SURFACE CHARACTERIZATIONS OF ULTRAFINE NI PARTICLES

Ultrafine Ni particles have been obtained by evaporating pure Ni in me thane gas atmosphere of 100 Torr, and in a mixture of H-2 and Ar of 76 0 Torr, respectively. The distinct characterization of the layers on t wo kinds of Ni particle surfaces were investigated by X-ray photoelect ron spectroscopy (XPS) and oxygen determination. The morphology and me an particle size were determined by transmission electron spectroscopy (TEM) and subsequent image analysis. The structure of ultrafine Ni pa rticles were identified by X-ray diffraction (XRD). The effect of oxid e and carbon layers on magnetization of the particles were studied by vibrating sample magnetometer (VSM). It was observed that a carbon-ric h and an oxide of Ni2O3 layers were formed on the surface of Ni partic les obtained in methane gas, and in a mixture of H-2 and A(r) gas atmo sphere, respectively, it was shown that the methane gas makes resistan ce to oxidization during evaporating Ni in this gas atmosphere and no nickel carbides or Ni-C solid solution formed. (C) 1998 Acta Metallurg ica Inc.