Surface characterizations of ultrafine Ni particles

Ultrafine Ni particles have been obtained by evaporating pure Ni in methane gas atmosphere of 100 Torr, and in a mixture of H-2 and Ar of 760 Torr, respectively. The distinct characterization of the layers on two kinds of Ni particle surfaces were investigated by X-ray photoelectron spectroscopy (XPS) and oxygen determination. The morphology and mean particle size were determined by transmission electron spectroscopy (TEM) and subsequent image analysis. The structure of ultrafine Ni particles were identified by X-ray diffraction (XRD). The effect of oxide and carbon layers on magnetization of the particles were studied by vibrating sample magnetometer (VSM). It was observed that a carbon-rich and an oxide of Ni2O3 layers were formed on the surface of Ni particles obtained in methane gas, and in a mixture of H-2 and A(r) gas atmosphere, respectively, it was shown that the methane gas makes resistance to oxidization during evaporating Ni in this gas atmosphere and no nickel carbides or Ni-C solid solution formed. (C) 1998 Acta Metallurgica Inc.