On the transparency of nanostructured alumina: Rayleigh-Gans model for anisotropic spheres

14 páginas, 6 figuras, 2 tablas.A light scattering model under the Rayleigh-Gans-Debye approximation has been developed for polycristalline alumina. The model states that transmittance of dense alumina ceramics basically depends not only on the maximum grain size but also on the preferential orientation of their c-axis, or texture. The effect of texture in transparency has been experimentally measured on several dense alumina samples with different grain size and compared to that obtained from x-ray Rietveld refinements with a very good agreement. The Rayleigh-Gans-Debye approximation also allows to represent optical data in a very simple way (logarithm of transmittance vs. the inverse of the wavelength square). Using these variables, a straight line is obtained for the Rayleigh-Gans-Debye approximation, its slope being proportional to the maximum grain size and textural parameter. Deviation from this law implies the presence of pores or grain of extremely large size.Peer reviewe

Conductivity and charge depletion aging of resistive electrodes for high rate RPCs

Trabajo presentado al 11th Workshop on Resistive Plate Chambers and Related Detectors (RPC2012).Development of new electrodes is a key element for the improvement of high rate Resistive Plate Chambers (RPC). In the particular case of resistive electrodes, the fabrication of these elements is a challenging problem from a material science point of view. The combination of resistivity, permittivity and stability requirements is really hard to satisfy for any known material. Only a few materials have been found to be suitable for fabrication of resistive plates. In this work, we have carried out electrical characterizations of some of the materials that are currently used in RPCs or are solid candidates to be used as resistive plates in high rate RPCs. As a result, we have found strong evidences that ion conduction processes under moderate to high electric fields are able to drift high amounts of charge which allow to understand the degradation nature of the involved processes.Peer reviewe

On the transparency of nanostructured alumina: Rayleigh-Gans model for anisotropic spheres

14 páginas, 6 figuras, 2 tablas.A light scattering model under the Rayleigh-Gans-Debye approximation has been developed for polycristalline alumina. The model states that transmittance of dense alumina ceramics basically depends not only on the maximum grain size but also on the preferential orientation of their c-axis, or texture. The effect of texture in transparency has been experimentally measured on several dense alumina samples with different grain size and compared to that obtained from x-ray Rietveld refinements with a very good agreement. The Rayleigh-Gans-Debye approximation also allows to represent optical data in a very simple way (logarithm of transmittance vs. the inverse of the wavelength square). Using these variables, a straight line is obtained for the Rayleigh-Gans-Debye approximation, its slope being proportional to the maximum grain size and textural parameter. Deviation from this law implies the presence of pores or grain of extremely large size.Peer reviewe

Faradaic current in differnt mullite materials: single crystal, ceramic and cermets

Faradaic current measurements have been carried out on three different types of mullite: 2 : 1 mullite single crystals (E ¿ c), 3 : 2 ceramics and 11 % mullite/Mo composites. Measurements were carried out on very thin samples (60 µm) at high voltages (500 to 1 000 V). Under these conditions, measurable currents were recorded even at room temperature. Results indicate notable differences between these three samples, which suggest that, although they share the same name and similar crystalline structure, binding energies and defect distributions seem to be very different. Finally, it has been seen that the excellent behaviour against dielectric breakdown of ceramic mullite does not hold for single crystals or mullite based cermets.Peer Reviewe

Electrical discharge machining of ceramic/semiconductor/metal nanocomposites

Electroconductive, homogeneous and dense ceramic/semiconductor/metal nanocomposites were obtained by hot pressing and subsequently machined by wire electrical discharge machining (EDM). The addition of semiconductor and metal phases to a high-performance ceramic material produces nanocomposites which preserve the excellent mechanical properties of the ceramic/metal material while possessing the electrical conductivity necessary for EDM. The role of the low concentration of metal has been investigated from a mechanical and an electrical point of view, and found to be critical to the final behavior.This research was supported by the European Union under the IP-NANOKER project (FP6-515784- 2), by the Spanish Ministry of Education and Science under the project MAT2006-10249-C02-01.Peer reviewe

Transparent alumina-ceria nanocomposites by spark plasma sintering

Publicado como artículo en: Advanced Engineering Materials 12(11): 1154–1160 (2010).I. Alvarez-Clemares wants to acknowledge FICYT for the support received.Peer Reviewe

Método de obtención de un material compuesto nanoestructurado de matriz cerámica y mecanizable por electroerosión, y producto obtenible por dicho método

Método de obtención de un material compuesto nanoestructurado de matriz cerámica y mecanizable por electroerosión, y producto obtenible por dicho método. Permite obtener un material compuesto cerámica/semiconductor/ metal nanoestructurado y mecanizable por electroerosión (EDM). Se utilizan como materiales de partida: un material cerámico de tamaño de partícula nanométrico, un material semiconductor de tamaño de partícula nanométrico, y una sal metálica, empleada como precursor del correspondiente metal. El método comprende las etapas de: a) preparación de un material en polvo de cerámica/óxido metálico mediante calcinación de un polvo seco obtenido a partir de una suspensión homogénea del material cerámico y la sal metálica precursora de metal; b) adición al polvo resultante de la etapa anterior del material semiconductor; c) molienda, homogeneización, secado y tamizado del polvo resultante de la etapa anterior; d) tratamiento térmico en atmósfera reductora del polvo resultante de la etapa anterior, y e) conformado y sinterizado del polvo de la etapa anterior.Peer reviewedConsejo Superior de Investigaciones Científicas (España)A1 Solicitud de patentes con informe sobre el estado de la técnic

Ceria doped alumina by spark plasma sintering for optical applications

El pdf del artículo es el manuscrito de autor.Al 2O 3-CeO 2 ceramics were found to be transparent in the IR range and high-traslucent in the visible range. The surface of nanometric α-alumina particles was modified by deposition-precipitation of small fractions of ceria nanoparticles. The powders were sintered using Spark Plasma Sintering. Values of Real In-line Transmittance up to 70% in the IR-Vis range have been measured. Transparency enhancement has been attributed to Cerium oxide nanoparticles located at the grain boundaries and triple points. These particles are hindering alumina grain growth during SPS at a temperature as high as 1430°C. This effect is found to be effective under SPS low vacuum conditions and short dwell times. The optimum ceria content was found to be 0.7wt.%. Diffusion in Al 2O 3-CeO 2 as a function of the atmosphere has been studied in diffusion couples. The results obtained by the proposed route are discussed considering the data reported in the literature for SPS ed transparent alumina. © 2012 Elsevier Ltd.This work was supported by the Spanish Ministry of Science and Innovation (MICINN) under the project MAT2009-14542-C02-02. Isabel Alvarez-Clemares wants to acknowledge the support received by Fundación para el Fomento en Asturias de la Investigación Científica aplicada y la Tecnologia (FICYT), under the program Severo Ochoa (BP07-050). Gustavo Mata-Osoro was supported by the Spanish Ministry of Education and Science under the project MAT2006-10249-C02-01.Peer Reviewe

Giant magneto-optical/faraday effect in flexible non-magnetic/plasmonic polymer matrix composites

Resumen del póster presentado al International Workshop on Nanopalsmonics for Energy and the Environment celebrado en Sanxenxo (España) del 8 al 10 de junio de 2011.In selected metals (Ag, Au), surface plasmon resonantes appear when monodisperse nanoparticles embedded into a transparent medium interact with visible radiation. One of the main difficulties for preparing plasmonic materials is the strong tendency of nanoparticles to aggregate. In this sense, a new approach is herewith presented in which, metallic nanoparticles were obtained on sepiolite (a hydrated magnesium silicate) microparticles. These microparticles which actas nanoparticle carriers were dispersed into transparent polymers (LDPE and PS) by conventional methods. As a result, tinted films (from 50 to 100 ?m thick) with very good mechanical stability were obtained. These films present a very good degree of transparency due to the index matching between sepiolite and polymeric matrices, which minimize the light scattering by defects. Additionally they present well defined surface plasmon resonance absorption peaks. Due to the excellent optical quality of these materials, it has been possible to measure a giant magneto-optical Faraday rotation. In fact, according to theoretical models, (Hui and Stroud, APL, 50, 950 (1987)) non-magnetic plasmonic dilutions may present a notable Faraday rotation. In this work, gold and silver sepiolites dispersed in 60 pm PS films present Faraday rotation of about 3.10(4) º/T.m in the neighbourhood of the SPR spectral region. More precisely, the Faraday rotation reaches the maximum at the long wavelength edge of the SPR absorption curve, being approximately O at the maximum of SPR absorption curve. The measured Faraday rotation value is of the same order of magnitude to that reported for transparent magnetic materials. Therefore, it is shown that gold and silver nanoparticles may be employed for fabricating magnetic field sensors in a simple procedure which can be easily scaled-up.Peer Reviewe