Dowa Mining Co., Ltd.

Takatoshi Fujino

Kenichi Inoue

Kazuyuki Matsumoto

Kimitaka Sato

Kozo Ogi

After a reducing agent is added to a water reaction system containing silver ions to deposit silver particles by reduction, the silver particles are dried to obtain a silver powder which is heat-treated at a temperature of higher than 100&#xb0; C. and lower than 400&#xb0; C. The silver powder thus heat-treated has a maximum coefficient of thermal expansion of not greater than 1.5% at a temperature of 50&#xb0; C. to 800&#xb0; C., and has no heating peak when the silver powder is heated from 50&#xb0; C. to 800&#xb0; C. The silver powder has an ignition loss of not greater than 1.0% when the silver powder is ignited until the weight of the silver powder is constant at 800&#xb0; C. The silver powder has a tap density of not less than 2 g/cmand a BET specific surface area of not greater than 5 m/g.

Silver powder and method for producing same

A ferromagnetic iron alloy powder for a magnetic recording medium is composed of acicular iron-base particles of an average major axis length (X) of not less than 20 nm and not greater than 80 nm and have oxygen content of not less than 15 wt % and coercive force (Hc) of not less than [0.0036 X&#x2212;1.1 X+110 X&#x2212;1390 (Oe)] (where X is average major axis length expressed in nm). The ferromagnetic iron alloy powder is obtained by reacting metal powder composed of acicular iron-base particles having an average major axis length of not less than 20 nm and not greater than 80 nm with pure water in substantial absence of oxygen to form a metal oxide film on the particle surfaces. Optionally, the particles can be reacted with a weak oxidizing gas by a wet or dry method.

Method of making ferromagnetic iron alloy powder for magnetic recording medium

A magnetic powder for magnetic recording is provided that has improved properties suitable for a magnetic recording medium used with a high-sensitivity read head utilizing an MR device. The magnetic powder is composed of iron-base acicular particles containing Co, Al, R (rare earth elements, including Y) and oxygen within the ranges of Co/Fe=10&#x2013;50 at. %, dissolved Al/(Fe+Co)=5&#x2013;50 at. %, R/(Fe+Co)=2&#x2013;25 at. % and oxygen=not greater than 25 wt %; and the acicular particles have an average major axis length of 25&#x2013;80 nm and a saturated magnetization &#x3c3;s of 10&#x2013;130 emu/g,

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Honjo, Japan

Takatoshi Fujino