The kinetics of Anodic dissolution of iron‐chromium alloys in weak acid solutions. Part I. Potentiodynamic and potentostatic investigations

Abstract

The kinetic of dissolution in the active and prepassive range of FeCrX alloys (X = 4.5; 11.7; 12.7; 13.6; 14.7 and 20.8 M%) was investigated in dearated borate solutions (pH 3.5-5.45) and compared with corresponding data for Fe. After cathodic reduction instationary current density-potential curves were measured by fast potentiodynamic polarisation (10 mV/s) supplemented by potentiostatic investigation of FeCr 11 and FeCr 13 in the quasisteady state.Alloys up to 12.7% Cr offers in the non-steady state iron like behaviour with regard to the kinetic data, but the anodic curves are shifted to more negative potentials and to smaller current densities. 'This is supposed to be caused by Cr(OH)3 formation at an early stage of polarisation.The data of the activeTafe1 range fit that of a Bockris-Type dissolution. At higher Cr-content only the prepassive range exists.In the quasi-steady state and pH 5 4.2 a pH-independent active range was found with the Tafel slope 40 mV/dec. A mechanism of Cr-controlled dissolution is supposed characterised by the activation of Cr by water molecules as the rate determining step.