Evidence of Chemical Passivity in Amorphous Ni-20P Alloy

摘要

Anodic polarization experiments in H sub 2 SO sub 4 and HCl electrolytes show that amorphous Ni-20P alloy passivates at potentials around O V (SCE) and dissolves transpassively above 0.2 V(SCE). In 0.2N HCl, in which crystalline Ni pits readily, Ni-20P resists pitting and passivates as effectively as in 0.2N H sub 2 SO sub 4 . Analysis by x-ray photoelectron spectroscopy of Ni-20P surfaces after polarization indicates the presence of hypophosphite ions and the absence of oxidized nickel species. Thus, Ni-20P alloy does not passivate by development of a three-dimensional oxide film, such as the NiO film that forms on nickel. A chemical passivation process is proposed that is controlled by the formation and surface retention of hypophosphite anion. (ERA citation 11:051286)