| 摘要 |
PURPOSE:To obtain a powder of acicular magnetite particles having high coercive force by depositing a spinel ferrite layer containing Co as a lower layer and a spinel ferrite layer containing Co and Mg as an upper layer on the surface of the particle. CONSTITUTION:A dispersion liquid of an acicular magnetite powder containing about 20-24wt.% Fe<2+> in water by about 20-1000-g/l density is added and mixed with an aq. alkali hydroxide such as NaOH and a Co salt soln. such as CoCl2 containing about <15wt.% Co calculated to the magnetite to prepare a suspension liquid. This suspension liquid is heated and stirred to cause the reaction to deposit Co on the surface of the acicular magnetite particles. In the process of this reaction, Mg salt soln. such as MgCl2 containing 0.27-4.5wt.% Mg calculated to the magnetite is added and the reaction is made to proceed. By this reaction, a spinel ferrite coating layer containing Co as a lower layer and a spinel ferrite coating layer containing Co and Mg as an upper layer are formed on the surface of the magnetite particles. Thus, the acicular Co-coated magnetite powder which is black and has high coercive force is obtd. |
