Ishihara Sangyo Kaisha, Ltd.

Masatoshi Amano

Ichiro Honma

Arata Koyama

Kazuo Nakata

Nobusuke Takumi

Masaharu Hirai

Tsuneo Ishikawa

Kokichi Miyazawa

A cobalt-containing magnetic iron oxide powder is provided by first coating a magnetic iron oxide base powder with a ferrous compound and then coating it with a cobalt compound. The cobalt-containing magnetic iron oxide powder provided is improved in stability of coercivity under aging and various other magnetic properties, and the magnetic tape produced by using the powder is also appreciably improved in stability of coercivity under aging as well as in various magnetic properties such as squareness, orientability and switching field distribution.

Process for producing cobalt-containing magnetic iron oxide powder

An aqueous slurry of a magnetic iron oxide powder is mixed with a suspension prepared by neutralizing an aqueous ferrous salt solution with an alkali to form ferrous hydroxide and then adding an aqueous cobalt salt solution thereto, and the excess OH concentration of the mixed slurry is adjusted to 0.05 to 3 mol/l, thereby obtaining a cobalt-and ferrous iron-containing ferromagnetic iron oxide. The cobalt-and ferrous iron-containing ferromagnetic iron oxide is excellent in coercivity, distribution of coercivity and other magnetic properties, and the magnetic tape produced by using such iron oxide is also excellent in coercivity and switching field distribution.

Process for producing cobalt-and ferrous iron-containing ferromagnetic

A phosphorus-containing magnetic iron oxide powder is subjected to the activation with an aqueous alkaline medium under pressure and then coated with a cobalt compound or a cobalt compound and other metallic compound(s) to produce a cobalt-containing magnetic iron oxide powder. The magnetic iron oxide powder obtained according to this process finds its best application to the production of magnetic recording media.

A process which comprises coating a cobalt compound or a combination of a cobalt compound and a ferrous compound on the surface of magnetic iron oxide particles and then heating the coated particles in the presence of water vapor. The cobalt containing ferromagnetic iron oxide produced by this process is excellent in coercivity and thermal stability. Further, magnetic tape produced from this iron oxide has a high coercivity and is excellent in squareness, orientability and remanent induction.

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Moriyama, Japan

Masatoshi Amano