Experimental and Theoretical Studies of α-Linolenic Acid as Green Corrosion Inhibitor for Carbon Steel in 0.5 M Sulfuric Acid.

I.A Hermoso-Diaz,E Sarmiento-Bustos,R Lopez-Cecenes,J.P Flores-De Los Rios,L.L Landeros-Martínez,J Uruchurtu-Chavarin,J.G Gonzalez-Rodriguez

doi:10.3390/molecules26206169

Abstract

A component of Salvia hispanica, α-linolenic acid, has been evaluated as a green corrosion inhibitor for 1018 carbon steel in 0.5 M sulfuric acid using weight loss tests, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) measurements. Theoretical calculations using Density Functional Theory (DFT) were used also. The results have shown that this compound is a good corrosion inhibitor, with an efficiency which increased with an increase in its concentration up to 600 ppm, but it decreased with a further increase in the concentration. α-linolenic acid formed protective corrosion products layer because it was chemically adsorbed onto the steel surface according to a Langmuir type of adsorption isotherms. Polarization curves have shown that α-linolenic acid is a good, mixed type of inhibitor with a predominant effect on the cathodic hydrogen evolution reactions. EIS measurements indicated a charge transfer-controlled corrosion process. DFT calculations indicated that α-linolenic acid was more efficient in an acidic environment than in a neutral one because has a high tendency to donate electrons and can be easily protonated. In addition to this, it had the highest EHUMO value, the best chemical reactivity, the greatest tendency to transfer electrons and a greater facility of modifying its electronic configuration in the presence of carbon steel specimens according to its chemical hardness value.

Highlights

The study of corrosion of metals and alloys is a very important fact from both academic and industrial points of view due to big economical losses and many accidents it causes to a country [1,2]
The results have shown that this compound is a good corrosion inhibitor, with an efficiency which increased with an increase in its concentration up to 600 ppm, but it decreased with a further increase in the concentration. α-linolenic acid formed protective corrosion products layer because it was chemically adsorbed onto the steel surface according to a Langmuir type of adsorption isotherms
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Summary

Introduction

The study of corrosion of metals and alloys is a very important fact from both academic and industrial points of view due to big economical losses and many accidents it causes to a country [1,2]. In another work [27], modified lignin was evaluated as a green corrosion inhibitor for mild steel in HCl by using the same electrochemical and gravimetric techniques. Banana peels were evaluated as green corrosion inhibitors for mild steel in HCl. The authors found big differences between raw and ripe banana peel extracts [29]. Brassica oleracea extract was evaluated as a naturally occurring inhibitor for X-52 pipeline steel in 0.5 M H2SO4 [30], finding an increase in the inhibitor efficiency with the inhibitor concentration and temperature up to certain values. Retama monosperma [31], Eleusine aegyptiaca and Croton rottleri leaf extracts [32] have been evaluated as green corrosion inhibitors for mild steel in HCl

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