Toyo Denka Kogyo Co., Ltd.

Isao Matsushita

Kazumichi Yanagisawa

This invention provides a method for producing calcite-type calcium carbonate single crystal available for optical elements, which can be carried out under relatively low temperature and low pressure conditions. The crystal growth process which comprises; a first step of filling a sealed pressure container of an autoclave with solvent and calcium carbonate as a raw material for growth, a second step of dissolving the starting rate in the solvent under predetermined conditions of pressure and temperature, a third step of crystallizing the calcium carbonate on a seed crystal suspended in the upper portion of the pressure container, on account of the difference of solubility caused by temperature gradient in the container; the method is characterized by that the aqueous solution of ammonium salt of mono-carboxylic acid is used as the solvent. The ammonium salt of mono-carboxylic acid is selected from the ammonium salts of carboxylic acid of whose alkyl group has 1 to 6 carbons, such as ammonium salts of acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid (equal to caproic acid), and heputanic acid (equal to enantic acid).

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Kochi, Japan

Isao Matsushita