Studies on accumulation of chloride ions in pits growing during anodic polarization

The concentration of Cl⁻ ions within pits grown on 18Cr---12Ni---2Mo---Ti austenitic stainless steel specimens immersed in vertical position in 0·5N NaCl + 0·1N H₂SO₄ and polarized to 860 mV_NHE was studied at 20°C. The Cl⁻ concentration within pits increases with time to a maximum and then decreases (for example, after 6 h 2N Cl⁻ is observed). The higher accumulation of Cl⁻ within pits, the slower their development. For slowly growing pits a maximum value of about 12N Cl⁻ was observed. The low pH values of the solution within pits are the consequence of high Cl⁻ contents occurring there.