Yttrium oxide ceramic body

Claim 1

A process for producing a sintered yttrium oxide body which is at least optically translucent having an in-line spectral transmission greater than 1% taken at a wavelength of 590 nanometers on a thickness of 0.85 millimeter of said sintered body and having an average grain size ranging from about 5 microns to about 50 microns which consists essentially of producing an yttrium oxide powder having an average particle size of less than about 5 microns and being free of particles greater than about 5 microns and having a specific surface area ranging from about 4 square meters per gram to about 25 square meters per gram, forming said powder into a compact having a density of at least about 45% of the density for yttrium oxide, firing said compact at a temperature ranging from about 1625° C. to about 1900° C. for a time sufficient to produce said sintered body, and reducing the firing temperature at a rate which has no significant deleterious effect on said sintered body, said firing being carried out in an atomosphere of hydrogen, said hydrogen atmosphere containing at least a sufficient partial pressure of oxygen at least after said compact becomes a closed pore body to produce said optically translucent sintered body, said yttrium oxide powder being produced by providing an aqueous yttrium nitrate solution of at least about 0.1 mole of yttrium per liter of solution, providing an aqueous oxalic acid solution having a concentration of at least about 10% excess of that required for complete reaction with said yttrium nitrate, admixing said solutions thereby precipitating yttrium oxalate hydrate, recovering said yttrium oxalate hydrate precipitate, washing said yttrium oxalate hydrate precipitate with water to substantially neutralize it, drying said yttrium oxalate hydrate precipitate to remove adsorbed water, comminuting the resulting yttrium oxalate hydrate powder in air at ambient temperature to produce a powder wherein the average agglomerate size is less than about 20 microns and which is free of agglomerates having a size greater than 20 microns, and thermally decomposing said yttrium oxalate hydrate at a temperature ranging from about 650° C. to about 1000° C. in air at ambient pressure to produce said yttrium oxide powder, said yttrium oxalate hydrate powder being comminuted sufficiently to produce on said thermal decomposition said yttrium oxide powder.