ABSTRACT

The inhibitive and adsorption characteristics of ethanol extracts of Gnetum africana, Heinsia crinata, Lasianthera africana, Piper guinensis, and Vernonia amygdalina on the corrosion of mild steel have been studied using weight loss, IR analysis, phytochemical analysis, gasometric and thermometric methods. The results obtained reveal that various concentrations of the extracts inhibited the corrosion of mild steel in H2SO4between the temperature range of 303-333K. Values of inhibition efficiency calculated from weight loss measurement at various concentrations of Heinsia crinata when used as an inhibitor were found to be 52.77% at 0.IM, 61.59% at 0.2M, 64.38% at 0.3M, 75.51% at 0.4M, and 79.01% at 0.5M. Thermometric values of inhibition efficiency for Heinsia crinata are 43.22% at 0.IM, 48.97% at 0.2M, 56.34% at 0.3M, 65.44% at 0.4M, and 70.32% at 0.5M concentration. 47.36%, 57.89%, 61.84% 68.42% and 84.21% were values of inhibition efficiency calculated from gasometric measurement at 0.IM, 0.2M, 0.3M, 0.4M and 0.5M concentrations respectively. Values of inhibition efficiency at various concentrations of Piper guinensis, Lasianthera africana, Gnetum africana and Vernonia amygdalina were also recorded. The inhibition efficiencies of these extracts increased with increase in concentration of the extracts, but decreased with increase in temperature. The effectiveness of Gnetum africana, Heinsia crinata, Lasianthera africana, Piper guinensis, and Vemonia amygdalina as good inhibitors is attributed to the presence of 0-H, N-H, C-H, C=0, C-N and C=C functional groups as observed in their JR spectra. However, the inhibition efficiencies of the extracts are not significantly improved by synergistic combination with KI, KCI and KBr. Kinetic study of the extracts reveals that the inhibited and unihibited corrosion of mild steel in the study medium proceeded via first order kinetics with half-life values for the inhibited reactions being higher than values for the uninhibited reactions. The adsorption of the inhibition on the mild steel surface as revealed by thermodynamic consideration is spontaneous and exothermic. The use of ethanol extract of Gnetum africana, Heinsia crinata, Lasianthera africana, Piper guinensis, and Vernonia amygdalina as inhibitors for the corrosion of mild steel is therefore recommended.