PREPARATION, OXIDATION AND MAGNETIC-PROPERTIES OF FE-CR ULTRAFINE POWDERS BY HYDROGEN PLASMA-METAL REACTION

Four kinds of Fe-Cr ultrafine particle (UFP) samples were synthesized by a hydrogen plasma-metal reaction method. The UFP samples were exami ned by X-ray diffraction, electron transmission microscopy and chemica l analysis and specific surface area analysis. The oxidation and magne tic properties of as prepared UFP samples were investigated. The cryst al structure of Fe-Cr UFP samples is the same as that of the master bu lk samples, but the Cr content in Fe-Cr UFP samples is richer than tha t in bulk samples. The characteristics of Fe-Cr UFP samples such as pa rticle shape, mean particle size and specific surface area show strong dependence on the Cr content. Oxidation for the Fe-Cr UFP occurs easi ly at a temperature even lower than 473 K and the oxided Fe-Cr UFP sam ples change from a acicular shape into angular shape with increasing C r content. Although the saturation magnetization of the UFP samples is smaller than that of the corresponding bulk samples, the difference i n saturation magnetization between the two kinds of samples becomes sm all as the Cr content increases.