Translucent polycrystalline ceramic and method for making same

A method for making a translucent polycrystalline ceramic capable of transmitting at least 50% of a light that enters the ceramic when a thickness of the ceramic is 1 mm, comprising the steps of:

• forming an unfired ceramic body from a mixture powder including a crystal powder having a mean particle size of less than 1.0 μm and a purity of at least 99.9%;
• firing the unfired ceramic body to form a primary sintered product;
• and
• applying a hot isostatic pressure to the primary sintered product at a temperature not exceeding by more than 125° C. of the temperature wherein the primary sintered product is fired so as to form a secondary sintered product having a density close to a theoretical density of the secondary sintered product and having a mean facet length of less than 700 nm, the mean facet length being defined as an average of lengths of sides forming polygons that appear in cross sections of the crystal particles constituting the ceramic.

A method for making a translucent polycrystalline ceramic capable of transmitting a visible light through the ceramic comprising the steps of:

• forming an unfired ceramic body from a mixture powder comprising an Al2O3 crystal powder having a mean particle size of less than 0.5 μm and a purity of at least 99.99% and a powder of oxide of metals selected from the metals belonging to IIIA and IVA groups of the Periodic Table excluding Ti;
• burning the unfired ceramic body to form a primary sintered product having a density of from 3.77 to 3.91 g/cm3;
• and
• applying a hot isostatic pressure to the primary sintered product so as to form a secondary sintered product having a density of at least 3.98 g/cm3 and having a mean facet length of less than 700 nm, the mean facet length being defined as an average of lengths of sides forming polygons that appear in cross sections of the crystal particles constituting the ceramic.