An ellipsometric, XPS and electrochemical study of the passivity of zircaloy-2

The electrochemical behaviour of zircaloy-2 in the annealed and quenched co nditions was determined in 0.5 M H2SO4 by the potentiodynamic polarization method. Passive films on zircaloy-2 obtained in air as well as in sulphuric acid under open circuit conditions, were characterised and their refractiv e index and thickness determined. It was seen that the beta quenched alloy showed a nobler potential (-270 mV against standard Calomel electrode) comp ared with the annealed alloy (-320 mV). It also showed a passive current de nsity about one order less than the annealed material. Ellipsometry showed that the films formed on the quenched alloy were thinner than those on the annealed alloy. After exposure to 0.5 M H2SO4 zircaloy developed films whic h were thicker with power refractive index than both the heat treated condi tions. XPS analysis of the films has confirmed incorporation of sulphate in to the film which probably leads to a defective and hence a thicker film in acid.