ABSTRACT

The corrosion inhibition of mild steel and zinc plates in 0.5M HCl in the presence and absence of 4-{[(Z)-(4-chlorophenyl)methylidene}amino)-N-(5-methy-l-furan-3-yl) benzenesulfonamide herein referred to as (MMBS) and 4-{[(Z)-(4-dimethyl amino) phenyl] methylidene} amino)-N-(5-methyl furan-3-yl) benzenesulfonamide herein refers to as (CMBS) was investigated at temperature ranges of 303 K to 343 K. Their inhibition performances were tested by weight loss and quantum chemical techniques and were characterised using Fourier Transform Infrared spectrophotometer (FT-IR). The FT-IR spectroscopy showed that the synthesised Schiff bases contained some functional groups which may have aided in the inhibition of the metal species under consideration. The results obtained from the weight loss method showed that inhibition efficiencies of the inhibitors increased as the concentrations of the Schiff-base molecules increased and with the highest inhibition efficiency observed at the optimum concentration of 1.0 g/L employed but decreased with rise in temperature. The inhibitor (MMBS) showed inhibition efficiency of 89.59 % while the inhibitor (CMBS) showed inhibition efficiency of 92.36 % for mild steel while for zinc plate, inhibition efficiencies were 38.19 % and 39.98 % for (MMBS) and (CMBS) respectively. Inhibition efficiencies were also found to decrease with increase in temperature. The inhibition efficiencies followed the order; (MMBS) < (CMBS). The Kinetic data obtained showed that the corrosion process followed first order kinetics. The following adsorption isotherms models including Langmuir and Freundlich employed in the interpretation of the inhibition data showed that Langmuir model provided the best fit to the experimental data (R²>0.96). Thermodynamic studies of the inhibition process showed that the ΔG_ads values for (MMBS) and (CMBS) were both negative indicating the spontaneity of the reaction and the values were less than -20 kJmol^-1, indicating that the mechanism of adsorption is physisorption. The enthalpy values were positive for (MMBS) (121.650 – 148.904 Jmol^-1K^-1) on mild steel but negative for (MMBS) (-2.1213 to - 0.4059 Jmol^-1K^-1) on zinc showing that the reaction was endothermic for inhibition of mild steel but exothermic for inhibition of zinc. The quantum chemical parameters such as HOMO, LUMO, E_Homo; E_lijmo, and Energy gap (ΔE), aided in the elucidation of the probable points of interaction of these inhibitors with mild steel and zinc. The results obtained from the chemical studies showed that there exists a relationship between the inhibitors’ efficiency and the energy gap (ΔE), energy of the highest unoccupied molecular orbital (E_Homo), energy of the lowest occupied molecular orbital (E_Lumo), dipole moment (µ), softness (σ), as well as the hardness (η) of the inhibitor. The quantum chemical parameter, as indicators to their comparative inhibition potentials, agreed with experimental data.