Abstract
The anti-corrosive nature of steels coated with a commercially available acidic water-borne latex primer has been demonstrated to be considerably enhanced by the formation of an interfacial film between the coating and metal substrate. Novel sample preparation has enabled microtomed cross-sections of latex polymer coated metals to be analysed by TEM to establish the morphology and structure of the interlayer. Combined EDX and electron diffraction presents evidence for a chlorine containing mixed valence iron oxide/hydroxide - a pyroaurite-type compound, green rust I - existing in this region and attributes this formation to the observed enhanced anti-corrosive properties. Modifications to the latex polymer by soluble ionic pigment additions was performed to attempt to enhance the anti-corrosive nature of the coating by formation of different pyroaurite-type compounds based on the formula Mg6Fe2(OH)16CO3.4H2O, where Mg may be substituted by a suitable divalent cation and likewise Fe substituted by a suitable trivalent cation. Analysis of these modified coatings by TEM, XPS and A.C. impedance spectroscopy has elucidated their anti-corrosive action and identified the presence of polymer/metal and polymer/air films formed by ionic additions. In particular, the ionic addition of Mg(II) is found to considerably increase corrosion resistance in these latex coatings immersed in 3% NaCl. Models are presented for green rust formation and corrosion protection enhancement by soluble ionic additions.