Toda Kogyo Corporation

Atushi Takedoi

Nanao Horiishi

Goro Matsui

Koji Toda

Hiroshi Sumita

Akira Mukaizaka

Hiroyuki Kondo

Shigeki Shimizu

Stabilization treatment of acicular ferromagnetic iron or iron-alloy fine particles against the oxidation thereof comprises the steps of (a) suspending acicular ferromagnetic iron or iron-alloy particles obtained by the reduction of acicular iron oxide which may contain Co or Ni in an aqueous alkaline solution having 0.01 to 18-N of hydroxyl ion concentration at a temperature of 5.degree. to 70.degree. C. while stirring the suspension in a non-oxidative atmosphere therethrough and thereby controlling the dissolution of ferrous ion from the surface of the acicular particles therein, (b) oxidizing the surface of the acicular particles in the resultant suspension by introducing an oxygen containing gas therein at a temperature of 60.degree. to 100.degree. C. to form dense and thin magnetite film on the surface of the acicular particles; and (c) drying the resultant particles in air at a temperature below 100.degree. C.

Stabilization treatment of acicular ferromagnetic iron or iron-alloy

A process for treating acicular magnetite containing Co to stabilize the magnetic properties thereof comprises the steps of heating acicular magnetite containing 0.1 to 2.5% by atom of Co with respect to Fe as starting material at a temperature in the range of 300 - 1000.degree. C in an inert gas atmosphere in which the partial pressure of oxygen is controlled at a value in the range of 0.001 - 1% by weight and for the time sufficient to homogenize the crystal structure of the acicular magnetite by thermal-diffusion of oxygen thereinto, and thereafter saturating the resultant acicular magnetite with oxygen by heating it at a temperature in the range of 40 - 100.degree. C in an oxygen rich atmosphere such as air.

Process for treating acicular magnetite containing Co to stabilize the

The process for producing acicular magnetic metallic particle powder with improved magnetic properties which include the characteristic steps for producing the acicular particles of metal oxide with homogeneous and dense coats of crystalline silica and to thereby protect the particles from heat-damages during the reduction thereof under high temperatures.

Process for producing acicular magnetic metallic particle powder

The present invention relates to a process for producing magnetic particle powder of acicular ferric oxide used for a magnetic recording material comprising (A) reducing acicular goethite particle powder to obtain acicular magnetite particle powder, (B) heating said acicular magnetite particle powder and thereby making the partial pressure of oxygen in said acicular magnetite particle powder reach the equilibrium value and (C) oxidizing said acicular magnetite particle powder to obtain gamma-hematite (maghemite) particle powder, and magnetic particle powder produced thereby.

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Hiroshima, Japan

Atushi Takedoi