Regina Fuchs-Godec,  Aljana Petek, Valter Doleček
Faculty of Chemistry and Chemical Engineering, University of Maribor, Smetanova 17,  2000 Maribor, Slovenia
 

ABSTRACT

The kinetics of the early stages of passive film formation on AISI 420 stainless steel in mixtures of 0.1M H2SO4 and 0.1M Na2SO4, with pH-values of 2.42, 2.85 and 3.33, were studied at different anodic potentials. The potentiostatic step method was used as an electrochemical technique in which the anodic current density was measured as a function of time. For analysis of the measured data, the theory of  “topochemical reaction” was applied for the characterization of the exponent n in that part where the steepest current decay was observed. Through this theory, which includes the Erofeev equation  (where n = s + a), the number of conversion steps s could be obtained, as well as the number of directions a in which the nuclei grow. It was found that this theory can be successfully applied to the passivation process of AISI 420 stainless steel.