The dipolar and conductivity relaxations of epoxy coating studied by EIS in aqueous solution

摘要

The organic polymer coatings are largely used to protect metallic structures from the corrosion in aqueous medium, but the absorption of water (water-uptake) induces the degradation of their protective effectiveness. An equivalent circuit model describing the electrochemical behavior of paint coated electrode involving flaw areas was proposed in our earlier work [1]. However, as shown in a previous paper [2], this model cannot represent EIS of flawless film and the dipolar relaxation of polymer layer itself, influenced by absorbed water, becomes the major phenomenon. With an epoxy-vinyl paint layer, we found that the water-uptake process is essentially determined with the diffusion process according to Fick's law [3]. In this paper, we will deal with an epoxy-amide paint layer, for which Fick's law alone did not allow explaining suitable the kinetics of water-uptake.