Static and Cyclic Fatigue of Alumina at High Temperatures: II, Failure Analysis

Failure mechanisms of an alumina, tested at 1200°C under static and various cyclic loading conditions, were examined. Slow crack growth of a single crack is the dominant mechanism for the failure in specimens under cyclic loading with a short duration of maximum stress at all applied stress levels, as well as at high applied loads for static loading and cyclic loading with a longer hold time at maximum stress. At low stress levels, failure of static loading and cyclic loading with a longer hold time at maximum stress might occur by formation and/or growth of multiple macrocracks. More importantly, for all the given loading conditions. The viscous glassy phase behind the crack tip could have a bridging effect on the crack surfaces. A simplified model for calculating effective stress intensity factor at the crack tip under static and various cyclic loading demonstrated a trend consistent with the stress–life data.     

阳极氧化工艺对氧化铝纳米孔膜形成过程及结构的影响

采用高纯度的铝片为阳极，以铂网为阴极，在3％～5％草酸溶液中，电压在30～70V，温度控制在17～25℃范围内进行恒压阳极氧化制备氧化铝膜，并采用环境扫描电镜观察纳米孔形貌，金相显微镜测量氧化膜厚度。研究了电解电压、电解液浓度、温度等条件对氧化铝多孔膜结构的影响。结果表明：氧化膜形成速度、纳米孔孔径、胞径、孔壁厚度、氧化膜厚度受电解电压影响显著，随着电解液浓度和温度的增大，氧化膜生长速度加快，纳米孔孔径、孔壁厚度等都随之增大，在相同时间内生成的氧化膜厚度增大。     

Mechanical Properties of Alumina/Silicon Carbide Whisker Composites

The improvement of mechanical properties of Al₂O₃/SiC whisker composites has been studied with emphasis on the effects of the whisker content and of the hot-pressing temperature. Mechanical properties such as fracture toughness and fracture strength increased with increasing whisker content up to 40 wt%. In the case of the high SiC whisker content of 40 wt%, fracture toughness of the sample hot-pressed at 1900° decreased significantly, in spite of densification, compared with one hot-pressed at 1850°. Fracture toughness strongly depended on the microstructure, especially the distribution of SiC whiskers rather than the grain size of the Al₂O₃ matrix.     

耐磨抗冲击氧化铝陶瓷异型件的研制

主要研究了高铝快速磨罐、弧形衬板、球磨机磨口、研钵等异型件的配方及注浆成型工艺。试验配制了高铝泥浆用复合稀释荆及复合添加剂，使制品的显微结构均匀，密度得到了显著提高。     

Enhanced Fracture Toughness in Layered Microcomposites of Ce-ZrO2 and Al2O3

Laminar composites, containing layers of Ce-ZrO₂ and either Al₂O₃ or a mixture of Al₂O₃ and Ce-ZrO₂, have been fabricated using a colloidal method that allowed formation of layers with thicknesses as small as 10 μm. Strong interactions between these layers and the martensitic transformation zones surrounding cracks and indentations have been observed. In both cases, the transformation zones spread along the region adjacent to the layer, resulting in an increased fracture toughness. The enhanced fracture toughness was observed for cracks growing parallel to the layers as well as for those that were oriented normal to the layers.     

Tensile Stress Relaxation of Alumina at High Temperature

The development of a tensile testing methodology for ceramics which enables a stress vs strain-rate response to be measured at high temperature is described. The test involves a carefully controled stress relaxation test at constant total strain using an experimental procedure and phenomenological analysis previously developed for metallic materials. It is demonstrated here with preliminary tests on alumina at 1050° and 1150°C. This offers, with further development, the possibility of establishing design stresses associated with low strain-rate behavior for structural applications. The results demonstrate that data covering four decades of strain rate may be generated in tests lasting a few hours. The inelastic strain consists of substantial anelastic recoverable strain in addition to a permanent creep strain.     

利用高铝矾土研制低温耐磨氧化铝瓷

着重介绍了以高铝矾土为主要原料的85瓷的合理配方和所采用的生产工艺，并对吸水率、体积密度、耐磨性、显微硬度、抗折强度和断裂韧性等物理性能进行了测试。还探讨了低温烧成机理、提高耐磨性的途径。结合显微结构分析了生产工艺对产品性能的影响。     

用烧结刚玉研制再结合刚玉砖

介绍了以烧结刚玉和板状刚玉为原料试制再结合刚玉砖的生产工艺。同时，研究了不同原料、氧化铝微粉、外加物及工艺条件对制品性能的影响。     

The influence of sulfur dioxide on propane oxidation activity over supported platinum and palladium

Earlier studies have shown that sulfur dioxide and metal-support interaction can strongly influence propane oxidation over platinum. In particular, oxidation activity is enhanced when platinum is supported on sulfated -alumina or zirconia compared to -alumina. Therefore, it is of interest to compare the performance of palladium under the same experimental conditions. Four model catalysts were examined: Pt/-alumina, Pt/zirconia, Pd/-alumina and Pd/zirconia. The metal loading was kept at or below 0.05 wt% to emphasize changes in activity attributable to metal-support interaction. Reaction rates were measured with and without sulfur dioxide. Surface sulfation was analyzed by measuring acid strength and evaluating spectra obtained by Fourier-transform infrared spectroscopy. In contrast to platinum, sulfation does not promote propane oxidation on Pd/-alumina, and Pd/zirconia is less active than Pd/-alumina.     

Ultrasonic Dispersion of Ceramic Powders

Ultrasonication is very effective in dispersing alumina and barium titanate slurries. When optimum conditions are used, very short durations (2 to 3 min) are enough to achieve well-dispersed, stable suspensions.