某些含氮化合物缓蚀作用的量子化学研究

用量子化学方法计算了苯胺及其卤代和甲基取代衍生物,N-苯基十二烷基胺及其甲基取代物等含氮化合物的电子结构,行讨论了在酸性介质中对软钢的缓蚀效果与其电子结构的关系。较好地解释了相同取代基不同取代位置以及同一取代位置不同取代基化合物的缓蚀率差异。从电子转移的角度说明了含氮有机化合物的缓蚀机理。为研制效果更好的有机缓蚀剂提供了有用的信息。     

Electrochemical and quantum chemical studies of new thiadiazole derivatives adsorption on mild steel in normal hydrochloric acid medium

In this work, a new class of thiadiazole derivatives, namely 3,5-bis(2-thienyl)-1,3,4-thiadiazole (2-TTH) and 3,5-bis(3-thienyl)-1,3,4-thiadiazole (3-TTH), have been studied as possible corrosion inhibitors for mild steel in molar hydrochloric acid (1 M HCl). Weight loss measurements, polarisation curves and AC impedance methods have been used. These studies have shown that the thiadiazole derivatives were very good inhibitors for mild steel in 1 M HCl. Comparison of results showed that 3-TTH was the best inhibitor. The potential of zero charge (PZC) of mild steel was studied by AC impedance method, and the mechanism of adsorption has been predicted. X-ray photoelectron spectroscopy surface analysis with thiadiazole derivatives shows that it chemisorbed at the mild steel/HCl interface. The adsorption of these inhibitors followed Langmuir’s adsorption isotherm. The electronic properties of 2-TTH and 3-TTH, obtained using the AM1 semi-empirical quantum chemical approach, were correlated with their experimental efficiencies using the linear resistance model (LR). These inhibitors are considered as non-cytotoxic substances.     

Adsorption and inhibitive properties of some new Mannich bases of Isatin derivatives on corrosion of mild steel in acidic media

Adsorption of four derivatives of piperidinylmethylindoline-2-one on mild steel surface in 1 M HCl solution and its corrosion inhibition properties has been studied by a series of techniques, such as polarization, electrochemical impedance spectroscopy (EIS), weight loss and quantum chemical calculation methods. The values of activation energy (E_a) for mild steel corrosion and various thermodynamic parameters were calculated and discussed. Potentiodynamic polarization measurements showed that all inhibitors are mixed type. The degree of surface coverage was determined by using weight loss measurements and it was found that adsorption process of studied inhibitors on mild steel surface obeys Langmuir adsorption isotherm.     

Molecular modeling of corrosion processes: development and engineering applications

Abstract

The effect of two polyacrylate based polyelectrolytes, one cationic, the other anionic, on the corrosion of mild steel in aqueous solutions has been examined. It is shown that under conditions where they accelerate corrosion the effect arises from different properties of the compounds in each case. The cationic polymer is a mild oxidising agent and, in alkaline solution, is aggressive to passive films producing localised attack. The anionic compound acts as an anodic stimulator in neutral and alkaline solutions possibly by virtue of its ability to form a complex ion with the emerging cation. Both compounds therefore accelerate corrosion in neutral and alkaline solutions. By contrast, the anionic polyelectrolyte is a mild mixed inhibitor in acid solutions. It is suggested that not all soluble polymers will adversely affect the corrosion of mild steel and that by redesign of the molecule it might be possible for polyectrolytes generally to act as both water treatment chemicals and corrosion inhibitors.     

Inhibitor protection and corrosion monitoring in Benfield installation to purify gas for synthesis

Abstract

The aggressive media in the Benfield processfor preparing gasfor use in synthesis by means of ‘potassium purification’ consist of KHCO₃ + K₂CO₃ solutions having total contents and molar ratios that vary over a very wide range which also contain diethanoloamine. Operating temperatures are typically 70–120°C. Despite the use of inhibitors, intensive corrosion of mild steel walls has been observed in several installations. In laboratory tests performed in simulated Benfield solutions, a relationship has been established between the inhibitor content necessary to suppress active dissolution and pitting corrosion and the total content and molar ratio of the carbonates. These results have been checked and verified in an industrial installation. The corrosion monitoring system applied to critical parts of the equipment allowed the solution composition to be controlled and an inhibitor content appropriate to the composition of the aggressive medium to be maintained. As a result, substantial decreases in corrosion have been achieved, as was confirmed by microscopic examination of disposable electrodes and by the observation of the inner surface of an installation during routine maintenance.     

Inhibition of mild steel corrosion in presence of fatty acid imidazolines in hydrochloric acid

The corrosive behavior of mild steel in 1M HCl solutions containing selected imidazolines of fatty acids with C₇-C₁₇ was investigated using weight-loss method, potentiodynamic polarization technique and scanning elecron microscopy. The results obtained revealed that all the studied imidazolines are effective in reducing corrosion of mild steel in HCl media. The adsorption of the inhibitors on the mild steel surface obeys Langmuir’s adsorption isotherm. The thermodynamic parameters of adsorption deduced reveal a strong interaction and spontaneous adsorption of inhibitors on the mild steel surface. The influence of inhibitor concentration, solution temperature, immersion time and acid concentration on the corrosion of mild steel has also been investigated. Scanning electron microscopy(SEM) of mild steels samples is performed to show adsorption of inhibitors on metal surface. Potentiodynamic polarization data showed that the compounds studied are mixed type inhibitors in the acid solution. Original Russian Text ? M.A. Quaraishi, M.Z.A. Rafiquee, Nidhi Saxena, Sadaf Khan, 2008, published in Zashchita Metallov, 2008, Vol. 44, No. 1, pp. 99–106.     

Carbonyl compounds as corrosion inhibitors for mild steel in HCl solutions

The paper gives an account of the performance of a number of carbonyl compounds as corrosion inhibitors of mild steel in 1–6 N solutions of hydrochloric acid. Furfuraldehyde seems to be the best inhibitor of all the carbonyl compounds investigated. Activation energies in the presence and absence of inhibitors have been evaluated. In cathodic protection studies furfuraldehyde reduces the protective current density considerably. The difference effect is positive in the absence and presence of inhibitors. Galvanostatic polarization data indicate that all these compounds are predominantly cathodic inhibitors. These substances are more effective in preventing the corrosion of aluminium alloys in hydrochloric acid solutions than the corrosion of mild steel.     

Effect of some Thioureas on the Corrosion and Dezincification of 63/37 Brass in Ammonia Solution

Abstract

The inhibitory action of thiourea and its derivatives, N-phenyl thiourea and diphenyl thiourea, towards the corrosion of 63/37 brass in ammonia solution has been investigated, using weight loss, solution analysis and potentiostatic polarisation techniques. All the inhibitors reduce the dissolution of both zinc and copper, but none of the inhibitors are effective in reducing the preferential dissolution of zinc. All the inhibitors give Langmuir type adsorption isotherms, and shift the corrosion potential towards the more passive region. Thiourea and N-phenyl thiourea act as mixed inhibitors while diphenyl thiourea acts as an anodic inhibitor only.     

Korrosionsuntersuchungen zur Entwicklung von Dekontaminationslösungen für Nuklearanlagen – Teil III: Das Korrosionsverhalten ferritischer Baustähle mit unterschiedlichen Kohlenstoffgehalten in Ameisensäure-Formaldehyd-Lösungen ohne und mit Inhibierung

Investigation of corrosion in the development of decontamination solutions for nuclear systems – Part III: The corrosion behaviour of ferritic steels with different carbon contents in formic acid-formaldehyde solutions with and without inhibitors In decontamination solutions of the type formic acid-formaldehyde, ferritic steels undergo heavy pitting corrosion or shallow pitting corrosion. The addition of formaldehyde to formic acid solutions scarcely influences the temperature dependency of the corrosion rates, the solution specific corrosion rates, however, increase with increasing carbon content of the steels. The high corrosion rates, especially of the steel 21 CrMoV 5 11, can be reduced by about two orders of magnitude by adding inhibitors as thiourea, ethyl thiourea, and phenyl thiourea to the formic acid-form-aldehyde solutions, but pitting corrosion is unavoidable.     

吡啶嗡离子衍生物的缓蚀作用及其吸附模型

用线性极化曲线法研究了N 癸基吡啶溴化铵 (DP) /N 癸基 3 羟基吡啶溴化铵 (D3OP)和N 癸基 3 羧基吡啶溴化铵 (D3CP)在 5 %氨基磺酸中对铁的缓蚀作用及其吸附模型。结果表明 :它们对 5 %氨基磺酸中的铁具有良好的缓蚀作用 ,在吡啶环上引入合适的取代基能提高吡啶嗡离子的缓蚀效果。它们在铁表面的吸附主要为物理吸附 ,其吸附遵循Langmuir吸附等温式 ;随着温度和使用浓度的提高 ,其缓蚀性能加强 ;三种缓蚀剂缓蚀能力大小为D3CP >D3OP >DP。     

Inhibition of mild steel corrosion in phosphoric acid solution by triazole derivatives

Corrosion inhibition by triazole derivatives (n-PAT) on mild steel in phosphoric acid (H₃PO₄) solutions has been investigated by weight loss and polarization methods. The results indicate that these compounds act as mixed-type inhibitors retarding the anodic and cathodic corrosion reactions with emphasis on the former and do not change the mechanism of either hydrogen evolution reaction or mild steel dissolution. Some kinetic parameters are obtained.     

A self-doped conducting polymer “polyanthranilic acid”: An efficient corrosion inhibitor for mild steel in acidic solution

In recent years, polyanilines have been reported as one of the efficient corrosion inhibitors for iron in acidic media. In view of the major limitation of insolubility of polyaniline, we propose the use of functionalized self-doped conducting polymer to get higher solubility and corrosion efficiency. The chemical synthesis of water soluble self-doped polyanthranilic acid using various oxidizing agents and for time intervals of polymerization is reported for the first time for the corrosion inhibition studies. The corrosion inhibition property of the polymer is demonstrated for mild steel in acidic environment using electrochemical impedance spectroscopy, Tafel polarization and weight loss methods.     

盐酸体系不锈钢缓蚀剂的开发

采用失重法和扫描电镜法,测定了五种缓蚀剂对浸没于8%盐酸介质中不锈钢的缓蚀作用,确定了在盐酸体系中对不锈钢具有较好缓蚀性的单组分、二元和三元缓蚀剂配方.实验结果表明:咪唑啉,十六烷基三甲基溴化铵具有较好的缓蚀效果;十六烷基三甲基溴化胺在使用浓度为700 mg/L时,缓蚀率为90.0%;十六烷基三甲基溴化铵与三乙醇胺、咪唑啉及硫脲复配后,缓蚀剂各组分浓度为单组分最佳浓度一半的情况下,缓蚀率分别达到为91.8%、90.8%和89.7%,缓蚀剂的成本得以下降;三元复配缓蚀剂中,咪唑啉-硫脲-乌洛托品和咪唑啉-硫脲-三乙醇胺两种缓蚀剂的缓蚀率均高于90%,且使用成本低,是理想的盐酸体系不锈钢缓蚀剂.扫描电镜图像表明,添加了缓蚀剂的金属表面腐蚀轻微,表面光滑,且不存在明显的点蚀倾向,缓蚀剂对金属表面起到很好的保护作用.     

Inhibition of mild steel corrosion in CO2 and H2S-saturated acidic media by a new polyurea-based material

Oil well acidizing is a common practice used to boost oil well productivity in the industry. This practice, however, exposes the mild steel components of the wells to extremely harsh corrosive environments. Under such conditions, highly efficient inhibitors are used to minimize corrosion attack. In the present study, corrosion inhibition of mild steel in simulated acidic medium saturated with CO₂ and H₂S gases by a newly synthesized polyurea-based material (PUCorr-1) was investigated. Electrochemical studies supported with quantum chemical density-functional theory calculations and surface characterization revealed that PUCorr-1 adsorbs onto mild steel through a chemisorption mechanism yielding a stable protective film. The polyurea exhibited an excellent efficiency of 99.9% at a temperature of 50°C and a low concentration of 100 ppm, yielding a corrosion current density of 0.3 µA/cm². In the presence of CO₂ and H₂S gases, PuCorr-1 exhibited a remarkable performance (>93% efficiency) making it a potential corrosion inhibitor in industrial processes that involve the use of acid solutions in the presence of CO₂ and H₂S gases.     

Experimental and quantum chemical studies on two triazole derivatives as corrosion inhibitors for mild steel in acid media

Two triazole derivatives [1‐phenyl‐2‐(5‐(1,2,4) triazol‐1‐ylmethyl‐(1,3,4) oxadizaol‐2‐ylsulphanyl)‐ethanone (PTOE) and 2‐(4‐tert‐butyl‐benzylsulphanyl)‐5‐(1,2,4) triazol‐1‐ylmethyl‐(1,3,4) oxadiazole (TBTO)] were synthesized as new corrosion inhibitors for the corrosion of mild steel in 1 M hydrochloric acid solutions. The inhibiting efficiency of the different inhibitors was evaluated by means of weight loss and electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and polarization curves. The electrochemical investigation results indicate that these compounds act as mixed‐type inhibitors retarding the anodic and cathodic corrosion reactions and do not change the mechanism of either hydrogen evolution reaction or mild steel dissolution. The studied compounds followed the Langmuir adsorption isotherm, and the thermodynamic parameters were determined and discussed. The effect of molecular structure on the inhibition efficiency has been investigated with ab initio calculations. The electronic properties such as highest occupied molecular orbital (HOMO) energy level, lowest unoccupied molecular orbital (LUMO) energy level, dipole moment (µ) and molecular orbital densities were calculated.     

Adsorbtion and inhibition effect of thiourea on mild steel in acidic media

The effect of thiourea on electrochemical corrosion behavior of mild steel was investigated in 0.5M HCl solution at room temperature by electrochemical impedance spectroscopy (AC Impedance) and Tafel polarization (DC Polarization) methods. The results show that thiourea act as mixed type inhibitor. The inhibition efficiency obtained from AC Impedance and DC polarization methods are in good agreement. The Nyquist plots show that the corrosion behavior of mild steel in 0.5M HCl solution in the absence and in the presence of thiourea, consist a simple capacitive loop. Changes in impedance parameters (R_ct and C_dl) are indicative of adsorption of thiourea on the metal surface, leading to the formation of protective film. Thiourea is found to adsorb on mild steel surface steel in 0.5M HCl solution, according to the Langmuir adsorption isotherm.     

硫脲衍生物对CO2饱和水溶液中碳钢缓蚀性能的研究

用失重法及极化曲线方法了在ＣＯ２饱和水溶液中几种硫脲衍生物对碳对钢的缓蚀作用。利用缓蚀协同效应得到了同温度下缓蚀效果良好的缓蚀剂。     

Hemmung der sauren Korrosion unterschiedlicher Kohlenstoffstähle unter Verwendung von Thioharnstoff

Inhibition of the acid corrosion of various carbon steels In the present paper the influence of carbon content in steel (0.002–1.05%C) on the corrosion rate in deacerated 2.0 M sulphuric acid containing thiourea in a concentration of 0.003-0.4% has been studied. The measuring effects of spontaneous dissolution and the potentiostatic measuring results for two different stirring rates of the disk electrode have been shown. It was found that the thiourea represses the corrosion of steel to a certain optimal concentration above which a corrosion stimulation takes place. The optimal concentration of the thiourea depends on the carbon content in steel and in a smaller degree on the stirring rate. In the absence of thiourea the anodic and cathodic polarisation curves have a run considerably depending on the carbon content in steel. The polarisation curves at the thiourea concentration of 0.010 and 0.100% show a Tafel run with an elevation practically independent on the carbon content in steel. The run of the polarisation curves as well as the metallographic observations allow to admit that the cementit and also the ferrite undergo an anodic dissolution at the presence of thiourea.     

Inhibiting effects of some mercapto-triazole derivatives on the corrosion of mild steel in 1.0 M HCl medium

The effect of some mercapto-triazole derivatives synthesized in the laboratory containing different hetero atoms and substituents in the organic structures on the corrosion and hydrogen permeation of mild steel in 1.0 M HCl was investigated by weight loss and various electrochemical techniques. Results obtained reveal that all the mercapto-triazole derivatives perform excellently as corrosion inhibitors for mild steel in 1.0 M HCl. Potentiodynamic polarization studies have shown that all these compounds suppress both the anodic and cathodic process and they behave as mixed-type inhibitors. Double layer capacitance and charge transfer resistance values were derived from Nyquist plots obtained from AC impedance studies. Changes in impedance parameters are indicative of the adsorption of these compounds on the metal surface. The inhibition efficiency mainly depends on the nature of the investigated compounds. The values of the inhibition efficiency calculated from these techniques are in reasonably good agreement. The extent of reduction of hydrogen permeation current through mild steel surface was studied by the hydrogen electropermeation technique. The adsorption of these compounds on mild steel surface is found to obey Langmuir adsorption isotherm. The free energy of adsorption for inhibiting process was determined on the basis of Langmuir adsorption isotherm.     

Effect of substituents on the inhibitive properties of newly synthesized 5-benzoyl-4-methyl-1,3,4,5-tetrahydro-2H-1,5-benzodiazepin-2-one derivatives against mild steel corrosion in an acidic medium

Inhibition performance of three newly synthesized 1,5-benzodiazepine derivatives with 4-methoxybenzoyl (methoxyBBD), 3-methylbenzoyl (methylBBD), and 2-chlorobenzoyl (chloroBBD) groups was investigated against mild steel corrosion in 1 M hydrochloric acid. The potentiodynamic polarization, electrochemical impedance spectroscopy, and adsorption isotherms were used for characterization of the corrosion processes. Surface morphology was studied by scanning electron microscope (SEM). Quantum chemical calculations were carried out to establish the active sites of the inhibitors. The results show that the inhibitors inhibit mild steel corrosion and their inhibition efficiencies (IE) increase with the increase in concentration. The methoxyBBD shows a higher inhibiting effect with IE of 89.13% at 10⁻³ M, followed by methylBBD. All three inhibitors act as mixed-type inhibitors with predominant control of cathodic reaction for chloroBBD and their adsorption obeys Langmuir isotherm. The SEM analysis confirms the inhibitors' adsorption on the mild steel surface. The active sites of the inhibitors were effectively established using the density functional theory method on the basis of natural atomic charge, highest occupied molecular orbital, and the lowest unoccupied molecular orbital frontier molecular orbitals. The experimental and quantum results prove the inhibition performance trend of the inhibitors as follows: methoxyBBD > methylBBD > chloroBBD.