38 research outputs found
Insights into the Second Law of Thermodynamics from Anisotropic Gas-Surface Interactions
Thermodynamic implications of anisotropic gas-surface interactions in a
closed molecular flow cavity are examined. Anisotropy at the microscopic scale,
such as might be caused by reduced-dimensionality surfaces, is shown to lead to
reversibility at the macroscopic scale. The possibility of a self-sustaining
nonequilibrium stationary state induced by surface anisotropy is demonstrated
that simultaneously satisfies flux balance, conservation of momentum, and
conservation of energy. Conversely, it is also shown that the second law of
thermodynamics prohibits anisotropic gas-surface interactions in "equilibrium",
even for reduced dimensionality surfaces. This is particularly startling
because reduced dimensionality surfaces are known to exhibit a plethora of
anisotropic properties. That gas-surface interactions would be excluded from
these anisotropic properties is completely counterintuitive from a causality
perspective. These results provide intriguing insights into the second law of
thermodynamics and its relation to gas-surface interaction physics.Comment: 28 pages, 11 figure
The effect of firing conditions on the characteris-tics of thick-film resistors for temperature sensors
Processing and electromechanical properties of lead zirconate titanate thick films by electrophoretic deposition
Smart thin-film piezoelectric composite sensors based on high lead zirconate titanate content
Parámetros de procesamiento para varistores basados en ZnO preparados por serigrafía
[EN] Thick film varistors based on the ZnO-Bi2O3-Sb2O3 system have been prepared by screen printing on dense alumina substrates.
Different processing parameters like the paste viscosity, burn out and sintering cycles, green and sintered thickness, have
been studied to improve the processing of ZnO-based thick film varistors. Starting powders were pre-treated in two different
ways in order to control both the Bi-rich liquid phase formation and the excessive volatilization of Bi2O3 during sintering due
to the high area/volume ratio of the thick films. Significant changes have been observed in the electrical properties related
to the different firing schedule and selection of the starting powders.[ES] Se han preparado varistores basados en el sistema ZnO-Bi2O3-Sb2O3 en forma de lámina gruesa sobre sustratos de alúmina
densa. Diferentes parámetros del procesamiento como la viscosidad de la pasta, los ciclos de calcinación y sinterización
y el espesor en verde y sinterizado han sido estudiados para mejorar el procesamiento de los varistores basados en ZnO
preparados en forma de lámina gruesa. Los polvos de partida fueron pretratados de dos formas diferentes con el objetivo de
controlar la formación de la fase líquida rica en bismuto y la excesiva volatilización de Bi2O3 durante la sinterización debida
a la alta relación área-volumen de las láminas gruesas. Se han observado cambios significativos en las propiedades eléctricas
relacionadas con los diferentes ciclos de calcinado y con la selección de los polvos de partida.This work has been developed within Marie Curie Training Site Ceramos (HPMT-CT-2001-00372) program and CYCYTMAT2004-04843-C02 project.Peer reviewe
Spatially Resolved Photoemission and Electrochemical Characterization of a Single-Chamber Solid Oxide Fuel Cell
Performance comparison of screen-printed piezoelectric structures on porous PZT and alumina substrates
In previous work, screen-printing technology was used to elaborate an integrated piezoelectric structure on a porous substrate [1]. The substrate was chosen to withstand the film sintering temperature which was lowered at 800°C thanks to the addition of PGO to a PZT composition. The acoustical impedance of this substrate is very close to that of the deposited piezoelectric thick film, making it an adequate backing to deliver a short pulse-echo response, but the resonance frequency is lowered. Intermediate functional layers were necessary between the substrate and the piezoelectric layer. The transducer based on a porous PZT structure including a dense barrier layer and a gold rear electrode is used as a reference device. Here, another set of materials is considered as possible candidate to fulfill both functions of substrate and backing: porous alumina associated with a dense alumina barrier layer and platinum rear electrode. Since the thicknesses of these layers is not negligible compared to the wavelength of the first thickness mode of the piezoelectric layer, they have a relatively strong influence on the electroacoustic response. The input acoustic impedance of this stack must be controlled very precisely in order to make it an adequate backing. The damping of the backing is optimized to deliver a relatively short pulse-echo response, without excessive lowering of the resonance frequency. The piezoelectric thick film on alumina substrate has similar properties to the one on porous PZT. A mean thickness around 30 micrometers and a thickness coupling factor around 40% were obtained in both cases. As a result of the damping, the structure resonates at 40 MHz, the anti-resonance of the piezoelectric thick film alone being around 65 MHz. Pulse-echo measurements allows comparison of the performance of the two devices in terms of sensitivity, axial resolution and bandwidth. The results are compared and discussed, showing that the sensitivity/bandwidth trade-offs of the two transducers are significantly different