Corrosion of Glassy (Ni8Nb5)99.5Sb0.5 Alloy and Stability of Passive Film

The corrosion of glassy (Ni8Nb5)99.5Sb0.5 alloy was investigated in 1, 6 mol/L HCl, 1 mol/L H2SO4 and 3% NaCl solutions, respectively, by immersion tests and electrochemical measurements and compared with that of pure Ni, Nb and Sb. The stability of passive film was studied using potentiostatic current transients and XPS depth profiling. The surface morphology of the glassy alloy after electrochemical potentiodynamic polarization test was observed using SEM. The result indicates that the Ni-Nb-Sb alloy shows good corrosion resistance in 1 mol/L HCl, 1 mol/L H2SO4 and 3 wt% NaCl solutions. The corrosion resistance, however, is poor in 6 mol/L HCl solution. The amorphous alloy is crystallized after electrochemical corrosion in chloride media. Transpassive dissolution is observed during potentiodynamic polarization test in chloride media, which appears to be associated with oxygen evolution. At low potentials, the growth of passive film is diffusion-controlled. At high potentials, however, the active corrosion is the predominant.