Sakai Chemical Industry Co., Ltd.

Hideji Yamamoto

Kiyoshi Fukai

Seiji Matsumoto

Mizuho Wada

Shinji Nakahara

Tadashi Koga

Yoshiki Fukatsu

Youichi Yamada

Tatsuya Hida

Disclosed herein is fine acicular .alpha.-ferric oxide which has the crystallite diameter (D.sub.1014) in the direction perpendicular to the (1014) plane and the crystallite diameter (D.sub.1120) in the direction perpendicular to the (1120) plane such that their ratio D.sub.1014 /D.sub.1120 is in the range of 1-2, and also has a specific surface area of 40-50 m.sup.2 g. Disclosed also herein is fine acicular .alpha.-ferric oxide which has the crystallite diameter (D.sub.1014) in the direction perpendicular to the (1014) plane and the crystallite diameter (D.sub.1120) in the direction perpendicular to the (1120) plane such that their ratio D.sub.1014 /D.sub.1120 is the range of 1-2, and also has an average aspect ratio of 10-15 and a specific surface area of 20-40 m.sup.2 /g. They are produced by wet process including the step of hydrothermal reaction.

Fine acicular .alpha.-ferric oxide and production thereof

A method of producing single crystalline, acicular .alpha.-ferric oxide particles of narrow particle size distribution is provided. The method comprises heating an aqueous suspension of ferric hydroxide at temperatures of 100.degree.-250.degree. C. at an alkaline pH in the presence both a water soluble organic or inorganic compound capable of forming complexes with iron as a growth regulating agent and .alpha.-ferric oxide seed crystals of minor axes not larger than 0.4 microns in average in amounts of 0.1-25 mole % in terms of the Fe content thereof in relation to the ferric hydroxide.

Method of producing single crystalline, acicular .alpha.-ferric oxide

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Hiroshima, Japan

Hideji Yamamoto