Electrochemical thermodynamic and kinetic studies of the behaviour of aluminium in hydrochloric acid containing various benzotriazole derivatives

Abstract

In this study the inhibitive behaviour of benzotriazole, 5-methyl benzotriazole, 5-chloro benzotriazole and 5-nitro benzotriazole on the corrosion of pure aluminium in 0.1M HCl has been investigated by the potentiostatic polarisation technique. For this purpose, corrosion potentials Ecorr, corrosion rates icorr, anodic and cathodic Tafel slopes βa, βc, inhibition efficiencies IE, and surface coverages θ, were determined in 0.1M HCl solutions containing various concentrations (i.e. 1×10-5 M, 5×10-5 M, 1×10-4 M, 5×10-4 M, 1×10-3 M) of benzotriazole derivatives. The efficiency of the studied benzotriazole derivatives at a concentration of 1×10-4 M was found be in the following order: 5-nitrobenzotriazole > 5-methyl benzotriazole > 5-chloro benzotriazole > benzotriazole. It was observed that the benzotriazole derivatives were behaving as cathodic inhibitors and the inhibiting action of these heterocyclic compounds was mainly due to adsorption on the metal surface, which parallels the total negative charge of each molecule. From the adsorption isotherms, values of the free energy of adsorption ΔGads and the equilibrium constant Kads for the adsorption processes were calculated. Corrosion rates were determined electrochemically at 20°C, 30°C, 40°C, 50°C and 60°C with 1×10-4 M or 1×10-3 M of these compounds in 0.1M HCl. From the corrosion rates obtained at different temperatures, activation parameters for the corrosion processes such as activation energies Ea, activation enthalpies ΔH* and activation entropies ΔS* were determined and possible mechanisms for the corrosion and inhibition processes have been proposed.