Method for the preparation of rare earth phosphate of low overst

Details Method for the preparation of rare earth phosphate of low overst Method for the preparation of rare earth phosphate of low overst

1997-07-07

1999-09-14

Langel, Wayne

Chemistry of inorganic compounds

Rare earth compound

2523014P, C01F 1700

Patent

active

059519584

ABSTRACT:
While a rare earth phosphate prepared by a conventional precipitation method by mixing an aqueous phosphoric acid solution and an aqueous solution of a rare earth salt usually contains an overstoichiometric amount of phosphorus, which is detrimental against luminescent phosphors prepared from the rare earth phosphate, the invention provides a method for the preparation of a rare earth phosphate of a greatly decreased overstoichiometric phosphorus content. The inventive method comprises adding, to either one of the aqueous phosphoric acid solution and the aqueous solution of a rare earth salt, a small amount of oxalic acid or a water-soluble oxalate such as ammonium oxalate so as to effect coprecipitation of a rare earth oxalate with the rare earth phosphate followed by calcination of the oxalate-containing phosphate so as to convert the excess of phosphorus into the phosphate by the reaction with the rare earth oxide formed from the rare earth oxalate by calcination.

REFERENCES:
patent: 5518703 (1996-05-01), Dissaux et al.
patent: 5562889 (1996-10-01), Collin et al.
Derwent Publications Ltd., Class L03, AN 77-01612Y, XP002043927 & SU 513,068 (Bredenfeld NV) May 21, 1976.
Patent Abstracts of Japan, vol. 009, No. 247, Oct. 3, 1985 & JP 60-103,008 A (Daiichi Kigenso Kagaku Kogyo KK), Jun. 7, 1985.
Derwent Publications Ltd., Class L03, AN 95-220929, XP002043959 & JP 07-133,485A (Toshiba Denshi Eng KK), May 23, 1995.

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