| 摘要 |
PURPOSE:To obtain the titled powder having high coercive force with a very small amount of Co or Co and Fe (II) by adding Co to needlelike magnetite or maghemite particles after introducing Mg into the particles. CONSTITUTION:An aqueous ferrous salt soln. is reacted with an aqueous alkali sonl. to prepare a suspension of >=11pH contg. Fe(OH)2, and by blowing a gas contg. O2 into the suspension, needlelike alpha-FeOOH particles are formed by oxidation. Prior to the oxidation, to the suspension is added a water soluble Mg salt by 0.5-0.7 atomic% as Mg to the total amount of Fe. Thus, needlelike alpha-FeOOH particles having 0.3-2.0mum average major axis and 20:>=1 average ratio of major axis; minor axis and contg. Mg by 0.5-0.7 atomic% to the total amount of Fe are formed. The particles are washed, separated by filtration, dried, and heat reduced. The resulting needlelike magnetite particles contg. Mg or needlelike maghemite particles obtd. by oxidizing the magnetite particles are modified with Co or Co and Fe (II). |
