SEDL / STP / STP830-EB / STP32522S

The Pitting Susceptibility of Zirconium in Aqueous Cl⁻, Br⁻, and I⁻ Solutions

Maguire, M
Research metallurgist, Metallurgical Research and Development, Teledyne Wah Chang Albany, Albany, Ore.

Pages: 13    Published: Jan 1984

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Abstract

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.