Characterization of Transport Processes in a Praseodymium-Containing Coating

Abstract

The electrochemical response of Pr-containing epoxy-polyamide primers on aluminum alloy 2024-T3 substrates was investigated. The effect of electrolyte pHs on corrosion behavior was studied before and after salt spray exposure. X-ray diffraction analysis confirmed that the praseodymium phase that was added to the primer converted into Pr(OH)3 in the as-deposited coating and remained present in the primer up to 3000 hours of salt spray exposure. Examination of panels prior to salt spray testing indicated that Pr was not detected in the scribes; however, following salt spray testing, Pr-rich species were found in localized clusters in scribes. Electrochemical tests were performed on test panels with machined defects using electrolyte pHs ranging from 5 to 8. The largest change in passivation range occurred at pH=8, and was two times higher than the change observed for bare Al 2024-T3. Corrosion protection of Pr-based primers is due to the ability of Pr-rich species to dissolve from coatings during exposure to corrosive environment and is influenced by pH.