Alkyl phosphonium-based ionic liquids as promising additives for the corrosion protection of epoxy coatings in saline medium: Effect of the anion

Alkyl phosphonium-based ionic liquids (ILs), namely trihexyl(tetradecyl)-phosphonium chloride (P66614Cl), ethyl-(tributyl)-phosphonium diethyl phosphate (P4442[dep]), trihexyl(tetradecyl)-phosphonium bis(trifluorosulfonyl)imide (P66614[TFSI]), and trihexyl(tetradecyl)-phosphonium zinc tetrachloride ([P66614]2[ZnCl4]) were used for the first time as anticorrosive additives for epoxy coatings on AISI 1020 carbon steel plates. The corrosion protection performance of intact and artificially scratched coatings was evaluated in 3.5 wt% NaCl aqueous solution by electrochemical impedance spectroscopy. Regarding the intact coatings, those containing 0.5 phr of [P66614]2[ZnCl4] and 1.0 phr of P66614[TFSI] and P4442[dep] presented excellent corrosion resistance up to 720 h of immersion with |Z|f=0.01Hz values higher than 1010 omega cm2. The scratched coatings loaded with P4442[dep] displayed the best anticorrosive response after 168 h of immersion. Furthermore, these coatings and that loaded with 0.5 phr of [P66614]2[ZnCl4] displayed an increase of corrosion resistance with increasing the immersion time, suggesting the formation of a passivating layer at the epoxy-substrate interface. The inhibition characteristic of the corresponding anions in the IL component contributes for this behavior. The hydrophobic characteristic of the coatings before and after the immersion in the saline solution was studied by measuring the water contact angle. Furthermore, the adhesion strength after immersion was also investigated by pull-off testing. Effect of ionic liquids on the anti-corrosive and self-healing properties of epoxy coatings.image