Electrochemical and Computational Studies for Mild Steel Corrosion Inhibition by Benzaldehydethiosemicarbazone in Acidic Medium

T A Salman, K A Samawi, J K Shneine
2019 Portugaliae Electrochimica Acta  
The inhibiting effect of benzaldehydethiosemicarbazone (BTSC) on the mild steel alloy corrosion in a 1 M sulfuric acidic solution was potentiostatically investigated at four temperatures, in the range of 298.15 to 328.15 K. Three BTSC concentrations, ranging from 100 to 300 mg/L, were tested. Mild steel corrosion feasibility decreases with increasing inhibitor concentrations, and also with the rise in temperature. A protection efficiency of 96% was obtained at 300 mg/L, and 328.15 K.
more » ... 28.15 K. Potentiostatic polarization studies showed that BTSC acted as a mixed type inhibitor. The main kinetic effect of the BTSC inhibitor added to the sulfuric acid solution was to considerably enhance activation energy values, pre-exponential factor and activation entropy of the alloy corrosion. This was because BTSC shifted the corrosion reaction on the mild steel surface to reaction sites where energy was relatively higher than that on which the corrosion occurred in the inhibitor absence. The inhibitor adsorption followed the Langmuir adsorption isotherm. The activation thermodynamic functions (Ea, Kads, ΔGads., ∆Hads. and ∆Sads) were evaluated. The obtained activated parameters revealed that BTSC adsorption took place through chemisorption. Scanning electron microscopy (SEM) technique was used to provide insight into the formation of a protective film on the alloy surface. To provide a relationship between the BTSC's molecular structure and its corrosion inhibition capability, quantum chemical studies were achieved using density functional theory (DFT) at the B3LYP/6-311G level. T.A. Salman et al. / Port. Electrochim. Acta 37 (2019) 241-255 242 corrosion inhibition in acidic solutions can be considered as one of the most serious solutions to decrease metal corrosion and excess acid consumption [3] . Generally, heterocyclic organic compounds, comprising oxygen, nitrogen, or sulfur hetero atoms and an electron conjugated system, are mostly applied as efficient corrosion inhibitors to retard mild steel alloys retrogradation [4] . The molecules adsorption onto the metallic surface can be considerably determined by the valence shell lone pairs in heteroatoms and by the geometrical planarity [5] . The corrosion inhibition efficiencies strongly depend on the inhibitor capability to adsorb onto the metal surface, and on the chemical, physical and structural properties of organic molecules [6] . Excellent corrosion inhibition can be obtained using organic compounds, which can form coordinate covalent bonds by connecting their occupied valence shell electrons to unoccupied metal surface d-orbitals, and accept free electrons from the metal surface, using unoccupied anti-bonding orbitals and forming resistant bonds [7] [8] . In order to elucidate the electronic structure and reactivity, and to determine the molecular structure, it is very useful to apply quantum chemical methods [9] . Density functional theory (DFT) can be considered as a very useful model to explain, predict and understand numerous features of chemical processes [10] [11] [12] . Generally, applied chemical reactivity functional elements, such as softness or hardness and electronegativity can be naturally shown in the DFT method [13] . The inhibitor functionality is strongly related to its frontier molecular orbital (FMO), involving lowest unoccupied molecular orbital (LUMO), highest occupied molecular orbital (HOMO), and other factors, such as softness or hardness. Theoretical investigations using quantum chemical methods have successfully explained and determined the relationship between corrosion inhibition efficiency and molecular orbital (MO) energy levels for specific types of organic molecules [14] . In the present work, the inhibiting effect of benzaldehyde thiosemicarbazone (BTSC) (Fig. 1 ) on mild steel corrosion in a 1 M H2SO4 solution, at four different temperatures in the range from 298.15 to 328.15 K, was investigated. Theoretical and electrochemical experiments were herein applied.
doi:10.4152/pea.201904241 fatcat:klzf6mojaje5tlbh35hshx2x74