Experimental and Quantum Chemical Studies on Ethanol Extract of Phyllanthus amarus (EEPA) as a Green Corrosion Inhibitor for Aluminum in 1 M HCl

This work investigates the effectiveness of the eth anol extract of Phyllanthus amarus (EEPA) as a possible green corrosion inhibitor for aluminum in a HCl solution, using weight loss, linear and potentiodynamic polarizatio n methods, in order to evaluate the inhibition efficiencies of the plant extract, at va rious concentrations. Scanning electron microscopy and Fourier transformed infra red spectr os opy were used to study the surface morphology and engagement of functional gr oups in the corrosion inhibition process. The results obtained at 303 K from weight loss, linear polarization resistance and potentiodynamic polarization methods recorded a n inhibition efficiency that ranged from 56.65 to 69.17, 65.00 to 93.93 and from 51.38 to 79.96 %, respectively. Generally, the inhibition efficiency increased with higher concentrations, but decreased with a rise in temperature. The potentiodynamic stu dy revealed that EEPA acted as a mixed type inhibitor, and formed an insoluble film, which protected the metal against corrosion. Examination of micrographs in the inhib itor presence and absence also confirmed the role of the protective film in blocki ng the corrosion active sites on the metal surface. Spectra analysis obtained from Fouri er t ansformed infra-red study indicated that EEPA was adsorbed onto the aluminum s rface via C=O and OH functional groups. The inhibitor adsorption was spo ntaneous, exothermic, and supported the physical adsorption mechanism. Calculated quant um chemical parameters for EEPA constituents revealed that Phyllanthusin D is the most active corrosion inhibitor in the compound. HOMO and LUMO diagrams of Phyllanthusin D supported the findings from FTIR analysis.