Sakai Chemical Industry Co., Ltd.

Tutomu Hatanaka

Shigefumi Kamisaka

Susumu Iwasaki

Iwao Yamazaki

Yoshihiko Nakane

A process for producing microcrystalline barium ferrite platelets which comprises: forming an aqueous alkaline dispersion containing coprecipitates of hydroxides of barium ions, iron (III) ions, and optionally ions of a substituent element; heating the dispersion to a temperature of not less than 50.degree. C. and not more than the boiling point of the dispersion under an atmospheric pressure to convert the coprecipitates to precursors of the barium ferrite; calcining the precursors to provide microcrystalline barium ferrite platelets; the improvement comprising the step of adding a carbonating agent such as sodium carbonate to the aqueous alkaline dispersion before or after the heating of the aqueous dispersion to insolubilize water soluble barium ions therein, and the step of calcining the barium ferrite precursors in the presnece of sodium sulfate at temperatures of 700.degree.-900.degree. C., to provide microcrystalline barium ferrite platelets of about 0.03-0.1 .mu.m in average particle size and 2-5 in planarity ratio.

Process for producing microcrystalline barium ferrite platelets

A process of producing a spinel structure Ni/Zn ferrite-modified, Co/Ti-substituted microcrystalline barium ferrite platelets having an average particle size of 0.03-0.15 .mu.m, a temperature coefficient of coercive force of not more than +1 Oe/.degree. C., including small absolute values in negative region, and a saturated magnetization of not less than 56 emu/g, which comprises: forming substantially amorphous preecursors of Co/Ti-substituted barium ferrites; adding an aqueous solution of nickel salts to the dispersion of the precursors of Co/Ti-substituted barium ferrites, and subjecting the slurry to hydrothermal reaction, thereby to provide precursors of spinel structure nickel ferrite-modified, Co/Ti-substituted barium ferrites; depositing a water insoluble zinc compound on the precursors; and calcining the precursors in the presence of barium chloride, washing the calcined products to remove therefrom the barium chloride, and drying.

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Osaka, Japan

Tutomu Hatanaka