Mitsui Minings & Melting Co., Ltd.

Takeshi Miyazono

Masachika Hashiuchi

Masahiro Miwa

Hiroyuki Watanabe

Tadashi Yamanishi

Magnetite particles continuously contain a total amount of 0.2 to 1.2 wt. %, based on magnetite, of a silicon component and an aluminum component expressed as silicon and aluminum, in a region ranging from the center to the surface of the particle, a total amount of 0.01 to 0.5 wt. % of the silicon component and the aluminum component, expressed as silicon and aluminum, being exposed on the surface of the particle, and an outer shell of the particle being coated with a metal compound comprising at least one metal component bound to the silicon component and the aluminum component, the metal component being selected from the group consisting of Zn, Mn, Cu, Ni, Co, Cr, Cd, Zr, Sn, Mg, Ti, Ce, W and Mo and a process for their preparation.

Magnetite particles and process for production thereof

Magnetite particles continuously containing 0.2 to 1.0 wt. %, based on magnetite, of a silicon component expressed as silicon, in a region ranging from the center to the surface of the particle; 0.01 to 0.3 wt. % of the silicon component being exposed on the surface of the particle; and an outer shell of the particle being coated with a metal compound comprising at least one metal component bound to the silicon component, the metal component being selected from the group consisting of Zn, Mn, Cu, Ni, Co, Cr, Cd, Al, Sn, Mg, Ti and Ce, and a process for preparing the particles.

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)

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

Takeshi Miyazono