To obtain highly packable metallic magnetic powder small in particle size, having high coercive force, highly saturated magnetization and narrow flux-reverse magnetic field distribution, high in oxidation resistance, free from any mutual agglomeration or fusing of the particles, and good in dispersibility, to obtain hydrous iron oxide to be used for producing the above metallic magnetic powder, and to obtain a magnetic recording medium using the metallic magnetic powder.
This hydrous iron oxide is obtained by mixing an aqueous solution of a ferrous salt with an aqueous solution of an alkali carbonate to form an alkaline suspension of terrous-contg. precipitate which is then aerated with an oxygen-contg. gas to form a hydrous iron oxide slurry followed by adjusting the slurry to ≤pH 6 to effect dispersion of the hydrous iron oxide. The second objective metallic magnetic powder is obtained by forming an oxide or hydroxide film on the surface of the hydrous iron oxide followed by washing the resultant hydrous iron oxide with water and then forming a carbon compound film thereon followed by dehydrating the hydrous iron oxide under heating in an inert gas atmosphere, carrying out a reduction with a reducing gas followed by oxidation with an oxygen-contg. gas. The third objective magnetic recording medium is obtained by coating a substrate with the metallic magnetic powder and a resin binder.
HASHIMOTO RYOICHI
SUZUKI KENICHI
FUJII SHIGEO
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