2016 年 54 巻 1 号 p. 25-34
The degradation process of a heavy-duty coating with blisters formed by a temperature difference across the resin was investigated by electrical impedance measurements and visual observations. The two effects of the coating thickness and the addition of the glass flakes were evaluated. From the coating impedance monitoring results for 105 days, it was demonstrated that the decrease of barrier property of the coating is inhibited by the addition of glass flakes. By visual observations, it was shown that the area of blisters and the black rust at the coating⁄steel substrate beneath blisters in thick coatings are larger than that in the thin coatings. On the other hand, the prolongation of the time for blistering of the coating could be achieved by the increase of the coating thickness. Finally, the electrical equivalent circuit (EEC) model was proposed for the residual lifetime evaluation of the coating. This model includes the constant phase element (CPE) , one of the circuit elements that can express coating impedance accurately. It was elucidated that the coating impedance can be well-described by the EEC model of the parallel combination of two CPEs.