Barrier properties and structure of inorganic layers at polyaniline–steel interface
Anticorrosive properties of inorganic layers formed on the surface of steel upon deposition of polyaniline doped with hydrochloric, sulfuric, or phosphoric acid were studied. It was found that the strongest anticorrosive protection is provided by the polymer containing chloride ions. An X-ray phase analysis demonstrated that the high packing order of chains of polyaniline doped with hydrochloric acid leads to formation of an inorganic barrier layer constituted by closely packed iron oxides and hydroxides. Application to the steel surface of polyaniline doped with sulfuric and phosphoric acids results in that barrier layers with weaker anticorrosive properties are formed. It is shown that, in the course of catalytic oxidation of iron by oxygen in the presence of polyaniline, there occur transitions between the emeraldine and pernigraniline forms of the polymer. IR spectroscopy confirmed that polyaniline doped with hydrochloric acid is the most active catalyst for steel surface oxidation.