2012 Volume 61 Issue 4 Pages 182-187
The corrosion mechanism and its modeling of Co-polyacetal (Co-POM) under nitric acid (HNO3) solution were investigated. The degree of degradation was evaluated by the changes in weight and molecular weight. The weight change in HNO3 solution was linearly decreased after the incubation period. From SEC measurements, it was observed that the occurrence of degradation of Co-POM by HNO3 solution was limited near the surface on a specimen, and the inside had remained original material. From this result, it was inferred that the degradation type of Co-POM by HNO3 solution is the corroded layer-forming type. The rate equation for corrosion by hydrolysis reaction between Co-POM and HNO3 solution was proposed with the rate constant for reaction which was calculated from molecular weight change of the surface on a specimen. The diffusion rate of nitric acid concentration was calculated from weight change (Wet–Dry in condition). Finally, the corrosion rate of Co-POM was estimated numerically by combining the concentration of diffused HNO3 solution into Co-POM over time and the previous equation for corrosion. This result of simulation agreed well with the experimental ones.