The corrosion mechanism and its modeling of Co-polyacetal (Co-POM) under nitric acid (HNO
3) solution were investigated. The degree of degradation was evaluated by the changes in weight and molecular weight. The weight change in HNO
3 solution was linearly decreased after the incubation period. From SEC measurements, it was observed that the occurrence of degradation of Co-POM by HNO
3 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 HNO
3 solution is the corroded layer-forming type. The rate equation for corrosion by hydrolysis reaction between Co-POM and HNO
3 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 HNO
3 solution into Co-POM over time and the previous equation for corrosion. This result of simulation agreed well with the experimental ones.
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