Artículos SCI
2012
2012
Reactividad de Sólidos
Thermal behaviour of ground and unground acid leached vermiculite
Perez-Maqueda, LA; Maqueda, C; Perez-Rodriguez, JL; Subrt, J; Cerny, Z; Balek, VJournal of Thermal Analysis and Calorimetry, 107 (2012) 431-438 DOI: 10.1007/s10973-011-1480-2
Abstract
Acid leaching of vermiculite is an interesting procedure to prepare high surface area porous silica. Thermal behaviour of unground and ground vermiculite leached with HCl solutions has been studied by TG, DTA, ETA and high temperature XRD. Important differences have been observed in the thermal behaviour of unground and ground vermiculite after the acid treatments. Thus, for the acid-treated unground vermiculite, dehydrated vermiculite, enstatite and cristobalite were formed during the heating, while for the acid-treated ground vermiculite only iron oxides and cristobalite phases were observed. Structural modifications due to acid treatment were responsible for changes in the transport properties determined by ETA for the vermiculite samples.
Febrero, 2012 | DOI: 10.1007/s10973-011-1480-2
Operando DRIFTS study of the redox and catalytic properties of CuO/Ce1−xTbxO2−δ (x = 0–0.5) catalysts: evidence of an induction step during CO oxidation
Martinez-Arias, A.; Hungria, A. B.; Fernandez-Garcia, M.; Iglesias-Juez, A.; Soria, J.; Conesa, J. C.; Anderson, J. A.; Munuera, G.Physical Chemistry Chemical Physics, 14 (2012) 2144-2151 DOI: 10.1039/C1CP23298C
Abstract
Catalysts of 1 wt% copper oxide supported on cerium oxide or cerium–terbium mixed oxides are comparatively examined with respect to their redox and catalytic properties for CO oxidation. Characterization of the catalysts had shown that they contain highly dispersed CuO-type entities on the corresponding nanostructured fluorite supports with copper dispersion increasing with increasing amounts of terbium in the support. In contrast, the CO oxidation catalytic activity decreases with increasing amounts of terbium in the support. On the basis of operando-DRIFTS experiments, one of the factors that could explain such behaviour is related to the greater difficulty in generating reduced copper sites active for the reaction in the presence of terbium, which in turn is evidenced to constitute an induction stage. Analysis of the redox properties is complemented by XPS which confirms the greater resistance to copper reduction in the presence of terbium.
Febrero, 2012 | DOI: 10.1039/C1CP23298C
Materiales Nanoestructurados y Microestructura
An international round-robin calibration protocol for nanoindentation measurements
Cabibbo, M; Ricci, P; Cecchini, R; Rymuza, Z; Sullivan, J; Dub, S; Cohen, SMicron, 43 (2012) 215-222 DOI: 10.1016/j.micron.2011.07.016
Abstract
Nanoindentation has become a common technique for measuring the hardness and elastic–plastic properties of materials, including coatings and thin films. In recent years, different nanoindenter instruments have been commercialised and used for this purpose. Each instrument is equipped with its own analysis software for the derivation of the hardness and reduced Young's modulus from the raw data. These data are mostly analysed through the Oliver and Pharr method. In all cases, the calibration of compliance and area function is mandatory. The present work illustrates and describes a calibration procedure and an approach to raw data analysis carried out for six different nanoindentation instruments through several round-robin experiments. Three different indenters were used, Berkovich, cube corner, spherical, and three standardised reference samples were chosen, hard fused quartz, soft polycarbonate, and sapphire. It was clearly shown that the use of these common procedures consistently limited the hardness and reduced the Young's modulus data spread compared to the same measurements performed using instrument-specific procedures. The following recommendations for nanoindentation calibration must be followed: (a) use only sharp indenters, (b) set an upper cut-off value for the penetration depth below which measurements must be considered unreliable, (c) perform nanoindentation measurements with limited thermal drift, (d) ensure that the load–displacement curves are as smooth as possible, (e) perform stiffness measurements specific to each instrument/indenter couple, (f) use Fq and Sa as calibration reference samples for stiffness and area function determination, (g) use a function, rather than a single value, for the stiffness and (h) adopt a unique protocol and software for raw data analysis in order to limit the data spread related to the instruments (i.e. the level of drift or noise, defects of a given probe) and to make the H and Er data intercomparable.
Febrero, 2012 | DOI: 10.1016/j.micron.2011.07.016
Materiales y Procesos Catalíticos de Interés Ambiental y Energético
Rapid microwave-assisted synthesis of one-dimensional silver–H2Ti3O7 nanotubes
Rodriguez-Gonzalez, V; Obregon-Alfaro, S; Lozano-Sanchez, LM; Lee, SWJournal of Molecular Catalysis A-Chemical, 353 (2012) 163-170 DOI: 10.1016/j.molcata.2011.11.020
Abstract
The formation of silver hydrogen trititanate nanotubes, based on the controllable microwave-assisted hydrothermal nanocrystalline TiO2 transition, was investigated by means of XRD, UV–vis–DRS, Raman, FESEM and HRTEM. The results show that the rapid formation of H-trititanate nanotubes is achieved by self-assemblage of silver nanoparticles in which the lamellar intermediates react with NaOH in hydrothermal conditions. The presence of Ag° nanoparticles in the precursor promotes rapid and more complete formation of layered H2Ti3O7 nanotubes. After reacting for 4 h without subsequent thermal treatment, the inner diameters of the cylinder-like nanotubes are in the range of 3.6–4.0 nm, while their outer diameters are in the range of 7.6–8 nm. In addition, some straight nanotubes form bundles which are hundreds of nanometers in length. As-synthesized ultrathin nanotubes and crystalline precursors were evaluated by methyl orange dye (MOD) UV photo-oxidation. The complete degradation of MOD is achieved after 3.5 h of UV irradiation in the presence of silver–TiO2 nanocomposites, resulting in 50% of dye mineralization.
Febrero, 2012 | DOI: 10.1016/j.molcata.2011.11.020
Materiales de Diseño para la Energía y Medioambiente
Effect of oxidation on the compressive strength of sintered SiC-fiber bonded ceramics
Ramirez-Rico, J; Martinez-Fernandez, J; Singh, MMaterials Science and Engineering A, 534 (2012) 394-399 DOI: 10.1016/j.msea.2011.11.085
Abstract
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.
Febrero, 2012 | DOI: 10.1016/j.msea.2011.11.085
Materiales y Procesos Catalíticos de Interés Ambiental y Energético
In Situ XAS Study of Synergic Effects on Ni-Co/ZrO2 Methane Reforming Catalysts
Gonzalez-delaCruz, VM; Pereniguez, R; Ternero, F; Holgado, JP; Caballero, AJournal of Physical Chemistry C, 116 (2012) 2919-2926 DOI: 10.1021/jp2092048
Abstract
Four different mono and bimetallic Ni–Co/ZrO2 catalysts have been studied by means of in situ XAS, X-ray diffraction, TPR, and measurements of the catalytic activity in the dry reforming reaction of methane (DRM). Even though the cobalt monometallic system has no activity for the methane reforming reaction, both bimetallic catalysts (with 1:1 and 1:2 Ni/Co ratio, respectively), showed a better activity and stability than the nickel monometallic system. The XRD data indicate that a mixed cobalt–nickel spinel is formed by calcination of the precursor solids, leading to the formation of an alloy of both metals after reduction in hydrogen. In situ XAS experiments showed a much better resistance of metals in the bimetallic systems to be oxidized under reaction conditions at temperatures until 750 °C. After these results, we proposed the formation in the bimetallic systems of a more reducible nickel–cobalt alloy phase, which remains completely metallic in contact with the CO2/CH4 reaction mixture at any temperature. The presence of adjacent nickel and cobalt sites seems to avoid the deactivation of cobalt in the DRM reaction. In the case of cobalt sites, the presence of adjacent nickel atoms seems to prevent the deposition of carbon over the cobalt sites, now showing its higher activity in the dry reforming reaction. Simultaneously, this higher activity of the cobalt sites in the bimetallic system produces more hydrogen as a product, maintaining the nickel atoms completely reduced under reaction conditions. This synergic effect accounts for the better performance of the bimetallic systems and points at both, the oxidation state of nickel particles under reaction conditions and the carbon deposition processes, as important factors responsible for differences in catalytic activities and stabilities in this hydrocarbon reaction.
Febrero, 2012 | DOI: 10.1021/jp2092048
Materiales Nanoestructurados y Microestructura - Tribología y Protección de Superficies - Materiales Coloidales
Microwave-Assisted Synthesis and Luminescence of Mesoporous REDoped YPO4 (RE = Eu, Ce, Tb, and Ce plus Tb) Nanophosphors with Lenticular Shape
Rodriguez-Liviano, S; Aparicio, FJ; Rojas, TC; Hungria, AB; Chinchilla, LE; Ocana, MCrystal Growth and Design, 12 (2012) 635-645 DOI: 10.1021/cg201358c
Abstract
Mesoporous tetragonal RE:YPO 4 nanophosphors (RE = Eu, Ce, Tb, and Ce + Tb) with a lenticular morphology, narrow size distribution, and high surface area have been prepared by an homogeneous precipitation procedure consisting of aging, at low temperature (80-120 °C) in a microwave oven, ethylene glycol solutions containing only yttrium acetylacetonate and phosphoric acid. This synthesis method involves important advantages such as its simplicity, rapidness (reaction time = 7 min), and high reaction yields. The mechanism of nanoparticle growth has been also addressed finding that the lenticular nanoparticles are formed through an ordered aggregation of smaller entities, which explains their porosity. In all cases, the doping levels were systematically varied in order to optimize the nanophosphors luminescence. All optimum nanophosphors presented a high luminescence quantum yield (QY). In particular, for the Eu and Tb doped systems, the obtained QY values (60% for Eu and 80% for Tb) were the highest so far reported for this kind of nanomaterial. The morphological, microstructural, and luminescent properties of these nanophosphors and their dispersibility in water make them suitable for biomedical applications.
Febrero, 2012 | DOI: 10.1021/cg201358c
Fotocatálisis Heterogénea: Aplicaciones
Photocatalytic Ethanol Oxidative Dehydrogenation over Pt/TiO2: Effect of the Addition of Blue Phosphors
Murcia, JJ; Hidalgo, MC; Navio, JA; Vaiano, V; Ciambelli, P; Sannino, DInternational Journal of Photoenergy, 2012 (2012) 687262 DOI: 10.1155/2012/687262
Abstract
Ethanol oxidative dehydrogenation over Pt/TiO2 photocatalyst, in the presence and absence of blue phosphors, was performed. The catalyst was prepared by photodeposition of Pt on sulphated TiO2. This material was tested in a gas-solid photocatalytic fluidized bed reactor at high illumination efficiency. The effect of the addition of blue phosphors into the fluidized bed has been evaluated. The synthesized catalysts were extensively characterized by different techniques. Pt/TiO2 with a loading of 0.5 wt% of Pt appeared to be an active photocatalyst in the selective partial oxidation of ethanol to acetaldehyde improving its activity and selectivity compared to pure TiO2. In the same way, a notable enhancement of ethanol conversion in the presence of the blue phosphors has been obtained. The blue phosphors produced an increase in the level of ethanol conversion over the Pt/TiO2 catalyst, keeping at the same time the high selectivity to acetaldehyde.
Enero, 2012 | DOI: 10.1155/2012/687262
Materiales Ópticos Multifuncionales
Collective osmotic shock in ordered materials
Paul Zavala-Rivera, Kevin Channon, Vincent Nguyen, Easan Sivaniah, Dinesh Kabra, Richard H. Friend, S. K. Nataraj, Shaheen A. Al-Muhtaseb, Alexander Hexemer, Mauricio E. Calvo & Hernan MiguezNature Materials, 11 (2012) 53–57 DOI: 10.1038/nmat3179
Abstract
Osmotic shock in a vesicle or cell is the stress build-up and subsequent rupture of the phospholipid membrane that occurs when a relatively high concentration of salt is unable to cross the membrane and instead an inflow of water alleviates the salt concentration gradient. This is a well-known failure mechanism for cells and vesicles (for example, hypotonic shock) and metal alloys (for example, hydrogen embrittlement). We propose the concept of collective osmotic shock, whereby a coordinated explosive fracture resulting from multiplexing the singular effects of osmotic shock at discrete sites within an ordered material results in regular bicontinuous structures. The concept is demonstrated here using self-assembled block copolymer micelles, yet it is applicable to organized heterogeneous materials where a minority component can be selectively degraded and solvated whilst ensconced in a matrix capable of plastic deformation. We discuss the application of these self-supported, perforated multilayer materials in photonics, nanofiltration and optoelectronics.
Enero, 2012 | DOI: 10.1038/nmat3179
Materiales y Procesos Catalíticos de Interés Ambiental y Energético
Mechanism of complete n-hexane oxidation on silica supported cobalt and manganese catalysts
Todorova, S; Naydenov, A; Kolev, H; Holgado, JP; Ivanov, G; Kadinov, G; Caballero, AApplied Catalysis A-General, 413-414 (2012) 43-51 DOI: 10.1016/j.apcata.2011.10.041
Abstract
Mono- and bi-component cobalt and manganese samples were prepared by impregnation of silica with aqueous solutions of Co(NO3)2·6H2O and/or Mn(NO3)2·6H2O. The bi-component samples were obtained by a common solution of Co- and Mn nitrates (CoMn-MS) or by deposition of cobalt on calcined Mn sample (Co + Mn). The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed reduction (TPR), Fourier transformed infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), elemental analysis and tested in reaction of complete n-hexane oxidation. It was observed that the well crystalline cobalt oxide partially covers poorly crystalline manganese oxide in the Co + Mn catalysts, while finely divided oxides (MnO2 and Mn2O3, Co3O4) are present on the surface of the (CoMn-MS) sample. Four Langmuir–Hinshelwood and two Mars–van Krevelen models were fitted with the experimental data from the catalytic tests. According to the model calculations and results from instrumental methods, the reaction pathway over single component manganese and bi-component Co-Mn catalysts proceeds through Mars–van Krevelen mechanism (the oxidation of the catalyst surface being the rate determining step), while Langmuir–Hinshelwood mechanism is more probable for the Co sample. A considerable increase in activity for the sample obtained from a mixed solution is explained by low crystallinity, simultaneous presence of Mn4+–Mn3+ and enrichment of the surface in oxygen species.
Enero, 2012 | DOI: 10.1016/j.apcata.2011.10.041
Redox and catalytic properties of CuO/CeO2 under CO + O2 + NO: Promoting effect of NO on CO oxidation
Martinez-Arias, A.; Hungria, A. B.; Iglesias-Juez, A.; Fernandez-Garcia, M.; Anderson, J. A.; Conesa, J. C.; Munuera, G.; Soria, J.Catalysis Today, 180 (2012) 81-87 DOI: 10.1016/j.cattod.2011.02.014
Abstract
A CuO/CeO2 catalyst has been studied with respect to its catalytic activity for CO oxidation under stoichiometric conditions employing either O2 or O2–NO mixture as oxidants. The obtained results are rationalised on the basis of analysis of redox properties upon interaction with CO and O2–NO by EPR as well as by redox/catalytic analysis by operando-DRIFTS. These provide useful insight into the processes involved during NO reduction, for which two well differentiated steps associated to a change in the type of active centres during the course of the reaction are evidenced. Nevertheless, the most interesting result is related to observation of a novel promoting effect of NO on CO oxidation. This is explained mainly on the basis of DRIFTS results and appears to be associated with phenomena of adsorption/desorption of NOx species at interfacial positions which apparently activate such interfacial region allowing formation of greater amounts of active reduced copper centres in the presence of NO.
Enero, 2012 | DOI: 10.1016/j.cattod.2011.02.014
Reactividad de Sólidos
Characterisation of ternary TixV1-xNy nitride prepared by mechanosynthesis
Roldan, MA; Alcala, MD; Real, CCeramics Intenational, 38 (2012) 687-693 DOI: 10.1016/j.ceramint.2011.07.057
Abstract
In the present manuscript the authors have systematically investigated the composition and microstructure of a series of ternary nitrides (TixV1-xNy) (0.0 <= x <= 1.0) prepared by mechanosynthesis, using XRD, SEM, EELS, XAS and TGA. The ternary titanium-vanadium nitride (TixV1-xNy) has been obtained in all range of compositions by the mechanical treatment of the two metals under nitrogen pressure in a planetary mill with a maximum milling time of 3 h and without any post-heating treatment. The materials' microhardnesses were measured after sinterisation and compared to those reported in the literature for these types of materials. When compared with the previously reported data for bulk samples, these values are similar or higher for compositions within the range x = 0.5 to x = 0.77 (TixV1-xN).
Enero, 2012 | DOI: 10.1016/j.ceramint.2011.07.057
Materiales y Procesos Catalíticos de Interés Ambiental y Energético
Effect of hydrothermal treatment on structural and photocatalytic properties of TiO2 synthesized by sol-gel method
Melian, EP; Diaz, OG; Rodriguez, JMD; Colon, G; Navio, JA; Pena, JPApplied Catalysis A-General, 411 (2012) 153-159 DOI: 10.1016/j.apcata.2011.10.033
Abstract
TiO 2 nanoparticles have been prepared by sol-gel precipitation and further hydrothermal treatment. In this way, the effect of the hydrothermal treatment on the structural properties and photocatalytic activity of sol-gel synthesized catalysts has been investigated. These catalysts have been produced by hydrolysis of a mixture of isopropanol-titanium tetraisopropoxide (iPrOH-TiiP). The prepared photocatalysts were characterized by means of X-ray diffraction (XRD), surface area analysis (BET), transmission microscopy (TEM), thermogravimetric analysis (TG), scanning electron microscopy (SEM) analysis, diffuse reflectance, sedimentability analysis and aggregate size study. Besides, the structural evolution with the temperature of the photocatalysts treated or not hydrothermally was studied. It was observed that the calcination produces approaching between the characteristics of both sets of photocatalysts. The photocatalytic activity of the obtained photocatalysts was investigated, using phenol as a model pollutant. The calcination temperature is the most remarkable factor that can affect the ultimate photocatalytic activity of the prepared photocatalysts. However, the hydrothermal treatment previous to calcination led to obtain photocatalysts which exhibit larger photocatalytic activity than their homologous photocatalysts without hydrothermal treatment. The obtained photocatalyst TiO 2ht600 exhibits the same photocatalytic activity per surface area than the commercial TiO 2 Degussa P25 but with much faster sedimentability.
Enero, 2012 | DOI: 10.1016/j.apcata.2011.10.033
Materiales de Diseño para la Energía y Medioambiente
Aluminum incorporation in alpha-PbO2 type TiO2 at pressures up to 20 GPa
Escudero, A; Langenhorst, FPhysics of the Earth and Planetary Interiors, 190 (2012) 87-94 DOI: 10.1016/j.pepi.2011.11.002
Abstract
Aluminum incorporation into the high pressure polymorph of TiO2 with the structure of alpha-PbO2 has been studied from 10 to 20 GPa and 1300 degrees C by XRD, high-resolution Al-27 MAS-NMR and TEM. Al-doped alpha-PbO2 type TiO2 can be recovered at atmospheric pressure. Al2O3 solubility in alpha-PbO2 type TiO2 increases with increasing the synthesis pressure. The alpha-PbO2 type TiO2 polymorph is able to incorporate up to 35 wt.% Al2O3 at 13.6 GPa and 1300 degrees C, being the substitution of Ti4+ by Al3+ on normal octahedral sites and the formation of oxygen vacancies the mechanism of solubility. The transition to the higher pressure TiO2 polymorph with the ZrO2 baddeleyite structure, akaogiite, has not been observed in the quenched samples at room pressure. The microstructure of the recovered sample synthesized at 16 GPa and 1300 degrees C points to the existence of an intermediate non-quenchable aluminum titanium oxide phase at these conditions.
Enero, 2012 | DOI: 10.1016/j.pepi.2011.11.002
XRF, μ-XRD and μ-spectroscopic techniques for revealing the composition and structure of paint layers on polychrome sculptures after multiple restorations
Franquelo, ML; Duran, A; Castaing, J; Arquillo, D; Perez-Rodriguez, JLTalanta, 89 (2012) 462-469 DOI: 10.1016/j.talanta.2011.12.063
Abstract
This paper presents the novel application of recently developed analytical techniques to the study of paint layers on sculptures that have been restored/repainted several times across centuries. Analyses were performed using portable XRF, μ-XRD and μ-Raman instruments. Other techniques, such as optical microscopy, SEM-EDX and μ-FTIR, were also used. Pigments and other materials including vermilion, minium, red lac, ivory black, lead white, barium white, zinc white (zincite), titanium white (rutile and anatase), lithopone, gold and brass were detected. Pigments from both ancient and modern times were found due to the different restorations/repaintings carried out. μ-Raman was very useful to characterise some pigments that were difficult to determine by μ-XRD. In some cases, pigments identification was only possible by combining results from the different analytical techniques used in this work. This work is the first article devoted to the study of sculpture cross-section samples using laboratory-made μ-XRD systems.
Enero, 2012 | DOI: 10.1016/j.talanta.2011.12.063
Materiales Nanoestructurados y Microestructura
Nanoscale mechanically induced structural and electrical changes in Ge 2Sb 2Te 5 films
Cecchini, R; Benitez, JJ; Sanchez-Lopez, JC; Fernandez, AJournal of Applied Physics, 111 (2012) 016101 (3 pages) DOI: 10.1063/1.3673592
Abstract
We demonstrate that the microstructure and electrical properties of Ge2Sb2Te5 films can be changed by a nanoscale mechanical process. Nanoscratching is used to define modified areas onto an as-deposited crystalline Ge2Sb2Te5 film. Scanning tunneling microscopy measurements show that the modified areas have a very low electrical conductivity. Micro-Raman measurements indicate that the mechanically induced microstructural changes are consistent with a phase transformation from crystalline to amorphous, which can be reversed by laser irradiation.
Enero, 2012 | DOI: 10.1063/1.3673592
Materiales Nanoestructurados y Microestructura
Influence of silver content on the tribomechanical behavior on Ag-TiCN bioactive coatings
Sanchez-Lopez, JC; Abad, MD; Carvalho, I; Galindo, RE; Benito, N; Ribeiro, S; Henriques, M; Cavaleiro, A; Carvalho, SSurface and Coatings Technology, 206 (2012) 2192-2198 DOI: 10.1016/j.surfcoat.2011.09.059
Abstract
Surface modification of bulk materials used in biomedical applications has become an important prerequisite for better biocompatibility. In particular, to overcome the particle generation, low-wear coatings based on carbon (nitrogen) and containing antimicrobial elements such as silver are promising candidates. Thus, the present work explores the potentialities of silver-containing carbonitride-based (Ag-TiCN) thin films prepared by direct current unbalanced reactive magnetron sputtering. The silver content in the coatings was varied from 0 to 26.7at.% by changing the targets and the fraction of C 2H 2 and N 2 in the gas mixture with Ar. The obtained Ag-TiCN based coatings were characterized in terms of composition and microstructure. Mechanical and tribological properties of the films were studied by nanoindentation and reciprocating pin-on disk testing in a fetal bovine serum solution, respectively. Raman, scanning electron microscope and energy dispersive X-ray analysis was carried out in the contact region after tribological tests to obtain information about the friction mechanism. The cytotoxicity of the coatings was assessed by in vitro tests using fibroblast cells. The coatings comprised a mixture of TiC xN 1-x, Ag and a-C(N) x phases whose relative proportion varied depending on the Ag/Ti ratio. The mechanical, tribological and cytotoxicity properties were correlated with the chemical and phase composition. When the Ag/Ti ratios were below 0.20 (Ag contents <6.3at.%) the films resulted harder (~18GPa) with higher wear resistance (~10 -6mm 3/Nm), showing similar friction coefficient (~0.3) and good biocompatibility.
Enero, 2012 | DOI: 10.1016/j.surfcoat.2011.09.059
Nanotecnología en Superficies y Plasma
Analysis of multifunctional titanium oxycarbide films as a function of oxygen addition
Chappe, JM; Fernandes, AC; Moura, C; Alves, E; Barradas, NP; Martin, N; Espinos, JP; Vaz, FSurface and Coatings Technology, 206 (2012) 2525-2534 DOI: 10.1016/j.surfcoat.2011.11.005
Abstract
Reactive magnetron sputtering was used to deposit titanium oxycarbide thin films. The overall set of results showed that the oxygen flow rate, and thus the composition of the atmosphere in the deposition chamber, controls the composition of the titanium oxycarbide thin films obtained by reactive sputtering. Rutherford Backscattering Spectroscopy analysis revealed the existence of three major types of films, indexed to their particular composition ratios. A detailed study by X-ray photoelectron spectroscopy was carried out in order to characterize the evolution of the Ti
Enero, 2012 | DOI: 10.1016/j.surfcoat.2011.11.005
Nanotecnología en Superficies y Plasma
Adsorption Geometry Determines Catalytic Selectivity in Highly Chemoselective Hydrogenation of Crotonaldehyde on Ag(111)
Brandt, Katrin; Chiu, May E.; Watson, David J.; Tikhov, Mintcho S.; Lambert, Richard M.Journal of Physical Chemistry C, 116 (2012) 4605-4611 DOI: 10.1021/jp208831h
Abstract
The chemoselective hydrogenation of crotonaldehyde to crotyl alcohol was studied by temperature-programmed desorption/reaction, high-resolution XPS, and NEXAFS. The organic molecule adsorbed without decomposition, all three possible hydrogenation products were formed and desorbed, and the clean overall reaction led to no carbon deposition. Selectivities up to 95% were found under TPR conditions. The observed behavior corresponded well with selectivity trends previously reported for Ag/SiO2 catalysts, and the present findings permit a rationalization of the catalytic performance in terms of pronounced coverage-dependent changes in adsorption geometries of the reactant and the products. Thus, at low coverages, the C═O bond in crotonaldehyde lies almost parallel to the metal surface, whereas the C═C was appreciably tilted, favoring hydrogenation of the former and disfavoring hydrogenation of the latter. With increasing coverage of reactants, the C═C bond was forced almost parallel to the surface, rendering it vulnerable to hydrogenation, thus markedly decreasing selectivity toward formation of crotyl alcohol. Butanol formation was the result of an overall two-step process: crotonaldehyde → crotyl alcohol → butanol, further hydrogenation of the desired product crotyl alcohol being promoted at high hydrogen coverage due to the C═C bond in the unsaturated alcohol being driven from a tilted to a flat-lying geometry. Finally, an explanation is offered for the strikingly different behavior of Ag(111) and Cu(111) in the chemoselective hydrogenation of crotonaldehyde in terms of the different degrees of charge transfer from metal to C═O π bond, as suggested by C 1s XPS binding energies.
Enero, 2012 | DOI: 10.1021/jp208831h
Analysis of the restoration of an historical organ: The case study of the Cavaillé-Coll organ of La Merced Church in Burgos, Spain
Justo-Estebaranz, A; Herrera, LK; Duran, A; Siguenza, B; de Haro, MCJ; Laguna, O; Justo, AStudies in Conservation, 57 (2012) 21-28 DOI: 10.1179/2047058411Y.0000000001
Abstract
The restoration of the Cavaille-Coll Romantic organ housed in La Merced Church of Burgos, Spain is described in this paper. The organ was affected by a fire that took place in the church. The effect of the fire on the pipes differed depending on their location within the instrument. A combination of analytical techniques (X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray analysis, particle-induced X-ray emission, metallography, and specific density) allowed the accurate determination of the microstructures and compositions of the alloys used to make the different pipes of the organ, some of which had a high tin content and others which had a high lead content. The most damaged pipes were replaced by reconstructed pipes made out of metallic sheets of the same composition as the originals, to ensure a historically accurate sound.
Enero, 2012 | DOI: 10.1179/2047058411Y.0000000001
Degradation of Two Historic Buildings in Northern Spain by Formation of Oxalate and Sulphate-Based Compounds
Duran, A; Robador, MD; Perez-Rodriguez, JLInternational Journal of Architectural Heritage, 6 (2012) 342-358 DOI: 10.1080/15583058.2010.551447
Abstract
This study focused on the degradation processes for two historic buildings, one in a rural and one in an urban environment. Samples collected from the Romanesque Church of Torme and from two areas of the Cathedral of Burgos were studied by using optical and electron microscopy, x-ray spectrometry, x-ray diffraction, Fourier transform infrared spectroscopy and thermal analysis (TG/DTA/DTG). As result of the action of microorganisms, weddellite and whewellite were found to have formed over the entire external walls of the Church of Torme, built with dolomitic rock. Gypsum, formed by the effects of atmospheric pollution, appeared on lime plasters applied as protective coatings on the external stones of Burgos' Cathedral. Also discussed in this study is the different composition of these plasters, based on the use of calcareous and siliceous aggregates.
Enero, 2012 | DOI: 10.1080/15583058.2010.551447
Materiales de Diseño para la Energía y Medioambiente
Microstructure, composition and P-T conditions of rutile from diamondiferous gneiss of the Saxonian Erzgebirge, Germany
Escudero, A; Miyajima, N; Langenhorst, FChemie der erde-geochemistry, 72 (2012) 25-30 DOI: 10.1016/j.chemer.2011.11.001
Abstract
The chemical composition and microstructure of rutile grains in a ultra-high pressure metamorphic gneiss of the Saxonian Erzgebirge, Germany have been studied by Raman spectroscopy, SEM, EMPA and TEM. Rutile inclusions in garnet contain free dislocations, iron-enriched dislocations and exsolved ilmenite lamellae, while subgrain boundaries are observed in rutile grains of the rock matrix. The previously reported alpha-PbO2 type TiO2 phase could not be confirmed by our TEM observations. On the basis of Zr solubility in the rutile and the presence of microdiamonds, minimum metamorphic peak conditions of 3.95 GPa and 915 degrees C are estimated.
Enero, 2012 | DOI: 10.1016/j.chemer.2011.11.001
Química de Superficies y Catálisis
Preferential oxidation of CO (CO-PROX) over CuOx/CeO2 coated microchannel reactor
Laguna, OH; Ngassa, EM; Oraa, S; Alvarez, A; Dominguez, MI; Romero-Sarria, F; Arzamendi, G; Gandia, LM; Centeno, MA; Odriozola, JACatalysis Today, 180 (2012) 105-110 DOI: 10.1016/j.cattod.2011.03.024
Abstract
The general aspects of the synthesis and characterization results of a CuO x/CeO 2 catalyst were presented. In addition the principal steps for manufacturing a microchannel reactor and for the coating of the CuO x/CeO 2 catalyst onto the microchannels walls, were also summarized. The catalytic activity of this microchannel reactor during the preferential oxidation of CO (CO-PROX) was evaluated employing a feed-stream that simulates a reformate off-gas after the WGS unit. Two activation atmospheres were studied (H 2/N 2 and O 2/N 2). The reducing pretreatment improved the resistance to deactivation by formation of carbonaceous species over the catalyst surface at high temperatures. The presence of H 2O and CO 2 in the feed-stream was also analyzed indicating that the adsorption of CO 2 inhibited the conversion of CO at lower temperatures because these compounds modified the active sites through the formation of carbonaceous species on the catalyst surface. Finally, the experimental results of the microreactor performance were compared with CFD simulations that were carried out using a kinetic for the CuO x/CeO 2 powder catalyst. The experimental results were reasonably well described by the model, thus confirming its validity.
Enero, 2012 | DOI: 10.1016/j.cattod.2011.03.024
Reactividad de Sólidos
Non-isothermal microcalorimetric evaluations in quenched and in cold-rolled Cu-9Ni-5.5Sn alloys
Donoso, E; Dianez, MJ; Criado, JMRevista de Metalurgia, 48 (2012) 67-75 DOI: 10.3989/revmetalm.1136
Abstract
The thermal aging of both a quenched and a cold rolled homogeneous supersaturated Cu-9 % wt Ni-5.5 wt % Sn alloy has been studied from differential scanning calorimetry (DSC) and microhardness measurements. An increase of the hardness during the aging of the quenched sample, because of the precipitation of a γ' phase, takes place. On the contrary, no hardness increase was observed during the aging of the cold rolled sample. A theoretical analysis of the enthalpy determined from the first DSC exothermic peak suggests that a segregation of the solute towards the dislocations occurs during the aging of the cold rolled alloy. The values of the n Avrami-Erofeev coefficients estimated from the kinetic analysis supports the above interpretations.
Enero, 2012 | DOI: 10.3989/revmetalm.1136
Química de Superficies y Catálisis
DRIFTS study of methanol adsorption on Mg-Al hydrotalcite catalysts for the transesterification of vegetable oils
Navajas, A; Arzamendi, G; Romero-Sarria, F; Centeno, MA; Odriozola, JA; Gandia, LMCatalysis Communications, 7 (2012) 189-193 DOI: 10.1016/j.catcom.2011.11.005
Abstract
Mg-Al hydrotalcites rehydrated after calcination are promising catalysts for the methanolysis of vegetable oils. To gain insight into the basis of their catalytic action, the adsorption of methanol over some commercial Mg-Al hydrotalcites was studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Different species formed after methanol adsorption were identified, being the total quantity of methoxy species related to the basic character of the sample. A linear correlation between the amount of adsorbed monodentate methoxy species and the catalytic activity in the biodiesel production was found. Therefore, it is proposed that these species are the mainly involved in the transesterification reaction.
Enero, 2012 | DOI: 10.1016/j.catcom.2011.11.005
Materiales Nanoestructurados y Microestructura
Analysis and application of the theories that rationalize the crystalline structures of fluorite-related rare earth oxides
Lopez-Cartes, C; Perez-Omil, JA; Rodriguez-Izquierdo, JM; Calvino, JJCatalysis Today, 180 (2012) 161-180 DOI: 10.1016/j.cattod.2011.04.032
Abstract
The main current theories dealing with the crystalline structures of the fluorite related rare earth oxides, including those corresponding to reduced oxides, one based on the distribution of the coordination defect inside the fluorite structure, and the other which proposes the establishment of modular sequences constituted by modules with fluorite structure, are presented and comparatively explored in detail. Our in-depth analysis of both approximations indicates that they in fact provide smart and efficient rationalizations of the currently known intermediate rare earth oxides structures. We prove however that the strict application of the principles and rules proposed by each theory does not yield unique and unambiguous results for most of the members of the homologous series, as it has been claimed up to now. Moreover, the controversy about the reliability of these two, apparently different and competing, theories is definitely clarified and the exact equivalence of their structural predictions is demonstrated. Finally, we propose new extra systematization rules, not considered up to now in neither of these theoretical approaches, to overcome the observed limitations to properly rationalize the structure of this so technologically important family of oxides.
Enero, 2012 | DOI: 10.1016/j.cattod.2011.04.032
Nanotecnología en Superficies y Plasma
Superhydrophobic supported Ag-NPs@ZnO-nanorods with photoactivity in the visible range
Macias-Montero, M; Borras, A; Saghi, Z; Romero-Gomez, P; Sanchez-Valencia, JR; Gonzalez, JC; Barranco, A; Midgley, P; Cotrino, J; Gonzalez-Elipe, ARJournal of Materials Chemistry, 22 (2012) 1341-1346 DOI: 10.1039/C1JM13512K
Abstract
In this article we present a new type of 1D nanostructures consisting of supported hollow ZnO nanorods (NRs) decorated with Ag nanoparticles (NPs). The 3D reconstruction by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) electron tomography reveals that the Ag NPs are distributed along the hollow interior of the ZnO NRs. Supported and vertically aligned Ag-NPs@ZnO-NRs grow at low temperature (135 °C) by plasma enhanced chemical vapour deposition on heterostructured substrates fabricated by sputtered deposition of silver on flat surfaces of Si wafers, quartz slides or ITO. The growth mechanisms of these structures and their wetting behavior before and after visible light irradiation are critically discussed. The as prepared surfaces are superhydrophobic with water contact angles higher than 150°. These surfaces turn into superhydrophilic with water contact angles lower than 10° after prolonged irradiation under both visible and UV light. The evolution rate of the wetting angle and its dependence on the light characteristics are related to the nanostructure and the presence of silver embedded within the ZnO NRs.
Enero, 2012 | DOI: 10.1039/C1JM13512K
2011
2011
Materiales Coloidales - Nanotecnología en Superficies y Plasma
Synthesis, through pyrolysis of aerosols, of YIn1−xMnxO3 blue pigments and their efficiency for colouring glazes
M. Ocaña, J.P. Espinós, J.B. CardaDyes and Pigments, 91 (2011) 501-507 DOI: 10.1016/j.dyepig.2011.03.009
Abstract
Mn-doped YInO3 blue pigments have been synthesised at a much lower temperature (1100 °C) than that required by the traditional solid state method (1400 °C). The developed procedure, which is based on the pyrolysis at 600 °C of aerosols generated from aqueous solutions of Y, In and Mn nitrates followed by an annealing treatment at 1100 °C, yields spherical pigments particles with heterogeneous size in the optimum range required for ceramic applications (<10 μm). The amount of Mn introduced in the YInO3 matrix has been systematically varied in order to evaluate the effects of the Mn content on the colour properties of the pigments. It has been found that the optimum pigment composition (bluer colour with the lowest Mn content) is given by the formula YIn0.90Mn0.10O 3. The technological performance of these YIn1-xMn xO3 blue pigments has also been evaluated by testing their efficiency for colouring ceramic glazes of different composition (boracic and plumbic) and properties, aiming to find a less toxic alternative for the Co-based pigments commonly used by the ceramic industry.
Diciembre, 2011 | DOI: 10.1016/j.dyepig.2011.03.009
Materiales Ópticos Multifuncionales
Porous one dimensional photonic crystals: novel multifunctional materials for environmental and energy applications
Mauricio E. Calvo, Silvia Colodrero, Nuria Hidalgo, Gabriel Lozano, Carmen López-López, Olalla Sánchez-Sobrado and Hernán MíguezEnergy and Environmental Science, 4 (2011) 4800-4812 DOI: 10.1039/C1EE02081A
Abstract
In recent times, several synthetic pathways have been developed to create multilayered materials of diverse composition that combine accessible porosity and optical properties of structural origin, i.e., not related to absorption. These materials possess a refractive index that varies periodically along one direction, which gives rise to optical diffraction effects characteristic of Bragg stacks or one-dimensional photonic crystals (1DPCs). The technological potential of such porous optical materials has been demonstrated in various fields related to energy and environmental sciences, such as detection and recognition of targeted biological or chemical species, photovoltaics, or radiation shielding. In all cases, improved performance is achieved as a result of the added functionality porosity brings. In this review, a unified picture of this emerging field is provided.
Diciembre, 2011 | DOI: 10.1039/C1EE02081A
Reactividad de Sólidos
An improved model for the kinetic description of the thermal degradation of cellulose
Sanchez-Jimenez, PE; Perez-Maqueda, LA; Perejon, A; Pascual-Cosp, J; Benitez-Guerrero, M; Criado, JMCellulose, 18 (2011) 1487-1498 DOI: 10.1007/s10570-011-9602-3
Abstract
In spite of the large amount of work performed by many investigators during last decade, the actual understanding of the kinetics of thermal degradation of cellulose is still largely unexplained. In this paper, recent findings suggesting a nucleation and growth of nuclei mechanism as the main step of cellulose degradation have been reassessed and a more appropriate model involving chain scission and volatilization of fragments has been proposed instead. The kinetics of cellulose pyrolysis have been revisited by making use of a novel kinetic method that, without any previous assumptions regarding the kinetic model, allows performing the kinetic analysis of a set of experimental curves recorded under different heating schedules. The kinetic parameters and kinetic model obtained allows for the reconstruction of the whole set of experimental TG curves.
Diciembre, 2011 | DOI: 10.1007/s10570-011-9602-3
Compositional and Quantitative Microtextural Characterization of Historic Paintings by Micro-X-ray Diffraction and Raman Microscopy
Julia Romero-Pastor, Adrian Duran, Alejandro Basilio Rodríguez-Navarro, René Van Grieken, Carolina CardellAnalytical Chemistry, 83 (2011) 8420-8428 DOI: 10.1021/ac201159e
Abstract
This work shows the benefits of characterizing historic paintings via compositional and microtextural data from micro-X-ray diffraction (μ-XRD) combined with molecular information acquired with Raman microscopy (RM) along depth profiles in paint stratigraphies. The novel approach was applied to identify inorganic and organic components from paintings placed at the 14th century Islamic University—Madrasah Yusufiyya—in Granada (Spain), the only Islamic University still standing from the time of Al-Andalus (Islamic Spain). The use of μ-XRD to obtain quantitative microtextural information of crystalline phases provided by two-dimensional diffraction patterns to recognize pigments nature and manufacture, and decay processes in complex paint cross sections, has not been reported yet. A simple Nasrid (14th century) palette made of gypsum, vermilion, and azurite mixed with glue was identified in polychromed stuccos. Here also a Christian intervention was found via the use of smalt, barite, hematite, Brunswick green and gold; oil was the binding media employed. On mural paintings and wood ceilings, more complex palettes dated to the 19th century were found, made of gypsum, anhydrite, barite, dolomite, calcite, lead white, hematite, minium, synthetic ultramarine blue, and black carbon. The identified binders were glue, egg yolk, and oil.
Noviembre, 2011 | DOI: 10.1021/ac201159e
Fotocatálisis Heterogénea: Aplicaciones
Influence of the strong metal support interaction effect (SMSI) of Pt/TiO(2) and Pd/TiO(2) systems in the photocatalytic biohydrogen production from glucose solution
Colmenares, JC; Magdziarz, A; Aramendia, MA; Marinas, A; Marinas, JM; Urbano, FJ; Navio, JACatalysis Communications, 16 (2011) 1-6 DOI: 10.1016/j.catcom.2011.09.003
Abstract
Two different catalysts consisting of Pt/TiO2 and Pd/TiO 2 were submitted to diverse oxidative and reductive calcination treatments and tested for photocatalytic reforming of glucose water solution (as a model of biomass component) in H2 production. Oxidation and reduction at 850°C resulted in better photocatalysts for hydrogen production than Degussa P-25 and the ones prepared at 500°C, despite the fact that the former consisted in very low surface area (6-8 m2/g) rutile titania specimens. The platinum-containing systems prepared at 850°C give the most effective catalysts. XPS characterization of the systems showed that thermal treatment at 850°C resulted in electron transfer from titania to metal particles through the so-called strong metal-support interaction (SMSI) effect. Furthermore, the greater the SMSI effect, the better the catalytic performance. Improvement in photocatalytic behavior is explained in terms of avoidance of electron-hole recombination through the electron transfer from titania to metal particles.
Noviembre, 2011 | DOI: 10.1016/j.catcom.2011.09.003
Materiales de Diseño para la Energía y Medioambiente
Application of the solid state NMR to the study of the alcohol/alkane mixtures adsorption onto graphite
María D. Alba, Miguel A. Castro, Stuart M. Clarke, Santiago Medina, Loic Messe, Carmen MillánSolid State Nuclear Magnetic Resonance, 40 (2011) 138-143 DOI: 10.1016/j.ssnmr.2011.11.002
Abstract
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.
Noviembre, 2011 | DOI: 10.1016/j.ssnmr.2011.11.002
Materiales de Diseño para la Energía y Medioambiente
Structure, Electrical Resistivity, and Thermal Conductivity of Beech Wood Biocarbon Produced at Carbonization Temperatures below 1000 degrees C
Parfen'eva, LS; Orlova, TS; Kartenko, NF; Smirnov, BI; Smirnov, IA; Misiorek, H; Jezowski, A; Muha, J; Vera, MCPhysics of the Solid State, 53 (2011) 2398-2407 DOI: 10.1134/S1063783411110230
Abstract
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.
Noviembre, 2011 | DOI: 10.1134/S1063783411110230
Química de Superficies y Catálisis
Structural and catalytic properties of lanthanide (La, Eu, Gd) doped ceria
Hernandez, WY; Laguna, OH; Centeno, MA; Odriozola, JAJournal of Solid State Chemistry, 184 (2011) 3014-3020 DOI: 10.1016/j.jssc.2011.09.018
Abstract
Ce0.9M0.1O2-δ mixed oxides (M=La, Eu and Gd) were synthesized by coprecipitation. Independent of the dopant cation, the obtained solids maintain the F-type crystalline structure, characteristic of CeO2 (fluorite structure) without phase segregation. The ceria lattice expands depending on the ionic radii of the dopant cation, as indicated by X-ray diffraction studies. This effect also agrees with the observed shift of the F2g Raman vibrational mode. The presence of the dopant cations in the ceria lattice increases the concentration of structural oxygen vacancies and the reducibility of the redox pair Ce4/Ce3. All synthesized materials show higher catalytic activity for the CO oxidation reaction than that of bare CeO2, being Eu-doped solid the one with the best catalytic performances despite of its lower surface area.
Noviembre, 2011 | DOI: 10.1016/j.jssc.2011.09.018
Química de Superficies y Catálisis
Influence of Al2O3 reinforcement on precipitation kinetic of Cu–Cr nanocomposite
S. Sheibani, A. Ataie, S. Heshmati-Manesh, A. Caballero, J.M. CriadoThermochimica Acta, 526 (2011) 222-228 DOI: 10.1016/j.tca.2011.09.024
Abstract
In this paper, the kinetic of precipitation process in mechanically alloyed Cu-1 wt.% Cr and Cu-1 wt.% Cr/3 wt.% Al2O3 solid solution was compared using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The ageing kinetics in Cu–Cr and Cu–Cr/Al2O3 can be described using Johnson–Mehl–Avrami (JMA) and Sestak–Berggren (SB) models, respectively. These different behaviors have been discussed in details. It was found that in presence of Al2O3 reinforcement, the ageing activation energy is decreased and the overall ageing process is accelerated. This behavior is probably due to higher dislocation density previously obtained during ball milling and Al2O3–Cu interface. TEM observations confirm that Al2O3–Cu interface and structural defects act as a primary and secondary nucleation sites, respectively.
Noviembre, 2011 | DOI: 10.1016/j.tca.2011.09.024
Materiales de Diseño para la Energía y Medioambiente
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
R. González-Núñez, M.D. Alba, M.M. Orta, M. Vidal, A. RigolChemosphere, 85 (2011) 1511-1517 DOI: 10.1016/j.chemosphere.2011.09.042
Abstract
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.
Noviembre, 2011 | DOI: 10.1016/j.chemosphere.2011.09.042
Materiales Nanoestructurados y Microestructura
Electrical properties and applications of carbon based nanocomposite materials: An overview
Sanjinés, R., Abad, M.D., Vâju, C., Smajda, R., Mionić, M., Magrez, A.Surface and Coatings Technology, 206 (2011) 727-733 DOI: 10.1016/j.surfcoat.2011.01.025
Abstract
The allotropic forms of carbon (amorphous and polycrystalline graphite, carbon black, fullerenes, nanotubes, graphene) exhibit a large variety of charge transport properties which have been stimulating fundamental and applied research for the development of new devices based on micro and nano-sized electronic systems. Carbon based nanocomposites offer the possibility to improve the device performances and to develop novel multifunctional material systems by combining the properties of each individual phase. In this paper we review the electrical properties of carbon materials and some of the most exciting carbon based nanocomposites, as well as their potential technological applications. First, the electrical properties of amorphous and polycrystalline graphitic materials and those of their related nanocomposites materials are discussed. Second, an overview of the state-of-art on research and applications of carbon nanotube-based composites is presented. Third, we discuss briefly the emerging area of research related to graphene materials. Finally, the electrical properties and applications of conducting carbon black aggregates and carbon black/polymer composites are overviewed.
Noviembre, 2011 | DOI: 10.1016/j.surfcoat.2011.01.025
Nanotecnología en Superficies y Plasma
Comments on "an essay on contact angle measurements": Determination of surface roughness and modeling of the wetting behavior
Terriza, A; Alvarez, R; Yubero, F; Borras, A; Gonzalez-Elipe, ARPlasma Processes and Polymers, 8 (2011) 998-1002 DOI: 10.1002/ppap.201100081
Abstract
This commentary addresses the problem of determining surface roughness values and their use to assess the wetting behavior of surfaces. For very rough surfaces it is shown that depending on the observation scale by atomic force microscopy (AFM) quite different RMS roughness values can be obtained and that only the values taken at saturation can be used for properly describing the roughness of the examined materials. This effect has clear consequences when trying to apply wetting models to account for the influence of roughness on contact angles. These ideas are discussed with examples taken from rough polymer surfaces subjected to plasma etching. Debate - Discussion: To account for the wetting behavior of real surfaces within the Wenzel and similar models only surface roughness values determined at saturation can be used. This implies to check different observation areas by AFM and to choose the RMS roughness values once a maximum value of this parameter has been reached.
Noviembre, 2011 | DOI: 10.1002/ppap.201100081
Reactividad de Sólidos
Formation of the complete range of Ti5Si3-xGex solid solutions via mechanically induced self-sustained reactions
José M. Córdoba, Ernesto Chicardi, Miguel A. Avilés, Francisco J. GotorIntermetallics, 19 (2011) 1688-1692 DOI: 10.1016/j.intermet.2011.07.005
Abstract
The complete range of Ti5Si3–Ti5Ge3 solid solutions was synthesised from elemental mixtures of Ti, Si, and Ge under an inert atmosphere via mechanically induced self-sustaining reactions (MSR). The stoichiometry of Ti5Si3−xGex solid solutions was controlled by adjusting the Si/Ge ratio of the initial mixture. The chemical composition and lattice parameters of the materials confirmed that Ti5Si3–Ti5Ge3 solid solutions with good chemical homogeneity could be produced via MSR.
Noviembre, 2011 | DOI: 10.1016/j.intermet.2011.07.005
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