Pitting Corrosion on Zirconium—A Review

A review is presented on the pitting corrosion of zirconium and Zr alloys when immersed in aqueous solutions at temperatures less than 100 C. The electrochemical methods (potentiokinetic, potentiostatic, and scratch) used to evaluate pitting susceptibility are described briefly. Zirconium is susceptible to pitting in halide solutions with chloride ions being the most aggressive, followed by bromide, and finally iodide. The effect of chloride ion content on the pitting potential of Zr is presented. Cations (e.g., Fe³⁺) can markedly increase the corrosion potential of Zr, but they do not affect the protection potential (E_pp). To control pitting on Zr, the effects of inorganic inhibitors and alloying are reviewed. The nitrate ions are more effective in raising the pitting potential of Zr to more noble potentials than the sulfate ions. Niobium additions increase the pitting potential more effectively than Ti when alloying contents are less than 10 Wt%. The addition of Mo (2 and 4 Wt% Mo) to Zr-Nb alloys raises the pitting potential slightly.