| 摘要 |
An translucent polycrystalline ceramic capable of transmitting a visible light and excellent in strength, hardness, abrasion resistance, light transmittance, transparency and high-temperature characteristics and usable as a material, for instance, for cutting tools, outer tubes for high pressure sodium lamps and high temperature furnace window plates. The translucent polycrystalline ceramic has at least one characteristic features that (1) a mean particle size of crystal particles formed inside the ceramic is not larger than 1.0 .mu.m, (2) a mean aspect ratio thereof is from 1.0 to 1.5, (3) a density thereof is substantially a theoretical density, (4) a light transmittance through its thickness of 1 mm is at least 50%, (5) a mean facet length of crystal particles formed inside the ceramic is not longer than a maximum wave length of the light. One of the embodiments is a translucent polycrystalline Al2O3 ceramic containing 0.02 - 2.0 mol% of oxide of metal belonging to IIIA and/or IVA group (excluding Ti), having its density of at least 3.98 g/cm3, a mean crystal particle size of 0.3 - 1.0 .mu.m, its bending strength of at least 1900 MPa and its Vickers hardness of at least 850 at 1000.degree.C. |
