MANUFACTURE OF NEEDLE IRON FINE PARTICLE FOR MAGNETIC RECORDING

摘要

PURPOSE:To obtain the magnetic metal fine particles which is extraminute magnetic metal fine particles and in which secondary aggregates are extremely diminished and is capable of easy compounding of the highly dispersible mag netic coating compositions by milling the surface denaturated iron oxyhydroxide or iron oxide till 90% or over of secondary aggregates of which pass the screen of 100 mesh particle degree followed by gas-phase catalytic reduction to make them ferromagnetic iron fine particles. CONSTITUTION:A specific surface area 20-150m2/gr. of alpha-iron oxyhydroxide or alpha-iron oxyhydroxide in which at least one element selected out of Al. Ti, Cr, Mn, Co, Ni, Zn and etc. coprecipitates is coated with at least one element selected out of B, Al, Si, P, Ti, Zn, Cr, Mn, Co, Ni, Cu, Zr, Sn, Pb, Ca, Ba and etc. Then the dried surface denaturated alpha-iron oxyhydroxide is milled to compound the powder 90% of secondary aggregate of which pass the screen of 100 mesh, more preferably, 200 mesh particle degree. If necessary, calcination at 300-800 deg.C is done to make the powder the surface denaturated alpha-iron oxide, after which that is subjected to the gas-phase catalytic reduction at 300-500 deg.C by use of a reducing gas consisting of hydrogen gas.