Corrosion Inhibition of Mild Steel in Acidic Solutions by Crude Leaf Extracts of Solanum melongena AND Chrysophyllum albidum

ABSTRACT

Corrosion of mild steel used in industrial and engineering enviroments has posed a serious problem in the society. Hence, this research investigated the effects of ethanol, water and sulphuric acid extracts of Solanum melongena(SM), (garden egg) and Chrysophyllum albidum (CA), (sherry) on the corrosion of mild steel in I M HCl and 0.5 M H2S04 solutions using gravimetric and electrochemical techniques. The results obtained indicated that all studied plant extracts were adsorption type inhibitors. Corrosion rate of mild steel in 0.5 M H2SO4 was higher than in I M HCl. However, with the introduction of the inhibitors, the rate highly reduced in both solutions. Gravimetric result showed that the extracts effectively inhibited mild steel corrosion with water extract of SM showing highest inhibition efficiency of 99.62% in I M HCl corrodent, while ethanol extract of SM showed highest inhibition efficiency of 99.58% in 0.5 M H2SO4 corrodent. Three extracting solvents were used and they gave good inhibition efficiency with ethanol extract giving highest of 99.58%, water extract gave 99.26% and 0.5 M H2S04 extract gave 96.82%. We observed that Inhibition efficiencies increased with increasing concentrations of the extracts. Both SM and CA were very good inhibitors with SM showing highest inhibition efficiency of 99.62% in 1 M HCl and CA showing highest inhibition efficiency of 99.44% in 0.5 M H2SO4. Potentiodynamic polarization result showed that all studied extracts were mixed type inhibitors. The GC-Mass Spectra of the ethanol extracts of Solanum melongena and Chrysophyllum albidum showed that they were rich in organic compounds like Methoxypyrimidine, Furan, 1,4-Eicosadiene, 2- Acetyl-6-Methoxynaphthalene, phytol, imidazole, 3,5-Dihydroxytoluene, 2,4-Diaminophenol, cyclopentane and many more. Compounds with nitrogen and oxygen, and nitrogen or oxygen in a conjugated system were found in abundance of 87-99% indicating that they can be extracted in large quantities, these compounds are the likely components responsible for the inhibitory behavior of the plants, and examples of such compounds are indole, methenamine, and 2- Methoxy-4-vinylphenol.