The corrosion behavior of AISI 310 stainless steel in thiosulfate ion containing saturated ammonium chloride solution

The effect of thiosulfate ion on the corrosion behavior of 310 SS in satura ted ammonium chloride and 5 M sodium chloride solutions, with or without th e addition of 0.01 M sodium thiosulfate, was investigated. Potentiodynamic polarization curves showed that a delayed pitting corrosion was found in sa turated ammonium chloride solution as compared with that in 5 M sodium chlo ride solution. The addition of 0.01 M sodium thiosulfate to the saturated a mmonium chloride solution caused a substantial effect on the electrochemica l behavior. At the potential in the range of -0.35 to +0.15V, both the anod ic polarization curves and the microscopic observation indicated that S2O3- participated in the electrochemical reactions. The anodic current density increase sharply and sulfide was formed on the specimen surface in this pot ential range. However, once the potential was greater than 0.15 V, the curr ent density decreased and a secondary passive behavior exhibited in the pol arization curve. The synergistic effect of Cl- and S2O3- on pitting corrosi on of 310 SS is also discussed. (C) 1999 Elsevier Science Ltd. All rights r eserved.