Effect of KSCN and its concentration on the reactivation behavior of sensitized alloy 600 in sulfuric acid solution

Abstract

The effects of KSCN addition and its concentration on the reactivation behavior of sensitized Alloy 600 in an H 2SO 4 solution were investigated. Single-loop electrochemical potentiokinetic reactivation (SL-EPR), potentiostatic and potential decay tests were conducted in H 2SO 4+KSCN solutions, including intermittent adjustment of the electrolyte composition and concentration. The SL-EPR results showed that the maximum current densities of the reactivation peaks increased with an increase in KSCN concentration from 0 to 0.05 M in the 0.5 M H 2SO 4 solutions. A decrease in the peak current density was observed, however, if the KSCN concentration was increased to 0.5 M. The potentiostatic test results at +400 mV SCE showed that sensitized Alloy 600 could be passivated in plain H 2SO 4 and KSCN solutions as well as in mixed H 2SO 4+KSCN solutions. Potentiostatic tests at +30 mV SCE revealed that the presence of low KSCN concentrations made the passive film less stable in H 2SO 4 solutions, but it enhanced passivation at 0.5 M. The adsorption and desorption of SCN − and its subsequent redox reaction at different concentrations was discussed in relation to the reactivation of passive film formed on sensitized Alloy 600.