Understanding of the corrosion protection by V(IV) conversion coatings from a sol-gel perspective

The mechanisms by which V(IV) (tetravalent vanadium) as a film ingredient protects the surface remain dim. This work gives a clear and concise understanding of the corrosion protection of hot-dip galvanized (HDG) steel by vanadyl oxalate (VOC₂O₄) conversion coatings from a sol-gel perspective, along with data from X-ray photoelectron spectroscopy (XPS) surface characterization, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. An elaborate integration of experimental results and thermodynamic analysis suggests that the protection can be exerted persistently as long as V(IV) is available in sufficient quantities at susceptible sites to maintain hydrolysis, condensation, and polymerization.