Cathodic delamination of polyurethane films on oxide covered steel – Combined adhesion and interface electrochemical studies

The stability of polyurethane/iron oxide/steel interfaces was evaluated for different chemically modified passive films in humid and corrosive atmosphere. Iron oxide layers were formed on polished steel by thermal annealing in oxygen rich atmosphere, water plasma modification, immersion in alkaline solution and by anodic polarisation in borate buffer solution. Scanning Kelvin Probe studies of the interface stability were performed under the conditions of cathodic delamination. The corresponding progress rates specifically depended on the iron oxide. Complementary measured peel-off forces of the respective coating/substrate systems showed the same trend as detected for the corrosive delamination process. Additional contact angle measurements and investigation of the interfacial ion mobility on the uncoated oxide surfaces confirmed a correlation between high peel forces, increasing oxide surface energy and decelerated cathodic delamination kinetics.