| 摘要 |
PURPOSE:To increase the coverage of ferrite particles on core particles by specifying the particle-size ratio between the core particles and ferrite particles. CONSTITUTION:Ferrite particles having particle sizes of 4-50nm which are very smaller than that of core particle, that is, 1/8 to 1/80 of the particle sizes of core particles are used. The core particles are scattered in water or an aqueous solution which is adjusted to 6-11 in pH and the aqueous solution of ferrous ions and aqueous solution of an oxidizing agent are added to the water or aqueous solution so that the relation between the pH and oxidation-reduction potential can be maintained within ranges of A(6, -440 mV), B(6, -130 mV), C(11, 430mV), and D(11, -740mV). In addition, the ratio of feeding speeds between the aqueous solutions of the oxidizing agent and ferrous ions is set at 1X10<-3> to 15X10<-3>. As a result, particles coated with the ferrite particles are obtained. |
