Aminophenols as Corrosion Inhibitors for Aluminium–Copper Alloy in Sodium Hydroxide

Abstract

The inhibition by aminophenols of the corrosion of Al–4% Cu alloy (B26S) in solutions of sodium hydroxide has been studied in relation to the concentration of alkali and of inhibitor, the period of immersion and temperature. In general, at constant alkaliconcentration, inhibitor efficiency increases with concentration of inhibitor but, at constant inhibitor concentration, decreases with increase in alkali concentration, the effect being less pronounced with o-aminophenol. The inhibitive efficiency remains almost constant with temperature in the range 20–50°c, but decreases as the period of immersion is increased. At an inhibitor concentration of O·01–2·0% in 0·1 M NaOH the efficiency increases in the order: p-aminophenol < m-aminophenol < phenol < o-aminophenol.

The inhibitors appear to function through adsorption following the Freundlich adsorption isotherm. The comparatively better inhibitive efficiency of o-aminophenol appears to be due to chelate formation. From galvanostatic polarisation data all thefour compounds appear to be mixed type inhibitors.     

Anilines as corrosion inhibitors for an aluminium-copper alloy in phosphoric acid

The inhibitive action of substituted anilines against the corrosion of B26S aluminium (Al-Cu alloy) in solutions of phosphoric acid has been studied. At 0.5% inhibitor concentration in 0.033M acid the efficiency of the inhibitors increases in the order: O-chloroaniline < N-N-diethylaniline < p-anisidine < p-chloroaniline < m-chloroaniline < N-N-dimethylaniline < m-toluidine < methylaniline < m-anisidine < O-toluidine < o-anisidine < aniline < p-toluidine. At constant acid concentration the inhibitor efficiency increases with increase in the concentration of the inhibitor, whereas at constant inhibitor concentration the efficiency decreases with increase in the concentration of the acid. Very little correlation appears to exist between the pK_b values or the molecular weight of the inhibitor and the extent of inhibition. N-substituted alkyl anilines have less inhibitive properties than aniline. In the case of toluidine and anisidine the para-compounds appear to be more effective, whereas in the case of chloro-aniline the meta-compound is more effective. Maximum inhibition is achieved in those cases where the pH of the inhibited solution lies in the range 3.55–5.75, but where the solution is required for use at low pH values, then meta- and parachloro-aniline appear to be the most suitable inhibitors.     

Amines as Corrosion Inhibitors for Aluminium-Manganese Alloy in Phosphoric Acid

Abstract

The corrosion of 3S aluminium (Al-Mn alloy) and its inhibition in solutions of phosphoric acid has been studied. The extent of corrosion increases with increase in acid concentration and with the length of the period of immersion. At 0·5% inhibitor concentration the efficiency of the inhibitors increases in the order: triethylamine < dicyclohexylamine < diethylamine < di-n-propylamine < cyclohexylamine < n-butylamine < ethylamine < trimethylamine < ethylenediamine < hexamine < isopropylamine < dimethylamine < methylamine < n-propylamine. At constant acid concentration the inhibitor efficiency increases with increase in the concentration of the inhibitor, whereas at constant inhibitor concentration the efficiency decreases with increase in the concentration of the acid. Very little correlation appears to exist between the pK_b values or the molecular weight of the inhibitor and the extent of inhibition. Maximum inhibition is achieved in those cases where the pH of the inhibited solution lies in the range 4·5 to 8·5, but where the solution is required for use at low pH values, then hexamine appears to be the most suitable inhibitor.     

Aldehydes as corrosion inhibitors for aluminium-manganese alloys in potassium hydroxide

Some aliphatic and aromatic aldehydes have been studied as corrosion inhibitors for 3S aluminium (Al-Mn alloy) in KOH solutions. At constant alkali concentration the inhibitor efficiency increases with the concentration of the inhibitor, the order of efficiency in 0.1 M KOH + 1.0% inhibitor being: paraldehyde (13.3%) < formaldehyde ≦ propionaldehyde < crotonaldehyde < furfuraldehyde < vanillin < salicylaldehyde (74.8%); 0.5% benzaldehyde and 0.1% cinnamicaldehyde gave efficiencies of only 19.3% and 18.5%, respectively. The aldehydes appear to act by adsorption on the metal surface, preferably through the oxygen atom. The inhibitive efficiency of paraldehyde increases with the alkali concentration, the duration of immersion and the temperature; that of formaldehyde, cinnamic aldehyde, furfuraldehyde (and crotonaldehyde) increases with alkali concentration and time; that of salicylaldehyde and vanillin increases with time as well as with temperature, while the efficiency of propionaldehyde and benzaldehyde increases with alkali concentration. The activation energy for the corrosion process is generally higher in inhibited than in plain alkali in the case of formaldehyde, propionaldehyde, crotonaldehyde, benzaldehyde, cinnamicaldehyde and furfuraldehyde; with other inhibitors the E values are lower. Except vanillin and paraldehyde, all the inhibitors increase the corrosion potential of Al in 0.1 M KOH suggesting polarization of local anodes. The inhibitor efficiencies calculated from extrapolation of cathodic Tafel lines are in agreement with weight loss efficiencies.     

‘Ternary alloys - a comprehensive compendium of evaluated constitutional data and phase diagrams’

Abstract

The inhibition of corrosion of A1-4% Cu alloy (Al B26 S) in solutions of sodium hydroxide, by o-substituted phenols, has been studied with respect to concentration of alkali and of inhibitor, period of immersion and temperature. In general, at constant alkali concentration, inhibitor efficiency increases with increase in concentration of inhibitor but, at constant inhibitor concentration, decreases with increase in alkali concentration. The inhibitive efficiency remains almost constant with temperature in the range 20–50°c, and with time of immersion up to one hour.

The general order of efficiency in 0·1 M NaOH at an inhibitor concentration of 1% (s as follows: 0-allylphenol < guiacol < o-nitrophenol < phenol ≤ o-cresol ≤ o-aminophenol < catechol < o-chlorophenol < salicylaldehyde. In general, ?OH, ?N0₂, ?Cl, and ?CHO groups in the ortho- position increase the efficiency of phenol, while ?OCH₃, ?NH₂, and ?CH₂ CHCH₂ groups decrease the efficiency. The most reliable inhibitors over the concentration range studied are catechol, o-chlorophenol, and salicylaldehyde.

Except catechol, all the inhibitors raise the open circuit potential of B26 S aluminium to slightly more noble values, indicating the polarisation of local anodes.     

Triphenylmethane dyes as corrosion inhibitors for aluminium-copper alloy in hydrochloric acid

The inhibition of the corrosion of B 26 S aluminium in HCl solutions by triphenylmethane, anthraquinoid and acridine dyes has been studied in relation to the concentration of acid and inhibitor, duration of immersion and temperature. In general, at constant acid concentration, the inhibiting efficiency of malachite green, methyl violet 6 B and light green increases, whereas that of fuchsine base and crystal violet decreases as the inhibitor concentration increases. At constant inhibitor concentration the efficiency of all the compounds except methyl violet 6 B and acridine orange increases with increasing acid concentration. The inhibitive efficiency of all the compounds increases with temperature in the range 20–50°C, but no dependence can be recognized on the duration of immersion. At an inhibitor concentration of 0.1% in 0.5 M HCl the efficiency increases in the order: fuchsine acid (32%) < acridine orange ≤ fuchsine base (39%) < alizarin red S (46%) < methyl violet 6 B (50%) < malachite green (64%) < crystal violet (70%) < light green (80%). The inhibitors appear to function through adsorption following the Langmuir adsorption isotherm. From the corrosion potentials the inhibitors appear to function through general adsorption but under galvanostatic polarisation conditions, the cathode appears to be preferentially polarised.     

Inhibition of acidic corrosion of pure aluminum by some organic compounds

Inhibition of the corrosion of aluminum (Al) in hydrochloric acid (HCl) by sulfonic acid (SA), sodium cumene sulfonate (SCS), and sodium alkyl sulfate (SAS) has been studied using weight-loss and potentiostatic polarization methods. The results drawn from the two techniques are comparable and exhibit small discrepancy. The inhibition action depends on the chemical structure and the concentration of the inhibitors, the concentration of the corrosive medium, and the temperature. The efficiency of inhibitors increases in the order: SAS < SCS < SA in the studied concentration range. Results for weight loss indicated inhibitor efficiency (I%) increased with increasing inhibitor concentration, reaching a maximum inhibiting power of 85.6% at its highest values. The inhibitor efficiency (I%) decreased as the concentration of HCl increases. For the tested additives, the increase in temperature resulted in decreasing of the inhibitor efficiency (I%) and decreasing in the degree of surface coverage (θ). These results were indicative of increased aluminum dissolution with increasing temperature. The degree of surface coverage (θ) increased linearly with the logarithm of the inhibitor concentration fitting a Temkin isotherm.     

N-heterocyclic compounds as corrosion inhibitors for aluminium-copper alloy in hydrochloric acid

The inhibition of the corrosion of Al---4Cu alloy (B26S) in solutions of hydrochloric acid by some N-heterocyclic compounds has been studied in relation to the concentration of the acid and of inhibitor as well as the temperature. In general, at constant acid concentration, inhibitor efficiency increases with concentration of inhibitor and also with a rise in temperature. Except for the three picolines the efficiency also increases with increase in acid concentration. In general, at an inhibitor concentration of 0.05-1.0% in 0.1–1.0 M HCl, the efficiency increases in the order: 4-picoline < 3-picoline < 2-picoline > pyridine < piperidine < acridine.The inhibitors appear to function through general adsorption following the Langmuir adsorption isotherm. However galvanostatic polarisation data suggest that in the case of all the six inhibitors the cathode is preferentially polarised under the influence of an external current.     

Electrochemical behaviour of carbon steel in acid chloride solution in the presence of dodecyl cysteine hydrochloride self-assembled on gold nanoparticles

In this work, the dodecyl cysteine hydrochloride surfactant was synthesized. The surface properties of this surfactant were studied using surface tension technique. The nanostructure of this surfactant with the prepared gold nanoparticles was investigated using TEM technique. The synthesized surfactant and its nanostructure with the prepared gold nanoparticles were examined as non-toxic corrosion inhibitors for carbon steel in 2 M HCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The results show that the percentage inhibition efficiency (η%) for each inhibitor increases with increasing concentration until critical micelle concentration (CMC) is reached. The maximum inhibition efficiency approached 76.6% in the presence of 175 ppm of dodecyl cysteine and 90.8% in the presence of the same concentration of dodecyl cysteine hydrochloride self-assembled on gold nanoparticles. Polarization data indicate that the selected additives act as mixed type inhibitors. The slopes of the cathodic and anodic Tafel lines (β_c and β_a) are approximately constant and independent of the inhibitor concentration. Analysis of the impedance spectra indicates that the charge transfer process mainly controls the corrosion process of carbon steel in 2 M HCl solution both in the absence and presence of the inhibitors. Adsorption of these inhibitors on carbon steel surface is found to obey the Langmuir adsorption isotherm. From the adsorption isotherms the values of adsorption equilibrium constants (K_ads) were calculated. The relatively high value of (K_ads) in case of dodecyl cysteine hydrochloride self-assembled on gold nanoparticles reveals a strong interaction between the inhibitor molecules and the metal surface.     

Antifungal drugs as corrosion inhibitors for aluminium in 0.1 M HCl

The inhibitive capabilities of Clotrimazole (CTM) and Fluconazole (FLC), two antifungal drugs, on the electrochemical corrosion of aluminium in 0.1 M HCl solution has been studied using weight loss measurements at 30 and 50 °C. The results indicate that both compound act as inhibitors in the acidic corrodent. At constant acid concentration, the inhibition efficiency (%I) increased with increase in the concentration of the inhibitors. Increase in temperature increased the corrosion rate in the absence and presence of the inhibitors but decreased the inhibition efficiency. CTM and FLC adsorbed on the surface of aluminium according to the Langmuir adsorption isotherm model at all the concentrations and temperatures studied. Phenomenon of physical adsorption is proposed from the activation parameter obtained. Thermodynamic parameters reveal that the adsorption process is spontaneous. The reactivity of these compounds was analyzed through theoretical calculations based on AM1 semi-empirical method to explain the different efficiencies of these compounds as corrosion inhibitors. CTM was found to be a better inhibitor than FLC.     

Molybdate and tungstate as corrosion inhibitors for cold rolling steel in hydrochloric acid solution

The inhibition effects of molybdate and tungstate on the corrosion of cold rolling steel (CRS) in hydrochloric acid solution (0.1-0.5 M) were investigated by weight loss and electrochemistry methods. The results reveal that both molybdate and tungstate are very good inhibitors with little concentration. The adsorption of inhibitors on the CRS surface basically obeys the Langmuir adsorption isotherm equation. The effect of temperature on the corrosion behavior of CRS was also studied at 25 °C and 35 °C, the thermodynamic parameters such as adsorption heat (ΔH⁰) and adsorption free energy (ΔG⁰) were calculated. In the same conditions, a comparative study of corrosion inhibition of molybdate and tungstate indicated that molybdate was the better inhibitor in 0.1 M HCl. However, the value of percentage inhibition efficiency (IE) was dependent on the concentration of inhibitors in 0.2-0.5 M HCl. It seemed that molybdate did not have the strong inhibitive effect compared to tungstate with relatively small concentration of inhibitors, but molybdate was a better inhibitor over a wide concentration range of inhibitors. A kinetic study of cold rolling steel in uninhibited and inhibited acid was also discussed. Various parameters such as rate constant k and the kinetic parameter B were calculated for the reactions of corrosion. Polarization curves showed that both molybdate and tungstate are mixed-type inhibitors in acidic media.     

Curcumin Derivatives as Green Corrosion Inhibitors for α-Brass in Nitric Acid Solution

1,7-Bis-(4-hydroxy-3-methoxy-phenyl)-hepta-1,6-diene-4-arylazo-3,5-dione I-V have been investigated as corrosion inhibitors for ??-brass in 2?M nitric acid solution using weight-loss and galvanostatic polarization techniques. The efficiency of the inhibitors increases with the increase in the inhibitor concentration but decreases with a rise in temperature. The conjoint effect of the curcumin derivatives and KSCN has also been studied. The apparent activation energy (E _a*) and other thermodynamic parameters for the corrosion process have also been calculated. The galvanostatic polarization data indicated that the inhibitors were of mixed-type, but the cathode is more polarized than the anode. The slopes of the cathodic and anodic Tafel lines (b _c and b _a) are maintained approximately equal for various inhibitor concentrations. However, the value of the Tafel slopes increases together as inhibitor concentration increases. The adsorption of these compounds on ??-brass surface has been found to obey the Frumkin??s adsorption isotherm. The mechanism of inhibition was discussed in the light of the chemical structure of the undertaken inhibitors.     

Gossipium hirsutum L. extracts as green corrosion inhibitor for aluminum in NaOH solution

The corrosion inhibition properties of Gossypium hirsutum L. leave extracts (GLE) and seed extracts (GSE) in 2 M sodium hydroxide (NaOH) solutions were studied using chemical technique. Gossypium extracts inhibited the corrosion of aluminium in NaOH solution. The inhibition efficiency increased with increasing concentration of the extracts. The leave extract (GLE) was found to be more effective than the seed extract (GSE). The GLE gave 97% inhibition efficiency while the GSE gave 94% at the highest concentration.     

Inhibition effect of novel nonionic surfactants on the corrosion of carbon steel in acidic medium

The inhibition effect of novel nonionic surfactants on the corrosion of carbon steel (CS) in 1 M HCl was studied at different temperatures (20-60 °C) by weight loss, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization methods. The CS surface morphology was investigated by SEM. The obtained results showed that the prepared nonionic surfactants are excellent inhibitor in 1 M HCl, and the inhibition efficiency (η) increases with the inhibitor concentration and temperature increasing. The adsorption of inhibitors on the CS surface obeys the Langmuir adsorption isotherm equation. Thermodynamic parameters have been obtained by adsorption theory. Polarization curves show that the synthesized inhibitors are mixed-type inhibitors in hydrochloric acid.     

Role of ClO4 in breakdown of tin passivity in NaOH solutions

The anodic behaviour of a tin electrode in NaOH solutions containing different concentrations of NaClO₄ was studied by employing potentiodynamic, potential transient under constant current density methods and complemented with scanning electron microscopy (SEM). In perchlorate-free NaOH solutions, the E/i response exhibits active/passive transition. The active region involves two anodic peaks corresponding to the formation of Sn(II) and Sn(IV) species respectively. The permanent passive layer is duplex and consists of SnO and SnO₂. Additions of NaClO₄ to the alkali solution, accelerates the active dissolution of tin and tends to breakdown the duplex passive layer at a certain breakdown potential. SEM examination confirms the occurrence of film breakdown. The breakdown potential decreases with an increase in ClO₄⁻ concentration, but increases with increasing both OH⁻ concentration and scan rate. The potential-time transients display that the incubation time for pit initiation decreases with increasing both ClO₄⁻ concentration and anodic current density.     

Corrosion of electroplated CuCd alloys and its inhibition

The compounds o-, m- and p-phenylenediamine have been studied as possible inhibitors for use in the HNO₃ pickling of 94/6 and 80/20 CuCd electrodeposits on copper. Weight-loss and polarization data indicate that effective inhibition can be obtained for short periods of treatment and that effectiveness increases in the order p < m < o.     

Electrochemical and theoretical investigation on the corrosion inhibition of mild steel by thiosalicylaldehyde derivatives in hydrochloric acid solution

Inhibitory effect of three Schiff bases 2-{[(2-sulfanylphenyl)imino]methyl}]phenol (A), 2-{[(2)-1-(4-methylphenyl)methylidene]amino}-1-benznethiol (B), and 2-[(2-sulfanylphen-yl)ethanimidoyl)]phenol (C) on corrosion of mild steel in 15% HCl solution has been studied using weight loss measurements, polarization and electrochemical impedance spectroscopy (EIS) methods. The results of the investigation show that the compounds A and B with mean efficiency of 99% at 200 mg/L additive concentration have fairly good inhibiting properties for mild steel corrosion in hydrochloric acid, and they are as mixed inhibitor. All measurements show that inhibition efficiencies increase with increase in inhibitor concentration. This reveals that inhibitive actions of inhibitors were mainly due to adsorption on mild steel surface. Adsorption of these inhibitors follows the Langmuir adsorption isotherm. Thermodynamic adsorption parameters (K_ads, ΔG_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, ΔH^∗, and activation entropies, ΔS^∗, were calculated by the obtained corrosion currents at different temperatures. Obvious correlation was found between the corrosion inhibition efficiency and the calculated parameters. The obtained theoretical results have been adapted with the experimental data.     

2,5-Bis(4-dimethylaminophenyl)-1,3,4-oxadiazole and 2,5-bis(4-dimethylaminophenyl)-1,3,4-thiadiazole as corrosion inhibitors for mild steel in acidic media

2,5-Bis(4-dimethylaminophenyl)-1,3,4-oxadiazole (DAPO) and 2,5-bis(4-dimethylaminophenyl)-1,3,4-thiadiazole (DAPT) have been synthesised and their inhibiting action on the corrosion of mild steel in 1 M HCl and 0.5 M H₂SO₄ at 30 °C has been investigated by various corrosion monitoring techniques. At constant acid concentration, the inhibitor efficiency of both the compounds is found to increase with inhibitor concentration. DAPT is slightly more efficient in 0.5 M H₂SO₄ than in 1 M HCl whereas DAPO is more efficient in 1 M HCl. Of the two, DAPT appears to be a better inhibitor. Potentiostatic polarisation studies show that both are mixed-type inhibitors in 1 M HCl but cathodic-type in 0.5 M H₂SO₄. The inhibitors function through adsorption following Langmuir isotherm in both the acids. The electronic properties of DAPO and DAPT, obtained using the AM1 semi-empirical quantum chemical approach, have been correlated with their experimental inhibition efficiencies using the linear resistance model (LR). These inhibitors are considered as a non-cytotoxic substances.     

Über den Einfluß von Thioharnstoff und Thioharnstoff-Derivaten als Beizinhibitoren auf die Wasserstoffaufnahme,die Inhibitorwirksamkeit und die Wechselbiegefestigkeit von Kohlenstoffstahl bei der Säurebeizung

Influence of thiourea and its derivatives as pickling inhibitors on hydrogen pickup, degree of inhibition and fatigue load of carbon steel during pickling in acids The influence of additions of thiourea (TU), N-methyl-TU, N, N′-tetramethyl-TU, N-phenyl-TU, N, N′-diethyl-TU and N, N′-diphenyl-TU upon the acid pickling of mild steel (1,0 M H₂SO₄ at 50° C) was investigated. Measured were inhibitor efficiency, uptake of hydrogen and alternating bending strength of the samples as functions of inhibitor type and inhibitor concentration. With all inhibitors a maximum of inhibitor efficiency and alternating bending strength and a minimum of hydrogen uptake was found in the same inhibitor concentration range of about 0,001 M. Compared to pickling in pure sulfuric acid at this optimum concentration the inhibitor efficiency is between 95,2 and 98,4%, the decrease of the hydrogen uptake between 8,6 and 63,3% and the increase of the alternating bending strength between 20,0 and 43,4%, depending upon the kind of inhibitor. The alternating bending strength increases roughly linearly with decreasing hydrogen content of the samples. In the optimum concentration range the inhibitor efficiency and the alternating bending strength increase, the hydrogen uptake decreases roughly linearly with increasing adsorption area or increasíng molecular weight of the inhibitors.     

Poly(4-vinylpyridine-poly(3-oxide-ethylene) tosyle) as an inhibitor for iron in sulphuric acid at 80 °C

The influence of poly(4-vinylpyridine-poly(3-oxide-ethylene) tosyle) P4VPPEO5000Ts, on the corrosion inhibition of iron in molar sulphuric acid solution is studied using weight-loss, polarisation resistance, potentiodynamic and EIS measurements. P4VPPEO5000Ts is an excellent inhibitor and its inhibition efficiency increases with the increase of concentration to attain 100% since 2.5 × 10⁻⁸ M. Potentiodynamic polarisation studies clearly reveal that it acts as a mixed-type inhibitor. The polymer studied reduces the corrosion rates. E% values obtained from weight-loss, corrosion current density, polarisation resistance and EIS methods are in good agreement. Adsorption of this compound on iron surface has an S-shaped adsorption isotherm with two consecutive steps.