Fabrication of spherical magnetite particles by the flame fusion method

Abstract

Fabrication of spherical magnetite powders was investigated in the propane-oxygen flame using sponge iron powders as a starting powder. Spherical particles produced by fusion, sphering and oxidation of iron powder were composed of residual Fe, FeO, Fe₃O₄ and α-Fe₂O₃ in the case of particles collected by a cyclone. The amount of Fe₃O₄ in the products was strongly dependent on the propane/oxygen ration and the flow rate of carrier air, but weakly on the feed rate of iron powder. Injection of quenching gas was found to be effective to improve the yield of Fe₃O₄. Particle size of products reflected directly that of starting powders, indicating fairly easy control of particle size of products. The saturation magnetization of the produced powder under the optimum condition was 88 emu/g. These facts suggest that the fusion and oxidation treatment of iron powders in the propane-oxygen flame is a suitable process for the manufacture of the magnetic carrier for plain paper copy (PPC) on an industrial scale. Powders collected by a bag filter were found to be fine γ-Fe₂O₃ particles with a diameter of about 100 nm.