Densification and Thermal Conductivity of AIN Doped with Y2O3, CaO, and Li2O

Small amounts of Li₂O result in sintering in the AIN-Y₂O₃-CaO and AIN-CaO systems at firing temperatures <1600°C. The effect is ascribed to reduction of the liquidus temperature. Furthermore, Li₂O is removed by volatization at temperatures from 1300° to 1600°C, and its content decreases several ppm from the initial 0.3 wt%. Li₂O-doped AIN specimens containing Y₂O₃ and CaO additives are well densified by firing at 1600°C for 6 h, and their thermal conductivity is 135 W^.m^−1.K⁻¹.The effect of Li₂O addition on sintering and thermal conductivity also is discussed through thermo-dynamic considerations.     

High Thermal Conductivity in Silicon Nitride with Anisotropie Microstructure

Silicon nitride was fabricated by tape casting of α-Si₃N₄ powder with 5 wt% Y₂O₃ and 5 vol% rodlike β-Si₃N₄ seed particles, followed by tape stacking, hot pressing under 40 MPa, and annealing at 1850°C for 2-66 h under a nitrogen pressure of 0.9 MPa. Silicon nitrides fabricated by this procedure exhibited a highly anisotropic microstructure with large elongated grains (developed from seed particles) uniaxially oriented parallel to the casting direction. Thermal conductivities parallel to the grain alignment were much higher than those measured in other directions and exhibited high values of up to 120 W/(m.K). The anisotropic thermal conductivity of the specimen could be explained by the rule of mixture, considering that large elongated grains developed from seeds have higher thermal conductivity than a small-grained matrix.     

Decay of material properties of degraded MEA caused by repeated cold starts under subzero conditions in polymer electrolyte fuel cells

This study investigated the characteristics of cell performance degradation, decline of component performance, and changes in the properties of membrane electrode assembly materials caused by repeated cold starts under a subzero condition of ?30 °C. It was made clear that functional decay appeared mainly at the cathode due to increased proton conductive impedance and reduction of reactivity of the electrode catalyst. Among the cathode components, an increase in proton conductive impedance in the cathode electrolyte was dominant. Furthermore, the application of ion chromatography and a newly developed proton‐induced gamma‐ray emission method to measure fluorine in the off‐gas drain revealed that decomposition of the electrolyte was dominant in the cathode catalyst layer. A decrease in fluorine in the cathode electrolyte measured by fluorine‐19 nuclear magnetic resonance confirmed this decomposition. A hypothesis is also presented concerning the cause of the performance degradation. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20394     

Reliability of Liquid Crystal Display

This paper reports the reliability of twisted nematic liquid-crystal display for basic applications such as watches and calculators. We have studied significant stress factors such as voltage, temperature and humidity, and their corresponding failure modes. The main failure mode is LCD misalignment; many different modes appear corresponding to different stress conditions as well as material and process for the LCD. We have analyzed the accelerated test results by Weibull distribution, elucidated accelerating factors, and estimated life time. The life is inversely proportional to 1.78-2.45 power of applied voltage, depending upon misalignment modes. The distribution of life is well expressed by Weibull distribution with shape parameter between 2.5-3.0, and proportional to the square of coefficient of variation of life. We conclude that the acceleration factors could be determined and 99.9% of tested displays will live more than 10 years. The knowledge on reliability of LCD can be now applied to new fields of LCD, such as industrial use, home appliance, and automotive instruments.