No abstract

Aluminium corrosion inhibition in 1.0 M hydrochloric acid solution by caffeine has been studied using mass loss technique and quantum chemical calculations based on DFT. The inhibition efficiency was found to increase with increasing concentration of caffeine but decreases with a rise in temperature. The molecule shows the highest inhibition efficiency of 74% at 10 −2 M for = 303 K. The experimental data were used to fit isotherms including Langmuir, Temkin, Freundlich, and El-Awady. The best fits were obtained with the Langmuir model and the kinetic-thermodynamic adsorption model of El-Awady. However, it was found that the adsorption parameters suit well with the isotherm of El-Awady which was chosen as the appropriate isotherm. To distinguish between physisorption and chemisorption, the Dubinin-Radushkevich adsorption model was used. The thermodynamic parameters governing the adsorption of caffeine onto aluminium and that of the metal dissolution were calculated and discussed. DFT study gave further insight into the mechanism of the inhibiting action of caffeine.

Corrosion behavior of copper in 1 M nitric acid containing either 2-mercaptobenzimidazole (MBI) or 2-thiomethylbenzimidazole (TMBI) was investigated experimentally and theoretically via weight loss method and quantum chemical approaches. It was found that the two compounds exhibit a very good performance as inhibitors for copper corrosion in the studied medium. Results show that the inhibition efficiencies increase with increasing temperature and increasing concentration of the inhibitors. It has been found that the studied compounds adsorb onto copper according to the modified Langmuir adsorption isotherm and the kinetic/thermodynamic isotherm of El-Awady. The thermodynamic adsorption parameters and kinetic corrosion parameters were determined and analyzed; on the bases of these parameters both physisorption and chemisorption were suggested for the studied compounds. Furthermore, the quantum chemical properties/descriptors most relevant to their potential action as corrosion inhibitors have been calculated. They include E HOMO , E LUMO , energy gap (ΔE), dipole moment (μ), hardness (η), softness (σ), the fractions of electrons transferred (ΔN), electrophilicity index (ω), and the total energy change (ΔE T ). The theoretical results were found to be consistent with the experimental data reported.