Allyl triphenyl phosphonium bromide, an ionic liquid as an eco-friendly and green inhibitor for corrosion of aluminium in hydrochloric acid: Mechanistic insights and experimental validation

Abstract

Allyl Triphenyl Phosphonium Bromide (ATPB), an ionic liquid was used as an inhibitor for mitigation of corrosion of aluminium in a 0.5 M hydrochloric acid. The mitigating properties of ATPB was experimentally evaluated through gravimetric, potentiodynamic polarization and electrochemical impedance techniques. The highest inhibition efficiency of 99.95 % was achieved at 308 K. The mitigation of corrosion was caused by the spontaneous assembly of an ATPB monolayer onto the aluminium surface. As the concentration of ATPB rises, the extent of adsorption also increases. The accumulation of ATPB molecules over aluminium surface obeys the Langmuir adsorption isotherm. The strength of adsorption is also enhanced through the electrostatic interaction of bromide anion with the surface of aluminium. The enhancement of charge transfer resistance (R_ct) values on addition of ATPB in electrochemical impedance spectroscopic studies in comparison over the R_ct value in HCl without ATPB reveals that charge transfer mechanism is involved in the inhibition process. The decrease in double layer capacitance (C_dl) also occurred along with an increase in concentrations. This suggests, the adsorption is the key to the inhibition of corrosion of aluminium. SEM micrograms and EDXS confirmed the presence of a protective ATPB layer on the aluminium surface. Density functional theory (DFT) calculation also supports the experimental observation.