Theoretical and Experimental Investigations of the Corrosion Inhibition Action of Piliostigma Thonningii Extract on Mild Steel in Acidic Medium

Abstract

The search for green corrosion inhibitor for mild steel in solution of HCl was implemented in this work by using electrochemical polarization, gravimetric and thermometric techniques to investigate the corrosion inhibition efficiency of ethanol extract of Piliostigma thonningiil leaf. Results obtained from weight loss and thermometric measurements indicated that the inhibition efficiency of ethanol extract of Piliostigma thonningii leaf ranged from 65.12 to 79.55 % and from 73.61 to 88.16 % respectively. The ranges for inhibition efficiencies from, linear and potentiodynamic polarization measurements were 66.40 to 89.97 % and 51.29 to 85.53 % respectively Active components of the extracts that synergistically cooperated to enhance their adsorption on mild steel surface (and hence corrosion inhibition) were identified through GCMS analysis and they included 1,1,7-trimethyl-4-methylenedecahydro-1H-cyclopropa[e]azulene; hydroquinone; 3-tridecene; 3,5-bis(1,1-dimethylethyl)-phenol; Pentadecanoic acid; 1- ethenyl-1-methyl-2,4-bis(1-methylethenyl)-cyclohexane and 9-oxa-bicyclo[3,3,1]nona-3,6- dien-2-one. Results from quantum chemical calculations revealed that these compounds (apart from meeting the basic requirements for corrosion inhibition) are characterized by frontier molecular energy values that are unique for well-known corrosion inhibitors.