MAGNETIC IRON OXIDE GRAIN POWDER AND ITS PRODUCTION

摘要

PURPOSE:To industrially provide magnetically and chemically stable grain powder of black color having high coercive force. CONSTITUTION:The objective grain powder having Fe3O4 grains as nuclear crystal grains and consisting of such spinel-type multiple grains that CoFe2O4 are being in crystal growth on the surface of the nuclear crystal grains. The grain powder can be obtained by the following method: (A) an alkaline dispersion of pH>=10 with Fe3O4 grains dispersed therein is incorporated with (B) a mixed solution containing Co<2+> and Fe<2+> at the molar ratio Fe<2+>/Co<2+> of 2 to 3 or a suspension containing Co<2+> hydroxide and Fe<2+> hydroxide so that the total concentration for the Co<2+> and Fe<2+> in the alkaline dispersion fall within the range from 0.005M to 0.5M, while aerating an oxygen-contg. gas in said alkaline dispersion at a temperature within the range of 50 deg.C to the boiling point.