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Abstract
The oxidation behaviour of zirconium in molten (Na,K)N03 eutectic containing various halide ions at 300°C was studied under open circuit and polarisation conditions. Under open circuit conditions, the metal is passivated in the presence of Cl-, Br-, and I- ions and the corrosion potential shifts to more positive values with time. In the presence of F- ions active corrosion occurs. In all cases the steady corrosion potential was found to decrease linearly with the logarithm of the halide ion concentration. The results in the presence of Cl-, Br- , and I- ions were explained in terms of the dependence of the Zr/ZrO2 electrode on the oxide ion concentration which depends on the halide ion concentration. In the presence of F- ions, a metal/metal ion electrode, is proposed. Under anodic polarisation, Cl- ions have no significant influence on the passivation behaviour of zirconium while I- and F- ions inhibit oxide formation. Br- ions showed an intermediate effect between Cl- and I- ions. The main anodic process at steady state is O2 evolution (Cl- and Br- ions) or halogen evolution (I- and Br- at concentrations > 0·3 molal).