Corrosion Inhibition of Copper in 2M Nitric Acid Solution by 2-(Thiobenzyl)-5-Nitro-1H-Benzimidazole

Abstract

Pickling with nitric acid is commonly practiced in industry for finishing metal surfaces. The use of inhibitors during the pickling operation is of very recent origin. The TBNBI inhibition effect on copper corrosion in 2M nitric acid solution was investigated by weight loss method in relation to the temperature (25 to 40°C) and inhibitor concentration range 10-4 to 5.10-3 M. The results show that TBNBI is a good inhibitor for copper and the inhibition efficiency increases with concentration of TBNBI but decreases with increase in temperature. The adsorption parameters (ΔGa0ds ,ΔHa0ds ,ΔSa0ds ) and the activation ones * * a a a (E ,ΔH ,ΔS ) for the corrosion process in inhibited and uninhibited nitric acid solution were also calculated using Arrhenius equations. It can be concluded that the adsorption of the compound is spontaneous and found to occur through both physisorption and chemisorption processes. The adsorbed film on copper surface was characterized using optic microscopy and Raman spectroscopy. The surface analysis confirmed the inhibition action of TBNBI. Quantum chemical calculations using Gaussian 09 at B3LYP level with 6-31G (d,p) basis set lead to obtain molecular descriptors such as EHOMO (energy of the highest occupied molecular orbital), ELUMO (energy of the lowest unoccupied molecular orbital), ΔE (energy gap) and μ (dipole moment). The global reactivity descriptors such as χ (electronegativity), η (hardness), S (softness) and ω (electrophilicity index) were derived using Koopman’s theorem and analyzed. We used the condensed Fukui function and softness indices, Mulliken population analysis for local reactivity study. The calculated results are consistent with the experimental data.