Kinetic Study of the Corrosion Behavior on Polyamide under Nitric Acid Solution
Takehiro HAMAMURA, Masatoshi KUBOUCHI, Saiko AOKI, Osamu YOSHIDA, Mitsuhiko EJIMA and Tetsuya SAKAI
Abstract:The corrosion mechanism and its modeling of Polyamide (PA) in nitric acid (HNO3) solution were investigated. The appearances on specimens in HNO3 solution were changed with discoloration while not happen in distill water (DH). The weight change on wet specimens in nitric acid solution linearly increased after the incubation period. The weight change showed that the diffusion of DH and HNO3 solution into PA obeyed Fickian diffusion model except in HNO3 30mass%. Thus, the diffusion rate of each nitric acid concentration and DH were calculated from weight change with wet specimens. From SEC measurements, it was observed that PA by HNO3 solution degraded gradually in the specimen wholly with increasing immersion time. The reaction rate of each HNO3 concentration was calculated from molecular weight change at the surface of the specimen. The corrosion rate equation between PA and HNO3 solution was estimated with the previous diffusion rate and reaction rate. This equation showed that the calculated molecular weight change agreed well with the experimental ones. From this result, it was observed that the degradation of PA by HNO3 solution was of the corroded layer-forming type in the early immersion stage and of the penetration type in the later stage. Key Words:Corrosion, Polyamide, Electric discharge, Nitric acid, Diffusion rate, Molecular weight