Effect of Impurity Elements on Localized Corrosion of Zirconium in Chloride Containing Environment

Abstract

To clarify the mechanism of localized corrosion on zirconium in chloride environments, corrosion tests of zirconium and its alloys were performed using conventional and micron-scale measurement systems with surface areas of 0.35 cm2 and less than 0.04 cm2, respectively. The pitting potential significantly dropped by more than 1 V when zirconium was alloyed with over 10 mol% of tin. Zr4Sn and Zr5Sn3 intermetallics hindered the formation of passive films on the substrate. Additionally, tin was found on the surface of a commercially pure zirconium. From the micron-scale measurement results, the inclusion with the highest concentration of tin (at least 0.44 mol%) in the tested area was selected as the preferential initiation site for pitting corrosion. Thus, tin played an important role in determining the corrosion resistance of zirconium in chloride environments.