Papers by Author: Wen Cheng J. Wei

Abstract: Two oxides, Y₂O₃ and Nb₂O₅, were doped into Bi₂O₃-based electrolyte in a composition of (Bi _1-x-y,Nb _x,Y _y)₂O ₃, where (x+y)=0.12 to 0.2 and the x:y ratio 3:1 to 1:3. The delta-phase retention, the oxygen vacancy order-disorder transformation, the ionic and electric conductivity were investigated by various techniques. The long-term conductivity of the dense electrolytes was determined showing moderate degradation due to phase transformation possible triggered by surface evaporation of Bi-oxide. The best retention of the conductivity is about 60% after 300 hr test.

Abstract: This work proposes three diffusion models used to simulate the reaction layer produced from silver electrode, which has been cofired with La-Si-B-O-mullite (LSBM) glass ceramic composites. In the beginning of the cofiring, the interface connection between Ag electrolyte and LSBM glass ceramic composites was full matched, and the curve of diffusion pattern fitted one of the general cases of diffusion model well. However, the interface became gradually and partially separated during the process of cofiring. As a result, the original concentration of Ag at the surface could not be maintained, and new diffusion model must be proposed. At a later stage of the experiment, the gradient of diffusion curve became smooth. The final distribution of Ag concentration didn’t reflect a general diffusion phenomenon. Total delaminated case and interfacial pitting case were considered in this research, respectively.

Abstract: Solid Oxide Fuel Cell (SOFC) has several non-replaceable advantages over the others, e.g. the issues of high volumetric power density and low cost. Those advantages have been appreciated in recent developments, and implemented in several micro-SOFC devices conducted by several international projects. ONEBAT System by ETH (with 4 other groups) in Switzerland, micro-tubular SOFC by AIST in Japan, micro-honeycomb fuel cell (FC) by Professor Ishihara at Kyushu University will be reviewed in this report. Some micro-devices have been built on Si-chip, or in associated with the accessory parts, such as fuel reformer, electric power collector, or micro-turbine. Those have demonstrated important technology breakthrough and also shown the potential for commercial applications. This report will also discuss two important issues, including gas transport limitation in small gaps and glass sealing for the practical applications of Micro-SOFCs.

Abstract: Al2O3 composites with different volume fractions of 3Y-TZP (3 mol% yttria-doped tetragonal zirconia polycrystalline) were prepared by using a colloidal process and pressure-casting into green specimens, then were pressureless sintered to full density at 1550oC. The resulted two-phase microstructure contained uniformly distributed and submicro- meter-sized grains. The addition of 15 vol% ZrO2 resulted in an increase in bending strength (average 656 MPa by 4 pt. test). Appreciate amount of m-ZrO2 phase was detected after fracture. The enhanced transformability results in an increase in flexural strength and toughness. The addition of 30 vol% ZrO2 resulted in best toughness (5.4 MPam0.5) and outstanding wear resistance (7.2×10-8 cm3/Nm).

Abstract: Sintering kinetics of the α-Al2O3 powders with average particle size 0.1 μm and ca.1% ZrO2 impurity was investigated. Several two-step sintering methods were tried, and the results were compared with the conventional (one-step) process. The temperature (<1600oC), holding time (up to 20 h), heating rate (2 oC /min to 90 oC/min), initial grain size, and porosity were controlled. The optimal results of two-step sintering, a smaller grain size (0.57 μm) and a good density (>98% TD) were achieved by heating to 1450oC, then holding at 1350oC for 20 h. The sintering mechanism was determined, belonging to lattice diffusion in the temperature region of 1400 to 1600oC. The activation energy was 688 kJ/mol, which was interpreted as a volume diffusion of Al3+ ions in polycrystalline matrix.

Abstract: Cerium hydrate fiber (CHF), which showed an aspect ratio greater than 100, was synthesized by a novel method, which used the mixing of cerium nitrate (Ce(NO3)3), sodium hydrate (NaOH) and citric acid (C6H8O7) synthesized at a relative low temperature and ambient pressure. The precipitates were characterized by XRD, SEM and TEM. The results showed that in addition to fibers, two morphologies could be obtained depending on the synthesizing conditions. Aging time and formulation were two key factors for the control of the aspect ratio of the precipitates. By a heating treatment at 600oC for 2 h, the homogenous and well-crystallized cerium dioxide (CeO2) fiber can be fabricated. The effects of synthesis parameters, such as the concentration of the starting solution, aging period, and pH value were reported and discussed.

Abstract: Ion-beam sputtering deposition is a physical deposited method which uses accelerated ionbeam to sputter oxide or metal targets, and deposits atoms on substrate. Thin films of yttrium-stabilized zirconia (YSZ) were deposited on Si (100) wafer and NiO/YSZ plate. Scanning electron microscopy and transmission electron microscopy with EDS were employed to study the microstructural and chemically stoichiometric results of the films and the crystal growth process by various heat treatments. X-ray diffraction was also used to analysis crystalline phase of the YSZ films. The influence of different targets, substrates deposited efficiency and the properties of the film will be presented and discussed.

Abstract: The effects of different kneading sequences, chemical additives, and solid loadings to the homogeneity and rheological behavior of the Al2O3/3Y-TZP (ZTA) feedstock were investigated. The properties of the feedstock were analyzed by the torque rheometry, transmission optical microscopy (OM) and scanning and transmission electron microscopy (SEM & TEM). The optimal kneading process was determined when good homogeneity was reached. The concepts of critical solid loading and the homogeneity of two-oxide systems, and the power consumption to reach best microstructure will be introduced and quantitatively analyzed.

Abstract: Monodispersive and uniform particles have many potential applications. The objectives of this study are trying to synthesize and control the morphology of monodispersive indium oxide (In2O3)particles through hydrothermal process with the help of PVP (polyvinylpyrrolidone) and urea additions. Various cubic, ellipse, or shuttle-like In2O3 particles were synthesized by using hydrothermal conditions (65-85oC). The effects of Sr nitrate were studied. Spherical particles could not be synthesized. The aspect ratio of the In2O3 particle reduced as the concentration of Sr nitrate increased. Crystalline In2O3 phase appeared above 300oC.