Pitting Mechanism of Passive 304 Stainless Steel in Weakly Basic Media Containing Chlorion

The pitting behavior of passive 304 stainless steel in pH8.4, H₃BO₃ (0.2mol/l)-Na₂B₄O₇ (0.05mol/l) and pH9.2, Na₂B₄O₇ (0.05mol/l) solutions containing chlorion has been investigated using impedance technique. The possible reaction mechanism as well as the corresponding equivalent circuit model is presented. It is proposed that an intermediate complex (MOHCl) and its further adsorbed product (MOHCl-Cl_n^-)ads will form during pit initiation and propagation stages.