Corrosion inhibitors : Part II: Quantum chemical studies on the corrosion inhibitions of steel in acidic medium by some triazole, oxadiazole and thiadiazole derivatives

The corrosion inhibition efficiencies of some triazole, oxadiazole and thiadiazole derivatives for steel in presence of acidic medium have been studied by using AM1, PM3, MINDO/3 and MNDO semi-empirical SCF molecular orbital methods. Geometric structures, total negative charge on the molecule (TNC), highest occupied molecular energy level (E_HOMO), lowest unoccupied molecular energy level (E_LUMO), core-core repulsion (CCR), dipole moment (μ) and linear solvation energy terms, molecular volume (V_i) and dipolar-polarization (π^*), were correlated to corrosion inhibition efficiency. Four equations were proposed to calculate corrosion inhibition efficiency. The agreement with the experimental data was found to be satisfactory; the standard deviations between the calculated and experimental results ranged between ±0.03 and ±4.18. The inhibition efficiency was closely related to orbital energies (E_HOMO and E_LUMO) and μ. The correlation between quantum parameters and experimental inhibition efficiency has been validated by single point calculations for the semi-empirical AM1 structures using B3LYP/6-31G^** as a higher level of theory. The proposed equations were applied to predict the corrosion inhibition efficiency of some related structures to select molecules of possible activity from a presumable library of compounds.     

Corrosion Inhibition Efficiency,Electrochemical and Quantum Chemical Studies of Some New Nonionic Surfactants for Carbon Steel in Acidic Media

In this work, three types of nonionic surfactant as corrosion inhibitors were synthesized. The chemical structure of the prepared inhibitors was confirmed using FT‐IR and ¹H‐NMR spectroscopy. The surface tension and thermodynamic properties of these inhibitors were investigated. The corrosion inhibition efficiency of these surfactants was investigated on a carbon steel surface in 1 M HCl solution by weight loss and electrochemical measurements. Untreated and treated steel surfaces were characterized by scanning electron microscopy. Results show that the inhibition efficiency of the prepared inhibitors increases with increasing the ethylene oxide units. Also, the potentiodynamic polarization curves indicated that the investigated inhibitors behave as a mixed type inhibitor. Adsorption of these surfactants on the carbon steel surface was found to obey Langmuir's adsorption isotherm. The computed quantum chemical properties viz., electron affinity (EA), highest occupied molecular orbital (E_HOMO), the lowest unoccupied molecular orbital (E_LUMO), energy gap ΔE = E_HOMO ? E_LUMO, dipole moment (μ), polarizability and total energy (E_T) show good correlation with experimental inhibition efficiency.     

Experimental and Quantum Chemical Studies on Corrosion Inhibition Performance of Thiazolidinedione Derivatives for Mild Steel in Hydrochloric Acid Solution

In the present investigation, two thiazolidinedione derivatives, 5-[(2-(3,4,5-trimethoxyphenyl)-6-phenylimidazo[2,1-b][1,3,4]thiadiazol-5-yl)methylidene]-1,3-thiazolidine-2,4-dione (Inh I) and 5-[2-(3,4,5-trimethoxyphenyl)-6-(4-methoxylphenyl)-imidazo[2,1-b][1,3,4]thiadiazol-5-yl)methylidene]-1,3-thiazolidine-2,4-dione (Inh II) were synthesized and investigated as inhibitors for mild steel corrosion in 15% HCl solution using the weight loss, electrochemical polarization, and electrochemical impedance spectroscopy (EIS) techniques. It was found that the inhibition efficiency of these inhibitors increased with increasing concentration. The effect of temperature on the corrosion rate was investigated, and some thermodynamic parameters were calculated. Polarization studies showed that both studied inhibitors were of mixed type in nature. The adsorption of inhibitors on the mild steel surface in acid solution was found to obey the Langmuir adsorption isotherm. Scanning electron microscopy (SEM) was performed on inhibited and uninhibited mild steel samples to characterize the surface. The semi-empirical AM1 method was employed for theoretical calculation of highest (E _HOMO), and lowest unoccupied molecular orbital (E _LUMO) energy levels, energy gap (E _LUMO ? E _HOMO), dipole moment (μ), global hardness (γ), softness (σ), binding energy, molecular surface area, chemical potential (Pi), and the fraction of electrons transferred from the inhibitor molecule to the metal surface (ΔN). The results were found to be consistent with the experimental findings.     

Electrochemical and DFT studies of β-amino-alcohols as corrosion inhibitors for brass

The electrochemical performance of 1-diethylamino-propan-2-ol (EAP) and 1,3-bis-diethylamino-propan-2-ol (DEAP) for brass in simulated atmospheric water is evaluated by potentiodynamic curves and electrochemical impedance spectroscopy (EIS). The experimental results show that the investigated compounds, which can effectively retard the anodic dissolution of brass, are anodic inhibitors. Furthermore, the inhibition efficiency of DEAP is higher than that of EAP at the same concentration. This observation is supported by density functional theoretical (DFT) parameters such as the highest occupied molecule energy level (E_HOMO), the lowest unoccupied molecule energy level (E_LUMO), the energy difference (ΔE) between E_HOMO and E_LUMO, Mulliken charges and the HOMO orbital.     

ac impedance, X-ray photoelectron spectroscopy and density functional theory studies of 3,5-bis(n-pyridyl)-1,2,4-oxadiazoles as efficient corrosion inhibitors for carbon steel surface in hydrochloric acid solution

The corrosion inhibition properties of a new class of oxadiazole derivatives, namely 3,5-bis(n-pyridyl)-1,2,4-oxadiazoles (n-DPOX) for C38 carbon steel corrosion in 1 M HCl medium were analysed by electrochemical impedance spectroscopy (EIS). An adequate structural model of the interface was used and the values of the corresponding parameters were calculated and discussed. The experimental results showed that these compounds are excellent inhibitors for the C38 steel corrosion in acid solution and that the protection efficiency increased with increasing the inhibitors concentration. Electrochemical impedance data demonstrate that the addition of the n-DPOX derivatives in the corrosive solution decreases the charge capacitance and simultaneously increases the function of the charge/discharge of the interface, facilitating the formation of an adsorbed layer over the steel surface. Adsorption of these inhibitors on the steel surface obeys to the Langmuir adsorption isotherm. X-ray photoelectron spectroscopy (XPS) and the thermodynamic data of adsorption showed that inhibition of steel corrosion in normal hydrochloric solution by n-DPOX is due to the formation of a chemisorbed film on the steel surface. Quantum chemical calculations using the Density Functional Theory (DFT) and the Quantitative Structure Activity Relationship (QSAR) approach were performed on n-DPOX derivatives to determine the relationship between molecular structure and their inhibition efficiencies. The results of the quantum chemical calculations and experimental inhibition efficiency were subjected to correlation analysis and indicate that their inhibition effect is closely related to E_HOMO, E_LUMO, and dipole moment (μ).     

Thiophene derivatives as effective inhibitors for the corrosion of steel in 0.5 <Emphasis Type="SmallCaps">m</Emphasis> H<Subscript>2</Subscript>SO<Subscript>4</Subscript>

The influence of thiophene and five of its substituted derivatives on the corrosion inhibition of steel in 0.5 m H₂SO₄ solution was studied using weight-loss, electrochemical polarisation, and impedance measurements. 5-tert-butoxythiophene-2-carbaldehyde phenylhydrazone (TBCP) is the best inhibitor and its inhibition efficiency increases with increase in concentration to attain 87% at 5×10⁻³ m. Potentiodynamic polarisation studies clearly reveal that it acts essentially as a cathodic inhibitor. The partial π-charge on atoms has been calculated. A correlation between the highest occupied molecular orbital E _HOMO and inhibition efficiencies was sought. The inhibition efficiency of TBCP is not affected by rise in temperature in the range 298–353 K. E% values obtained from weight-loss and electrochemical methods were in good agreement. Adsorption of TBCP on steel has an S-shaped adsorption isotherm.     

Studies of iron corrosion inhibition using chemical, electrochemical and computer simulation techniques

The inhibitive action of some benzimidazole derivatives namely 2-(2-furanyl)-1H-benzimidazole (FB), 2-(2-pyridyl) benzimidazole (PB) and 2-(4-thiazolyl) benzimidazole (TB), against the corrosion of iron in solutions of nitric acid has been studied using density function theory calculations (DFT), weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The calculated electronic parameters involved in the activity of the benzimidazole derivatives confirmed that the position of the side chain in the benzimidazole moiety affects the pattern of activity. The effectiveness of the benzimidazole derivatives is following the order TB > PB > FB. The same order is supported by the experimental chemical and electrochemical measurements. The relationships between inhibition efficiency of iron in 1.0 M HNO₃ and the molecular orbitals of the studied molecules as well as number of electrons transferred ΔN from the inhibitor molecules to the iron surface were calculated by DFT method. The inhibition efficiency increased with the increase in E_HOMO and decrease in E_LUMO-E_HOMO. TB had the highest inhibition efficiency because it had the highest HOMO energy and ΔN values, and it was most capable of offering electrons. Molecular modeling was used to evaluate the structural, electronic and reactivity parameters of the selected benzimidazole derivatives in relation to their effectiveness as corrosion inhibitors. Results obtained from weight loss, dc polarization and ac impedance measurements are in reasonably good agreement and show increased inhibitor efficiency with increasing inhibitor concentration.Data obtained from EIS were analyzed to model the corrosion inhibition process through equivalent circuit.     

Quantitative Structure-Activity Relationships Study on the Rate Constants of Polychlorinated Dibenzo-p-Dioxins with OH Radical

The OH-initiated reaction rate constants (k_OH) are of great importance to measure atmospheric behaviors of polychlorinated dibenzo-p-dioxins (PCDDs) in the environment. The rate constants of 75 PCDDs with the OH radical at 298.15 K have been calculated using high level molecular orbital theory, and the rate constants (k_α, k_β, k_γ and k_OH) were further analyzed by the quantitative structure-activity relationships (QSAR) study. According to the QSAR models, the relations between rate constants and the numbers and positions of Cl atoms, the energy of the highest occupied molecular orbital (E_HOMO), the energy of the lowest unoccupied molecular orbital (E_LUMO), the difference ΔE_HOMO-LUMO between E_HOMO and E_LUMO, and the dipole of oxidizing agents (D) were discussed. It was found that E_HOMO is the main factor in the k_OH. The number of Cl atoms is more effective than the number of relative position of these Cl atoms in the k_OH. The k_OH decreases with the increase of the substitute number of Cl atoms.     

The Oil from Mentha rotundifolia as Green Inhibitor of Carbon Steel Corrosion in Hydrochloric Acid

The corrosion inhibition potentials of Mentha rotundifolia oil on carbon steel in 1 M HCl was studied at different concentrations via gravimetric, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. Polarization curves reveal that Mentha rotundifolia oil is a mixed-type inhibitor. Changes in impedance parameters (charge transfer resistance R_t, and double-layer capacitance C_dl) were indicative of adsorption of Mentha rotundifolia on the metal surface, leading to the formation of a protective film. The effect of the temperature on the corrosion behavior with addition of the optimal concentration of Mentha rotundifolia oil was studied in the temperature range 308 and 338 K. Adsorption of oil on the carbon steel surface is found to obey the Langmuir adsorption isotherm. Attempts to explain the inhibitory action were carried out using density functional theory (DFT) at B3LYP/6-31G(d,p) level. Quantum chemical parameters most relevant to its potential action as corrosion inhibitor such as E_HOMO (highest occupied molecular orbital energy), E_LUMO (lowest unoccupied molecular orbital energy), energy gap (ΔE), and Mulliken charges have been calculated and discussed. The theoretical results were found to be consistent with the experimental data.     

The influence of some new 2,5-disubstituted 1,3,4-thiadiazoles on the corrosion behaviour of mild steel in 1 M HCl solution: AC impedance study and theoretical approach

The new 2,5-disubstituted 1,3,4-thiadiazoles were investigated as corrosion inhibitors of mild steel in 1 M HCl using AC impedance technique. Four of these compounds exhibit good inhibition properties, while two of them, 2,5-bis(4-nitrophenyl)-1,3,4-thiadiazole and 2,5-bis(4-chlorophenyl)-1,3,4-thiadiazole, stimulate the corrosion process especially at low concentrations. The experimental data obtained from this method show a frequency distribution and therefore a modelling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. Possible correlations between experimental inhibition efficiencies and quantum chemical parameters such as dipole moment (μ), highest occupied (E_HOMO) and lowest unoccupied (E_LUMO) molecular orbitals were investigated. The models of the inhibitors were optimised with the Density Functional Theory formalism (DFT) using hybrid B3LYP/6-31G (2d,2p) as a higher level of theory. The Quantitative Structure Activity Relationship (QSAR) approach has been used and composite index of some quantum chemical parameters were constructed in order to characterize the inhibition performance of the tested molecules.     

The inhibition of benzimidazole derivatives on corrosion of iron in 1 M HCl solutions

The inhibitive action of some benzimidazole derivatives namely 2-aminobenzimidazole (AB), 2-(2-pyridyl)benzimidazole (PB), 2-aminomethylbenzimidazole (MB), 2-hydroxybenzimidazole (HB) and benzimidazole (B), against the corrosion of iron (99.9999%) in solutions of hydrochloric acid has been studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). At inhibitor concentration range (10⁻³-10⁻² M) in 1 M acid, the results showed that these compounds suppressed both cathodic and anodic processes of iron corrosion in 1 M HCl by adsorption on the iron surface according to Langmuir adsorption isotherm. The efficiency of these inhibitors increases in the order AB>PB>MB>HB>B. Both potentiodynamic and EIS measurements reveal that these compounds inhibit the iron corrosion in 1 M HCl and that the efficiency increases with increasing of the inhibitor concentration. Data obtained from EIS were analyzed to model the corrosion inhibition process through equivalent circuit. A correlation between the highest occupied molecular orbital E_HOMO and inhibition efficiencies was sought.     

新型离子液体的合成及其阳离子基团缓蚀性能

以高纯环烷酸为原料,合成了一系列含咪唑啉环的新型离子液体Ⅰ～Ⅴ,探讨了阳离子咪唑啉基团中N_（3）原子上取代基与缓蚀性能的关系.采用碳钢挂片失重法和电化学测试法,评价了它们在酸性溶液中的缓蚀性能;采用量子化学法和极化效应指数法,分别计算了离子液体Ⅰ～Ⅴ阳离子咪唑啉基团的前线轨道能量及其相应的PEI等参数.实验结果和理论分析表明：离子液体Ⅰ～Ⅴ阳离子咪唑啉基团的缓蚀效率呈现如下关系,Ⅴ＞Ⅳ＞Ⅲ＞Ⅱ＞Ⅰ;其缓蚀效率与E_HOMO、ΔE_L-H和PEI等参数间均具有良好的线性关系.     

Quantum chemical studies on corrosion inhibition for series of thio compounds on mild steel in hydrochloric acid

Quantum chemical calculations were performed on ten thio compounds using semi-empirical method PM3 within program package of Material Studio 5.5. The effect of molecular structure on the corrosion inhibition efficiency was investigated using the quantum chemical calculations. The electronic properties such as highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels, (LUMO–HOMO) energy gap, dipole moment (λ) and fraction of electron transfer (ΔN) were calculated and discussed. A relationship between the corrosion inhibition efficiency and several quantum parameters was established with coefficient correlation (R²) of 0.8894.     

Theoretical study of the structural effects of polymethylene amines on corrosion inhibition of iron in acid solutions

Quantum chemical calculations were performed on azacyclo C5 to C14 amines, open chain C6 to C14 amines and phenylazacyclo C5 to C14 amines. Inspection of the calculated parameters and corrosion inhibition efficiencies were made to observe any clear links, which might exist between the two. Possible correlations between experimental inhibition efficiencies and parameters such as dipole moment (μ), highest occupied (E_HOMO) and lowest unoccupied (E_LUMO) molecular orbitals and the differences between them, HOMO-LUMO gap (Δ), as well as some structural characteristics were investigated. The models of the inhibitors were optimized with the Modified Neglect of Diatomic Overlap (MNDO) method. The Quantitative Structure Activity Relationship (QSAR) approach has been used and a composite index of some quantum chemical parameters were constructed in order to characterize the inhibition performance of the tested molecules. The inhibition effect of polymethylene amines is closely related to orbital energies and/or energy gap and dipole moment.     

Inhibition Effects of a Synthesized Novel 4-Aminoantipyrine Derivative on the Corrosion of Mild Steel in Hydrochloric Acid Solution together with Quantum Chemical Studies

1,5-Dimethyl-4-((2-methylbenzylidene)amino)-2-phenyl-1H-pyrazol-3(2H)-one (DMPO) was synthesized to be evaluated as a corrosion inhibitor. The corrosion inhibitory effects of DMPO on mild steel in 1.0 M HCl were investigated using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, open circuit potential (OCP) and electrochemical frequency modulation (EFM). The results showed that DMPO inhibited mild steel corrosion in acid solution and indicated that the inhibition efficiency increased with increasing inhibitor concentration. Changes in the impedance parameters suggested an adsorption of DMPO onto the mild steel surface, leading to the formation of protective films. The novel synthesized corrosion inhibitor was characterized using UV-Vis, FT-IR and NMR spectral analyses. Electronic properties such as highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy (EHOMO and ELUMO, respectively) and dipole moment (μ) were calculated and discussed. The results showed that the corrosion inhibition efficiency increased with an increase in the EHOMO values but with a decrease in the ELUMO value.     

铁卟啉催化剂前线轨道能量与其催化活性的关系

采用量化计算和分子模拟方法,设计、合成了9种不同结构的氯化金属卟啉铁催化剂,并对其前线轨道能量进行了计算,将计算结果与其催化氧气液相氧化对硝基甲苯制取对硝基苯甲酸反应的活性数据相结合,研究了不同结构的五配位金属卟啉铁催化剂的微观结构（E_HOMO和ΔE_L-H）与催化活性(产物收率)之间的关系,建立了相应的定量构效关系(QSAR)式.经统计检验量检验,发现五配位金属铁卟啉的E_HOMO对催化活性的影响大于ΔE_L-H对催化活性的影响.根据拟合的定量关系,对环外取代基为甲基的2种五配位金属铁卟啉催化剂的活性进行了预测,并经实验验证,证明所预测的活性与实测的活性相符.     

Electrochemical and quantum chemical study of purines as corrosion inhibitors for mild steel in 1 M HCl solution

The purines and its derivatives, such as, guanine, adenine, 2,6-diaminopurine, 6-thioguanine and 2,6-dithiopurine, were investigated as corrosion inhibitors for mild steel in 1 M HCl solution by weight loss measurements, electrochemical tests and quantum chemical calculations. The polarization curves of mild steel in the hydrochloric acid solutions of the purines showed that both cathodic and anodic processes of steel corrosion were suppressed. The Nyquist plots of impedance expressed mainly as a depressed capacitive loop with different compounds and concentrations. For all these purines, the inhibition efficiency increased by increasing the inhibitor concentration, and the inhibition efficiency orders are 2,6-dithiopurine > 6-thioguanine > 2,6-diaminopurine > adenine > guanine with the highest inhibiting efficiency of 88.0% for 10⁻³ M 2,6-dithiopurine.The optimized structures of purines, the Mulliken charges, molecular orbital densities and relevant parameters were calculated by quantum chemical calculations. The quantum chemical calculation results inferred that the adsorption belong to physical adsorption, which might arise from the π stacking between the π electron of the purines and the metal surface.     

Evaluation of some bipyridinium dihalides as inhibitors for low carbon steel corrosion in sulfuric acid solution

Inhibition of low carbon steel (LCS) corrosion in 0.5 M H₂SO₄ solution by three bipyridinium dihalides (TMbPyBr₂, HMbPyBr₂ and MPhbPyCl₂) was evaluated by potentiodynamic polarization curves, EIS and SEM techniques. The effectiveness of the inhibitors is ranked as follows: MPhbPyCl₂ ≅ TMbPyBr₂ > HMbPyBr₂. The compounds behave as mixed-type inhibitors and their adsorption on the steel surface obeys the Langmuir adsorption isotherm. EIS measurements indicate that charge transfer controls the corrosion of steel in the absence and presence of the inhibitors and the equivalent circuit R_e(R_ctQ_dl) represents the electrode/solution interface either at the corrosion potential or at −75 and 30 mV versus E_corr. The compounds show maximum inhibition efficiency at 35 °C. The mechanism of corrosion inhibition was discussed in the light of the molecular structure of the bipyridinium salts.     

Effects of structure of the ionic head of cationic surfactant on its inhibition of acid corrosion of mild steel

Two n-alkyl-quaternary ammonium compounds were studied as corrosion inhibitors for acid corrosion of mild steel using electrochemical and weight loss methods. The two compounds are hexadecylpyridinium bromide (HDPB) and hexadecyltrimethyl ammonium bromide (HDTB). The influence of the structure of the ionic head on the inhibition action of the two cationic surfactants was studied by analyzing the data at different concentrations and temperatures. The inhibition efficiency increases with the concentration. It increases with temperature in the case of HDPB but decreases in the case of HDTB. The apparent activation energy, E _a of corrosion in the presence of HDPB was found to be lower than in blank (0.5 m H₂SO₄). In the case of HDTB, E _a was larger than that of the blank. A larger extent of adsorption for HDPB on the metal surface was evident from the larger negative values of the free energy of adsorption. The results yielded the extent and mode of adsorption of the inhibitors on mild steel. The stronger adsorption of HDPB was attributed to the differences in the molecular structures of the inhibitors.     

Structural investigation of pyrazole derivatives as corrosion inhibitors for delta steel in acid chloride solutions

The effect of type and position of the substituted group of pyrazole derivatives for corrosion inhibition of Delta steel in acid chloride solutions has been investigated. It was found that increase of inhibitor concentration decreased both the corrosion rate,R _corr, and the corrosion current,i _corr, and shifted the corrosion potential,E _corr, to more positive values, i.e. the predominant action was as an anodic inhibitor. The results showed that the adsorption isotherm is S-shaped. The inhibition efficiency of the different substituted pyrazole derivatives follows the order: methyl相似文献