm, 9 mW). The catalyst sieved and calcinated at 1023 K, ECT-1023t, showed phenol degradation rates 2.7 times higher than those of Degussa P-25. Also in the degradation of different phenolic compounds, this catalyst showed a higher activity than that of the commercial one. The high photoactivity of this new catalyst has been attributed to the different distribution of surface defects (determined from FTIR studies) and its increased capacity to yield H2O2.


Octubre, 2010 | DOI: 10.1016/j.apcatb.2010.08.011

Microstructural study of the LiBH4-MgH2 reactive hydride composite with and without Ti-isopropoxide additive


Deprez, E; Justo, A; Rojas, TC; Lopez-Cartes, C; Minella, CB; Bosenberg, U; Dornheim, M; Borrnann, R; Fernandez, A
Acta Materialia, 58 (2010) 5683-5694
Materiales Nanoestructurados y Microestructura

ABSTRACT

An exhaustive microstructural characterization is reported for the LiBH4-MgH2 reactive hydride composite (RHC) system with and without titanium isopropoxide additive. X-ray diffraction with Rietveld analysis, transmission electron microscopy coupled to energy dispersive X-ray analysis, selected-area electron diffraction and electron energy loss spectroscopy are presented in this paper for the first time for this system for all sorption steps. New data are reported regarding average crystallite and grain size, microstrain, phase formation and morphology; these results contribute to the understanding of the reaction mechanism and the influence of the additives on the kinetics. Microstructural effects, related to the high dispersion of titanium-based additives, result in a distinct grain refinement of MgB2 and an increase in the number of reaction sites, causing acceleration of desorption and absorption reactions. Considerations on the stability of phases under electron beam irradiation have also been reported.


Octubre, 2010 | DOI: 10.1016/j.actamat.2010.06.043

Surface nanostructuring of TiO2 thin films by high energy ion irradiation


Romero-Gomez, P; Palmero, A; Ben, T; Lozano, JG; Molina, SI; Gonzalez-Elipe, AR
Physical Review B, 82 (2010) - 115420 (8 pages)
Nanotecnología en Superficies y Plasma

ABSTRACT

The effects of a high ion dose irradiation on TiO2 thin films under different conditions of temperature and ion nature are discussed. We have shown that anatase TiO2 thin films irradiated with N+ ions at room temperature develop a typical microstructure with mounds and voids open to the surface whereas irradiations at 700 K generate a surface pattern of well-ordered nanorods aligned with the ion beam. The formation of these patterns is caused by the simultaneous effect of ion irradiation near the film surface and a film temperature favoring the structural mobilization of the defective network of the material. To explain these phenomena, a qualitative model has been proposed and further tested by irradiating the TiO2 thin films with F+ and S+ ions under different conditions. The obtained results demonstrate that ion irradiation techniques enable the formation of tilted nanorod surface patterns with lengths of about 100 nm on anatase TiO2 thin films.


Septiembre, 2010 | DOI: 10.1103/PhysRevB.82.115420

Citrate mediated synthesis of uniform monazite LnPO(4) (Ln = La, Ce) and Ln:LaPO4 (Ln = Eu, Ce, Ce plus Tb) spheres and their photoluminescence


Nuñez, NO; Liviano, SR; Ocaña, M
Journal of Colloid and Interface Science, 349 (2010) 484-491
Materiales Coloidales

ABSTRACT

A simple method for the synthesis of spherical LaPO4 (monazite) particles with narrow size distribution and tailored size in the 150-500 nm range is reported. The procedure is based on a homogeneous precipitation process at low temperature (120 degrees C) from solutions containing La3+, citrate and phosphate ions under a very restrictive set of experimental conditions, which involves the use of La nitrate, citric acid and phosphoric acid as precursors and ethylene glycol as solvent. The growth mechanism of the spheres was investigated aiming at explaining the differences in particle size and shape observed when varying the experimental conditions. The applicability of this method for the synthesis of spherical particles of other lanthanide (Ce, Tb, Eu) phosphates is also analyzed. Finally, it is shown that the developed procedure can be used to dope the lanthanum phosphate particles with lanthanide cations, which resulted in spherical phosphors as illustrated for the Eu-doped, Ce-doped and Ce, Tb codoped systems, whose luminescent properties are also evaluated.


Septiembre, 2010 | DOI: 10.1016/j.jcis.2010.05.079

Uniform YF3:Yb,Er up-conversion nanophosphors of various morphologies synthesized in polyol media through an ionic liquid


Nuñez, NO; Quintanilla, M; Cantelar, E; Cusso, F; Ocaña, M
Journal of Nanoparticle Research, 12 (2010) 2553-2565
Materiales Coloidales

ABSTRACT

We describe a facile procedure for the synthesis at low temperature (120 A degrees C) of water-dispersible uniform YF3:Yb,Er up-conversion nanophosphors of various morphologies (rhombic and spheroidal) by homogeneous precipitation in polyol solutions containing different lanthanide salts and an ionic liquid (1-butyl, 2-methylimidazolium tetrafluoroborate) as fluoride source. It is shown that the shape of the obtained nanoparticles is mainly determined by the nature of both, the polyol and the lanthanide precursors, which also affects to their colloidal stability in water suspensions. These morphological differences are explained on the basis of a different mechanism of particle formation. The efficiency of the up-conversion processes in the synthesized rhombic and spheroidal nanoparticles is also comparatively analyzed and the observed differences are justified on the basis of the different impurities incorporated to the nanophosphors during their synthesis process.


Septiembre, 2010 | DOI: 10.1007/s11051-009-9824-6

On the microstructure of thin films grown by an isotropically directed deposition flux


Alvarez, R; Romero-Gomez, P; Gil-Rostra, J; Cotrino, J; Yubero, F; Palmero, A; Gonzalez-Elipe, AR
Journal of Applied Physics, 108 (2010) 64316
Nanotecnología en Superficies y Plasma

ABSTRACT

The influence of isotropically directed deposition flux on the formation of the thin film microstructure at low temperatures is studied. For this purpose we have deposited TiO2 thin films by two different deposition techniques: reactive magnetron sputtering, in two different experimental configurations, and plasma enhanced chemical vapor deposition. The obtained results indicate that films grown under conditions where deposition particles do not possess a clear directionality, and in the absence of a relevant plasma/film interaction, present similar refractive indices no matter the deposition technique employed. The film morphology is also similar and consists of a granular surface topography and a columnarlike structure in the bulk whose diameter increases almost linearly with the film thickness. The deposition has been simulated by means of a Monte Carlo model, taking into account the main processes during growth. The agreement between simulations and experimental results indicates that the obtained microstructures are a consequence of the incorporation of low-energy, isotropically directed, deposition particles.


Septiembre, 2010 | DOI: 10.1063/1.3483242

AISI 304 austenitic stainless steel monoliths: Modification of the oxidation layer and catalytic coatings after deposition and its catalytic implications


Martinez, LMT; Sanz, O; Centeno, MA; Odriozola, JA
Chemical Engineering Journal, 162 (2010) 1082-1090
Química de Superficies y Catálisis

ABSTRACT

Monolithic CeO2 and Au/CeO2 catalysts were prepared using austenitic stainless steel (AISI 304) as metallic substrate. Both monolithic and powdered catalysts were characterized before and after CO oxidation reaction by N-2 adsorption desorption, XRD, SEM, TEM and GD-OES. Catalyst deposition on the stainless steel surface results in modifications of the catalyst, the oxide scale and the oxide scale/alloy interface through the interaction between the coating and the steel oxidation layer. Besides this, oxidation of the alloy is also detected. The extension and nature of these modifications depends on the catalyst nature, and on the reaction conditions. As a result of these modifications CO oxidation on Au/CeO2 catalysts is enhanced and gold surface dynamics is modified.


Septiembre, 2010 | DOI: 10.1016/j.cej.2010.07.005

Aleuritic (9,10,16-trihydroxypalmitic) acid self-assembly on mica


Heredia-Guerrero, JA; San-Miguel, MA; Sansom, MSP; Heredia, A; Benitez, JJ
Physical Chemistry Chemical Physics, 12 (2010) 10423-10428
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT

Aleuritic (9,10,16-trihydroxypalmitic) acid self-assembly on mica from solution has been studied using AFM, ATR-FTIR and MD simulations. The goal of this study is to define the role of hydroxyl groups in the interaction between molecules as reference data to understand the mechanism of formation of synthetic and natural biopolyesters from polyhydroxylated long chain carboxylic acids. In a confined structure, such as the one imposed by a vertically self-assembled layer on mica, aleuritic acid has a tendency to adopt a monolayer configuration ruled by the lateral interactions between molecules via the two secondary hydroxyl groups. This (2D) growth competes with the multilayer formation (3D), which is conditioned by the terminal primary hydroxyl group. As the self-assembly spatial constraint is relaxed, MD has shown that the structure tends to become an amorphous and crosslinked phase that can be characterized by topographic and friction force AFM data.


Septiembre, 2010 | DOI: 10.1039/c0cp00163e

Tunable In-Plane Optical Anisotropy of Ag Nanoparticles Deposited by DC Sputtering onto SiO2 Nanocolumnar Films


Sanchez-Valencia, JR; Toudert, J; Borras, A; Lopez-Santos, C; Barranco, A; Feliu, IO; Gonzalez-Elipe, AR
Plasmonics, 5 (2010) 241-250
Nanotecnología en Superficies y Plasma

ABSTRACT

This work reports an easy-to-handle method for growing two-dimensional assemblies of Ag nanostructures presenting a tunable in-plane optical anisotropy. Ag is deposited by DC sputtering in an Ar plasma at room temperature onto bundled nanocolumnar SiO2 thin films grown by glancing angle physical vapor deposition. In contrast with previously reported processes involving the grazing angle deposition of the metal, DC sputtering is performed at normal incidence. By varying the deposition angle of SiO2 and the Ar pressure, it was possible to tune the deposited amount of Ag and thus the topology of the Ag deposit from isolated spherical Ag nanoparticles with isotropic optical properties to strongly dichroic Ag nanostripes oriented along the bundling direction of the SiO2 nanocolumns. Based on simple calculations taking into account the shadowing effects during metal deposition, it is proposed that the width and shape of the tip of the bundled SiO2 nanocolumns influence significantly the metal local atom flux arriving to them and thus the final structure of the deposit.


Septiembre, 2010 | DOI: 10.1007/s11468-010-9139-6

Sintering by SPS of ultrafine TiCxN1-x powders obtained using mechanically induced self sustaining reaction


Borrell, A; Fernandez, A; Torrecillas, R; Cordoba, JM; Aviles, MA; Gotor, FJ
Boletin de la Sociedad Española de Cerámica y Vidrio, 49 (2010) 357-360
Reactividad de Sólidos

ABSTRACT

In this work high purity and nanometer character titanium carbonitride TiCxN1-x powders were obtained by mechanically induced self sustaining reaction (MSR) in a high-energy planetary ball mill, from a mixture of titanium with graphite or carbon nanofiber (CNFs) in a nitrogen atmosphere. A promising method for developing these materials is the coupling of the MSR with SPS sintering technique. The product is sintered at 1400 degrees C and 1700 degrees C, obtaining a completely dense monolithic ceramic (>99% t.d). In this work, the influence of SI'S treatment and carbon precursor on material microstructures was studied and the main mechanical properties of the end material were evaluated.


Septiembre, 2010 | DOI: 10.3989/cyv.2010.v49.i5

Determination of the local structure of a highly dispersed Pd-Nanosystem located on a titanium dioxide carrier


Kriventsov, VV; Novgorodov, BN; Yakimchuk, EP; Kochubey, DI; Zyuzin, DA; Simakova, IL; Chistyakov, AV; Zhmakin, VV; Bukhtenko, OV; Tsodikov, MV; Kozitsyna, NY; Vargaftik, MN; Moiseev, II; Maksimovskii, EA; Nechepurenko, SF; Navio, JA; Nikitenko, SG
Journal of Surface Investigation-X-Ray Synchrotron and Neutron Techniques, 4 (2010) 636-639
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

This work is devoted to a structural study of a highly dispersed Pd nanosystem, which is stabilized in the TiO2 matrix, by XAFS spectroscopy. Nanocomposite was prepared from bimetallic PdCo(mu-OOCMe)(4)(NCMe) precursor followed by processing in several ways: calcination in air and in argon and microwave irradiation. The local structure of Pd catalysts formed by different methods was studied. Possible structural models were considered in detail.


Agosto, 2010 | DOI: 10.1134/S1027451010040166

Mechanochemical synthesis of vanadium nitride


Roldan, MA; Lopez-Flores, V; Alcala, MD; Ortega, A; Real, C
Journal of the European Ceramic Society, 30 (2010) 2099-2107
Reactividad de Sólidos

ABSTRACT

Vanadium nitride (VN) has been prepared by mechanosynthesis from vanadium metal under a pressurized nitrogen atmosphere in a short milling time. The characterization of the final product by X-ray diffraction, scanning electron microscopy, electron energy loss (EELS), and X-ray absorption spectroscopy (XAS) is presented. The final product, VN with 96% of purity, is obtained at room temperature with nanometric particle size and a very high microhardness after sintering. A relationship between microstructure and microhardness as well as a comparison between the VN obtained mechanical and thermal method is also presented.


Agosto, 2010 | DOI: 10.1016/j.jeurceramsoc.2010.04.008

Tailored synthesis of nanostructured WC/a-C coatings by dual magnetron sputtering


Abad, MD; Munoz-Marquez, MA; El Mrabet, S; Justo, A; Sanchez-Lopez, JC
Surface and Coatings Technology, 204 (2010) 3490-3500
Materiales Nanoestructurados y Microestructura

ABSTRACT

Nanostructured coatings with variable contents of tungsten carbide (WC) and amorphous carbon (a-C) are prepared by controlling the sputtering power ratio using WC and graphite targets. XRD and TEM/ED analysis shows that increasing the C incorporation. the WC nanocrystalline phases evolve from gamma-W2C to beta-WC1-x. Further C enrichment leads to a nanocomposite structure of small WC1-x crystals dispersed in a-C matrix. The a-C at.% is estimated by XPS analysis and correlated with the observed tribo-mechanical properties. The hardness and friction properties vary from hard/high friction (36-40 GPa; mu=0.6-0.8) to moderate-hard/low friction (16-20 GPa; mu similar to 0.2) coatings depending on the film composition. The transition point is found for a-C content of 10 at.%. This correlates with a change from nanocrystalline WC to nanocomposite WC1-x/a-C coatings. The overall study will help to understand the previous literature data and will serve as guide for a tailored synthesis of these WC/a-C nanocomposites.


Agosto, 2010 | DOI: 10.1016/j.surfcoat.2010.04.019

Study of the Dehydroxylation-Rehydroxylation of Pyrophyllite


Perez-Rodriguez, JL; Duran, A; Sanchez-Jimenez, PE; Franquelo, ML; Perejon, A; Pascual-Cosp, J; Perez-Maqueda, LA
Journal of the American Ceramic Society, 93 (2010) 2392-2398

ABSTRACT

Pyrophyllite is a raw material of significant interest due to its large number of applications. Most of these applications require a thermal transformation of pyrophyllite; this thermal transformation implies the release of structural OH groups and the formation of new phases. In this paper, we report on the dehydroxylation of pyrophyllite and the reversibility of the process. A value of 224 +/- 16 kJ/mol for the dehydroxylation of pyrophyllite was obtained. In addition, it was observed that the partially or totally dehydroxylated pyrophyllite suffered a partial reversible rehydroxylation when cooled to room temperature. This rehydroxylation was substantiated by thermogravimetric measurements, while infrared spectroscopic studies showed that, during the rehydroxylation, the intensity of the OH band at 3675 cm-1 increased as two new bands at 3690 and 3702 cm-1 appeared. This rehydroxylation process was heavily influenced by the particle size of the pyrophyllite. Thus, smaller particles (< 1 mu m) showed a larger rehydroxylation percentage (about 12%), while the larger ones (20-40 mu m) showed a smaller percentage (about 1.6%). The extent of rehydroxylation also depended on the dehydroxylation temperature and reached a maximum value at 750 degrees C.


Agosto, 2010 | DOI: 10.1111/j.1551-2916.2010.03750.x

Characterization of Ti1-xAlxN coatings with selective IR reflectivity


Godinho, V; Philippon, D; Rojas, TC; Novikova, NN; Yakovlev, VA; Vinogradov, EA; Fernandez, A
Solar Energy, 84 (2010) 1397-1401
Materiales Nanoestructurados y Microestructura

ABSTRACT

Ti1-xAlxN thin films were deposited by reactive magnetron sputtering. The obtained different stoichiometries give rise to different optical properties as the films change from metallic to dielectric. In this work the IR reflectivity of these coatings is investigated taking into account different application fields for IR selective Ti1-xAlxN thin films. Low Al content coatings present high reflectivity, high absorptance and low thermal emittance. High Al compositions give raise to coatings with high absorptance and high thermal emittance. The composition of the coatings was evaluated combining electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy. Scanning electron microscopy (SEM) revealed a columnar structure. Reflectance spectra for the visible and infrared spectral ranges were used to obtain the solar absorptance and thermal emittance values, used to calculate the equilibrium temperature of the coatings. The thermal stability in air from 300 to 600 degrees C was also evaluated.


Agosto, 2010 | DOI: 10.1016/j.solener.2010.04.021

TiO2-SiO2 one-dimensional photonic crystals of controlled porosity by glancing angle physical vapour deposition


Gonzalez-Garcia, L; Lozano, G; Barranco, A; Miguez, H; Gonzalez-Elipe, AR
Journal of Materials Chemistry, 20 (2010) 6408-6412
Materiales Ópticos Multifuncionales, Nanotecnología en Superficies y Plasma

ABSTRACT

Herein we present a synthetic route to attain porous one-dimensional photonic crystals of high optical quality. The method employed, based on the alternate deposition of TiO2 and SiO2 porous layers by glancing angle physical vapour deposition, yields a highly accessible interconnected pore network throughout the entire multilayer structure. Furthermore, it allows a strict control over the average size and density of the interstitial sites, which results in the precise tuning of the refractive index of the individual layers and thus of the optical response of the ensemble. The controlled environmental response of the multilayer is confirmed by the optical monitoring of the infiltration of liquids of different refractive index.


Agosto, 2010 | DOI: 10.1039/C0JM00680G

Generalized Kinetic Master Plots for the Thermal Degradation of Polymers Following a Random Scission Mechanism


Sanchez-Jimenez, PE; Perez-Maqueda, LA; Perejon, A; Criado, JM
Journal of Physical Chemistry A, 114 (2010) 7868-7876
Reactividad de Sólidos

ABSTRACT

In this paper, the f(alpha) conversion functions for random scission mechanisms have been proposed to allow for the construction of generalized master plots suitable for these kinds of mechanisms. The master plots have been validated by their application to simulated data and to the thermal degradation of poly(butylene terephthalate), polyethylene, and poly(tetrafluoroethylene).


Agosto, 2010 | DOI: 10.1021/jp103171h

Mechanochemical preparation of BaTiO3-Ni nanocomposites with high dielectric constant


Sanchez-Jimenez, PE; Perez-Maqueda, LA; Dianez, MJ; Perejon, A; Criado, JM
Composite Structures, 92 (2010) 2236-2240
Reactividad de Sólidos

ABSTRACT

A mechanochemical procedure is proposed for an easy preparation of a BaTiO3-Ni composite in a single step. BaTiO3 and Ni powders available in the market are mixed by dry ball milling producing a decrease of particle size and an evenly distribution of both phases. In the sintered pellets the nickel particles are homogeneously distributed into the BaTiO3 matrix and isolated from others Ni particles. The dielectric constant of the composite is considerably higher than that of the barium titanate. Moreover, the temperature of the ferroelectric <-> paraelectric transition of the BaTiO3-Ni composite here prepared is much lower than the one of the pure BaTiO3 single phase.


Agosto, 2010 | DOI: 10.1016/j.compstruct.2009.08.011

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