Effect of Nitrate on the Repassivation Potential of Alloy 22 in Chloride-Containing Environments

Abstract

The study of Alloy 22 was undertaken in several selected nitrate/chloride (NO{sub 3}{sup -}/Cl{sup -}) electrolytes with chloride concentrations [Cl{sup -}] of 1.0, 3.5 and 6.0 molal with [NO{sub 3} {sup -}]/[Cl{sup -}] ratios of 0.05, 0.15 and 0.5 at temperatures up to 100 C. Results showed that the repassivation potentials increased with increase in [NO{sub 3} {sup -}]/[Cl{sup -}] ratio and decreased with increase in temperature. The absolute [Cl{sup -}] was found to have less of an effect on the repassivation potential compared with temperature and the NO{sub 3} {sup -}/Cl{sup -}. Regression analyses were carried out and expressions were derived to describe the relationship between the repassivation potential, temperature, [Cl{sup -}] and [NO{sub 3} {sup -}] for the conditions tested.