Patent ID: 8501081

Claim:
A method for manufacturing a transparent polycrystalline alumina article comprising: providing a powder of substantially alpha phase alumina; dispersing the powder in a liquid to form a slurry comprising powdered solids and liquid; adding one or more sintering aids; removing excess of the liquid to form a green body; heating the green body at a temperature of at least about 600° C. for at least about 1 hour to provide a prefired body; sintering the prefired body at a temperature of from about 1275 to about 1300° C. in a dry hydrogen-containing gas atmosphere for a time that is sufficient to provide a sintered body having a density greater than about 95.5% of theoretical density; hot isostatically pressing the sintered body at a pressure of at least about 103 MPa (15,000 psi) gas pressure at a temperature of at least about 1225° C. to accomplish a density greater than about 99.90% of theoretical density; and annealing the hot isostatically pressed body in a flowing dry inert gas at about 1100° C. for a time calculated using a diffusion rate of about 6×10 −8 cm 2 /second such that the resultant transparent polycrystalline alumina article has substantially no OH − absorption band when exposed to light at wavelengths from between about 2000 nm and about 5000 nm.