Alumina ceramic materials such as low density, high temperature resistant, corrosion resistance, high hardness, wear resistance and excellent chemical stability, etc, are widely used in aerospace, machinery and electronics, medical and chemical industry, etc. Due to the crystal structure of the Al2O3 ceramics corundum and in combination with the ionic bond and covalent bond by strong directivity, lead to its high brittle characteristics of the low toughness, and this feature is restricted the practical application of Al2O3 ceramics. Al2O3 has many homogenous polycrystals, and the typical crystal structure has alpha-al2o3, beta-al2o3 and gamma-al2o3. Alpha-al2o3 is a corundum structure, which belongs to the trigonal crystal system, and the unit cell is a pointed rhomboid, of which the O2- is closely stacked with the six sides, Al3+ is filled with the octahedral space of 2/3, and the structure is shown in FIG.
1. Alpha-al2o3 has the most compact structure and lowest activity. It is the most stable crystal of the three main forms, which can be stable at all temperatures. Only exist in the nature of alpha Al2O3, when the temperature of 1000 ~ 1000 ℃, the other crystal type into alpha A12O3 will be irreversible. The main crystal of Al2O3 ceramics is alpha-al2o3.
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