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.

Development of Electrochemical Surface Treatment to Visualize Critical Corrosion-Inducing Inclusions of Zr in Chloride Environments

“…These results indicate that the corrosion-inducing properties of the inclusions are different. 26 The E pit value of Zr-0.5O-0.5C was approximately 0.8 V, and this was consistent with the repeated measurements. This corrosion behavior of Zr-0.5O-0.5C was unique compared to that of pure Zr and other Zr alloys.…”

“…By using the micron-scaled electrochemical technique, inclusions such as Fe and Sn were found to trigger pitting corrosion. 26 However, there was a large difference in the degree of corrosion inductivity of each inclusion, resulting in a wide scattering of the pitting potential in the polarization curves. The reason for the large variation in the pitting potential of Zr is that the critical inclusions that trigger pitting z E-mail: manaka.met@tmd.ac.jp; TSUTSUMI.Yusuke@nims.go.jp corrosion at the lowest range of the applied potential seem to be rarely exposed to the surface of Zr.…”

“…Therefore, these inclusions have a low probability of being exposed to the surface of the electrochemical testing area. 26 This also makes the identification of these inclusions difficult. In other words, it is almost impossible to determine in advance the site where the localized corrosion of Zr will occur.…”

EFFECT OF MINORITY ALLOYING ELEMENTS Zn AND Zr ON THE CORROSION BEHAVIOR OF AMORPHOUS ALLOYS АLCUMG(Zn) AND ALCUMG(Zr) AND THEIR NANOCRYSTALLINE ANALOGUES

“…It is found that zirconium and its alloys are sensitive to pitting corrosion in environments containing chloride ions [29], which is expressed in destruction of the tin passive film and subsequent localization of the corrosion process. There is insufficient evidence in the scientific literature on the mechanism of corrosion of Zr-amorphous alloys and the reasons for propensity of Zr-amorphous alloys to pitting corrosion have not yet been clarified.…”

Development of Electrochemical Surface Treatment for Improvement of Localized Corrosion Resistance of Zirconium in Chloride Environment

“…The authors' group investigated the relationship between the inclusions and the pitting corrosion of Zr using micron-scale electrochemical measurements. The numerous non-critical Fe-rich inclusions on the pure Zr surface trigger pitting corrosion under high applied potentials of more than 2 V. 28,32) The pitting potentials of more than 2 V under condition E indicated the elimination of all the critical inclusions via the A d v a n c e V i e w electrochemical treatment. However, the electrochemically treated Zr specimens under condition F occasionally underwent pitting corrosion at relatively low potentials of 1.4 and 1.8 V. The treatment efficiency per cycle under condition F was lowered possibly because the dissolution and release of the inclusions remained incomplete owing to the short anodic polarization time.…”