Mitsui Minings & Melting Co., Ltd.

Tadashi Yamanishi

Masachika Hashiuchi

Katsuhiko Yoshimaru

Takeshi Miyazono

Akira Oyama

Hiroyuki Watanabe

The present invention provides magnetite particles having a particle shape of an octahedron, a specific surface area of 5 m.sup.2 /g or more as determined by the BET method and. a coercive force of 40 to 100 Oe, or a particle shape of a hexahedron, a specific surface area of 6 m.sup.2 /g or more as determined by the BET method and a coercive force of 40 to 80 Oe, and a process for production of magnetite particles

Magnetite particles and process for production of the same

There are provided magnetite particles characterized in that they have surfaces each covered with a thin film or iron-zinc oxides or further covered thereon with a thin film of iron-silicon oxides and have a saturation magnetization of at least 79 emu/g, a degree of blackness (L) of at most 19.5 as measured with a differential colorimeter, and an absorption of at least 30 ml/100 g as measured according to JIS K 5101. There is also provided a process for preparing magnetite particles as described above.

Magnetite particles and process for preparing the same

This invention provides magnetite particles containing a silicon component inside and also a silicon component exposed on the surface of each particle, which are improved in the properties of electrical resistance, remanent magnetization, and fluidity in a well-balanced way and suited for use principally as powdery material for magnetic toner for electrostatic copying and as black pigment powder for coating materials; and also relates to a process for producing the particles.

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Tamano, Japan

Tadashi Yamanishi