Stochastic approach to the pit growth kinetics of Inconel alloy 600 in Cl ion-containing thiosulphate solution at temperatures 25-150 °C by analysis of the potentiostatic current transients

The pit growth kinetics of Inconel alloy 600 in aqueous 0.1 M Na₂S₂O₃ + 0.1 M NaCl solutions was investigated as a function of solution temperature by analysis of the potentiostatic current transient, based upon a stochastic theory. Potentiostatic current transients revealed that time necessary for pit embryo formation, t_pit,form decreased with increasing solution temperature. Analysis of the statistical distribution of t_pit,form demonstrated that the pit embryo formation rate function at higher solution temperature exhibits a weaker dependence on exposure time compared with that at lower solution temperature. This is attributable to the increase in the active sites necessary for pit embryo formation due to the increase of the defects in oxide film grown at higher solution temperature. Moreover, it was found that the rate of pit growth decreased with increasing solution temperature over the whole applied potential range. Based upon the experimental findings, the kinetics of pit growth with respect to solution temperature is discussed in terms of the changes of the shape parameter derived from the stochastic theory, the pit growth rate parameter determined from the logarithmic potentiostatic current transient and fractal dimension of the pits formed on the electrode surface.