The effect of tungsten additive on the surface characteristics of amorphous Ni-P alloy

The variation of surface compositions on amorphous Ni80.4W1.5P18.1 alloy by O-2 oxidation and H-2 reduction treatments have been studied by XPS, UPS a nd ISS. It shows that addition of tungsten in the amorphous Ni-P alloy lead s to dramatic changes of the relating component distributions in the surfac e layers before and after these treatments. Oxidation of a Ni80.4W1.5P18.1 amorphous alloy in 1 bar of oxygen at 513 K caused a significant segregatio n of nickel in different oxide states at the surface. The subsequent reduct ion of the oxidized surface with I bar hydrogen at 553 K resulted in only a small portion of Ni and P being reduced into elemental states, while most of them was found to combine to form a kind of nickel phosphate compound. O n the other hand, under the same conditions, the oxidation and reduction of a Ni80P20 alloy gave rise to metallic Ni and elemental P as the predominat e species on the alloy surface. The addition of W in the amorphous alloy mi ght act as nuclei for a favorable formation of the phosphate structure whic h was proposed to be an active species for hydrogen-relating catalytic reac tions. (C) 1999 Elsevier Science B.V. All rights reserved.