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AssigneeGeneral Electric Company
InventorsCurtis E. Scott, Jack M. Strok, Lionel M. Levinson
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A solid state seed crystal process for bulk conversion of a polycrystalline ceramic body to a single crystal body (of the same chemical composition) having the same crystal orientation as the seed crystal. The process comprises heating said body to form a monolithic join between the body and the seed crystal, heating the joined structure to reduce grain growth inhibitors and further heating the joined structure above the minimum temperature required for crystallite growth of the crystalline material, but not hot enough to melt and distort the original shape of the polycrystalline ceramic body during its conversion to a single crystal. This process has been used to convert polycrystalline alumina (PCA) bodies to sapphire having the same crystal orientation as the seed crystal by heating the PCA body, monolithically joined to a sapphire seed crystal, at a temperature above 1700.degree. C. without melting the body.
A solid state process for bulk conversion of a solid PCA body, having a density of at least 3.9 g/cc, to sapphire which comprises monolithically joining said solid PCA body to a solid sapphire seed crystal and heating said PCA body and said seed crystal at a temperature above the minimum temperature for alumina crystal grain boundary mobility, but without melting said PCA body, for a time sufficient to convert said PCA body to a sapphire body.
A solid state process for bulk conversion of a PCA body to a sapphire which comprises:
A solid state process for bulk conversion of a PCA body to sapphire wherein said PCA body comprises alpha alumina having less than 100 wppm magnesia and having a relatively uniform grain size below 70 microns, said process comprising joining said PCA body with a sapphire seed crystal and heating the joined structure at a temperature above 1100.degree. C. for a time sufficient to convert said PCA body to a sapphire body but without causing said PCA body to melt.
Dependencies are inferred from the claim text.