Method of producing a tubular body of polycrystalline alumina

Claim 1

A method of producing a tubular body of sintered polycrystalline alumina consisting essentially of relatively uniform size equiaxed grains of alumina which contains no more than about 150 ppm magnesium and essentially no secondary phase or pores, said alumina body exhibiting improved in-line transmission, which comprises (a) preparing a mixture of high purity alumina powder having relatively uniform surface area and particle size distribution with a small but effective amount up to 0.1 weight percent finely divided magnesia and a binder, (b) extruding the mixture to form a green tubular body having a density of at least 30 percent of theoretical density for a single crystal of alumina, (c) presintering the green tubular body in an oxygen containing atmosphere at a temperature from about 950° C. to about 1200° C. for a sufficient time period to remove said binder, and (d) sintering the presintered tubular body at about 1700°-1950° C. in an environment selected from the group consisting of vacuum and hydrogen for a sufficient time period to produce a sintered body of polycrystalline alumina consisting essentially of relatively uniform size equiaxed grains of alumina which contains no more than about 150 ppm magnesium and essentially no secondary phase and pores, said body exhibiting improved optical transmission characterized by especially improved in-line transmission.

Claim 2

A method of producing a tubular body of sintered polycrystalline alumina consisting essentially of relatively uniform size equiaxed grains of alumina which contains no more than about 150 ppm magnesium and essentially no secondary phase or pores, said alumina body exhibiting improved in-line transmission, which comprises (a) preparing a mixture of high purity alumina powder having relatively uniform surface area and particle size distribution with a small but effective amount up to 0.1 weight percent finely divided magnesia and a binder, (b) extruding the mixture to form a green tubular body having a density of at least 30 percent of theoretical density for a single crystal of alumina, (c) presintering the green tubular body in an oxygen containing atmosphere at a temperature from about 950° C. to about 1200° C. for a sufficient time period to remove said binder, and (d) sintering the presintered tubular body at about 1700°-1950° C. in an environment selected from the group consisting of vacuum and hydrogen for a sufficient time period to produce a sintered body of polycrystalline alumina consisting essentially of relatively uniform size equiaxed grains of alumina which contains no more than about 150 ppm magnesium and essentially no secondary phase and pores, said body exhibiting improved optical transmission characterized by especially improved in-line transmission.