The Inhibition of Aluminum Corrosion in Sulfuric Acid by Poly(1-vinyl-3-alkyl-imidazolium Hexafluorophosphate)

Compounds of poly(ionic liquid)s (PILs), derived from imidazole with different alkylic chain lengths located in the third position of the imidazolium ring (poly(1-vinyl-3-dodecyl-imidazolium) (PImC(12)), poly(1-vinyl-3-octylimidazolium) (PImC(8)) and poly(1-vinyl-3-butylimidazolium) (PImC(4)) hexafluorophosphate) were synthesized. These compounds were tested as corrosion inhibitors on aluminum alloy AA6061 in diluted sulfuric acid (0.1–1 M H(2)SO(4)) by weight loss tests, polarization resistance measurements and inductively coupled plasma optical emission spectroscopy. Langmuir’s isotherms suggested film formation on bare alloy while standard free energy indicated inhibition by a physisorption process. However, compound efficiencies as inhibitors ranked low (PImC(12) > PImC(8) > PImC(4)) to reach 61% for PImC(12) in highly diluted acidic solution. Apparently, the high mobility of sulfates favored their adsorption in comparison to PILs. The surface film displayed general corrosion, and pitting occurred as a consequence of PILs’ partial inhibition along with a continuous dissolution of defective patchy film on formation. A slight improvement in efficiency was displayed by compounds having high molecular weight and a long alkyl chain, as a consequence of steric hindrance and PIL interactions.