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

The electrochemical behaviour of zircaloy-2 in the annealed and quenched conditions was determined in 0.5 M H 2 SO 4 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 refractive index and thickness determined. It was seen that the beta quenched alloy showed a nobler potential (-270 mV against standard Calomel electrode) compared with the annealed alloy (-320 mV). It also showed a passive current density 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 H 2 SO 4 zircaloy developed films which were thicker with power refractive index than both the heat treated conditions. XPS analysis of the films has confirmed incorporation of sulphate into the film which probably leads to a defective and hence a thicker film in acid.