A Comparative Study of the Inhibitory Effect of the Extracts ofOcimum sanctum,Aegle marmelos, andSolanum trilobatumon the Corrosion of Mild Steel in Hydrochloric Acid Medium

M. Shyamala,P. K. Kasthuri

doi:10.1155/2011/129647

Abstract

A comparative study of the inhibitory effect of plant extracts,Ocimum sanctum, Aegle marmelos, andSolanum trilobatum, on the corrosion of mild steel in 1N HCl medium was investigated using weightloss method, electrochemical methods, and hydrogen permeation method. Polarization method indicates plant extracts behave as mixed-type inhibitor. The impedance method reveals that charge-transfer process mainly controls the corrosion of mild steel. On comparison, maximum inhibition efficiency was found inOcimum sanctumwith 99.6% inhibition efficiency at 6.0% v/v concentration of the extract. The plant extracts obey Langmuir adsorption isotherm. The SEM morphology of the adsorbed protective film on the mild steel surface has confirmed the high performance of inhibitive effect of the plant extracts. From hydrogen permeation method, all the plant extracts were able to reduce the permeation current. The reason for the reduced permeation currents in presence of the inhibitors may be attributed to the slow discharge step followed by fast electrolytic desorption step. Results obtained in all three methods were very much in good agreement in the orderOcimum sanctum>Aegle marmelos>Solanum trilobatum.

Highlights

Mild steel is a structural material widely used in automobiles, pipes and used in most of the chemical industries
The weight loss studies were done in 1N hydrochloric acid in the absence and presence of various concentrations of the plant extracts ranging from 2% to 10% v/v
The optimum concentration for Ocimum sanctum was found to be 6% v/v with maximum inhibition efficiency of 99.6%, Aegle marmelos at 8% v/v with maximum inhibition efficiency of 97.5%, and Solanum trilobatum at 10% v/v with maximum inhibition efficiency of 90.2% for a period of 3 hours of immersion time. This result indicated that the plant extracts could act as effective corrosion inhibitors for mild steel in 1N HCl

Summary

Introduction

Mild steel is a structural material widely used in automobiles, pipes and used in most of the chemical industries. Organic compounds containing O, N, and S atoms are normally used as inhibitors to reduce the corrosion of mild steel in hydrochloric acid medium [1, 2]. Due to the diversity of their structures, many extracts of common plants have been used as corrosion inhibitors for materials in pickling and cleaning processes. Polysaccharides, polycarboxylic acids, tannin, alkaloids, and so forth These compounds are potential acid corrosion inhibitors for many metals [3]. Leaf extracts of three medicinal plants, namely, Ocimum sanctum (Tulasi), Aegle marmelos (Vilvam), and Solanum trilobatum (Thuthuvalai), have been selected to study the inhibition effect on the corrosion of mild steel in 1N hydrochloric acid medium using weight loss method, the potentiodynamic polarization method, electrochemical impedance method, and hydrogen permeation method

Experimental Procedure

Results and Discussion

Conclusion