CHANGE OF pH IN THE CREVICE DUE TO CREVICE CORROSION OF STAINLESS STEELS.

Crevice specimens were immersed in NaCl solutions, and the pH and Cl** minus ion concentration in the crevices were determined. The potential inside the crevice was also measured with an inserted capillary. The results show that the crevice pH decreases with increasing corrosion. The stationary pH of the SUS304 crevice is 2. 5 to 4. The enrichment ratio of the Cl** minus ion in the crevice is increased as the concentration of the Cl** minus ion in the test solution or the crevice volume is decreased. Judging from the pH and the potential inside the crevice, the active state is attained in the SUS304 crevice. Steels which contain more than 2% Mo tend to have lower pH values in the crevices than steels with lower Mo contents.