An XPS study of passive films on corrosion-resistant Cr-Zr alloys prepared by sputter deposition

X-ray photo-electron spectroscopy (XPS) has been used to examine spontaneously passivated films formed on sputter-deposited Cr-Zr alloys in 6 M HCl solution open to air at 30°C, for a better understanding of the high corrosion resistance of these alloys. The open circuit potentials of the Cr-Zr alloys are located in the passive regions of both chromium and zirconium, and all of the Cr-Zr alloys examined are spontaneously passivated. An increase in chromium content of the alloys enhances the cathodic activity for oxygen reduction and content of the alloys enhances the cathodic activity for oxygen reduction and decreases the anodic current density with a consequent ennoblement of the open circuit potential. XPS analysis indicates that the air-formed films on these alloys are composed of homogeneous double oxyhydroxide consisting of both chromium and zirconium ions. The cationic composition of the film is almost the same as the alloy composition although slight enrichment of zirconium occurs. The air-formed film is protective enough to lead to spontaneous passivation of these alloys. The immersion for a long period of time results in a slight deficiency in zirconium in the exterior of the passive film as a result of gradual dissolution of zirconium. At the same time, the total amount of chromium in the passive film increases. The passive film consists of double oxyhydroxide of chromium and zirconium, in which the cationic composition is almost the same as the alloy composition. The formation of the passive film consisting of double oxyhydroxide of chromium and zirconium is responsible for the higher corrosion resistance of these Cr-Zr alloys in comparison with chromium and zirconium metals.