Pitting Corrosion on Zirconium in KCl and KCl-H₂SO₄ Solutions

Electrochemical investigations of commercially pure zirconium and Zr-2.5 wt% Nb immersed in KCl and KCl-H₂SO₄ solutions were performed. The potentiokinetic pitting potential $(Ep′)$ was affected by the scanning rate but the repassivation potential (E_r) was only slightly affected. In KCl-7.26 H₂SO₄ solutions, the $Ep′$ decreased with increasing KCl content, while E_r increased slightly. The formation of a salt film in the periphery of the pit may have inhibited pit growth and affected E_r.

In measurements of E_r by the scratch method, the repassivation potential of zirconium decreases logarithmically with increasing KCl content. In KCl-7.26 N H₂SO₄ solutions, the E_r decreases with increasing KCl, although the logarithmic trend does not occur. For 1 N KCl- H₂SO₄ solutions, E_r remains constant for H₂SO₄ contents <0.1 molar (M) and decreases with increasing H₂SO₄ content in higher acidic concentrations. This was attributed to the transformation of SO₄^2- – H⁺ association within the bulk solution to an HSO₄⁻ – H⁺ association.