Thermodynamic Characterisation and Density Functional Theory Investigation of 1, 1', 5,5'-Tetramethyl-1H, 1'H-3, 3'-Bipyrazole as Corrosion Inhibitor of C38 Steel Corrosion in HCl

The corrosion inhibition by a 1, 1', 5 ,5'-tetramethyl-1H, 1'H-3, 3'-bipyrazole (Bip) on C38 steel in hydrochloric acid (HCl) solution has been investigated by weight loss at 308-343K. The results obtained revealed that the inhibition efficiency decreased with increase in temperature. Inhibition occurred through adsorption of the Bip molecules on the metal surface. The value of activation energy (Ea), Arrhenius factor, enthalpy and entropy for the Bip corrosion inhibition and the thermodynamic parameters such as adsorption equilibrium constant (Kads), free energy of adsorption (ΔG°ads), adsorption heat (ΔH°ads) and adsorption entropy (ΔS°ads) values were calculated and discussed. Adsorption of Bip on the C38 steel surface in 1M HCl follows the Langmuir isotherm model. Quantum chemical calculations using DFT at the B3LYP/6-31G* level of theory was further used to calculate some electronic properties of the molecule in order to ascertain any correlation between the inhibitive effect and molecular structure of 1, 1', 5,5'-tetramethyl-1H, 1'H-3, 3'-bipyrazole (Bip).

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