Kinetic Study of the Corrosion of Co-polyacetal Resin under Nitric Acid Solution

Abstract

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.

Corrosion Behavior of Co-Polyacetal Resin in Nitric Acid Solutions

“…However, the corroded resin partially dissolves leaving a residual part consisting of the corroded resin that is bonded to the uncorroded portion of the material. Therefore, in the surface reaction type, the residual strength after corrosion is considered to be equal to the initial strength, whereas in the case of the corroded layer-forming type, it depends on the strength of the uncorroded layer 15) .…”

“…The authors have examined the resistance of Co-polyacetal resin (Co-POM), which is one of the major building blocks of electrostatic atomizers, to solvents and the by-products from electro discharge [12][13][14][15][16] . POM resin is synthesized from formaldehyde and has two polymer types: the first is a homopolymer, which was industrialized by DuPont in 1960; the second is a copolymer, which is used in chemical, electrical, and automobile industries because of its excellent chemical endurance, mechanical strength, and workability 17) .…”