Single crystal conversion process
A solid state method for converting polycrystalline alumina components to single crystal or sapphire. The single crystal conversion method includes sintering a pre-fired polycrystalline alumina component doped with a magnesia sintering aid in an atmosphere containing a gas mixture of hydrogen and an inert gas, such as nitrogen in one embodiment. A sintering temperature is selected that preferably depends on the percentage of hydrogen selected. The component is held at the sintering temperature for a time sufficient to convert the polycrystalline component into a component formed of a single crystal. In one embodiment, the sintering temperature may be between at least about 1600 DEG C. and less than 2050 DEG C., and the amount of hydrogen in the sintering atmosphere may be between about 4% to about 10%. The method forms a wetting type intergranular film associated with the nucleation and growth of a single abnormal grain in the polycrystalline alumina component.
DILLON SHEN J [US]; HARMER MARTIN P [US]
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