Compositionally graded YSZ–NiO composites by surface laser melting

El pdf del artículo es la versión post-print.Laser surface melting has been applied to near eutectic NiO–YSZ sintered ceramics. The objective is to generate a functional gradient composite material with graded microstructure and composition. At low solidification rates the resultant material has a graded composition, with a severe NiO segregation towards the surface. A thick NiO layer whose thickness depends on the travelling speed is formed. Below this layer the microstructure is eutectic like with composition varying with depth. In contact with the ceramic, excess YSZ coming from the hypereutectic composition forms an almost continuous YSZ layer. The thickness of both segregated layers, NiO and YSZ can be controlled by traverse speed. Thickness decreases as travelling speed increases until a limiting travelling rate of 110 mm/h, at which no more segregation is found. Possible causes to explain the relevant NiO segregation towards the surface are discussed.Financial support from the Ministerio de Educación y Ciencia of Spain and the CE program FEDER under grant MAT2006-13005-C03-01 is gratefully acknowledged.Peer Reviewe

Component release after exposure of Staphylococcus aureus cells to pulsed electric fields

The objective of this work was to get further insights on the mechanism of inactivation of bacterial cells by pulsed electric fields (PEF) through the study of the release of intracellular components after exposing Staphylococcus aureus cells in McIvlaine buffer (pH 7.0, 2 mS/cm) to PEF treatments of different intensity (18 and 25 kV/cm) and treatment times (from 20 to 400 mu s). Release of most compounds, except proteins, was almost immediate after the treatment, but the relative amount released depended on the molecule studied. A good correlation between the release of the smallest components studied (particularly ions) and membrane permeabilization (as measured by NaCl sensitization and PI entry) was observed. On the other hand, results obtained suggested that S. aureus inactivation by PEF would be related to the exit of cytoplasmic proteins of a molecular weight higher than 6 kDa. Results obtained in this work indicated that increasing PEF treatment time would reduce the capability of S. aureus cells to repair the electropores formed and suggested that this might be due to the formation of pores of a larger size, which S. aureus cells would be unable to reseal in a situation of homeostasis loss. Industrial relevance: Results reported here can help to design more effective treatments for microbial inactivation using PEF on food, and therefore facilitate its industrial implementation

Thermogravimetry and neutron thermodiffractometry studies of the H-YBa2Cu3O7 system.

The high Tc superconducting oxide YBa2Cu3O7¿x reacts with hydrogen gas. Thermogravimetric, X-ray and neutron scattering experiments allow us to propose a two-step type of hydrogen bonding. Firstly, a few hydrogen atoms fill some oxygen vacancies and may favourably modify the electron state, giving rise to a slight increase in the critical temperature. Secondly, after a prolonged heating period, the collapse of the YBa2Cu3O7¿x type framework and of superconductivity were observed, and a new, highly hydrogenated material appeared

Anode supported microtubular solid oxide fuel cells running on methane

Trabajo presentado al "III Iberian Symposium on Hydrogen, Fuel Cells and Advanced Batteries" celebrado en Zaragoza (España) del 27 al 30 de Junio de 2011.We would like to thank grants MAT2009-14324-C0.2-01 and CIT-120000-2007-50 financed by the Spanish Government and Feder program of the European Community for funding project. M. A. Laguna-Bercero would also like to thank the JAEprogram (CSIC) for financial support.Peer Reviewe

Directionally solidified Al2O3-Yb3Al5O12 eutectics for selective emitters

Al2O3-Yb3Al5O12 eutectic rods were directionally solidified using the laser floating zone method at rates between 25 and 750 mm/h. The microstructure consisted of an interpenetrated network of both eutectic phases for all the growth rates. The size of the phases was strongly dependent on the growth rate, the eutectic interspacing decreasing from 4.5 µm at the lowest growth rate to 600 nm at 750 mm/h. The optical transmission of the sample with coarser microstructure was measured and compared with that of an Yb3Al5O12 single crystal grown "ad hoc" using the same method. The apparent "oscillator strength" of the single 2F7/2¿2F5/2 Yb3+ absorption band was larger in the eutectic sample than in the single crystal, which was attributed to the increase in the light path caused by multiple refractions at the eutectic interphases. The thermal emission of the eutectic rod was studied between 1000 °C and 1500 °C. An intense and relatively narrow emission band at about 1 µm corresponding to the 2F5/2¿2F7/2 Yb3+ electronic transition was observed in the whole temperature range. The intensity of the band increased with the temperature up to about 1300 °C. At higher temperatures a saturation of the selective emission was observed which was attributed to the competition between the increase in the thermal population of the excited state and the enhancement of the non-radiative de-excitation channels with the temperature

Procedimiento de preparación y materiales conformados basados en compuestos eutécticos binarios o ternarios de circonia

Referencia OEPM: P9600891.-- Fecha de solicitud: 19/04/1996.-- Titular: Consejo Superior de Investigaciones Científicas (CSIC).Procedimiento de preparación y materiales conformados basados en compuestos eutécticos binarios o ternarios de circonia. La presente invención está relacionada con la preparación de materiales con estructuras eutécticas micrométricas basados en mezclas de óxidos, conformados con dimensiones mili y submilimétricas mediante fusión zonal por láser con diferentes sistemas ópticos de focalización y control de los haces de los láseres. Su utilización es en el sector de la producción y conservación de energía, como elementos calefactores, refractarios, cátodos para plasmas de aire, electrodos, en componentes para celdas de combustión, microsensores de gas oxígeno, etc.Peer reviewe

Laser-assisted surface melting of Al2O3-YSZ eutectic ceramics

[ES] Se presenta un procedimiento para la densificación y/o texturado superficial de cerámicas de Al2O3-YSZ (circona estabilizada con itria) con composición eutéctica mediante fusión zonal asistida por láser. Haciendo un barrido con la radiación proveniente de un láser de potencia sobre piezas cerámicas conseguimos modificar la microestructura y densificar completatmente la capa superficial, con un espesor que va de 30 a 1000 μm. Por ejemplo, con línea estrecha de láser de diodo, fluencia de 1.23 kW/cm2 y velocidades de barrido de 0.14 mm/s, solidificamos capas de 560 μm. El resultado es una superficie de baja rugosidad y no porosa. La microestructura de la muestra es fina debido a su composición eutéctica. La interfase sólido-líquido en el proceso de crecimiento determina la orientación de la microestructura. Se estudia la forma de esta interfase tanto en cortes transversales como longitudinales, lo que permite analizar el efecto que sobre la microestructura tiene la superposición de barridos, que es una alternativa para tratar superficies extensas. Macroscópicamente la frontera entre barridos contiguos es suave. Sin embargo, su microestructura presenta discontinuidad en el espaciado entre las fases debido a la evolución microestructural en la región no fundida sometida a altas temperaturas y a la nucleación preferencial de Al2O3 al comenzar el crecimiento cristalino. Se analizan distintas posibilidades para disminuir el choque térmico inherente al proceso y que conduce a la formación de grietas paralelas a la dirección de procesado y de delaminación. Se observa una mejora importante cuando se precalienta la pieza a tratar, de modo que es posible procesar superficies de cerámicas eutécticas 99% densas.[EN] A procedure for surface densification and/or texturing of Al2O3-YSZ (yttria stabilised zirconia) ceramics with eutectic composition by means of laser surface melting is presented. By scanning a high-power laser beam on a ceramic surface, we achieve a textured and fully dense surface layer from 30 to 1000 microns thick. For example, using a thin diode laser line with fluence 1.23 kW/cm2 and 0.14 mm/s scan rate, the solidified layer has 560 μm depth. We get a low roughness and dense surface. The microstructure is fine (micron size) due to the eutectic composition. The orientation of the microstructure is determined by the shape of the solid-liquid interface in the solidification process. We study the shape of this interface in transverse and longitudinal cross-sections in single as well as overlapping scans, which are required to process large surfaces. From the macroscopic point of view, the transition between adjacent scans is smooth. However, the microstructure presents discontinuity in the interphase spacing due to microstructural evolution in the heat affected region as well as the nucleation of an Al2O3 layer at the beginning of the crystal growth. The thermal shock inherent to the procedure generates cracks longitudinal and transverse to the scanning direction, as well as delaminating cracks. We analyse different possibilities to reduce this thermal shock. The best results are obtained by preheating the substrate, allowing us to process surfaces of Al2O3-YSZ eutectic ceramics 99% dense.Financiación del Ministerio de Ciencia y Tecnología a través de los proyectos MAT2000-1495 y MAT2000-1533-C03-02.Peer reviewe

Fabrication and microstructure of self-supporting thin ceramic electrolytes prepared by laser machining

Self-supporting thin Yttria Stabilized Zirconia (YSZ) ceramics electrolytes have been prepared by laser machining. They are carved from a sintered YSZ plate to shape a 20 µm thick and 8 mm in diameter central region, surrounded by an unprocessed 150 µm thick supporting zone. Scanning Electron Microscopy (SEM) and Electron BackScattering Diffraction (EBSD) studies confirmed that the strains produced by the laser processing are small and limited to only one or two layers of YSZ grains (~5 µm). SEM and Transmission Electron Microscopy (TEM) have been also used to characterize the surface of the membrane. It is corrugated and coated with YSZ nanoparticles as a result of the laser plasma deposition. Electrochemical characterization by Impedance Spectroscopy (EIS) showed that this surface morphology improves the electrical performance of the membrane slightly but clearly, reducing the cathode polarization resistance by about 5% in the 650-850 ºC range.This study was funded by the MAT2012-30763 project, which is financed by the Spanish Government (Ministerio de Economía y Competitividad) and the Feder program of the European Union.Peer Reviewe

Interacting plasmon and phonon polaritons in aligned nano- and microwires

The availability of macroscopic, nearly periodic structures known as eutectics opens a new path for controlling light at wavelength scales determined by the geometrical parameters of these materials and the intrinsic properties of their component phases. Here, we analyze the optical waveguiding properties of eutectic mixtures of alkali halides, formed by close-packed arrangements of aligned cylindrical inclusions. The wavelengths of phonon polaritons in these constituents are conveniently situated in the infrared and are slightly larger than the diameter and separation of the inclusions, typically consisting on single-crystal wires down to submicrometer diameter. We first discuss the gap mode and the guiding properties of metallic cylindrical waveguides in the visible and near-infrared, and in particular we investigate the transition between cylinder touching and non-touching regimes. Then, we demonstrate that these properties can be extended to the mid infrared by means of phonon polaritons. Finally, we analyze the guiding properties of an actual eutectic. For typical eutectic dimensions, we conclude that crosstalk between neighboring cylindrical wires is small, thus providing a promising platform for signal propagation and image analysis in the mid infrared

Multifunctional RNA-binding proteins influence mRNA abundance and translational efficiency of distinct sets of target genes

RNA-binding proteins (RBPs) can regulate more than a single aspect of RNA metabolism. We searched for such previously undiscovered multifunctionality within a set of 143 RBPs, by defining the predictive value of RBP abundance for the transcription and translation levels of known RBP target genes across 80 human hearts. This led us to newly associate 27 RBPs with cardiac translational regulation in vivo. Of these, 21 impacted both RNA expression and translation, albeit for virtually independent sets of target genes. We highlight a subset of these, including G3BP1, PUM1, UCHL5, and DDX3X, where dual regulation is achieved through differential affinity for target length, by which separate biological processes are controlled. Like the RNA helicase DDX3X, the known splicing factors EFTUD2 and PRPF8 - all identified as multifunctional RBPs by our analysis - selectively influence target translation rates depending on 5' UTR structure. Our analyses identify dozens of RBPs as being multifunctional and pinpoint potential novel regulators of translation, postulating unanticipated complexity of protein-RNA interactions at consecutive stages of gene expression