Phosphonate-functionalized ORMOSIL coatings for magnesium alloys

Hybrid organically modified silicates, or ORMOSIL materials, with covalently attached pendant phosphonate groups were processed by a sol–gel method. A hydrolysis and condensation route was used involving a phosphonato-silane and resultant films were evaluated as prospective coatings for magnesium AZ31B alloy substrates. The inclusion of phosphonate functionalities into the coating matrix was achieved by a co-condensation of the phosphonato-silane with other organo-functional silanes followed by blending the resultant phosphonate-functionalized silicate oligomers with another sol–gel matrix material to form an interpenetrating network structure. The effect of synthesis composition on the hydrophobic/hydrophilic balance and film barrier properties was examined by several methods, including constant immersion and electrochemical tests. The observed enhancement in corrosion protection properties was attributed to a combination of the barrier properties of the organo-silicate matrix along with strengthening of the coating/substrate interface due to chemical bonding of the phosphonate groups to the metal surface.