The inhibitor effect of thiosemicarbazide and tetrazol derivatives on the corrosion of copper in a chloride solution

The present work investigates the corrosion inhibition of copper using seven corrosion inhibitors namely: Salicylaldehyde thiosemicarbazide (STSC), 5-Mercapto-1-methyle tetrazole (MMTA), 5-phenyl-1-H-tetrazole (PTA), 5-Amino-tetrazole mono hydrate (ATA), 4-allyl-3-thiosemicarbazide (ATSC), Exo-2-Norbornyl thiosemicarbazide (NTSC), and 4-(2-phenyl ethyl-3-thiosemicarbazide (PETSC). Copper samples were tested using potentiodynamic polarization and electrochemical impedance spectroscopy techniques in the absence and in the presence of corrosion inhibitors. The effect of immersion time on the inhibitors efficiency was also addressed. Some samples tested by scanning electron microscopy (SEM) were examined. Results show that tetrazole derivatives ATA and PTA give inhibition efficiencies exceeding 90% whereas MMTA give low inhibition efficiency (<71% ). On the other hand thiosemicarbazide derivatives; PETSC, NTSCand ATSC show corrosion inhibition efficiencies exceeding 95% while STSC thiosemicarbazide derivative show lower inhibition efficiencies (<82% ). Adsorption of the inhibitors on the copper surface conforms to the Langmiur adsorption isotherm. The adsorption constant and standard adsorption free energy (ΔGº) of the inhibitor was determined from this isotherm and it was understood that the inhibitors used were bound to the metal by chemical adsorption according to the obtained values. Quantum chemical calculations based on density functional theory (DFT) method were performed on the selected tetrazoles and thiosemicarabazide derivatives used as corrosion inhibitors for copper in sea water to determine the relationship between the molecular structure of inhibitors and inhibition efficiency. The structural parameters, such as energy and distribution of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), the charge distribution of the studied inhibitors, the absolute electronegativity (𝜒) values were calculated and correlated with inhibition efficiencies. The results showed that the inhibition efficiency of inhibitors increased with the increase in energy of HOMO and decrease in energy of LUMO, and the areas containing N and S atoms are most possible sites for bonding the copper surface by donating electrons to the Cu.