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The pitting susceptibility of zirconium in hydrogen chloride solutions is discussed and possible methods to avoid pitting in HCl-ferric chloride (FeCl3) environments are presented. Susceptibility is evaluated using potentiodynamic and potentioscratch electrochemical techniques to determine the critical repassivation potential. Ecp, and the open circuit potential. The effects of Cl−, Br−, and I− concentration, pH, temperature below boiling, and Fe+3 impurity are included. Ecp is linearly related to the log of the halide concentration and is not effected by pH from 0 to 12.8 or temperature. The reduction reaction of Fe+3 to Fe+2 polarizes zirconium's surface to Ecp causing instability of the passive film. Stabilizing the Fe+2 oxidation state or controlling the surface potential below Ecp can restore zirconium's passivity.
zirconium, hydrochloric acid, ferric chloride, bromide, iodide, passivity, pitting, electrochemical polarization, electrochemical protection
Research metallurgist, Metallurgical Research and Development, Teledyne Wah Chang Albany, Albany, Ore.