An electrochemical study of corrosion protection by in situ oxidative polymerization in phenylenediamine crosslinked sol–gel hybrid coatings

The three isomers of phenylenediamine have been used as crosslinking agents for epoxide decorated silica colloids generated by high water content sol–gel chemistry techniques. The resulting materials were used as corrosion protection thin films for aluminum alloys in corrosive environments. These hybrid epoxy-amine crosslinked sol–gel materials have demonstrated an order of magnitude improvement over similar materials crosslinked with aliphatic diamines along with novel electrochemical and coloration behavior. The processes behind these performance improvements are explored and two possibly complementary mechanisms are identified, namely exposure-triggered toughening of the materials through oxidative polymerization of the phenylenediamines and an increase in corrosion inhibition via the formation of electroactive phenylenediamine oligomers.