Ishihara Sangyo Kaisha, Ltd.

Arata Koyama

Ichiro Honma

Masatoshi Amano

Kazuo Nakata

Nobusuke Takumi

Tsuneo Ishikawa

Shigeru Takatori

Tokuo Suita

Masaharu Hirai

Kokichi Miyazawa

Makoto Ogasawara

Kiyoshi Asano

Kouichi Tamura

Cobalt-containing magnetic iron oxide particles extremely suitable for magnetic recording mediums, especially for image recording mediums and a process for producing the same from the precursor, .gamma.-FeOOH which is advantageous in industry are disclosed. Cobalt-containing magnetic iron oxide particles satisfying the following equations (1), (2) and (3):

Cobalt-containing magnetic iron oxide and process for producing the same

A process for producing magnetic ion oxide particles for magnetic rcording which comprises heat-treating a magnetic iron oxide particles of magnetite, berthollide or maghemite as a starting materials, in the presence of a zinc component or both a zinc component and a silicon component at a temperature of 400.degree. to 700.degree. C. in a specific atmosphere, and if necessary, subjecting the heat-treated particles to wet treatment and/or dry treatment, thereby doping the particles with zinc ions resulting in magnetic iron oxide particles having an improved saturation magnetization, a proportion of said zinc ions being 2 to 9 at. % by weight relative to the total amount of iron ions.

Process for producing magnetic iron oxide particles for magnetic

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.

Process for producing cobalt-containing magnetic iron oxide powder

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.

Growing community of inventors

Moriyama, Japan

Arata Koyama