Effects of sulphate, nitrate and bicarbonate ions on occurrence and repassivation of crevice corrosion for 13Cr stainless steel healds in diluted NaCl solution

摘要

This paper was investigated the effects of nitrate, sulphate and bicarbonate ions, NO3-, SO42- and HCO3-, which are components of the tap water, on occurrence and repassivation for creviced corrosion of flat healds, 13Cr stainless steel components used for a water jet loom (WJL), in 0.11-5.6 mM chloride ion, Cl-, solution when the electrode potential of test piece was kept at 570 mV vs. SHE. An occurrence of creviced corrosion in Cl - solution was inhibited by presence of more than an equimolar amount of NO3- to Cl-, or in excess of an equimolar amount of SO42- to Cl-. A growth creviced corrosion in Cl- solution was passivated by presence of more than an equimolar amount of NO3- to Cl-, or more than six molar amount of SO42- to Cl-. The term required to repassivate crevice corrosion completely after NO3 -or SO42- was added to Cl- solution decreased with increasing NO3- or SO4 2- concentration. HCO3- did not inhibit an occurrence of creviced corrosion and not repassivate a growth creviced corrosion for flat healds in Cl- solution. This is because that HCO 3- exists in H2CO3 as non-dissociation form in the pH 2.2 acidic solution in corroding crevice on test piece, due to dissociation equilibrium. A growth creviced corrosion on test piece was repassivated in Cl- solution, as a result of the addition of NO3 -, SO42-. This results that corrosion current decreases with increasing pHC.C., and then the pH of solution inner the crevice corrosion, the pHC.C., exceeds depassivation pH, pHd, irrespective of the type of anion.