Computational and electrochemical studies of some amino acid compounds as corrosion inhibitors for mild steel in hydrochloric acid solution

The corrosion inhibition behaviour of four selected amino acid compounds, namely l-cysteine, l-histidine, l-tryptophan and l-serine on mild steel surface in deaerated 1 M HCl solution were studied electrochemically by Tafel polarization and electrochemical impedance spectroscopy methods and computationally by the quantum chemical calculation and molecular dynamics simulation. Electrochemical results show that these amino acid compounds inhibit the corrosion of mild steel in 1 M HCl solution significantly. The order of inhibition efficiency of these inhibitors follows the sequence: l-tryptophan > l-histidine > l-cysteine > l-serine. The quantum chemical calculations were performed to characterize the electronic parameters which are associated with inhibition efficiency. The molecular dynamics simulations were applied to find the equilibrium adsorption configurations and calculate the interaction energy between inhibitors and iron surface. Results obtained from Tafel and impedance methods are in good agreement. The electrochemical experimental results are supported by the theoretical data.     

Inhibition effects of acetyl coumarines and thiazole derivatives on corrosion of zinc in acidic medium

The corrosion inhibition characteristics of acetyl coumarine (AC), bromo acetyl coumarine (BAC) and thiazole derivatives (BTMQ and BTCQ) on the corrosion of zinc in 0·1 M HCl solution were investigated by weight loss, potentiodynamic polarization and impedance techniques. The inhibition efficiency increased with increase in inhibitor concentration upto 5 ×10^− 4  M, then gave almost same inhibition efficiency. The polarization measurements indicated the mixed nature of inhibitors. The adsorption of compounds obeyed Langmuir’s adsorption isotherm. The thermodynamic functions for adsorption processes were evaluated.     

Influence of phytic acid concentration on performance of phytic acid conversion coatings on the AZ91D magnesium alloy

In this study, the phytic acid conversion coating, a new environmentally friendly chemical protective coating for magnesium alloys, was prepared. The influences of phytic acid concentration on the formation process, microstructure, chemical state and corrosion resistance of the conversion coatings on AZ91D magnesium alloy were investigated by means of weight gain measurement, field-emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS), respectively. And the depth profile of all elements in the optimal conversion coatings was analyzed by auger electron spectroscopy (AES).The results show that the growth, microstructure, chemical state and corrosion resistance of the conversion coatings are all obviously affected by the phytic acid concentration. The concentration of 5 g l⁻¹ corresponds to the maximum weight gain. The main elements of the coating are Mg, Al, O, P, and C, which are distributed gradually in depth. The functional groups of conversion coatings formed in higher concentration phytic acid solution are closer to the constituent of phytic acid than those formed in lower concentration phytic acid solution. The coatings formed in 1–5 g l⁻¹ are integrated and uniform. However, those formed in 20–50 g l⁻¹ have some micro-cracks on the α phase. The coating formed in 5 g l⁻¹ has the best corrosion resistance, whose open circuit current density decreases about six orders than that of the untreated sample, although the coatings deposited in 1–20 g l⁻¹ can all improve the corrosion resistance of AZ91D.     

Aminethiocarbamide-containing polyelectrolytes as inhibitors of acid corrosion in steel

We study a new class of organic compounds, namely, polyethylenepolyaminethiocarbamides, hexamethylenediaminethiocarbamides, and their nitrile derivatives, and their application as inhibitors of corrosion in steel placed in a 5N hydrochloric acid. The high efficiency of these compounds is confirmed by the gravimetric and volumetric methods. It is shown that the inhibitors efficiently protect steel against corrosion for 40–60 min. After the indicated period, we observe the intensification of corrosion processes. As the temperature of the ambient medium increases (40–60°C), the efficiency of the action of inhibitors increases as a result of the chemisorptions of molecules of compounds on the steel surface resulting in the formation of protective films.     

Inhibitive effect of some thiadiazole derivatives on C-steel corrosion in neutral sodium chloride solution

Electrochemical techniques were used to investigate the effect of concentration of three new thiadiazole derivatives (I–III) on the corrosion behavior of C-steel in 0.5 M NaCl solution through the analysis of electrochemical measurements including open circuit potential (OCP), Tafel polarization and electrochemical impedance spectroscopy (EIS). Polarization curves showed that the compounds studied act as anodic type inhibitors, where the inhibition efficiency increases with increase in inhibitor concentration and decreases with rise in temperature. An adherent layer of inhibitor molecules on the surface is proposed to account for their inhibitive action in which the organic molecules adsorb on the active anodic sites following Langmuir isotherm. The thermodynamic parameters of adsorption and corrosion processes were determined and discussed. The results also indicated that pitting potential at higher anodic polarization of C-steel in 0.5 M NaCl solution becomes more positive the higher the concentration of the additive, suggesting that these inhibitors acts as retarding catalyst for pitting corrosion. EIS data confirm well the electrochemical dc results and the results are all in good agreement with the calculated quantum chemical HOMO and LUMO energies of the tested molecules, as well as with surface examination via scanning electron microscope.     

Inhibition of mild steel corrosion in sulfuric acid by some newly synthesized organic compounds

The corrosion inhibition of mild steel in 0.5 M sulfuric acid solutions by some new synthesized organic compounds namely (E)-2-acetyl-3-(butyl amino)-N-phenyl buten-2-thioamide (compound A), (E)-3-(4-(dimethyl amino) phenyl amino)-2-acetyl-N-phenyl buten-2-thioamide (compound B) and (E)-3-(2,3-dimethyl phenyl amino)-2-acetyl-N-phenyl buten-2-thioamide (compound C) was investigated using weight loss and potentiostatic polarization techniques. These measurements reveal that the inhibition efficiency obtained by these compounds increased by increasing their concentration. The inhibition efficiency follows the order A > B > C. Polarization studies show that these compounds are of the mixed-type but dominantly act as an anodic inhibitors for steel in 0.5 M H₂SO₄ solutions. These inhibitors function through adsorption following Langmuir isotherm. Activation energy and Gibbs free energy for adsorption of inhibitors are calculated. Molecular modeling has been conducted to correlate the corrosion inhibition properties with the calculated quantum chemical parameters.     

The inhibition of mild steel corrosion in hydrochloric acid media by two Schiff base compounds

Schiff bases of 2-({-1-methyl-3-[(2-sulfanylphenyl)imino]butylidene}-amino)-1-benzenethiol and 2-({-1,2-diphenyl-2-[(2-sulfanylphenyl)imino]ethylidene}amino)-1-benzenthiol are investigated as corrosion inhibitors in acid solution. Polarization, electrochemical impedance spectroscopy, and weight loss measurements were performed on mild steel in 15% HCl with and without the inhibitors. A significant decrease in the corrosion rate of mild steel was observed in the presence of investigated inhibitors. Polarization curves indicate that both compounds are mixed inhibitors, affecting both cathodic and anodic corrosion currents. The adsorption of inhibitors on mild steel surface in 15% HCl was found to follow Langmuir adsorption isotherm. Thermodynamic adsorption parameters (K _ads, ∆G _ads) of studied Schiff bases were calculated using the Langmuir adsorption isotherm. Activation parameters of the corrosion process such as activation energies, E _a, activation enthalpies, ∆H*, and activation entropies, ∆S*, were calculated by the obtained corrosion currents at different temperatures.     

Inhibitory Effect of some carbazides on corrosion of aluminium in hydrochloric acid and sodium hydroxide solutions

The dissolution of aluminium in hydrochloric acid and sodium hydroxide solutions in the presence of semicarbazide, thiosemicarbazide and sym.diphenylcarbazide as corrosion inhibitors has been studied using thermometric, weight-loss and polarization methods. The three methods gave consistent results. The higher inhibition efficiency of these compounds in acidic than in alkaline madia may be due to the less negative potential of aluminium in hydrochloric acid solution, favouring adsorption of the additive. The adsorption of these compounds were found to obey Frumkin adsorption isotherm. Cathodic polarization measurements showed that these compounds are cathodic inhibitors and their adsorption in the double layer does not change the mechanism of the hydrogen evolution reaction. The results are analysed in terms of both molecular and cationic adsorption.     

Microstructure and mechanical properties of a high nitrogen titanium alloy

High nitrogen titanium alloy with the chemical composition of Ti–4%Cr–0.6%N was produced by solution nitriding to nitrogen-free Ti–4%Cr alloy, and then its microstructure was controlled to have fine (α + β) dual phase structure by aging treatment to improve the ductility. As solution-nitrided specimen has a platelet hcp-martensitic structure (α′) and is characterized by hard but brittle nature that has been produced by solid solution of 0.6% of nitrogen. On the following aging treatment, fine β phase formed along the original plate boundaries, resulting in a fine (α + β) dual phase microstructure. X-ray and EELS analyses revealed that nitrogen is greatly concentrated in the tempered α′ phase. Although the hardness of as-quenched material gradually decreases during the aging treatment with increasing volume fraction of β, the hardness can be kept much higher than that of the aged Ti–4%Cr alloy without nitrogen. As a result of tensile testing, it was found that the aged Ti–4%Cr–0.6%N alloy has high tensile strength over 1 GPa with moderate ductility.     

Corrosion inhibition of benzyl triethanol ammonium chloride and its ethoxylate on steel in sulphuric acid solution

The inhibitive effect of benzyl triethanol ammonium chloride (BTAC) and ethoxylated benzyl triethanol ammonium chloride (EBTAC) on the corrosion of carbon steel in sulphuric acid solution is measured by the weight loss method. The adsorption of these compounds (surfactants) leads to the formation of a monolayer on the metal surface. The relationships between the concentrations of these inhibitors and their surface properties, thermodynamic properties, surface coverage (θ) and inhibiting efficiency have been investigated. The results indicate that EBTAC is superior to BTAC.     

Computational and electrochemical studies on the inhibition of corrosion of mild steel by <Emphasis Type="SmallCaps">l</Emphasis>-Cysteine and its derivatives

This article presents the investigation of l-Cysteine (CYS) and its derivatives including N-Acetyl-l-Cysteine (NACYS), N-Acetyl-S-Benzyl-l-Cysteine (NASBCYS), and N-Acetyl-S-Hexyl-l-Cysteine (NASHCYS) as green chemical corrosion inhibitors for mild steel in 1 M HCl solutions. Weight loss method and Tafel polarization measurement were performed to determine the corrosion parameters and inhibition efficiencies. Experimental results showed that these compounds suppressed both anodic and cathodic reactions, and the inhibition efficiency of the four inhibitors followed the order NASBCYS > NASHCYS > NACYS > CYS. In order to further study the corrosion mechanisms, quantum chemical calculation and molecular dynamics method were applied. The relationships between quantum chemical parameters and corrosion inhibition efficiency were discussed. Molecular dynamics method was used to simulate the adsorption behavior of each inhibitor in solvent. The results showed that these four inhibitors can adsorb on mild steel surface by donor acceptor interactions between lone-pair electrons of heteroatoms/π-electrons of aromatic ring and vacant d-orbital of iron.     

Intramolecular synergistic effect of glutamic acid, cysteine and glycine against copper corrosion in hydrochloric acid solution

The corrosion protection of copper by glutamic acid, cysteine, glycine and their derivative (glutathione) in 0.5 M hydrochloric acid solution has been studied by the electrochemical impedance spectroscopy and cyclic voltammetry. The inhibition efficiency of the organic inhibitors on copper corrosion increases in the order: glutathione > cysteine > cysteine + glutamic acid + glycine > glutamic acid > glycine. Maximum inhibition efficiency for cysteine reaches about 92.9% at 15 mM concentration level. The glutathione can give 96.4% inhibition efficiency at a concentration of 10 mM. The molecular structure parameters were obtained by PM3 (Parametric Method 3) semi-empirical calculation. The intramolecular synergistic effect of glutamic acid, cysteine and glycine moieties in glutathione is attributed to the lower energy of the lowest unoccupied molecular orbital (E_LUMO) level and to the excess hetero-atom adsorption centers and the bigger coverage on the copper surface.     

Synthesis of carbazole derivatives with high quantum yield and high glass transition temperature

A series of fluorescent compounds derived from carbazole were synthesized via the Wittig–Horner reaction. The compounds had high glass transition temperatures (T_g), in the region of 172–232 °C, and high decomposition temperatures (T_d), ranging from 456 to 491 °C. The derivatives showed very high fluorescence efficiency in solution, with fluorescence quantum yields in the range of 0.88–1.00. The substituent effects on fluorescence emission differed between solution and solid state. In dichloromethane solutions, the substituents had only a minimal effect on the maximum emission wavelength of the compounds with the same bridge.     

Effect of heat treatment on the Inhibition of the acidic corrosion of aluminum alloy

The effect of heat treatment on the inhibition of acid corrosion of duralumin has been studied using gasometry, mass loss measurements and potentiodynamic technique. All the data reveal that the duralumin generally developed good corrosion resistance after heat treatment and the corrosion rate ranked as follows: Non treated > Naturally aged > quenched. This improvement in the corrosion resistance was attributed to the structural homogeneity of the heat-treated alloys. The presence of some selected aryl and alkyl triazoline derivatives at the thershold concentration of 5 × 10^?3 M indicate that these compounds retard the corrosion rate of duralumin and the extend of inhibition depends on the molecular structure of the inhibitors. Polarization curves show that the triazoline compounds act as mixed-type inhibitors affecting both the cathodic and anodic process. Moreover, there is no noticeable difference in the degree by which the triazoline derivatives inhibit the corrosion of pure aluminium and heat treated duralumin alloy.     

Copper corrosion inhibition by Azadirachta indica leaves extract in 0.5 M sulphuric acid

Azadirachta indica leaves extract (AI) was investigated as a copper corrosion inhibitor in 0.5 M sulphuric acid. Inhibition efficiency of AI was compared to that of the already proven good inhibitors 2-acetamino-5-mercapto-1,3,4-thiadiazole (AAMTDA) and 1,2,3-benzotriazole (BTAH). The inhibition properties were studied using electrochemical polarization and weight loss techniques. In the region of active copper dissolution, the highest inhibition efficiency was exhibited by AAMTDA (92.7%). AI exhibited somewhat higher efficiency (86.4%) than the widely used BTAH (85.5%), showing that the extract could serve as a effective substitute for currently preferred copper corrosion inhibitors in sulphuric acid. The weight loss results were interpreted by means of the Frumkin isotherm of adsorption on the metal surface. The values of ΔG_ads equal to − 41.96 kJ mol^− 1 for AAMTDA and − 35.22 kJ mol^− 1 for BTAH indicate strong spontaneous adsorption while the surface coverage dependence on the log c following the Frumkin isotherm is suggestive of chemisorption in case of all three tested inhibitors.     

Microstructure and corrosion characteristics of laser-alloyed magnesium alloy AZ91D with Al–Si powder

Blown-powder laser surface alloying was performed on the magnesium alloy AZ91D with Al–Si alloy powder to improve corrosion resistance. Characterization by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD) analysis revealed that intermetallic compounds (IMCs) of Mg₂Si, Al₁₂Mg₁₇ and Al₃Mg₂ were formed in the matrix of α-Mg and Al solid solutions in Al–Si alloyed layers. The anodic polarization test in 3.5% NaCl aqueous solution showed that preferential corrosion occurred in the α-Mg matrix of the AZ91D base metal. The Al–Si alloyed layers exhibited a lower corrosion rate and a higher polarization resistance than AZ91D. The compactly dispersed dendritic Mg₂Si phase, and the dendritic and angular phases of Al₁₂Mg₁₇ and Al₃Mg₂ in the alloyed microstructure were observed to be corrosion-resistant, constituting a barrier that retards corrosion. Corrosion initiated at the interface between IMCs and the solid solution matrix, and at substructures of the matrix, subsequently pervaded into the surrounding microstructure.     

Effect of Mn on damping capacities, mechanical properties, and corrosion behaviour of high damping Mg–3 wt.%Ni based alloy

The effect of Mn on the damping capacities, mechanical properties, and corrosion behaviour of high damping Mg–3 wt.%Ni based alloys has been studied. The damping vs. strain amplitude spectrum of the studied alloys could be divided into three parts. The strain amplitude weakly dependent part appears again when the microplastic strain occurs at high strain amplitude. The mechanical properties of as-cast Mg–3 wt.%Ni alloy could be improved by the addition of Mn, which is due to the refinement of α-Mg dendrites and solid solution strengthening by Mn. In addition, the corrosion resistance of the alloys could also be improved remarkably by the addition of Mn.     

A new resource-saving, high manganese and nitrogen super duplex stainless steel 25Cr–2Ni–3Mo–xMn–N

A new family of resource-saving, high manganese and nitrogen super duplex stainless steels (DSSs), with a composition of 25 wt.%Cr, 2 wt.%Ni, 3 wt.%Mo, 8–12 wt.%Mn, and 0.45–0.55 wt.%N, have been developed by examining the effect of Mn and N on the microstructure, mechanical properties and corrosion properties. The results show that these alloys have a balanced ferrite–austenite relation. The ferrite content increases with the solution treatment temperature, but it decreases with an increase in Mn and N. The element Mn accelerates σ phase precipitations. The increases in manganese and nitrogen, especially nitrogen, enhance the ultimate tensile strength (UTS) and ductility of the material. The pitting corrosion potential increases first and then decreases with an increase in the amount of Mn, which is due primarily to the presence of a small amount of σ phase when the amount of Mn is 12 wt.%. Among the designed DSS alloys, 25Cr–2Ni–3Mo–10Mn–0.5N is found to be an optimum alloy with proper phase proportion, a better combination of UTS and elongation, and higher pitting corrosion resistance compared with those of the other alloys. The mechanical strength and corrosion resistance and lower production cost of the materials are better than those of SAF2507.     

Influence of salts of alkylphenol sulfonic acid on the corrosion of St3 steel in HCl–kerosene systems

We study the influence of salts of alkylphenol sulfonic acid on the corrosion of St3 steel in a 0.1 N HCl–kerosene system. All salts have inhibiting properties beginning with a concentration of 25 mg/liter and, in some cases, completely inhibit corrosion. It is shown that the protective effect increases with temperature. Within the range of concentrations of the inhibitor 25–200 mg/liter, the activation energy of corrosion becomes 5–6 times higher. Thus, the investigated compounds inhibit corrosion of St3 steel as a result of chemical adsorption. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 5, pp. 69–74, September–October, 2008.     

The bromination kinetics of phenolic compounds in aqueous solution

The purpose of this study was to investigate the bromination kinetics of selected phenolic compounds in aqueous solutions over the pH range of 5–11. The experiment results indicated that the reaction of hypobromous acid with the phenoxide ions controlled the overall reaction rate, whereas the reaction between hypobromite ion and the phenoxide ions and the reaction between hypobromous acid and the undissociated phenolic species were considered to be negligible respectively in the pH range of 7–9. The apparent second-order rate constants of the reaction of hypobromous acid with the phenoxide ions ranged from 7.9 × 10⁶ M⁻¹ s⁻¹ for 3-chlorophenol to 6.5 × 10⁸ M⁻¹ s⁻¹ for 3-methoxyphenol, respectively. The Hammett correlation could be successfully used to estimate the reactivity of bromine with substituted phenols and the linear regression was log(k₂) = −2.85б + 8.00. The rate constants of the reaction of bromine with phenol-like organic compounds were about three orders of magnitude higher than with chlorine and two to three orders of magnitude lower than with ozone.