Environmental Factors Affecting the Pitting Corrosion Potential of a Zinc–Titanium Alloy in Sodium Hydroxide Solutions

Abstract

AbstractThe susceptibility of a commercial Zn–Ti alloy to pitting corrosion by Cl−, Br− and I− ions isfollowed, in oxygen-free NaOH solutions of a concentration which allows the formation of a passivating film on the alloy surface, using the potentiostatic polarisation technique. Lower concentrations of halide ions have no effect on the dissolution kinetics of the passivating film, while higher concentrations cause the formation of visible pits. Additions of increasing concentrations of chromate, phosphate and carbonate ions cause a shift of the critical pitting potential in the noble direction, accounting for increased resistance to pitting attack. Sufficient concentration of the carbonate ions causes complete inhibition of pitting corrosion. The pitting corrosion potential varies with the concentration of the inhibitive anions, in the presence of a constant concentration of chloride ion, according to S-shaped relationships, from which one can determine the minimum concentrations of the inhibitive ions w...