STABILITY OF THE PASSIVE STATE OF NI-ZR GLASSY ALLOYS

Electrochemical and microscopic investigations provided an insight into the anodic behavior of nickel-zirconium (Ni-Zr) glasses with 25 at% to 70 at% Zr in borate buffer solution containing up to 1 M sodium chloride (NaCl). Stability of the passive state of the glasses was high in the absence of Cl-. Oxygen evolution was observed at sufficiently noble potentials in contrast to the corresponding behavior of crystalline Zr, which formed an insulating film during anodization. Measurements of pit nucleation potential showed Ni-Zr glasses were less resistant to pitting than crystalline Zr at any Cl- concentration. Glasses of > 50% Zr were less resistant than of crystalline Ni. Pit nucleation potential decreased at almost-equal-to 80 mV/dec of Cl- concentration, suggesting chemical breakdown of passivity However, the short induction period of pitting for Zr-rich alloys was compatible with another mechanism of pit initiation involving structural effects within the passive film at high concentrations of Zr.