Effect of Phase on the Electrochemical and Morphological Properties of Praseodymium-Based Coatings

Abstract

The corrosion protection of epoxy-polyamide primers containing either hexagonal Pr2O3 or cubic Pr6O11 inhibitors deposited on chromate conversion coated Al 2024-T3 substrates was studied. Electrochemical evaluations, scanning electron microscopy with energy dispersive spectroscopy, and x-ray diffraction were used to characterize primers. The electrochemical response of coated panels prior to and following ASTM B117 salt spray exposure was also studied. The addition of PrOx species to the primer matrix improved the corrosion protection of artificial defects by decreasing icorr values from ~10-7 to ~10-9 A/cm2, increasing the passivation range (> 300 mV), and shifting Ecorr values to more negative potentials. After salt spray testing, Pr-hydroxide/hydroxycarbonate species were present on the surfaces of the primers. The addition of Pr2O3 afforded enhanced corrosion protection compared to the addition of Pr6O11 because Pr2O3 is a more reactive phase that provided more Pr3+ species for transport and reaction than Pr6O11.