Pitting of AISI 304 stainless steel in bicarbonate and chloride solutions |
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Authors: | M DROGOWSKA H ME´NARD L BROSSARD |
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Affiliation: | (1) De´partement de Chimie, Universite´ de Sherbrooke, Sherbrooke, Que´bec, Canada, J1K 2R1;(2) Institut de recherche d'Hydro-Que´bec (IREQ), Varennes, Que´bec, Canada, J3X 1S1 |
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Abstract: | Metastable and stable pitting on 304 stainless steel (SS304) in 0.1–0.5 m NaCl aqueous solution (pH ~8) has been investigated using a potentiodynamic, a potentiostatic and a weak anodic current galvanostatic techniques. The addition of bicarbonate (0.025–0.5 m) to the solution had an inhibiting effect, manifested by a shift of the pitting potentials to more positive values, a longer induction time for pitting and reduced pit nucleation. The pit nucleation frequency and growth, in the metastable and stable states, decrease as the NaHCO3/NaCl molar concentration increases and pitting is no longer observed for NaHCO3/NaCl molar ratios higher than 3 (four times larger % wt of NaHCO3). Pitting events never occurred at a potential below –0.1 V, fewer metastable events were observed at higher temperature (50°C) and none were observed in chloride free bicarbonate solutions. The inhibiting behaviour of oxyanions is discussed. |
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