The influence of silicate and sulphate anions on the anodic corrosion and the transpassivity of iron and silicon-rich steel in concentrated KOH solution

The effect of sulphate and silicate addition in a 10 M KOH electrolyte on the anodic corrosion and transpassivity of iron and steel rich in silicon are explored by cyclic and linear sweep voltammetry. Formation of ferrate(VI) in the iron transpassivity region is noticed in all explored electrolytes. The electrochemical sulphato- and silico-ferrate(VI) formation is discussed as a possible result of Fe3III(Si1.32Fe0.68)O5(OH)4 and [Fe(II)4Fe(III)2(OH)12]SO4 oxidation in the 10 M KOH electrolytes with silicate and sulphate, respectively. The presence of Fe3(Si1.32Fe0.68)O5(OH)4 in the anodic layer of silicon steel and the crystal structure of electrochemically synthesised Ba(Fe, S)O4 have been revealed by XRD.

► Anodic behaviour of Fe and steel in 10 M KOH with sulphate and silicate is examined.
► X-ray diffraction confirmed the formation of Fe3(Si1.32Fe0.68)O5(OH)4 in anodic layer.
► X-ray diffraction confirmed the formation of Ba(Fe, S)O4 at anodic oxidation.