Adsorption of Quaternary Ammonium Pickling Inhibitors at a Dropping Mercury Electrode

Abstract

Differential capacitance and interfacial tension measurements have been carried out at a dropping mercury electrode in 0·5 M H₂SO₄ and M KCl solutions of n-alkylquaternary ammonium bromides containing C₃, C₁₂ and C₁₆ chains paired to trimethyl-, triethyl-, tripropyl-, and tributylammonium headgroups.

For n-alkyl chain lengths of 8 and 12 carbon atoms, the adsorption of the quaternary ammonium ions on mercury increases with the size of the headgroup, and the calculated surface concentrations indicate that, at optimum potentials, the larger headgroups are always adsorbed in excess of a monolayer. The compounds with alkyl chains of 16 carbon atoms all show multilayer adsorption behaviour which appears to be practically independent of the headgroup.

The results are discussed in relation to the performance of the n-alkylquaternary ammonium compounds as inhibitors of the acid pickling of steel.     

Amine carboxylates as vapour phase corrosion inhibitors

Abstract

Fifty three products, mostly carboxylate salts of amines, were evaluated as vapour phase corrosion inhibitors for mild steel. Fifteen compounds showed effectiveness in excess of 90%. Morpholine was the most effective amine and caprylic acid the most effective acid constituent. The effectiveness of ammonium monocarboxylates decreased with increase in the length of the carbon chain of the carboxylic acid. The other carboxylates did not show such a clear trend.     

EuroCorr 2015 ‘Earth,Water, Fire,Air, Corrosion Happens Everywhere’: Part 3

Abstract

Previous work in this Laboratory showed that many inhibitors of the acid corrosion of steel cause large changes in the anodic Tafel slope, b_a, particularly in 0·5 M H₂SO₄. It was found that cationic inhibitors, such as long-chain n-alkylquaternary ammonium compounds, mostly reduced b_a whereas non-ionic compounds, such as thiourea derivatives, increased it. With the latter there was some differentiation according to the substituent, the aliphatic derivatives giving the largest increases and the aromatic derivatives the smallest.

The decreases in b_a caused by the n-alkylquaternary ammonium compounds are considered to be due to their initial adsorption at anodic sites and also to the structure of their adsorbed layers which involves a layer of positive charges at the metal surface. The non-ionic compounds, on the other hand, appear to be adsorbed generally over the metal surface, causing inhibition mainly by steric hindrance to the anodic and cathodic reactions. These differences are considered in relation to their possible effects on the potential energy curve for the transition of Fe²⁺ ions from the steel surface to the aqueous layer.

The adsorption of the positively charged n-alkylquaternary ammonium ions on the metal surface stimulates the co-adsorption of Br^? ions, and this effect increases with the length of the alkyl chain. With the C_l6 and C_l8 compounds the Br^? ion is adsorbed in such high concentration that the positive field of the adsorbed quaternary ammonium ions is largely neutralised, so that these compounds behave more like non-ionic inhibitors and give increases in b^a.     

In search of functionality for efficient inhibition of mild steel corrosion both in HCl and H2SO4

Abstract

While the organic ammonium compounds are known to be effective against mild steel corrosion in HCl, these cationic salts are not as effective in sulphuric acid media. A new series of tertiary diallylamines containing C₁₂, C₁₄, C₁₆ and C₁₈ alkyl hydrophobes, N-hexadecylpyrrolidine and their corresponding ammonium salts were found to be among a rare class of inhibitors in arresting mild steel corrosion in HCl as well as in H₂SO₄ media effectively. While all the inhibitor molecules exhibited excellent inhibition efficiencies (%IEs) (～99%) in 1M HCl, ammonium salts containing alkyne moiety at 400 ppm provided 93–97%IE even in 7·7M HCl. The inhibitors (400 ppm) containing diallyl moiety demonstrated the %IEs in the range 80–97% in 0·5M H₂SO₄. The interactions of the π electrons in the diallyl moiety with the low lying vacant d-orbitals of iron help the inhibitor molecules to undergo adsorption and interfere with the anodic dissolution process.     

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

Acid inhibitors. II. Influence of quarternary ammonium salts on the hydrogen absorption of mild steel in H₂S-free and H₂S-saturated hydrochloric acid The influence of organic ammonium salts (pyridine hydrochloride and its derivates, trialkylbenzylammonium halides, pyridines, quinolinium and isoquinolinium compounds quaternarized with benzyl halides and substituted benzyl chlorides) on the hydrogen absorption of mild steel treated with H₂S-free and H₂S-saturated 16% hydrochloric acid at 25 °C was studied using electrochemically controlled hydrogen permeation measurements. Investigations on structure-efficiency correlations revealed that the inhibitors can influence the kinetics of the hydrogen absorption and the rate of metal dissolution with significantly different efficiency. Describing the efficiency profil of acid inhibitors it is therefore necessary to test inhibitors in both respects. This is valid especially in the presence of H₂S which can change the efficiency of inhibitors fundamentally. Besides by structural and electronic variations in the organic molecule the efficiency of the inhibitors tested was influenced by the type of anion (e.g. bromide, iodide). With benzylquinolinium chloride the best results were found in both H₂S-free and H₂S-saturated acid.     

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.     

N-[Isononylphenoxypoly(ethyleneoxy)carbonylmethyl]ammonium Chlorides as Inhibitors of Metal Corrosion. I. Inhibition of Steel Corrosion in Aqueous Hydrochloric Media

New ammonium compounds, namely, N-[isononylphenoxypoly(ethyleneoxy)carbonylmethyl]ammonium chlorides, were synthesized and found to be highly effective inhibitors of steel corrosion in aqueous hydrochloric media. The dependence of the inhibitive properties of the title compounds on their structure is discussed.     

Inhibition of Nitrate-Induced Corrosion of Tinplate Cans

Abstract

Procedures for inhibiting nitrate-induced de-tinning of tinplate cans are suggested. Adjustment of pH to greater than 6·0 should be effective for foods of low acidity but could not be used for more acidic foods. Several ‘soft’ compounds were found to inhibit de-tinning in acid foods and their inhibitory power was correlated with their ability to reduce the hydrogen discharge potential of tinplate. A possible mode of action of the inhibitors is discussed and the properties required in inhibitors are listed to stimulate the search for commercially acceptable compounds.     

Organic corrosion inhibitors for zinc pigment

Abstract

A severe problem with waterborne paints containing zinc pigments is hydrogen corrosion of the zinc in the aqueous alkaline paint media. The subject of the present study is the examination of corrosion inhibition of the zinc pigment in aqueous alkaline media by different high and low molecular weight organic inhibitors compared with that given by potassium dichromate. Potassium dichromate inhibits this corrosion reaction moderately, but a 4·0 mmol addition in 100 mL of the corrodent (1·2 wt-%) is required. Heterocyclic compounds are very poor corrosion inhibitors and less effective than potassium dichromate. Certain polymers with low acid numbers and low molecular weights and one particular epoxy ester resin are more effective inhibitors than potassium dichromate. Thus, some non-toxic polymers or paint resins can be considered as possible substitutes for toxic potassium dichromate.     

Comparison of inhibition efficiency of some azoles on corrosion of type 304 stainless steel in acidic solutions

Abstract

Inhibition efficiencies have been investigated for two types of azole, namely 2-mercaptobenzoazole (CBA) and 2-methylbenzoazole (MBA), containing nitrogen, sulphur, oxygen, or selenium atoms, on the corrosion of type 304 stainless steel in 2M sulphuric acid (H₂SO₄) and 3M hydrochloric acid (HCl). The study was conducted using weight loss, gasometry, and polarisation methods. It was shown that some of the compounds tested provide 90% inhibition efficiency at a concentration of 5 × 10^-4M and that the efficiency depends on the heteroatom and decreases in the order Se > S > N > O. These inhibitors were more efficient in H₂SO₄ than in HCl whereas the opposite is true for inhibitors with nitrogen alone. Adsorption isotherms were fitted to the experimental findings and some thermodynamics functions were obtained.     

Studies on a Few Substituted Piperidin-4-one Oximes as Corrosion Inhibitor for Mild Steel in HCl

The corrosion inhibition of mild steel in 1 M hydrochloric acid by a few piperidin-4-one oxime derivatives, namely, 1,3-dimethyl-2,6-diphenyl piperidin-4-one oxime (I), 3,3-dimethyl-2,6-diphenyl piperidin-4-one oxime (II), and 3-isopropyl-2,6-diphenyl piperidin-4-one oxime (III) was studied using chemical weight loss method, electrochemical polarization and impedance spectroscopy, SEM with EDS, XRD, FT-IR measurements, and semi-empirical AM1 method for electronic properties. The weight loss measurements at four different temperatures such as 30, 40, 50, and 60 °C showed that the percentage inhibition efficiency (IE) of these compounds increased with increase of concentration and decreased with increase of temperature. The IE followed the order III < II < I. It was found that these inhibitors function through physical adsorption mechanism obeying Temkin’s isotherm. Polarization studies showed that these compounds act as mixed-type inhibitors. Impedance measurements revealed the increase of charge transfer resistance with inhibitor concentration. Surface analysis using SEM, XRD, and FT-IR revealed the formation of protective film over the mild steel surface. The electronic properties calculated using AM1 semi-empirical method explained the inhibition characteristics. The quantum chemical studies showed that ring nitrogen and phenyl rings are the probable active centers to inhibit corrosion process.     

Inhibitive properties of quaternary ammonium bromides of N-containing heterocycles on acid mild steel corrosion. Part I: Gravimetric and voltammetric results

Four quaternary ammonium bromides of different heterocyclic compounds were investigated as corrosion inhibitors of mild steel in 1 M HCl and 1 M H₂SO₄. Polarisation curves, polarisation resistance and gravimetric methods were used. The inhibitor efficiency was found to depend on both concentration and temperature. The inhibitors were of mixed type, influencing predominantly the anodic process. From the temperature dependences the apparent activation energy in 1 M HCl was determined in the presence of all studied compounds, found to be inferior to the activation energy in absence of inhibitor. The adsorption of the inhibitors was well described by the Frumkin or the Langmuir adsorption isotherms in both acidic media and the adsorption isotherm parameters were determined at room temperature. The influence of the molecular structure was discussed taking into account the different number of positive charges and the different heterocycles. The best inhibitive properties had 1-(carbamoylethyl)-4-methylpyridinium bromide.     

Inhibition of the Acid Corrosion of Steel by n-Alkyltrimethyland n-Alkyltriethyl-ammonium Compounds

Abstract

Previous experiments with a dropping-mercury electrode indicated that n-alkyltriethylammonium ions are more strongly adsorbed than the corresponding n-alkyltrimethylammonium ions. In parallel with this, it has now been found that the former are better inhibitors of the acid corrosion of steel.

At concentrations giving up to 50% corrosion inhibition, the compounds of either series have no effect on the steel electrode potential, indicating that the anodic and cathodic reactions are equally inhibited. This is taken as evidence that the inhibitor ions are adsorbed generally over the metal surface rather than at specific anodic or cathodic sites.

With increasing concentration of inhibitor above the level for 50% inhibition, the potential begins to be displaced in a positive direction, suggesting that the anodic reaction is being inhibited more than the cathodic reaction. The results show that the proportion of cathodic inhibition is larger with the triethylammonium than with the trimethylammonium compounds.

The cathodic part of the inhibition appears to be due mainly to hindrance of the surface diffusion and recombination of adsorbed hydrogen atoms.     

Inhibition by some Thiocompounds of the Corrosion of Copper in Monochloracetic Acid Solution

Abstract

The inhibitory action of ethanolthiol, 2-mercaptoethanol and dodecyl mercaptan towards the corrosion of copper (99·8 %) in 0·1 M monochloracetic acid has been investigated. The inhibitive efficiency of these compounds may be arranged in the following order: dodecyl mercaptan > 2-mercaptoethanol > ethanolthiol. Polarisation measurements indicated that the compounds were principally cathodic corrosion inhibitors. I.R. spectra of the protective film formed on copper in solution inhibited with 2-mercaptoethanol, and of the pure chelate synthesised from 2-mercaptoethanol and copper ions in solution, were found to be identical.     

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.     

New corrosion inhibitors based on fatty materials—II. Epoxidized fatty materials modified with aromatic amines

Eight compounds prepared by modification of epoxidized linseed oil and oleic acid with aniline, p-chloro-aniline, p-toluidine and p-anizidine, were tested as corrosion inhibitors. The test coupons were mild steel and the environment consisted of 0.05N HCl at 70°C or mixed vapours of gasoline and HCl. In HCl, the percentage inhibition ranged from 26.0 to 59.5% for linseed oil and from 88.0 to 94.5% for oleic acid derivatives. In the gas phase, the ranges were from 70.3 to 85.98 and from 62.5 to 74.0%, respectively. The values obtained for two commercial inhibitors tested under the same conditions were 34.5 and 91.7% in HCl and 57.0 and 64.0% in the mixed vapours. The results conformed with a simple Langmuir model and with predictions based on NMR measurements, basicity values (pK_a) and Hammett constants. A ranking of the compounds according to percentage inhibition agreed with the order of increasing electron density on the nitrogen atom in these compounds.     

Inhibitive Efficiency of some Substituted Thioureas for the Corrosion of Aluminium in Nitric Acid

Abstract

The inhibitive efficiencies of thiourea and some of its derivatives have been studied in relation to the corrosion of aluminium (Grade 1060) in nitric acid at 25°c, 35°c and 45°c. The efficiency in 20% HNO₃ at 25°c decreases in the order: p-chlorophenyl thiourea > m-chlorophenyl thiourea ≥ o-chlorophenyl thiourea ≥ phenyl urea > 1:3 di-phenyl thiourea ≥ 1:3 di-p-chlorophenyl thiourea. ≥ 1:3 di-m-chlorophenyl thiourea > thiourea. The adsorption of the compounds is in agreement with Langmuir's adsorption isotherm equation up t a concentration of 250 ppm, at all the three temperatures studied. The percentage efficiencies of the inhibitors were found to increase with increase in temperature from 25° to 45°c. There is no relation between the relative efficiencies of the inhibitors and their critical current densities or primary passivation potentials. All the inhibitors were found to act predominantly on local cathodes although partially effective on the anodes.     

Mono- and dicationic benzothiazolic quaternary ammonium bromides as mild steel corrosion inhibitors. Part I: Gravimetric and voltammetric results

Seven quaternary ammonium bromides of different heterocyclic compounds were investigated as corrosion inhibitors of mild steel in 1 M HCl using gravimetric and polarisation techniques. For comparison gravimetric experiments were carried out in 1 M H₂SO₄ as well. The inhibitor efficiency was found to depend on both concentration and molecular structure of the inhibitor. The polarisation curves revealed that the inhibitors were of mixed type. The adsorption of almost all inhibitors was well described by the Frumkin isotherm. The adsorption isotherm parameters were determined. Conformational changes in the molecular structure favour the adsorption and thus increase the inhibitive effect.     

Thioamidines as novel class of corrosion inhibitors

Abstract

Four nitrogen substituted thiobisformamidines – phenyl thiobisformamidines (PTBF), tolyl thiobisformamidines (TTBF), anisidyl thiobisformamidines (ATBF), and 4-chlorophenyl thiobisformamidines (CPTBF) – were synthesised and their corrosion inhibiting behaviour for mild steel in 1M, 3M, and 5M HCl was studied. The optimum concentration of these compounds for maximum inhibition efficiency was determined by weight loss methods. All the investigated thiobisformamidines gave more than 95% inhibition in the presence of 1M HCl, and CPTBF showed the best inhibition efficiency (98% in 5M HCl). Potentiodynamic polarisation studies revealed that all the tested compounds are of mixed inhibitor type. The adsorption of these compounds from the acid solution obeyed Temkin's adsorption isotherm. All the inhibitors were able to reduce hydrogen permeation through the steel surface and their performance was enhanced by the addition of iodide ions. Electron impedance spectroscopic studies were also carried out in order to understand the mechanism of inhibition. Auger electron spectroscopic analysis confirmed that the adsorption of these compounds on the surface of the mild steel occurs through nitrogen and sulphur atoms.     

Schiff-base derivatives as corrosion inhibitors for carbon steel materials in acid media: quantum chemical calculations

Quantum chemical calculations based on Hartree–Fock, AM1 and B3LYP functions were performed on the three Schiff-base compounds used as corrosion inhibitors for carbon steels in acid media. The quantum chemical calculations were conducted to determine the relationship between inhibition efficiency (IE) and the molecular structure of inhibitors. Several quantum chemical parameters, such as charge distribution, energy and distribution of the highest occupied molecular orbital (E_HOMO) and lowest unoccupied molecular orbital (E_LUMO), absolute electronegativity (χ) and the fraction of electrons (ΔN) transferred from inhibitors to the steel surface, were calculated and correlated with inhibition efficiencies. The results showed that the IE of Schiff-base compounds enhanced with increasing E_HOMO or decreasing E_LUMO; meanwhile, N atoms on Schiff-base molecules were the most probable sites for adsorption of inhibitor molecules on the metal surface. The inhibition mechanisms of three Schiff-base compounds were obtained from different calculation methods, and the results from each method are consistent.