Schiff bases as corrosion inhibitors for mild steel in hydrochloric acid solutions

Seven Schiff bases have been examined as corrosion inhibitors of mild steel in 1.0–6.0 N solutions of HCl. Activation energies in the presence and absence of inhibitors have been evaluated. Galvanostatic polarization data indicate that all these compounds are predominantly cathodic inhibitors. All the inhibitors reduce cathodic current and aniline N-(p-methoxybenzylidene) reduces the protective current significantly. The difference effect is positive in the absence as well as in the presence of inhibitors.     

Alicyclische Verbindungen als Korrosionsinhibitoren für Aluminium 65-S in Salzsäure

Alicyclic compounds as corrosion inhibitors for aluminium-65 S in hydrochloric acid Cyclohexanone, cyclohexanol, methylcyclohexanol and cyclohexylamine have been investigated as corrosion inhibitors for aluminium-65 S in hydrochloric acid solutions. All the four substances are predominantly cathodic inhibitors and reduce the protective current. The difference effect is negative in 2.0 N hydrochloric acid but becomes positive in the presence of inhibitors.     

Methylamine als Korrosionsinhibitoren für Aluminium 57-S in Salzsäure

Methylamines as corrosion inhibitors for Al-57 S in hydrochloric acid solutions Methylamine, dimethylamine and trimethylamine have been investigated as corrosion inhibitors for aluminium-57 S in hydrochloric acid solutions. Of the three substances studied, dimethylamine is the best inhibitor as indicated by loss in weight measurements and polarisation studies. Studies of cathodic protection to aluminium-57 S in 2.0 N hydrochloric acid but becomes positive in the presence of inhibitors.     

4-amino-3-substituted-5-mercapto-1,2,4-triazolines as inhibitors for the acid corrosion of steel

Corrosion inhibition by 4-amino-3-H-5-mercapto-1,2,4-triazoline and some related compounds on the dissolution of mild steel in sulphuric acid solutions was measured using chemical and electrochemical methods. Polarization curves indicated that these compounds act as mixed-type inhibitors, that is, both the cathodic and anodic curves were affected. The effect of the structural changes in these compounds on their inhibition efficiency has been studied. Mass-loss measurements indicated that the rate of corrosion of mild steel rapidly increases with temperature over the range 25 – 60 °C both in the absence and in the presence of inhibitors, with an apparent activation energy in all instances of about 15 kcal mol^-1.     

Inhibition of corrosion of aluminium-51S in hydrochloric acid solutions

The paper describes the performance of aliphatic polyamines and ethanolamine as corrosion inhibitors for Al-51S in hydrochloric acid solutions. These inhibitors function mainly by adsorption and their neutralizing effect has a secondary role in inhibition. Activation energies in the presence and absence of inhibitors have been given. The performance of inhibitors under the influence of external cathodic polarization has been evaluated. The protective potential is not a constant value and varies with each system, and changes with inhibitor concentration. It seems that an increase in ethylenediamine units in the linear chain does not favour inhibitive action. All inhibitors are predominantly cathodic in action.     

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.     

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.     

Corrosion inhibition of mild steel in acidic medium by some sulfa drugs compounds

The inhibiting effect of four sulfa drugs compounds (e.g. sulfaguanidine, sulfamethazine, sulfamethoxazole and sulfadiazine) on mild steel corrosion in 1.0 M HCl solutions were evaluated using both galvanostatic polarization and weight loss techniques. All the examined sulfa drug compounds reduce the corrosion of mild steel. Among the compounds studied, sulfadiazine exhibited the best inhibition efficiency and sulfaguanidine the lowest. The inhibition efficiency goes through a maximum for sulfaguanidine while it increases continuously with concentration to a limit with sulfadiazine, sulfamethoxazole and sulfamethazine respectively. Galvanostatic polarization measurements indicate that all the examined compounds are of mixed inhibitor type with predominant cathodic effectiveness. Moreover, the results revealed a better performance for these compounds as corrosion inhibitors in HCl than in H₂SO₄ solutions. Also, the corrosion inhibition mechanism is discussed.     

Säureinhibitoren. III. Einfluß von quartären Ammoniumsalzen auf die Wasserstoffaufnahme von unlegiertem Stahl in H2S-freier und H2S-gesättigter Ameisensäure

Acid inhibitors. II. Influence of quarternary ammonium salts on the hydrogen absorption of mild steel in H₂S-free and H₂S-saturated formic acid The influence of quaternary ammonium compounds (benzylpyridinium chloride, benzylquinolinium halides, p-dodecylbenzylquinolinium chloride, benzylisoquinolinium chloride, tri-n-butylbenzylammonium halides, benzyldabcolinium chloride) on the rate of metal dissolution and absorption of corrosion hydrogen in the metal was studied at mild steel in chloride containing 10% formic acid at 25 °C in the presence and absence of H₂S. Generally the same effects were observed like in the system steel/hydrochloric acid. Depending on the kind of inhibitor the presence of H₂S increased or decreased the efficiency of inhibitors to block the H-absorption. Regardless of the presence of H₂S p-dodecylbenzylquinolinium chloride and benzylquinolinium iodide exhibited the best efficiencies in decreasing the rate of metal dissolution and inhibiting the H-absorption in the metal.     

酸性介质中氮杂环类缓蚀剂在碳钢上的吸附行为

合成了一种新型含氮杂环有机物:2-(4-叔丁基-苯甲基硫)-5-(1,2,4-三氮唑)-甲基-(1,3,4-噁二唑)(TBTO),通过交流阻抗、动电位极化、失重实验研究了其在酸性介质中的缓蚀效率,并用扫描电镜方法分析了碳钢表面的腐蚀形貌变化.结果表明:TBTO在0.5mol/L H2SO4中对Q235钢的缓蚀作用高达96.2%,能同时抑制碳钢腐蚀的阴、阳极反应过程;化合物在碳钢表面上的吸附行为服从Langmuir吸附等温式.同时用量子化学中的从头算方法对缓蚀剂的分子结构与缓蚀性能的关系进行了研究.     

新型巯基三唑化合物对HCl介质中碳钢的缓蚀作用研究

合成了两种新型巯基三唑化合物，分别采用腐蚀失重法、动电位扫描极化曲线和交流阻抗法研究了其在1．0mol／L HCl介质中对Q235钢的缓蚀作用，分析了缓蚀作用机理．结果表明：对碳钢在1．0mol／L HCl溶液中，合成的巯基三唑化合物是性能优异的缓蚀剂．     

Rhodanine azosulpha drugs as corrosion inhibitors for corrosion of 304 stainless steel in hydrochloric acid solution

The effect of rhodanine azosulpha drugs on the corrosion behaviour of 304 stainless steel in 1.0 M hydrochloric acid solution as corrosive medium has been investigated using weight loss and potentiostatic polarization techniques. Some corrosion parameters such as anodic and cathodic Tafel slope, corrosion potential, corrosion current, exchange current densities, surface coverage and inhibition efficiency were calculated. The polarization measurements indicated that the inhibitors are of mixed type and inhibit corrosion by parallel adsorption on the surface of steel due to the presence of more than one active centre in the inhibitor molecule. The adsorption is obeyed Langmuir adsorption isotherm. The activation energy and thermodynamic parameters were calculated at different temperature.     

Effects of arylthio-and arylseleno(methoxy)methanes on acid corrosion of CT3 steel

The effects of various arylthio-and arylseleno(methoxy)methanes on corrosion of CT3 steel in sulfuric and hydrochloric acid solutions were studied by gravimetric and voltammetric methods. Some compounds of theses classes were found to be effective inhibitors of the acid corrosion of CT3 steel. The presence of the-X-CH₂-O-CH₃ groups (X = S or Se) in aromatic amines and their derivatives enhanced their inhibitive properties. However, because these groups are highly hydrophobic, the molecules of inhibitors should contain other fragments that ensure sufficient solubility.     

Untersuchungen zum Korrosionsmechanismus von unlegiertem Stahl in sauerstofffreien Kohlensäurelösungen. Teil I. Kinetik der Wasserstoffabscheidung

Investigations into the corrosion mechanism of unalloyed steel in oxygen-free carbonic acid solutions. Part I – Kinetics of hydrogen evolution Polarisation measurements with rotating disc electrodes showed that the corrosion of mild steel in ogygen-free carbon dioxide solutions is not limited by transport processes but is controlled by cathodic activation polarisation. The reason, why oxygen-free carbon dioxide solutions are more corrosive than diluted solutions of mineral acids at the same pH, is explained by the findings that the cathodic reaction is controled by the reduction of both hydrogen ion and adsorbed undissociated carbonic acid, thus stimulating the Volmer-reaction. Electrochemical hydrogen permeation measurements showed that in carbon dioxide solutions the uptake of hydrogen in mild steel is approximately twice as high as in comparable sulfuric acid solutions. Considering the results of comparing experiments with carbon monoxide the possibility of hydrogen embrittlement of mild steel in condensates under high partial pressure of carbon dioxide must be taken into account.     

Synergistic effects of formaldehyde and alcoholic extract of plant leaves for protection of N80 steel in 15%HCl

Abstract

The synergistic effects of formaldehyde and an alcoholic extract of plant leaves have been studied by weight loss measurements at temperatures up to 363 K using various concentration ratios of the two inhibitors to protect N80 steel against corrosion in 15% hydrochloric acid. The inhibition efficiency was found to decrease with increasing temperature for all except two of the various concentration ratios that were studied. After identifying these two most promising mixtures, their corrosion prevention effects for N80 steel in hydrochloric acid were studied in more detail by weight loss and potentiostatic polarisation measurements. The corrosion rate of the steel was decreased by the presence of small additions of the inhibitors. The extent of decrease was found to depend on the nature of the corrosion inhibitor and its concentration. The inhibition efficiencies of the two plant based inhibitor mixtures were compared with those of two commercially available oil industry corrosion inhibitors. In all cases the adsorption of the inhibitors on the steel appeared to follow the Frumkin or Langmuir adsorption isotherm. The inhibition efficiencies of the two plant based inhibitors and the two commercial inhibitors were evaluated at a concentration level of 0.8% for temperatures in the range 303 K to 363 K) and exposure times of between 1 h and 24 h. Thermodynamic parameters including the free energy of adsorption, activation energy, enthalpy and entropy were calculated in both the absence and presence of inhibitors. Potentiostatic polarisation tests have revealed that inhibitors are primarily of the anodic type.     

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.     

Investigation of the inhibiting effect of N-[(Z)-1-phenylemethyleidene]-N-{2-[(2-{[(Z)-1phenylmethylidene]amino}phenyl)disulfanyl]phenyl} amine and its derivatives on the corrosion of stainless steel 304 in acid media

The effect of newly synthesized S₂N₂-Schiff bases is investigated on stainless steel 304 corrosion in 15% hydrochloric acid. The Tafel curves of the steel in hydrochloric acid containing Schiff bases show inhibition for both cathodic and anodic processes. Moreover, double layer capacitance and charge transfer resistance values are derived from Nyquist plots. The inhibition efficiency of Schiff bases increases with the increase in inhibitor concentration and temperature. Moreover, Langmuir adsorption isotherm is suitable to fit experimental data of the studied inhibitors. Effect of temperature on the efficiency of the corrosion inhibition shows chemisorption of inhibitors on the surface of metal.     

Inhibition effect of 3,5 bis (2-pyridil) 4-amino 1,2,4 triazole and 1-10 phenantrolin on corrosion of mild steel in acid solutions

Abstract

The inhibition effects of 3,5 bis (2-pyridil) 4-amino 1,2,4 triazole (NBTA) and 1-10 phenantrolin (PHEN) , on corrosion of mild steel in acid solutions, (sulphuric acid and hydrochloric acid) were studied. The Tafel polarisation and ac impedance techniques were employed. Results obtained reveal that both compounds are relatively good inhibitors. The inhibition efficiencies of NBTA are higher in hydrochloric acid than in sulphuric acid. This has been attributed to the synergistic effect of chloride ions present in hydrochloric acid. The mechanism of inhibition of PHEN is believed to be owing to the formation of insoluble chelates between the organic molecules and atom/ion on the metal surface. The adsorption of NBTA is believed to occur through the formation of an iron-nitrogen coordinate bond. The adsorption isotherms were also determined and found to be of the Langmuir type.     

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.     

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.