The Preparation and Properties of Superfine Metal Particles

Superfine iron and iron alloy particles have been prepared by reduction from the parent oxide. The superfine iron particles were rather uniform and cubic in shape, with sides 500A. The coercivities of these particles depended on reduction temperature. In particular, too high a reduction temperature led to sintering of the particles with a loss in coercivity. This effect could be overcome by coating the oxide particle with sodium silicate prior to reduction.Coercivities as high as 1100 Oe were obtained 4 K. whereas room temperature coercivities peaked at 700-900 Oe. The coercivities of the coated iron particles were independent of packing fraction in a polymer matrix. The particles were found to be porous under certain reduction conditions. However, this porosity collapses if the reduction is run for long enough at a high enough temperature. The final particles were essentially single crystallites The kinetics of the reduction are complex and could not be adequately described by simple models. Rate constants estimated from the data were much lower than those reported in the literature. Keywords: Magnetic properties; Superfines; Superfine iron particles. (KT)