Formamidine-Based Thiuram Disulfides as Efficient Inhibitors of Acid Corrosion of Mild Steel: Electrochemical, Surface, and Density Functional Theory/Monte Carlo Simulation Studies.

Electrochemical, surface, and density functional theory (DFT)/Monte Carlo (MC) simulation studies were used in investigating the characteristics of N,N'-(disulfanne-1,2-dicarbonothioyl)bis(N,N'-bis(2,6-dimethylphenyl)formimidamide) (DS1), N,N'-(disulfanne-1,2-dicarbonothioyl)bis(N,N'-bis(2,6-diisopropylphenyl)formimidamide) (DS2), N,N'-(disulfanne-1,2-dicarbonothioyl)bis(N,N'-dimesitylformimidamide) (DS3), and N,N'-(disulfanne-1,2-dicarbonothioyl)bis(N,N'-bis(2,6-dichlorophenyl)formimidamide) (DS4) as inhibitors of acid corrosion of mild steel. The inhibitors were found to effectively reduce the rates of steel dissolution at the anode as well as cathodic hydrogen evolution. The order of inhibition efficiencies of studied compounds is DS1 (PDP/LPR/EIS: 98.60/97.98/96.94%) > DS2 (PDP/LPR/EIS: 98.36/96.86/96.90%) > DS3 (PDP/LPR/EIS: 94.66/87.44/94.30%) > DS4 (PDP/LPR/EIS: 83.57/77.02/75.17%) at 1.00 mM, and the overall efficiencies appeared to depend on the molecular and electronic structures of the compounds. The compounds offered high resistance to charge transfer across the electrode/electrolyte system by forming adsorbed film whose resistance increased with an increase in concentration. Findings suggested that the adsorption process involved combined chemisorption and physisorption. DFT calculations and MC simulations provided theoretical justifications for the experimental results.

Predicting protection capacities of pyrimidine-based corrosion inhibitors for mild steel/HCl interface using linear and nonlinear QSPR models.

Pyrimidine compounds have proven to be effective and efficient additives capable of protecting mild steel in acidic media. This class of organic compounds often functions as adsorption-type inhibitors of corrosion by forming a protective layer on the metallic substrate. The present study reports a computational study of forty pyrimidine compounds that have been investigated as sustainable inhibitors of mild steel corrosion in molar HCl solution. Quantitative structure property relationship was conducted using linear (multiple linear regression) and nonlinear (artificial neural network) models. Standardization method was employed in variable selection yielding five top chemical descriptors utilized for model development along with the inhibitor concentration. Multiple linear regression model yielded a fair predictive model. Artificial neural network model developed using k-fold cross-validation method provided a comprehensive insight into the corrosion protection mechanism of studied pyrimidine-based corrosion inhibitors. Using a multilayer perceptron with Levenberg-Marquardt algorithm, the study obtained the optimal model having a MSE of 8.479, RMSE of 2.912, MAD of 1.791, and MAPE of 2.648. The optimal neural network model was further utilized to forecast the protection capacities of nine non-synthesized pyrimidine derivatives. The predicted inhibition efficiencies ranged from 89 to 98%, revealing the significance of the considered chemical descriptors, the predictive capacity of the developed model, and the potency of the theoretical inhibitors.

Chromeno-carbonitriles as corrosion inhibitors for mild steel in acidic solution: electrochemical, surface and computational studies.

Three novel N-hydrospiro-chromeno-carbonitriles namely, 2-amino-7,7-dimethyl-1',3',5-trioxo-1',3',5,6,7,8-hexahydrospiro[chromene-4,2'-indene]-3-carbonitrile (INH-1), 3-amino-7,7-dimethyl-2',5-dioxo-5,6,7,8-tetrahydrospiro[chromene-4,3'-indoline]-2-carbonitrile (INH-2) and 3'-amino-7',7'-dimethyl-2,5'-dioxo-5',6',7',8'-tetrahydro-2H-spiro[acenaphthylene-1,4'-chromene]-2'-carbonitrile (INH-3) were synthesized using the principles of green chemistry and applied as corrosion inhibitors for mild steel in acidic medium using computational simulations and experimental methods. Experimental and computational studies revealed that inhibition effectiveness of the INHs followed the sequence: INH-3 (95.32%) > INH-2 (93.02%) > INH-1 (89.16%). The investigated compounds exhibit mixed-type corrosion inhibition characteristics by blocking the active sites on the surface of mild steel. EIS study revealed that the INHs behave as interface-type corrosion inhibitors. EDX analyses supported the adsorption mechanism of corrosion inhibition. A DFT study carried out for gaseous and aqueous forms of inhibitor molecules indicated that interactions of INHs with the mild steel surface involve charge transfer phenomenon or donor-acceptor interactions. A Monte Carlo (MC) simulation study revealed that only a fractional segment of the molecule lies parallel to the steel surface, since the INH molecules are not completely planar. The results of computational studies and experimental analyses were in good agreement.

Synthesis and structures of divalent Co, Ni, Zn and Cd complexes of mixed dichalcogen and dipnictogen ligands with corrosion inhibition properties: experimental and computational studies.

The structural and corrosion inhibition properties of four different transition-metal complexes of heteroleptic S-donor atom dithiophosphonate and N-donor atom phenanthroline ligands are reported. Full structural characterization of the Co, Ni, Zn and Cd complexes was achieved with the aid of single-crystal X-ray crystallography. Structural elucidation revealed the formation of a 4-coordinate Zn(ii) complex, and 6-coordinate Ni(ii) and Cd(ii), as well as a novel dithiophosphonato Co(ii) complex. The ability of the complexes with this ligand type to act as inhibitors of mild steel corrosion in 1 M HCl solution is reported for the first time. Corrosion inhibition potentials of the complexes were assessed using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and density functional theory (DFT). The open circuit potential (OCP) time profile showed the system achieved a steady-state potential before the first 600 s after submerging the working electrode in the corrosive medium. The studied metal complexes are good inhibitors of mild steel corrosion in 1 M HCl and were found to retard the corrosion rate by forming an adsorbed pseudocapacitive film on the steel surface. The order of inhibition efficiencies was in the order Ni (94.14%) > Cd (92.28%) > Zn (91.14%) > Co (72.53%).

Zinc Oxide Nanocomposites of Selected Polymers: Synthesis, Characterization, and Corrosion Inhibition Studies on Mild Steel in HCl Solution.

Nanocomposites of ZnO and some selected polymers, namely, poly(ethylene glycol), poly(vinylpyrrolidone), and polyacrylonitrile, were synthesized and characterized using Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) techniques. The FTIR and UV-vis spectra confirmed the successful formation of the polymer nanocomposites. TGA results revealed that the synthesized polymer nanocomposites are more thermally stable than the polymers alone. ZnO nanoparticles were about 50-75 nm in size, assumed a rodlike shape, and got embedded in the polymer matrices, as revealed by TEM images. Corrosion inhibition potentials of the synthesized ZnO/polymer nanocomposites were investigated for mild steel in 5% HCl solution using potentiodynamic polarization (PDP), linear polarization resistance, and electrochemical impedance spectroscopy measurements. The results showed that each ZnO/polymer nanocomposite inhibits mild steel corrosion in 5% HCl solution better than the respective polymer alone. The nanocomposites, according to PDP studies, behaved as a mixed-type inhibitor. The predominant mode of adsorption of the nanocomposites to a mild steel surface was found to be mixed type, and the adsorption process obeys the Langmuir adsorption isotherm model. Scanning electron microscopy images also revealed the protective attributes of the ZnO/polymer nanocomposites for mild steel in 5% HCl solution.