Monomers of lignin as corrosion inhibitors for mild steel: study of their behaviour by factorial experimental design

Abstract

This paper investigates the role of monomers of lignin on the corrosion inhibition of mild steel and their main and interaction effects on the corrosion parameters. A combination of statistical analysis and interaction contour plots has been employed to obtain an in depth understanding of the corrosion variables. Electrochemical tests were performed on three lignin monomers namely p-coumaric acid (CA), ferulic acid (FA) and hydroxybenzaldehyde (HB) on mild steel in near neutral solution. The CA and FA showed better inhibition of more than 70%, especially at higher concentrations. A full factorial method was used to study the main and interaction effects on these monomers. P-coumaric acid and FA have shown good inhibition with the greatest interaction effect with each other on the inhibition efficiency. Although HB had the lowest effect on inhibitor efficiency (%IE), its interaction with other monomers was significant. An empirical equation has been derived from test results to describe the relationship between the variables. Analysis of variance on the corrosion parameter shows a normalised distribution and confirms the suitability of this model. Scanning electron micrographs also showed an increase in inhibition with the metal surface with increasing inhibitor concentration.