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.     

Umschlagspunkt or Flade Potential of Iron

Abstract

Flade potentials if iron and redox potentials of the Fe³⁺/Fe²⁺ system have been determined in de-aerated sulphate solutions, pH 3–5, and the effect of air on the Flade potential of iron in borate buffers, pH 6–9, has been examined.

The results extend the range of previous work and it is sho,wn that under anaerobic conditions over the pH range 3–5 the Flade potential is given by EF = 0·960 ? 0·158pH ? 0·064 log Fe²⁺whereas in the presence of air, in the pH range 7· 0?9·3, the normal Flade equation is obeyed.It is concluded that the Flade potential corresponds to the redox potential of the Fe³⁺/Fe²⁺ system, both in the presence and absence of air, the effect of oxygen being to modify the ferrous ion concentration.     

Examination of Oxides on Tin Surfaces by Cathodic Reduction

Abstract

Oxides formed on tin surfaces were examined by electrochemical reduction in galvanostatic and potentiodynamic experiments and also by electron diffraction. Reduction of oxide occurred at three distinct potentials (NHE scale): ?0·115 ?0·06 pH, ?0·150 ?0·06 pH and ?0·345 ?0·06 pH, although sometimes only one or two of them were observed. The most negative reduction step rarely appeared for electrodeposited tin coatings oxidised in air but was well developed for pure tin sheet and for hot-dipped tin coatings. Impurities in tin modified both the speed of oxidation and the form of the oxide reduction curves but their effect cannot account for the difference between electrodeposiied coatings and other tin surfaces. This difference is probably due to exposure of differing crystal faces. The two less negative reduction steps appeared for all forms of tin, but were not always clearly separated and they cover the possible reduction of both SnO and SnO₂. The most negative step is associated with SnO₂ only and its development is favoured by chemical or electrochemical oxidation, which may produce it for electrodeposited tin, or by high humidity of air. SnO₂ is also formed on all surfaces during long term storage at room temperature. Some thicker oxide films, formed during long storage or by anodic oxidation, may be partly undermined during reduction and the total reduction charge is not an accurate measure of their character.     

The Anodic Passivation of Iron in Solutions Of Inhibitive Anions*

Abstract

The anodic passivation of iron in air-saturated and de-aerated solutions of a number of inhibitive anions has been studied by the determination of potentiostatic polarisation curves. The critical passivation potential, critical passivation current density and leakage currents through the passive films have been found to depend on pH and on the nature of the anion present in the solution. The critical passivation potential (N.H.E. scale) in solutions of anions, where passivation occurs relatively easily, varies with pH in the range 6–12 according to E_p = + 0.09 – 0.06 pH volt For the anions studied, the critical passivation current densities in de-aerated 0·1 M-solution increase (and the difficulty of passivation increases) in the order: nitrite < hydroxide < chromate < borate < phosphate < carbonate < benzoate < bicarbonate < nitrate.     

Corrosion-electrochemical properties of α-Fe + Fe3C + TiC nanocomposites in neutral environments

The corrosion-electrochemical properties of α-Fe + Fe₃C + TiC three-phase nanocrystalline composites in borate solutions with pH 6.3–9.0 both with and without NaCl are studied. α-Fe + Fe₃C + TiC composites are found to have heightened resistances at active-oxidation potentials of α-Fe and cementite due to the formation of xFeO · yTiO₂ mixed surface oxides. The protective properties of passive films based on xFeO · yTiO₂ and their resistance to local activation are worse than those of Fe₃O₄/γ-Fe₂O₃ (γ-FeOOH) passive films formed on iron and α-Fe + Fe₃C composites.     

Effect of phosphate ions on electrochemical behaviour of copper in sulphate solutions

Abstract

The effect of phosphate ions on the corrosion behaviour of copper in sulphate solutions was investigated at different temperatures (293, 313, 333, and 353 K) and at different pH values (pH = 2·1, 7·2, and 12·3). A three electrode electrochemical technique was used for the measurements, using a saturated calomel electrode (SCE) for reference purposes. Both anodic and cathodic polarisation curves were established, from which the anodic and cathodic Tafel constants were determined. Corrosion potentials were determined by extra trapolation of the anodic and cathodic Tafel lines to the point of zero current density. The results showed that for a pH value of 2·1, the corrosion rate of copper showed a marked tendency to increase with increasing temperature in solutions containing either sulphate alone or sulphate plus phosphate. However, at pH values of 7·2 and 12·3, this tendency became less pronounced in solutions containing sulphate alone and in solutions containing sulphate plus phosphate together, max imum corrosion rates were greatly reduced and showed less tendency to increase with increasing temperature. Anodic and cathodic reaction mechanisms are proposed to explain the observations for the corrosion of copper.     

Zur anodischen auflösung von reineisen im bereich zwischen aktivem und passivem verhalten

The kinetics of anodic iron dissolution in sulphate ions containing solutions, which are free of oxygen, are investigated in a over potential range between active and passive states of the metal. The measurements were carried out on a rotating disk electrode in the pH-range between 3·5 and 5·5 using the potentiostatic triangular voltage sweep method under quasi-steady-state conditions. The measured current density-potential curves show two current maxima. At relatively low anodic overvoltages, i.e. before the maxima I is reached, the used recrystallized iron dissolves in the active state corresponding to the consecutive (Bockris-) mechanism. At high anodic overvoltages the passive state arises after passing the maxima II. In the transition range, i.e. in the potential range of the maximum I, a second mechanism of iron dissolution is discussed. This mechanism takes place parallel to the consecutive one. An intermediate [Fe (OH)₂]_ads will be formed, which dissolves in a following rate-determining chemical step or is changed in an oxide phase respectively.     

Inhibitive Effect of Tannic Acid on the Corrosion of Copper in Acid Solutions

Abstract

The behaviour of copper has been studied in lM solutions of HCl, HNO₃ and an HCl–HNO₃ mixture, containing various amounts of tannic acid (0 · 25, 0·5 and 1·0%). As tannic acid is a mixture of galloylglucoses, the same acids containing gallic acid (0·1, 0·2 and 0·5%) or glucose (0·1, 0·5 and 1·0%) have also been studied.

Glucose inhibits the corrosion of copper in HNO₃ solution to a very slight extent and has no effect in other solutions. Gallic and tannic acids have no effect in HCl but, at the highest concentrations tested, show an inhibitive efficiency of 80% and 70%, respectively, in HNO₃ and about 65–70% in HCl–HNO₃ mixtures.

Gallic acid may be considered to be a cathodic inhibitor that does not interfere directly with the cathodic process but modifies the corrosive environment. Tannic acid behaves both as a cathodic inhibitor and also as an anodic inhibitor due to the formation of an oxidation compound that is adsorbed on the copper surface.     

Über die Inhibitorwirkung der Fettsäuren bei der Korrosion des Eisens in saurer Lösung

Inhibiting effect of fatty acids on the corrosion of iron in acid media Fatty acids (C₁–C₁₂) in acid media (0.01 M HClO₄ + 0.2 M NaClO₄) have partially inhibiting and partially stimulating effects on the corrosion of iron. Short chain acids (C₁ to C₇) in concentrations below 5·10^?5 M act as stimulators, in higher concentrations as inhibitors. Beyond C₈ the stimulating effect gradually disappears. As to the inhibition mechanism the fatty acids are of the mixed type (though the anodic control predominates); they are not chemisorbed but only physically adsorbed by van der Waals forces and become desorbed when the temperature is increased.     

Nature of the Oxide Film Present on Iron after Inhibition in 0·05 M Chromate Solutions

Abstract

Chemical and microprobe analyses have been used to study the composition of the oxide films formed on iron by 0·05 M potassium chromate, pH 4–8.

Chemical analyses have shown that the air-formed oxide film was thinned and evenly reinforced with a normal iron chromium spinel having a composition in the range Fe²⁺ (Fe³⁺_0·5 Cr³⁺_1·5)O₄ — Fe³⁺ Cr³⁺ O₃

Microprobe analyses indicated enrichment of chromium at scratch lines, but the effect was small compared with the overall thickening of the films.     

Galvanic cells encountered in the corrosion of steel reinforcement — II. Differential salt concentration cells

Two differential salt concentration cells have been studied at pH 6·5, 10, 12 and 12·5. The rest potentials of uncoupled steel immersed in chloride solutions of pH 6·5 and 10 were more negative than those obtained in pH 12 and 12·5. This is ascribed to the occurrence of general attack in the former and pitting in the latter solutions. The results of coupling showed that steel electrodes immersed in the half cells of the lower Cl^? ion concentration were completely protected from corrosion. The galvanic currents obtained from the differential salt concentration cells at pH 6·5 or 10 were considerably higher than those obtained at pH 12 or 12·5. In the anodes of the former cells general corrosion occurred while in those of the latter cells pitting corrosion occurred. The increase of the salt concentration range caused an increase in the galvanic current and in the cell e.m.f., negativation of the mixed potential and depolarization of the anodic and cathodic processes. The controlling factors of corrosion in the cells, at different pH values, were mainly determined by the kinetics of the anodic and to a lesser extent by the cathodic process.     

Impedance of Cr18Ni10 stainless steel in sulphate solutions after a low‐temperature plasma nitriding

The 00Cr18Ni10 stainless steel was examined before and after plasma nitriding in a 80%N₂/20%H₂ gas mixture at 425°C for 30 h, resulting in the formation of a supersaturated solid solution of nitrogen in austenite (S phase) with 12.9 wt.% N at the surface. Electrochemical measurements were made on the as‐nitrided surface and after abrasion to various depths. Polarisation curves and impedance were measured in 0.1 M Na₂SO₄ acidified to pH 3.0; some measurements were also made at pH 6 and 9. It was found that nitrogen decreased the corrosion resistance of the steel in the acidified solution (pH 3.0), but increased it in the neutral and near‐neutral solutions (pH 6.0 and 9.0). The deleterious effect of nitrogen at pH 3.0 was at potentials of the active state much stronger and more dependent on the nitrogen concentration than in the passive state. It was suggested that the increased anodic reactivity of the nitrided steel in the active state is inherent for the lower thermodynamic stability of the supersaturated solid solution of nitrogen, whereas the increased corrosion resistance in the neutral and near‐neutral sulphate solutions is associated with the effect of nitrogen on anodic films.     

Untersuchungen zum Einfluß von Sulfid- und Sulfationen auf die Korrosion des Eisens in alkalischer Lösung

Investigation into the influence of sulfide and sulfate ions on the corrosion of iron in alcaline solution The corrosion behaviour of Armco iron as well as that of a technical high-strength steel was investigated in sulphide - and sulphate-containing electrolytes of pH ～ 12.6. Current density - potential curves show that iron, after successful passivation, remains passive and protected against corrosion in a solution saturated with CaS, CaSO₄ and Ca(OH)₂ at potentials up to 800 mV(EH). Passivation experiments conducted by changing from the active region to various anodic potentials yielded a critical potential region around 300 mV(EH), above which corrosion appeared. Up to E_H = 200 mV complete passivation was observed. The same critical potential region was observed in experiments of repassivation after mechanical damaging of a protective passive layer. Additional tensile stresses of 85%· σ_0,2 caused no stress corrosion cracking at a potential of 500 mV(EH). After damaging the passive layer, through scratching of the stressed wires fracture occured at and above potentials of 300 mV(EH). At 200 mV(EH) repassivation was observed even under tensile load. In a sulphate-free Na₂S/Ca(OH)₂ solution of the same sulphide ion concentration no stress corrosion cracking of the samples occured at any potential up to 800 mV(EH) even after scratching the steel samples. The observed stress corrosion in sulphide - and sulphate-containing electrolytes is to be ascribed to the action of sulphate and not to sulphide ions.     

Effects of Hydrostatic Pressure on the Corrosion of Copper in Sea Water

Abstract

A study has been made of the effect of hydrostatic pressure, ranging from 1 to 300 atm. (0·102 to 30·6 N.mm^?2) on the corrosion of copper in sea water at pH 7·8 and at a temperature of 10°c. The experimental technique ensured that the content of dissolved oxygen in the sea water was virtually constant over the pressure range, at a value of 7·0 ppm. The same test series was also carried out in a 3·5% NaCl solution.

The weight loss of the copper was found to increase with increase in pressure, both in sea water and in NaCl, and reached a maximum at a pressure of 150 atm. (～15 N.mm^?2) in both solutions. The increased pressure has no influence on the anodic dissolution process for copper, but accelerates the cathodic process. Protective films adhering to the corroded surfaces are identical for the two solutions at ambient pressure. However, at higher pressures adherent corrosion products form only in NaCl solutions. These products were found to be the same as those formed at ambient pressure.     

Annual Contents

Abstract

The electrochemical reduction of Bi₂S₃ films deposited using the successive ionic layer adsorption and reaction method in a Bi(III) solution with a sulphidation agent Na₂S was investigated in Ni²⁺ free background and Ni²⁺ containing electrolytes at different pH. This investigation was carried out by means of cyclic voltammetry, electrochemical quartz crystal microbalance and X-ray photoelectron spectroscopy. It has been established that during the reduction of a bismuth sulphide film in the Ni²⁺ free background solution the electrode mass decreases due to Bi₂S₃ film reduction to metallic Bi and the transfer of sulphide ions into the bulk of the solution. At pH=3, the Bi₂S₃ film reduces under the potential region from –0·2 to –0·4 V, while at pH=4 and 5 from –0·4 to –0·6 V. The processes occurring during the reduction of Bi₂S₃ film in the Ni²⁺ containing electrolyte depend on the electroreduction medium. At pH=3, the reduction of Bi₂S₃ film to metallic Bi and Ni²⁺ ions occurs simultaneously under the potential region of the cathodic current peak (–0·2 to –0·4 V). When pH is 4 or 5, the increase in electrode mass is caused by the incorporation of Ni²⁺ ions into the bismuth sulphide film with their partial reduction to the metallic or close to metallic state with the occurrence of structural changes in the film.     

Passive film formed on nickel in a neutral solution

A bright nickel was passivated in the pH 8·39 boric acid-borate buffer solution. The oxide formation reactions were mainly investigated by means of polarization experiments, alternating anodic and cathodic polarization, potential decay experiments and colorimetric analysis. From the results, the chemical composition and structure of passive films formed on nickel were discussed. The experimental results are summarized as follows.1. A considerable amount of nickel ions dissolved during the anodic formation of passive films. The dissolution ceased because of the formation of NiO₂. 2. The passive films on bright nickel has a duplex structure consisting of NiO and Ni₃O₄. At higher potentials, NiO₂ was produced on them. NiO and Ni₃O₄ were formed directly from Ni, and NiO₂ was transformed from Ni₃O₄. 3. NiO and NiO₂ were reversibly produced and reduced, but Ni₃O₄ was very difficult to be reduced. 4. It was observed that there was a reversible charging and discharging layer at the potential where Ni₃O₄ formed. The electric capacity was calculated to be about 100 μF/cm², assuming that roughness factor was 2. It would be reasonable to think that a space charge was established on nickel surface.     

Studies on copper-semiconducting layer-electrolyte systems—I. Electrode potentials of copper and electrodeposited copper sulphide in S2− and Cu2+ media

Copper sulphide layers electrodeposited from a Na₂S bath consist chiefly of cuprous sulphide. Calculated values of the specific conductance of the deposited sulphide average around 3·8 × 10^?5 ohm^?1.cm^?1.Electrode potentials, E_H, of the Cu/Cu_2?δS in unbuffered Na₂S solutions and in solutions buffered at pH 9, correspond to the behaviour of a Cu/Cu_2?δS, overlayered with CuS/electrolyte. Steady reproducible potentials are obtained with the above electrodes in 0·5–10^?3M CuSO₄ solutions, closely comparable with those of the reversible Cu/Cu²⁺ couple.     

Untersuchungen Zur Inhibition Der Lochfraßkorrosion Von Nickel Und Stahl Mit Benzyl-n-propylsulfid

Measurements of pitting potentials of nickel single crystals and stainless steel in solutions with different concentrations of NaCl, pH 2–7, in the presence and absence of benzyl-n-propylsulphide (BPS) by potentiostatic polarisation measurements are described.Amperostatic polarisation curves in the cathodic and anodic active range have been measured in 0·5 m NaCl.The decomposition of BPS was studied by use of iodometrical measurements of SH-groups. The adsorption of BPS³⁵ has been investigated with the aid of tracer techniques.The results show an inhibiting effect on pitting corrosion at conditions allowing the formation of SH^? and BPSH⁺-ions, indicating secondary processes to play the most important role in inhibiting mechanism. Additions of Na₂S lead to increasing efficiency.     

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.     

工艺参数对低pH值2.0~2.5柠檬酸水溶液电沉积铼铱基合金薄膜特征影响

研究了在低pH值2.0~2.5的柠檬酸水溶液中恒电流电沉积富Re+Ir的Re-Ir-Ni合金薄膜特征,以及镀液温度、镀液pH、电流密度和镀液化学组成对薄膜表面形貌、化学成分和晶体结构的影响。采用环境扫描电子显微镜、X射线能谱仪和X射线衍射仪分别对合金薄膜的形貌、成分和物相进行了表征。结果表明：在电流密度为60 mA·cm^-2、pH为2.0时,获得致密光亮的Re-Ir合金薄膜。在pH=2.5时,提高镀液温度可获得质量良好的合金薄膜,而pH=2.0时,则相反。在镀液温度60~70 ℃、pH=2.0时,沉积的合金薄膜由非晶相组成;在镀液温度80 ℃时,薄膜由ReO₃相组成。在电流密度为60 mA·cm^-2、pH值从2.0增加到2.5时,合金薄膜的晶形结构由非晶态转变为晶态和非晶态的混合结构。结晶相为hcp-Ir_0.4Re_0.6和hcp-Ni。