Corrosion Process of Acrylic Polyurethane Coating in Marine Atmosphere Environment

The degradation of wildly used acrylic polyurethane coating exposed to seawater atmosphere was investigated. The water diffusion process during coatings aging process was studied by EIS and numerical value analysis technique. The lnCc-t1/2 curves of acrylic polyurethane coating indicated that the coating capacitance (lnCc) presented two typical stages as the experimental time (t1/2) increased, the coating capacitance increased rapidly in the beginning time of test, and then tended to be a slow growth stage. According to the linear part of lnCc-t1/2 period, the water diffusion coefficient D is obtained and the value is 5.45×10-10cm2/s. It is found that the degradation process of acrylic polyurethane coating exposed to marine atmosphere can be divided into three periods, i.e., the water permeation process, the corrosion process of metal substrate under coating and the complete failure period of coating.