Method of purifying alkaline-earth and alkali-earth halides...

Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Havin growth from molten state

Reexamination Certificate

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C117S082000, C117S083000, C117S940000

Reexamination Certificate

active

10977523

ABSTRACT:
An improved technique that reduces the potential for trapped impurities and/or ensuring desired stoichiometry of a grown crystal. Improved contaminant removal is obtained by bubbling a scavenger gas, such as fluorine gas or hydrogen fluoride gas, through a melt of alkaline- or alkali-earth halides, to improve the purity of the melt by removing more volatile metal halides and oxygen contained within the melt. By reacting after the raw material has melted, any oxygen or metal impurities trapped in the raw material is free to react with the scavenger. A desired stoichiometry is achieved as the alkaline- or alkali-earth metals react with the halide in the scavenger gas. Decreasing the amount of impurities in the melt, and using a desired stoichiometeric melt, improves the radiation hardness and transmission properties of resulting ingot grown from the purified raw material. Additionally, this method may decrease the amount of time needed for outgassing. The method may also be used to form a high purity pre-melt, which in turn may be used to grow an ingot with higher purity.

REFERENCES:
patent: 2550173 (1951-04-01), Swinehart et al.
patent: 3935302 (1976-01-01), Pastor et al.
patent: 6238479 (2001-05-01), Oba
patent: 6773501 (2004-08-01), Kerdoncuff et al.
patent: 2003/0217688 (2003-11-01), Meyer-Fredholm et al.
Pastor, R.C. et al. “Crystal growth of alkaline earth fluorides in a reactive atmosphere.” Materials Research Bulletin USA. 10.6 (Jun. 1975): 493-500. XP002381050.
Written Opinion from International Patent Application No. PCT/US2005/037892.
R. C. Pastor et al., Crystal Growth of Alkaline Earth Fluorides in a Reactive Atmosphere PART II, Mat. Res. Bull., vol. 11, pp. 1037-1042, 1976. (XP 002381051).

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