| 摘要 |
PURPOSE:To obtain the titled powder having uniform particle size and free from resinous particles by adding water soluble silicate to an aqueous soln. prepared by reacting an aqueous ferrous salt soln. and an aqueous soln. of water soluble Co salt, oxidizing the silicate-added soln., and heat treating the resulting particles. CONSTITUTION:An aqueous ferrous salt soln. and an aqueous soln. of water soluble Co salt are reacted with an aqueous alkali soln. to prepare a mixed aqueous soln. of >=12pH contg. Fe(OH)2 and Co(OH)2, and to this soln. is added water soluble silicate by 0.1-1.1 atomic% as Si to the total amount of the metals in the soln. This mixed soln. is oxidized by blowing oxygen-contg. gas to form Co-contg. needle crystal goethite particles. The particles are then separated by filtration, washed, dried, heat dehydrated, heat calcined under an atmosphere of heated steam and nonreducing gas, and heat reduced to obtain needle crystal magnetite particles, which may further be oxidized to give needle crystal maghemite particles. |
