Corrosion protection behaviour of electrogalvanised steel sheet by tetravalent vanadium ion

The corrosion protection behaviour of electrogalvanised steel sheets (EG) by the tetravalent vanadium ion was investigated. Immersion of the bare EG in a NaCl solution revealed that the addition of vanadium(IV) oxide sulphate to the solution led to a transition of the open circuit potential to less noble and the formation of vanadium oxides on the EG surface. The oxide layer included not only vanadium(III) oxides but also a small amount of ZnO, indicating that Zn on the EG surface was oxidised while the vanadium(IV) species was reduced to the vanadium(III) species. The corrosion current density of the EG with the adhering vanadium(III) species was one order of magnitude smaller than that of the bare EG, clearly suggesting that zinc corrosion was reduced by suppressing the reduction reaction of dissolved oxygen. The vanadium(IV) species could be a candidate as a self-healing inhibitor for chromate-free coating technologies by controlling the coupling of Zn oxidation and vanadium(IV) reduction.