Cyclic voltammetry, x-ray photoelectron spectroscopy, secondary-ion-mass spectrometry, and ion-scattering spectrometry examination of zirconium passive film breakdown in the presence of sulfate

Passive films on zirconia were prepared by potentiodynamic polarization in the presence of a range of anions and at various pH values. With sulfate an d chloride anions in the electrolyte we found unique transpassive peaks in the cyclic voltammograms that appear to be associated with an amorphous-to- crystalline transition and subsequent enhanced species transport along the resulting grain boundaries. X-ray photoelectron spectroscopy, secondary-ion -mass spectrometry, and ion-scattering spectrometry have been used to chara cterize the films before and after the passive film breakdown. The passive film breakdown can be qualitatively described by E-np = E-c + eta + Phi + E -inh Where E-np is the pitting potential, E-c the corrosion potential in ac idified solution, eta the polarization necessary to obtain a current densit y high enough to maintain acidity inside the pit,Phi the potential drop ins ide of the pit, and Einh the contribution to the pitting potential resultin g from inhibitors present. The results of these surface studies along with the variation in the cyclic voltammetry scans have been used to describe th e process and to present a model that involves chemically bound water oxida tion and local oxygen evolution. The effects of either Ohmic drop and/or lo cal acidification are presented as well. (C) 2000 American Vacuum Society. [S0734-2101(00)08504-3].