Thermodynamic Behaviour of Mild Steel Corrosion in an Environment of Bilberry Cactus Plant Extracts in Hydrochloric Acid Solution

The inhibitive action of bilberry cactus plant extracts (BCPE) on mild steel in 1.5 M Hydrochloric acid with addition of different concentrations (0.1-0.5 g/l) was investigated using weight loss and hydrogen evolution measurement methods. The inhibitor organic structures were characterized for their functional groups using Gas Chromatography Mass Spectrometer (GCMS) and Fourier Transformation InfraRed (FTIR) analyses. The results revealed that the protective film formed on the surface of mild steel by the adsorption of extracts in 1.5 M HCl solution obeyed Langmuir adsorption isotherm. It was observed from thermodynamic adsorption parameters (∆????????????????, ∆????????????????, ???????????? ∆????????????????) that the inhibitor adsorbed via physical adsorption and the negative values obtained indicate exothermic reaction and spontaneous process. Finally, the effect of substituents type in inhibition efficiency was investigated using Linear Free Energy Relationship (Hammett relationship) and the reaction of adsorption favored by electron donation of the extract substituent groups.