Positron annihilation behavior in several corrosion protective polymeric coatings

Positron annihilation was studied in a vinyl ester and four epoxy coatings on steel. Measurements were made on coatings in equilibrium with air at approximately 50% relative humidity and on coatings immersed in liquid water for 24 h. Three spectral components were identified: a short-lived component associated with annihilation largely in the steel substrate; a medium-lived component associated with annihilation in small voids in the coating; and a long-lived component associated with annihilation of o-positronium in the polymer matrix and within large voids in the polymer and at the polymer/metal interface. An excellent correlation was observed between the effect of water exposure on the annihilation spectra and the protective properties of the coating in an aggressive H₂SO₄ environment. Other correlations between the annihilation spectra and the protective properties were also identified.