Investigation of mechanism of inhibition of corrosion of mild steel by fast green

Abstract

This research work investigated the potential of fast green (C₃₇H₃₄N₂O₁₀S₃Na₂) as inhibitor of corrosion for mild steel in 1M HCl. Gravimetric method was employed for the studies. The influence of concentration, time of immersion and temperature on corrosion rate were investigated. The corrosion rate was found to decrease from 3.50 x 10^-4 to 1.8 x 10^-4 g/cm²/h as the concentration of the fast green was increased from 1 to 5 %v/v. The inhibition efficiency (IE %) thus increased from 30 to 65 % within the concentration range (1-5 v/v %) of the inhibitor within 24 h at room temperature (30 ^oC). The corrosion rate also increased from 2.44 x 10^-4 to 9.03 x 10^-4 g/cm²/h as the experimental hours was increased from 24 to 120 h for the studies at room temperature. The adsorption studies confirmed that Langmuir isotherm was the best model to explain the adsorption characteristics of fast green on the mild steel, with a correlation efficiency (r²) of 0.9847. The standard free energy associated with the adsorption, ΔG°_ads, was calculated to be -25.78 kJmol^-1. The value being up to -20 kJmol^-1 suggest that the adsorption of fast green molecules on to the mild steel surface is essentially by physisorption. It can concluded that the inhibitor acted as a mixed type inhibitor since the experimental data fit into the Langmuir model, which is characteristics of chemisorption.