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Thermodynamic, Chemical and Electrochemical Investigations of 4-Hydrobenzoic Acid as Corrosion Inhibitor for Mild Steel Corrosion in Hydrochloric Acid Solutions

Paul O Ameh, Pius Ukoha, Paul Ejikeme and Nnabuk O Eddy

The corrosion inhibition of mild steel in 0.1M HCl solution by 4-hydrobenzoic acid was studied at temperature range 303, 313, 323 and 333 K using weight loss measurement, thermometric, Polarization Resistance, Potentiodynamic Polarization, Electrochemical Impedance Spectroscopy, Scanning Electron Microscopy (SEM) and Fourier transformed infra-red spectroscopy (FTIR) techniques. The results obtained at 303 K indicated that the studied inhibitor had established >88% inhibition efficiency at an optimum concentration of 0.10 M. The adsorption of 4-hydrobenzoic acid takes place according to Langmuir`s adsorption isotherm. Kinetic parameters (activation energy, Ea and pre-exponential factor, A) as well as thermodynamic parameters (enthalpy, entropy and free energy of adsorption; ΔH_ads ^o ΔSads ^o, and ΔGads o respectively) were calculated and discussed. Potentiodynamic polarization studies indicate that 4-hydrobenzoic acid acts as a mixed type of inhibitor. Data collected from EIS studies has been analyzed to model the appropriate equivalent circuit for better explanation of corrosion inhibition process. The surface analysis study using SEM confirms the corrosion of the mild steel and its inhibition by the inhibitor. FTIR spectra of the inhibitor and the corrosion product of mild steel (in the presence of the inhibitor) reveal that there were shifts in frequencies of adsorption suggesting that some functional groups were used in adsorption and some new bonds were formed.