52 research outputs found
Influence of the different processing steps on the microstructure of PZT-based multilayer
[ES] Se ha realizado un estudio comparativo de la influencia de los parámetros reológicos y de procesamiento sobre la microestructura
y consistencia de chips multicapa de PZT obtenidos mediante un proceso de colado en cinta. Para ello se han realizado
medidas de viscosidad de distintas barbotinas con diferente contenido en sólidos y su relación con el espesor y densidad
en verde de las cintas obtenidas, se han identificado los puntos crÃticos del ciclo de quemado-sinterización y, mediante
MEB se ha estudiado la microestructura en verde de las láminas coladas y la microestructura final de los chips multicapa
fabricados.[EN] A comparative study of the influence of both rheological and processing parameters on the microstructure and reliability of
multilayer ceramic chips based on PZT has been conducted. The multilayer chips were obtained by tape casting. Viscosity
measurements of different slurries with various solids content have been correlated with both the thickness and the green
density of the casted layers. The critical points of the thermal treatments, organics burn-out and sintering, have been identified.
The green microstructure of the layers and the final microstructure of the sintered chips have been studied by SEM.Los autores quieren agradecer al CSIC y al Proyecto
EUREKA 2309 FACTORY-PAMIS su apoyo en la realización
de este trabajo.Peer reviewe
Sintering and microstuctural characterization of W6+, Nb5+ and Ti4+ iron-substituted BiFeO3
The sintering behaviour and the microstructural evolution of W6+, Nb5+ and Ti4+iron-substituted BiFeO3 ceramics have been analyzed. The obtained results show that W6+ and Nb5+ ions interact with the secondary phases usually present in these materials, thus altering the solid state formation of the BiFeO3 phase. In contrast, Ti4+ ions incorporate into the perovskite structure, leading to an exceptionally low proportion of secondary phases. In addition to this, BiFe0.95Ti0.05O3 materials present a dense microstructure with submicronic and nanostructured grains, clearly smaller than those in the undoped materials
Soft solution fluorine-free synthesis of anatase nanoparticles with tailored morphology
TiO2 nanoparticles with tailored morphology have been synthesized under exceptionally soft conditions. The strategy is based on the use of a non-aqueous alcoholic reaction medium in which water traces, coming either from the air (atmospheric water) or from an ethanol–water azeotropic mixture (ethanol 96%), are incorporated in order to accelerate hydrolysis of the Ti–precursor. Moreover, organic surfactants have been used as capping agents so as to tailor crystal growth in certain preferential directions. Combinations of oleic acid and oleylamine, which lead to the formation of another surfactant, dioleamide, are employed instead of fluorine-based compounds, thus increasing the sustainability of the process. As a result, TiO2 nanostructured hierarchical microspheres and individual nanoparticles with exposed high-energy facets can be obtained at atmospheric pressure and temperatures as low as 78 °C
Influencia de la segregación de Ti4+ en la respuesta multiferroica de materiales basados en BiFeO3
Los materiales multiferroicos han cobrado un interés creciente en los últimos años dada la potencialidad de sus aplicaciones prácticas. Los materiales basados en BiFeO3 pueden considerarse los más estudiados hasta la fecha dentro de los pocos multiferroicos conocidos. No obstante, sus propiedades aún no son adecuadas para su empleo en dispositivos pues suelen presentar una elevada conductividad eléctrica y/o una respuesta antiferromagnética. La modificación de estos materiales mediante dopado con Ti4+ puede disminuir las pérdidas dieléctricas y proporcionar un comportamiento ferromagnético. Sin embargo, los cambios producidos en la estructura, microestructura y propiedades de los materiales de BiFeO3 como consecuencia del dopado con Titanio no están claros. En este trabajo se presenta una caracterización detallada de cerámicas de composición nominal BiFe0.95Ti0.05O3 con una elevada resistencia y una respuesta magnética extraordinaria. Los resultados evidencian la formación de una nanoestructura relacionada con la segregación del dopante en borde de grano que es la responsable de los cambios producidos en las propiedades magnetoeléctricas de estos materiales
Ejected Particles after Impact Splash on Mars: Aggregates and Aerodynamics
Our earlier laboratory measurements showed that low-velocity sand impacts
release fine <5 {\mu}m dust from a Martian simulant soil. This dust will become
airborne in the Martian atmosphere. Here, we extend this study by measuring
aerodynamic properties of ejecta and characterizing deviations from the
behavior of spherical, monolithic grains. We observe the settling of particles
emitted as part of an impact splash. The sizes (20 to 280 {\mu}m) and
sedimentation velocities (0.1 to 0.8 ms^{-1} ) of the particles are deduced
from high-speed videos while the particles sediment under low ambient pressure
of about 1 mbar. The particles regularly settle slower than expected, down to a
factor of about 0.3. Using optical microscopy, the shape of the captured
particles is characterized by simple axis ratios (longest/smallest), which show
that the vast majority of particles are irregular but typically not too
elongated, with axis ratios below 2 on average. Electron microscopy further
reveals that the particles are typically porous aggregates, which is the most
likely reason for the reduction of the sedimentation velocity. Due to the
reduced bulk density, aggregates up to 10 {\mu}m in diameter should regularly
be a part of the dust in the Martian atmosphere.Comment: 8 pages, 7 figure
Biocompatible Probes Based on Rare-Earth Doped Strontium Aluminates with Long-Lasting Phosphorescent Properties for In Vitro Optical IMAGING
In recent decades, the demand for biomedical imaging tools has grown very rapidly as a key feature for biomedical research and diagnostic applications. Particularly, fluorescence imaging has gained increased attention as a non-invasive, inexpensive technique that allows real-time imaging. However, tissue auto-fluorescence under external illumination, together with a weak tissue penetration of low wavelength excitation light, largely restricts the application of the technique. Accordingly, new types of fluorescent labels are currently being investigated and, in this search, phosphorescent nanoparticles promise great potential, as they combine the interesting size-dependent properties of nanoscale materials with a long-lasting phosphorescence-type emission that allows optical imaging well after excitation (so avoiding autofluorescence). In this work, core-shell structures consisting of SrAlO:Eu,Dy luminescent cores encapsulated within a biocompatible silica shell were prepared, showing a green persistent phosphorescence with an afterglow time of more than 1000 s. A high-energy ball milling procedure was used to reduce the size of the starting phosphors to a size suitable for cellular uptake, while the silica coating was produced by a reverse micelle methodology that eventually allows the excitation and emission light to pass efficiently through the shell. Confocal fluorescence microscopy using HeLa cancer cells confirmed the potential of the all-ceramic composites produced as feasible labels for in vitro optical imaging
Microwave-induced fast crystallization of amorphous hierarchical anatase microspheres
The fabrication of hierarchical anatase microspheres with potential photocatalytic properties eventually comprises a consolidation step in which a high degree of crystalline order is typically achieved through conventional electric heating treatments. This however entails a substantial reduction in the specific surface area and porosity of the powders, with the consequent deterioration in their photocatalytic response. Here, we have tested the employ of microwave heating as an alternative energy-saving sintering method to promote fast crystallization. The results obtained suggest that under the microwave radiation, the TiO(2) hierarchical structures can effectively crystallize in a drastically reduced heating time, allowing the specific surface area and the porosity to be kept in the high values required for an improved photocatalytic performance
Effect of ZnO on the microstructure and electrical properties of WO3-Bi4Ti3O12 ceramics
The aim of the present work is to explore the possibility of incorporate a small amount of ZnO to improve the microstructure control of W-doped BIT based materials. Two different processing routes have been used according to previous results reported for other materials: reaction and sintering in one single step and a previous calcination step. The sintering behaviour of the samples, the obtained crystalline phases and the microstructure analysis indicate that the reaction between ZnO and Bi2O3 plays a critical role during sintering. Both Bi2Ti2O7 and Zn2TiO4 secondary phases are stabilised when adding ZnO. Actually, when WO3 and ZnO are incorporated simultaneously to BIT materials, they interact stabilizing the Bi2Ti2O7 phase and avoiding the incorporation of W6+ into the BIT lattice. As a consequence, the electrical conductivity of the samples with ZnO is two orders of magnitude higher than that of the samples doped only with WO3, suggesting that WO3 does not form a solid solution with BIT. The curve dielectric constant vs temperature also reveals the role played by the Bi2Ti2O7 phase.Peer reviewe
Diseño de materiales cerámicos de Bi4Ti3O12 dopados con WO3
Tesis Doctoral inédita leÃda en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de QuÃmica Inorgánica, Fecha de Lectura 24-03-200
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