Mitsui Minings & Melting Co., Ltd.

Hiroyuki Watanabe

Masachika Hashiuchi

Takeshi Miyazono

Tadashi Yamanishi

Magnetite particles containing a silicon component inside, and having the silicon component exposed on the surface in a proportion of 0.05 to 2.0% by weight as silicon which have improved moisture resistance as indicated by moisture content of magnetite (% by weight), measured under high-temperature, high-humidity conditions (200.degree. C., Karl Fischer technique), and given by the equation (1)

Magnetite particles and process for production thereof

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.

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Tamano, Japan

Hiroyuki Watanabe