Effects of inhibitors (TiO2, CeB6, ZnO) on the repassivation kinetics and metastable pitting behavior of alloy 600 in caustic solution

Effects of inhibitors (TiO2, CeB6, ZnO) on the repassivation kinetics and electrochemical noise of alloy 600 were examined using the rapid scratching electrode techniques, the step potential technique and the electrochemical noise analysis. Summary drawn from this work is as follows. 1. Repassivation rate of alloy 600 increased by the addition of inhibitors (TiO2, CeB6, ZnO) to solution; this was confirmed by the reduction in repassivation time and also in the charge flowed during the repassivation time in 1 M H2SO4 and pH 10 solutions, which were measured by the step potential technique. The increase in the repassivation rate of alloy 600 is also confirmed by the decrease in cBV value in solution with the inhibitors, measured by the rapid scratch electrode technique. 2. The steady state current density of alloy 600 after repassivation in alkaline solution is much lower in solution with the inhibitors than in without the inhibitors, suggesting that the passive film formed in solution with inhibitors is more protective. 3. The susceptibility of metastable pitting of alloy 600 reduced in alkaline solutions with the inhibitors, as confirmed by the decrease in PSD value in those solutions. 4. Among the inhibitors, TiO2 is found most effective either in increasing the repassivation rate or in decreasing the susceptibility to metastable pitting of alloy 600. (author)