ABSTRACT

Inhibitive action of methanol extracts of Kalanchoe crenata (K C) and Landoiphia dulcis (L.D) leaves for corrosion of mild steel in 5.0 M H2SO4solution was studied using gravimetric and gasometric methods. The results showed that K C and L.D are good corrosion inhibitors in 5.0 M H2SO4solution. K.0 showed higher efficiency thanL.D in gravimetric with values of 86.96% and 82.6 1% respectively. Also, in gasometric analysis, the inhibition efficiency of K.0 was higher than L.D with values of 84.43% and 83.99% respectively .The corrosion inhibition efficiency increased with increase in the concentration of the extracts and decreased with increase in exposure time and temperature. It was observed that the rate of hydrogen evolution increased with increase in temperature. The corrosion inhibition action exhibited by the two plant extracts is attributed to the presence of some notable functional groups as observed in the FTIR spectra of the plant extract which indicates presence of some phytochemicals in theplant extracts. Considering the trends and values of the activation energy, heat of adsorption, Gibbs free energy, entropies and adsorption isotherms, the mechanism of adsorption proposed for the two extracts in 5.0 M H2SO4was physical adsorption. Theoretical fittings of different isotherms were tested and the experimental data best fitted into Langmuir isotherm for K C plant extract and that of L. D. fitted best into Temkin isotherm.