Polypyrrole-Polymolybdate Composite Film for the Corrosion Protection of Steels

Abstract

Conductive polymer film of polypyrrole (PPy) doped by polymolybdate (PMo) anions was prepared on mild steels by anodic polymerization for corrosion prevention of the steels. The PPy-PMo conductive film prepared exhibits good adherence to the steel substrate. The mass and thickness of the PPy-PMo film linearly increase with electricity during constant current polymerization at 5mA·cm^-2. The density of the PPy-PMo polymer film was evaluated to be 2.5g·cm^-3 from the ratio of the mass to thickness. A corrosion test in neutral and acidic 3.5wt% NaCl solutions was done for the steels covered by the PPy-PMo film. Corrosion of the steels is suppressed by the films: the corrosion rate in the neutral solution decreases by 1/3 compared with that of the bare steel and the rate in the acidic solution by 1/4. The film was gradually reduced during immersion in the solutions with progress of the corrosion reaction of Fe dissolution to Fe²⁺, which is accompanied with the dissolution from PMo in the film to MoO₄^2- in the neutral solution, or with pickup of protons and sodium ions in the acidic solution.