先进陶瓷材料概论(英文)第二章讲述.pptx

?A quick?review of the last class;?1. Try to get a Reference book (hardcopy?or?e-book) by every possible means. (For everyone);;Part II: Advanced Structural Ceramics;;Alumina (Al2O3);An overview of the important properties of alumina ceramics is provided in Table 7.1 . The wide range of values attests to the fact that alumina ceramics depend on processing parameters, including the sintering temperature, sintering atmosphere, impurity content, grain size, and other extrinsic and intrinsic factors. For example, the extremely pure and fine - grained alumina specifications used in femoral heads for hip endoprostheses demonstrate noticeably higher strengths, toughness, and hardness characteristics.;掌握词汇： 相对密度 热膨胀系数 抗压强度 抗拉强度 抗弯强度 抗磨损强度 断裂韧性 热导率 比热 弹性模量 剪切模量 体积弹性模量 显微硬度 介电强度 介电常数 体积电阻;High - purity alumina parts and devices can be utilized in both oxidizing and reducing atmospheres to 1925 ?C. The mass loss in vacuum between 1700 ?C and 2000 ?C ranges from 10 ? 5 to 10 ? 7 g cm ? 2 ? s ? 1 . Alumina resists attack by all gases except for wet fluorine, and is resistant to all common reagents except for hydrofluoric and hot orthophosphoric acids. An elevated temperature corrosion occurs in the presence of alkali metal vapors, particularly at lower purity levels ( 90% Al2O3 content). The additions of either chromium oxide or manganese oxide is known to improve the material ’ s hardness and toughness. Other additions can be made to improve the ease and consistency of metal films fired to alumina ceramics for subsequently brazed and soldered assemblies.;Processing of Alumina The process of producing pure alumina from bauxite ore (Bayer process) has changed very little since its inception in 1893, and can be divided into three stages of extraction, precipitation, and calcination.;The ore is washed, crushed and milled (step A) to reduce the particle size and make the minerals more available for extraction. It is then combined with the process caustic liquor and sent as slurry t