No abstract

Abstrac't-Fe-Co f i n e p a r t i c l e s w i t h high CO content were prepared by reducing CO-substituted iron oxide particles. The saturation iagnetization o f the p a r t i c l e s increased w i t h CO concentration. The saturation magnetization was 153.8 emu/g w i t h 15.0 w t l CO content compared t o 133.0 emu/g f o r i r o n p a r t i c l e s with the same surface area. The Fe-Co p a r t i c l e s showed superior corrosion resistance compared t o iron particles. A CO-ferrite layer formed on the surface o f the p a r t i c l e s helped minivize the progress o f the oxidation.

Acicular γ-Fe2O3 particles were heated at 90°C in alkali solution containing Co2+ and Fe2+. The coercivity of the resultant particles remarkably increased with the increasing Co2+/Fe2+ ratio, and in the neighborhood of the Co2+/Fe2+ ratio of 0.4, reached a maximum value. When the particles with a Co2+/Fe2+ ratio of 0.5 were dissolved in hydrochloric acid, the cobalt content and the coercivity were rapidly decreased with increasing dissolved weight. Iron-cobalt ferrite was expected to grow on the surface of γ-Fe2O3 particles. The increase of coercivity was attributed to the iron-cobalt ferrite.

Acicular iron particles with high coercivity and high saturation magnetization were prepared by reduction of the hematite particles which were obtained by dehydration of the silica-coated goethite particles in the process of heat treatment in air. Variations in specific surface area, micropore distribution, crystallite size, and magnetic properties with the dehydration temperature were measured. For the iron particles prepared by reduction of the silica-coated hematite particles obtained by dehydration at 800 °C, a maximum coercivity of 1250 Oe was obtained, and the crystallite size reached the minimum value of 220 Å which was close to the critical value of single domain particle. The highly acicular iron particles consisting of the closely packed small crystallites were obtained.

No abstract