Inhibiting Effect of some Monosaccharides on the Corrosion of Copper in Nitric Acid

Abstract

A study has been made of the inhibitive efficiency of some monosaccharides (glucose, fructose, mannose, galactose, in the concentration range 10^?3M–1·0M) on copper corrosion in HNO₃ (0·01, 0·1 and 1·0 M) at temperatures of 15°, 25° and 35°c. It was found that the structures of the various saccharides (pyranosic or furanosic) affected neither the efficiency nor the mechanism of inhibition. Inhibition was practically zero at concentrations of the monosaccharides between 10^?3 and 10^?1 M, whereas, at 1·0 M, 65–70% inhibition was reached in 0·01 and 0·1 M HNO₃, and 50–60% in 1·0 M HNO₃.

In 1·0 M HNO₃ the saccharides act as cathodic inhibitors (reducing HNO₂ present in the HNO₃ solutions), whereas in 0·1 and 0·01 M HNO₃ they also acted as anodic inhibitors through theformation of an organometallic compound with Cu²⁺, which gave slight protection to the metal surface.     

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.     

Calendar of Meetings

Abstract

Ethylene diamine was evaluated as a short-term inhibitor for aluminium alloys, 2S, 57Sand 65S in hydrochloric acid. At 43·5 ml/l concentration, it afforded complete protection to all the alloys in 1·0 N hydrochloric acid for up to three hours in the temperature range 35–55°c. At higher concentrations of hydrochloric acid, its efficiency was 97–99·5%. Ethylenediamine reduced the externalcathodic protective current, gave cathodic protection and inhibition by lowering the potential requirements and by increasing the anodic and cathodic polarisation characteristics of the metal surface. At concentrations up to 17·4 ml/l, ethylenediamine accelerated corrosion of the 2S alloy.     

Nickel electrodeposition from novel lactate bath

Abstract

A new electroplating bath for nickel deposition has been developed. Lactic acid was used as a complexing agent in the bath replacing boric acid. The effect of bath composition, current density, pH and temperature on the cathodic polarisation, cathodic current efficiency, morphology and structure of the deposit was carried out. Optimum conditions for producing sound and satisfactory nickel deposits were: 0·30M NiSO₄.7H₂O, 0·50–1·0M lactic acid and 0·3M Na₂SO₄ at pH=10, c.d.=0·98 to 9·80 mA cm^?2 and 25°C. The surface morphology of the deposited nickel was investigated using SEM. The crystal structure was examined by X-ray diffraction analysis. The results showed that the nickel deposits have a face centred cubic structure.     

Influence of chromium content on corrosion resistance of low alloyed chromium steels in hydrofluoric acid and in other acid environments

Abstract

The influence of chromium content on the corrosion resistance of low alloyed chromium steels is studied in 1·7M (3%) HF, 1·4M (5%) HCl, 0·75M H₂S0₄, and 1·5M HClO₄ at 45°C. The presence of chromium in the steels decreases their corrosion resistance in HF solutions, and to a lesser extent in H₂SO₄ and HClO₄ acid solutions. There was little effect in the HCl solution.     

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.     

Electrochemical and Weight Loss Measurements of Inhibition of the Acid Corrosion of Steel

Abstract

Stern-Geary and Tafel polarisation relationships have been obtained for steel in 0·5 M H₂SO₄ and 1 M HCl containing different concentrations of a wide range of n-alkylquaternary ammonium compounds and thiourea derivatives. The shape of the Stern-Geary polarisation relationship is found to depend on the difference between the anodic and cathodic Tafel slopes, b_a and b_c, in agreement with electrode kinetic theory.

For each solution the corrosion rate was derived from the electrochemical data in two different ways:

1. Substitution of the Stern–Geary gradient, ?I/?E, and the measured values of b_a and b_c in the Stern-Geary equation: II. Extrapolation of the Tafel lines to the point of intersection. The results from the two methods were in good agreement for all of the solutions tested.The corrosion inhibition values calculated from the Stern-Geary corrosion rates were also compared with those measured in separate experiments by weight loss. The agreement was good except for the n-alkylquaternary ammonium compounds in 0·5 M H₂SO₄, which gave considerable discrepancies at the lower levels of inhibition. This was shown to be due to differences in the pre-immersion treatment of the steel samples.     

Coal Tar Base Fractions as Pickling Inhibitors in Hydrochloric and Sulphuric Acid Solutions

Abstract

Four coal-tar-base fractions were found to be effective in preventing the dissolution of low-carbon steel and in limiting the absorption of hydrogen by steel during pickling in 2 N- and 4 N-hydrochloric acid at 100° and 150°F. The crude quinoline bases and distilled quinoline bases were also effective inhibitors in 2 N-sulphuric acid solutions at 100°F, but at 200°F these same fractions afforded no better than 78% inhibition when tested at 0·25 vol.-%.

Previous investigations have shown that NaCl, NaBr and NaI are moderately effective inhibitors in 2 N-sulphuric acid at 200°F. In the presence of coal-tar bases, these and other inorganic halides display a remarkable synergistic effect. When used at relatively low halide concentrations, the inhibitor properties of the mixtures are much better than those of the halides or tar bases used alone in sulphuric acid. The superior performances of the tar-base fractions in HCl may be associated with the fact that HCl is a halogen acid. Moreover, the tar base–halide mixtures studied, in addition to being superior in limiting the dissolution of steel, were more effective than many commercial inhibitors in limiting hydrogen absorpiion by during pickling at 200°F.

Although the other tar-base fractions can be used as inhibitors with proper halide additions, the crude and distilled quinoline bases were effective when used with NaCl and, therefore, such formulations would be of relatively low cost. Inhibitor formulaiions for use in H₂SO₄ solutions up to 10 N in concentration have been evaluated.     

Determination of inhibition effects of various imidazole derivatives on copper corrosion in 0·1M HCl media

Abstract

In the present study the inhibitive behaviour of 1H-imidazole, 1-methyl imidazole, imidazolidin-2-one, 4-(imidazole-1-yl)acetophenone, 4-(imidazole-1-yl) phenol and L-hystidine on the corrosion of copper in 0·1 M HCl has been investigated by potentiodynamic polarisation and polarisation resistance techniques. Except for 2-imidazolidone, the tested imidazole derivatives were found to behave as cathodic inhibitors. 1-methyl imidazole, 4-(imidazole-1-yl) acetophenone, 4-(imidazole-1-yl) phenol and L-hystidine were adsorbed on copper surface according to Temkin isotherm model. By using semi-empirical quantum chemical methods, physical parameters such as charge on the heteroatoms of imidazole derivatives q _n, energies of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and dipole moments were calculated. Possible correlations between these calculated physical parameters and inhibitor efficiencies were considered. Finally, the mechanistic information relating to the inhibition process was elucidated.     

Study of inhibition mechanism and efficiency of indole-5-carboxylic acid on corrosion of copper in aerated 0·5M H2 SO4

Abstract

Inhibition of the corrosion of copper in aerated 0·5M sulphuric acid solutions containing various concentrations of indole-5-carboxylic acid was studied in the temperature range 25–55°C using potentiodynamic curves (Tafel lines), weight loss, analytical methods, and determination of double layer capacitance. The corrosion rates reveal good corrosion inhibition, up to 95% in the concentration range of 1 × 10^-4–4 × 10^-3M. Tafel anodic slopes in inhibited acid solutions are considerably higher than those in uninhibited acid solutions. This points to a change in the corrosion mechanism of copper in the presence of indole-5-carboxylic acid. Under these conditions, copper could electro-oxidise primarily to Cu⁺ rather than to Cu²⁺, forming slightly soluble [Cu–(indole-5-carboxylic)_n ]⁺_(ads) complexes. Corrosion rates determined by the weight loss method in both the absence and presence of inhibitor are much higher (on average by a factor of about 6) than those obtained with the potentiodynamic method. This points to a limitation of the Tafel line extrapolation method in corrosion rate determination. The double layer capacitance–potential curves indicate considerable adsorption of the inhibitor over a wide potential range (-600 to +200 mV with regard to E_corr ).     

Chlorine inclusion mechanism in high purity copper electrorefining from nitric acid system

A practical approach was introduced to study the inclusion mechanism of chlorine in high purity copper electrorefining from nitric acid system via cyclic voltammetry (CV) combined with electrodeposition experiments. The CV curves display an obvious reduction peak of CuCl intermediate, which can provide an insight into the electrochemical behavior of this inclusion. Experimental results show that the increase of HNO₃ concentration is favorable to reducing the quantity of chlorine inclusion although there is a slight decline in cathodic current efficiency. The optimum conditions for copper electrorefining in nitric acid system are HNO₃ concentration in solution of 1−2 mol/L, moderate temperature of ~35 °C with current density not exceeding 25 mA/cm². Based on the theoretical studies, an optimized copper electrorefining experiment was designed to simulate the industrial electrolysis, by which high purity copper can be obtained with chlorine inclusion less than 10 μg/g and current efficiency higher than 90%.     

The Corrosion Resistance of Electrodeposited Tin-Nickel Alloy

Corrosion tests have been carried out with electrodeposits of tin-nickel alloy (65% tin) using exposure to natural and simulated atmospheres for deposits up to 0·001 in. thick and using a wide variety of agents for thick pore-free coatings. At 30°C, the alloy is unaffected by alkalis, neutral solutions, nitric acid and by solutions of other acids with a pH value greater than 1·2. It is untarnished in atmospheres grossly polluted by SO₂ and H₂S, but tarnishing may occur on prolonged immersion in some aqueous solutions. There is some evidence that a protective film is formed on the alloy, but this is easily replaced if destroyed and corrosion in crevices is not serious.

The alloy is cathodic to steel and brass. A coating 0·0005 in. thick keeps pore corrosion to tolerable limits on brass for moderately severe exposure; on steel an undercoating of 0·0005 in. of copper is desirable for outdoor service.     

Synergistic action of vinyl triphenyl phosphonium bromide with various anions on corrosion of steel

Abstract

The effect of mixtures of vinyl triphenyl phosphonium bromide containing various anions on the corrosion rate of steel in 0·5M H₂ SO₄ has been investigated. The inhibition mechanism has been studied by conducting electrochemical polarisation measurements. The inhibitor acts by covering the cathodic area of the metal surface through adsorption of the phosphorus atom. A synergistic effect has been observed for KBr, KI, and KSCN with vinyl triphenyl phosphonium bromide. Thus, an improvement in inhibition was obtained by using mixtures compared with that given by individual components. A probable mechanism for this process is suggested. The degree of surface coverage of iron in acid solution containing 10^-5 M inhibitor was determined for various concentrations of Br^-, I^-, and SCN^-. The inhibiting effectiveness was in the order KI > KSCN > KBr. Protection of 93·8% was given by a mixture of 10^-5 M inhibitor + 10^-2 M KI. It was observed that the protection efficiency was sharply enhanced in the presence of 10^-3 M KI with very low concentrations (10^-5 M–10^-4 M) of the inhibitor.     

Control of corrosion of carbon steel in crude oil distillation units

Abstract

Experiments were conducted to investigate the behaviour of different concentrations of 3–amino–1,2,4–triazole (ATR), 2–amino-thiazole (ATH), and 2,6–diamino-pyridine (DAP) as corrosion inhibitors for carbon steel exposed to a kerosene-water mixture containing 3ppm HCl and 800ppmH₂S/day at 55–60°C and pH 6–6·5 with different exposure times, using ammonia as a neutralising agent. Screening tests over,a period of 50 h showed that the presence of 10ppm of the compounds (ATR, ATH, and DAP) with ammonia as a neutralising agent in the absence and in the presence of 10ppm octylamine gave good inhibitor efficiencies (～90%). After 400 h of exposure the inhibitor efficiencies ranged between 50–75% depending on the material added to the test solution. XPS studies of the layer formed on the carbon steel surface indicate the formation of Fe(II) and Fe(III) complexes with the organic compounds used.     

Influence of Thiourea on the Dissolution of Mild Steel in Strong Hydrochloric Acid

Abstract

The dependence of the corrosion rate of a 0·06 % C steel upon the pH and chloride ion activity of solutions of hydrochloric acid at 30°–50° has been examined. A significant amount of simultaneous chemical dissolution takes place as the strength of acid is increased and this leads to anomalously high values of the Tafel parameters, and renders the Stern ‘polarisation resistance’ treatment inoperative. Additions of thiourea produce cathodic stimulation at low concentrations and general inhibition at high concentrations. The results are mterpreted in terms of thiourea dissociation to hydrosulphide ion.     

The mechanism of dezincification and the effect of arsenic. II

Abstract

Dezincification occurs by dissolution of both zinc and copper, followed by redeposition of copper from the oxygen-free cuprous chloride/zinc chloride anolyte. Deposition of copper from such a solution by reduction of Cu⁺ requires a potentIal below ?0·41 V but Cu²⁺, formed by disproportionation of cuprous chloride, can be reduced to copper at potentials up to ?0·16 V. As the potential of film-free beta-brass iS ?0·56 V, reduction of copper at the advancing front of dezincification in beta-brass can occur by direct cathodic re~uction of cuprous ions. Alpha-brass, with a potential of ?0·38V, can only reduce cupricions; dezincification of alpha-brass therefore depends upon formation of Cu²⁺ by disproportionation of cuprous chlonde at the advancing front.

Under the conditions existing at the advancing front, disproportionation of cuprous chloride can be suppressed by a small amount of arsenic, acting through reactions in which it cycles between the As³⁺ and AS_(solid)states. Arsenic consequently inhibits dezincification of alpha-brass but the dezincification of beta-brass, which does not require the formation of cupric ions, is unaffected.     

Formation and Breakdown of Surface Films on Copper in Sodium Hydrogen Carbonate and Sodium Chloride Solutions: II. Effects of temperature and pH

Abstract

The anodic behaviour of copper in air-saturated solutions at 25°, 60° and 90°c has been determined by stepwise potentiortatic polarisation. In 0·01 M NaHCO₃, the critical breakdown potential of the protective oxide layer is displaced to considerably more positive potentials as the temperature increases. In 0·01 M NaHCO₃ containing 0·01 M NaCl, the critical breakdown potential is displiiced tornore negative values with increasing temperature, but the corrosion potential–breakdown potential difference undergoes little change. In 0·01 M NaCl, the surface film on copper is essentially non-protective, and linear Tafelplots are observed. A change in the pH of 0·01 M NaHCO₃, with or without 0·01 M NaCl, from 8·6 to 7·3 has little effect on the valuesof the breakdown potentials. The significance of the results in relation to the initiation of pitting corrosion of copper in natural waters is discussed.     

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.     

Determination of Corrosion and Inhibition of Mild Steel in HNO3 by the Thermometric (Mylius) Technique

Abstract

The thermometric (Mylius) technique has been found to be suitable for determining the action of nitric acid on steel and the effectiveness of inhibitors. This technique may be usefully applied in controlling pickling and acid-cleaning baths by determining the threshold concentrations of inhibitors and checking their depletion during service.

The increase in the rate of attack on steel by HNO₃ with increase in concentration is shown by both weight-loss measurements and the value of the reaction number (R.N.) derived from the thermometric measurements. In HNO₃ at concentrations producing passivity no temperature rise occurs. Lower RN values and, accordingly, lower corrosion rates are obtained in the presence of thiourea, KI, NaCl, and HCl. The presence of an accelerator (NaNO₂) produces higher RN values. Thiourea is able to arrest corrosion occurring in uninhibited HNO₃. Progressive additions of an inhibitor and the recording of the accompanying temperature rise enable the threshold concentration of an inhibitor to be determined.     

The effect of changes in the microstructure of steel on the inhibitive properties of some anodic and cathodic inhibitors

The electrode behaviour of spectroscopically pure Fe, steel samples containing 0·15–1·3%C and grey cast Fe in aerated 0·1M solutions of NaNO₂, Na benzoate and ZnSO₄, in 0·01M quinoline and in saturated CaCO₃ has been studied. The anodic (and cathodic) behaviour of these samples under potentiostatic or galvanostatic conditions has been followed in de-aerated NaNO₂ and ZnSO₄ solutions. It has been shown that anodic inhibitors are more sensitive to changes in the C-content of the samples than cathodic inhibitors, ZnSO₄ being almost indifferent to these changes.The protective nature of the cubic oxide formed in NaNO₂ or Na benzoate solutions is less efficient in presence of separate phases of ferrite, carbide or graphite than in its absence. Quinoline is more preferentially adsorbed on these separate phases. The effectiveness (in situ) of precipitated Ca(OH)₂ in blocking cathodic sites is counteracted by the presence of separate phases.