Scientific Papers in SCI


Title: Effect of ytterbium doping on the microstructure and plastic deformation of BaCeO3 perovskite oxide
Author(s): Jimenez-Melendo, M; Vaquero-Aguilar, C; Huaman-Mamani, FA
Source: Fuel Processing Technology, 103 (2012) 146-150

abstract | fulltext

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

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

Title: Photocatalytic Ethanol Oxidative Dehydrogenation over Pt/TiO2: Effect of the Addition of Blue Phosphors
Author(s): Murcia, JJ; Hidalgo, MC; Navio, JA; Vaiano, V; Ciambelli, P; Sannino, D
Source: International Journal of Photoenergy, 2012 (2012) 687262

abstract | fulltext

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.

January, 2012 | DOI: 10.1155/2012/687262

Title: Phase composition and tribomechanical properties of Ti-B-C nanocomposite coatings prepared by magnetron sputtering
Author(s): Sanchez-Lopez, JC; Abad, MD; Justo, A; Gago, R; Endrino, JL; Garcia-Luis, A; Brizuela, M
Source: Journal of Physics D: Applied Physics, 45 (2012) 375401

abstract | fulltext

Protective nanocomposite coatings based on hard ceramic phases (TiC, TiB2) combined with amorphous carbon (a-C) are of interest because of their adequate balance between mechanical and tribological performances. In this work, Ti–B–C nanocomposite coatings were prepared by co-sputtering of graphite and TiB2 targets. Varying the discharge power ratio applied to the graphite and TiB2 targets from 0 to 2, the a-C content in the coatings could be tuned from 0 to 60%, as observed by means of Raman and x-ray photoelectron spectroscopy (XPS). The microstructural characterization demonstrated a progressive decrease in crystallinity from an initial nanocrystalline (nc) TiB2-like structure to a distorted TiBxCy ternary compound with increasing C concentration. X-ray absorption near-edge structure measurements on the B K-edge helped to determine a hexagonal arrangement around the B atoms in the ternary TiBxCy phase. A fitting analysis of the C 1s XPS peak allowed us to evaluate the relative amount of a-C and TiBxCy components. A drastic change in hardness (from 52 to 13 GPa) and friction coefficient values (from 0.8 to 0.2) is noticed when moving from nc-TiB2 to TiBC/a-C nanocomposites. The fraction of a-C necessary to decrease the friction below 0.2 was found to be 45%. Raman observation of the wear tracks determined the presence of disordered sp2-bonded carbon phase associated with the diminution of the friction level.

September, 2012 | DOI: 10.1088/0022-3727/45/37/375401

Title: Microstructural and chemical characterization of nanostructured Tialsin coatings with nanoscale resolution
Author(s): Godinho, V; Rojas, TC; Trasobares, S; Ferrer, FJ; Delplancke-Ogletree, MP; Fernandez, A
Source: Microscopy and Microanalysis, 18 (2012) 568-581

abstract | fulltext

Nanoscale resolution electron microscopy analysis combined with ion beam assisted techniques are presented here, to give answers to full characterization of morphology, growth mode, phase formation, and compositional distribution in nanocomposite TiAlSiN coatings deposited under different energetic conditions. Samples were prepared by magnetron sputtering, and the effects of substrate temperature and bias were investigated. The nanocomposite microstructure was demonstrated by the formation of a face-centered cubic (Ti,Al)N phase, obtained by substitution of Al in the cubic titanium nitride (c-TiN) phase, and an amorphous matrix at the column boundary regions mainly composed of Si, N (and O for the samples with higher oxygen contents). Oxygen impurities, predicted as the principal responsible for the degradation of properties, were identified, particularly in nonbiased samples and confirmed to occupy preferentially nitrogen positions at the column boundaries, being mainly associated to silicon forming oxynitride phases. It has been found that the columnar growth mode is not the most adequate to improve mechanical properties. Only the combination of moderate bias and additional substrate heating was able to reduce the oxygen content and eliminate the columnar microstructure leading to the nanocomposite structure with higher hardness (>30 GPa).

June, 2012 | DOI: 10.1017/S1431927612000384

Title: Microstructural Characterization of Silver Nanoparticles for Bioimaging Applications
Author(s): Zaderenko, AP; Caro, C; de la Mata, M; Sanchez, JA; Sayagues, MJ
Source: Microscopy and Microanalysis, 18 (2012) 53-54

abstract | fulltext

Silver nanoparticles are emerging as a powerful tool in bioimaging applications owing to their unique plasmonic properties i.e., extremely high molar extinction coefficients, resonant Rayleigh scattering and enhanced local electromagnetic fields. Through the optimization of these properties, by controlling composition, size, shape, and interparticle spacing of nanoparticles and their assemblies, highly enhanced local electromagnetic fields in the vicinity of nanoparticles are achievable giving rise to IR, Raman and fluorescence surface enhanced spectroscopies (SEIRS, SERS and MEF, respectively).

August, 2012 | DOI: 10.1017/S1431927612012925

Title: Microstructural Characterization of Silver Nanoparticles for Biomedical Applications
Author(s): A. P. Zaderenkoa1, P. M. Castillo, M. de la Mata, M.J. Sayagués and J. A. Sánchez
Source: Microscopy and Microanalysis, 18 (2012) 55-56

abstract | fulltext

There is a growing interest in nanoparticles as carriers of chemotherapeutic agents in order to improve their administration and minimize their side effects. Despite the fact that silver nanoparticles can be conjugated to therapeutic agents, offering additionally advantages due their unique and tunable optical properties, few examples have been described yet.

August, 2012 | DOI: 10.1017/S1431927612012937

Title: A CFD study on the effect of the characteristic dimension of catalytic wall microreactors
Author(s): Arzamendi, G; Uriz, I; Navajas, A; Dieguez, PM; Gandia, LM; Montes, M; Centeno, MA; Odriozola, JA
Source: AlChE Journal, 58 (2012) 2785-2797

abstract | fulltext

A three-dimensional computational fluid dynamics study of the steam methane reforming (SMR) in microreactors is presented. Emphasis has been made on investigating the effects of the characteristic dimension (d: 0.35, 0.70, 1.40, and 2.80 mm) on the performance of two microreactor geometries: square microchannels and microslits. Results have shown that for both geometries the SMR conversion decreases markedly as d increases. Conversely, the microchannels provide a methane conversion slightly higher than that of the microslits. The different performance of the microreactors is only partially due to the different surface-to-volume ratio. Pronounced transverse temperature and concentration gradients develop as the characteristic dimension increases especially for microslits in the first half of the reactor. Therefore, external transport limitations can affect the performance of microreactors for SMR, although the characteristic dimensions are of the order of very few millimeters.

September, 2012 | DOI: 10.1002/aic.12790

Title: Charge collection properties of dye-sensitized solar cells based on 1-dimensional TiO2 porous nanostructures and ionic-liquid electrolytes
Author(s): Gonzalez-Garcia, Lola; Idigoras, Jesus; Gonzalez-Elipe, Agustin R.; Barranco, Angel; Anta, Juan A.
Source: Journal of Photochemistry and Photobiology A-Chemistry, 241 (2012) 58-66

abstract | fulltext

Dye solar cells consisting of mesoporous TiO 2 nanocolumnar films sensitized with a highly absorptive indoline dye were studied to estimate the charge collection efficiency provided by porous 1-dimensional (1-D) nanostructures in combination with viscous, fast-recombining electrolytes. The TiO 2 mesoporous nanostructured films were prepared by physical vapor deposition at glancing incidence (GLAD-PVD). Electrochemical Impedance Spectroscopy (EIS) in the dark was utilized to extract the transport and recombination properties of the fabricated devices. Due to their high porosity, the TiO 2 nanocolumnar electrodes incorporated a dye amount similar to that admitted by nanoparticulated electrodes with higher thickness. This fact, together with the longer lifetimes of electrons obtained for the GLAD-PVD electrodes, lead to an overall improvement of the charge collection and photovoltaic properties with respect to randomly packed electrodes. Measured diffusion lengths were improved by a factor between 2 and 3 with respect to the disordered nanostructure. The present results demonstrate the capability of partially ordered nanostructures to improve charge collection in devices constructed with fast-recombining electrolytes.

August, 2012 | DOI: 10.1016/j.jphotochem.2012.05.015

Title: Microstructural characterization of hydrophobic Ti1−xAlxN coatings with moth-eye-like surface morphology
Author(s): Godinho, V; Lopez-Santos, C; Rojas, TC; Philippon, D; de Haro, MCJ; Lucas, S; Fernandeza, A
Source: Journal of Alloys and Compounds, 536 (2012) S398-S406

abstract | fulltext

Ti1−xAlxN thin films with different Al content were deposited by magnetron sputtering. The combination of electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy (EDS) was used to evaluate the composition of the coatings. The effect of Al content on the morphology and properties of the coatings was investigated. High resolution electron microscopy and related techniques revealed the formation of a pillared moth-eye-like nanostructure with variable size and distribution of meso- and nano-columns and different degree of open porosity that depends on the Al content on the coating. For low Al content (x ≤ 0.21) c-(Ti,Al)N highly porous columns ending in a sharp pyramidal shape present low reflectivity and high hydrophobicity. While the precipitation of h-AlN phase at the column boundaries for x = 0.71 suppresses the c-(Ti,Al)N columnar growth and produces a smother surface, with higher reflectivity and less hydrophobic character.

September, 2012 | DOI: 10.1016/j.jallcom.2012.02.178

Title: Microstructure and high-temperature mechanical behavior of melt-growth Al2O3/Er3Al5O12/ZrO2 ternary eutectic composites
Author(s): Huaman-Mamani, FA; Jimenez-Melendo, M; Mesa, MC; Oliete, PB
Source: Journal of Alloys and Compounds, 536 (2012) S527-S531

abstract | fulltext

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

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

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