Effects of water and solvent properties on the corrosion of passive alloys in organic solvents: Uniform dissolution and pitting of C-22 in HCl

The influence of non-aqueous solvents on the corrosion behavior of passive alloys is yet largely unknown. The corrosion of alloy C-22 was studied in organic aprotic solvents containing HCl with various water concentrations using electrochemical techniques and SEM. C-22 is passive in nearly anhydrous solvents. When HCl is present at 0.1 M, passivity breaks down and either uniform corrosion or pitting is observed, depending on the solvent. Residual water can stimulate or inhibit active dissolution depending on its concentration. The phenomena of passivation, transpassivation, active dissolution, and pitting are discussed considering the chemical properties of solvents on electrochemical mechanisms.