Stability control of adhesional interaction in a protective coating/metal system

The adhesion failure area ( n ) at the polymer coating/steel interface in aggressive media was measured using an a.c. impedance technique. A n value of 0.2-5.0% of the total surface was found for different film-formers (epoxy, vinyl, divinyl acetylene) after 10 days' exposure in electrolyte. It was shown that the n value and its changes during exposure [ n = f(τ)] depend on the nature of the film-former, the solution composition, and the dissolved oxygen (C O2 ) and chloride ion (C Cl -) concentrations. It was found that the epoxy coating adhesion stability was much higher in comparison with the vinyl and divinyl acetylene coatings. An increase in the chloride ion concentration resulted in an increase of n for the coatings studied, i.e. destruction of adhesional bonds, but at the same time relative increments δ n /δτ and δ n /δCO 2 , were confined within the same range. The mechanism of the observed processes is explained from the point of view of competitive adsorption of hydroxide and chloride ions at the metal surface and the activating effects of the chloride ions on the metal dissolution.