Evaluation of the current transients in metastable pitting of pure zinc in chloride containing solution alkaline solution

摘要

The pitting corrosion of a passive metal exposed to chloride containing solution takes place in three stages: nucleation, metastable pitting and stable growth. In the present study the metastable pitting events on pure zinc in 0.1 M NaOH solution were studied. The metastable pits were characterized in terms of frequency of occurrence, peak pit current and repassivation time over a range of potentiostatically applied potential (i.e. 500 mVAg/AgCl, 750 mVAg/AgCl and 1000 mVAg/AgCl) and chloride concentration (i.e. 0.01 M, 0.1 M and 1 M). It was found that the current transients resulting from metastable pits formed on pure zinc in the presence of chloride ion have a characteristic shape. The current abruptly increases above the background passive current as the pit nucleates and begins to grow. After reaching the peak the current gradually decreases to the level of the original passive current, which implies the repassivation of the metastable pit. Statistical evaluation of the results showed that the frequency of events increases with increasing applied potential and chloride concentration. Furthermore, the chloride ion increased the probability distribution of metastable pit peak current and repassivation time.