Effect of Benzotriazole on the dissolution of copper single crystal planes in dilute sulphuric acid

The kinetics of the dissolution of copper single crystal planes in aerated 0·1N H₂SO₄ containing various concentrations (10⁻⁶−10⁻²M) of Benzotriazole have been studied. The dissolution rates which were controlled by surface reaction, were a function of the temperature, crystallographic orientation and the concentration of Benzotriazole. The stabilities of the crystal planes were in the order (100) > (110) > (111). At 7·5 × 10⁻³M Benzotriazole, Cu-Benzotriazole film appeared on the surface, bringing mechanical passivity. Benzotriazole acted as cathodic inhibitor at low concentrations and anodic inhibitor at high concentrations. The corrosion potentials of the crystal planes were in the order (100) > (110) > (111) at all concentrations of benzotriazole.     

Effect of halide ions on the dissolution of copper single crystal planes in dilute sulphuric acid

The rates of dissolution of copper single crystal planes in dilute sulphuric acid containing various concentrations (10⁻⁸ to 10⁻²M) of Cl⁻, Br⁻ and I⁻ are determined at 30°C. The dissolution rates, which are controlled by transport process in solution, are a function of the temperature, stirring rate, oxygen solubility, crystallographic orientation and the concentration of halide ions. Halide ions acted as anodic inhibitor at low concentrations and cathodic inhibitor at high concentrations. The changes in the dissolution rates have been attributed to specific adsorption of halide ions or precipitation of cuprous halides on the surface of the crystal planes.     

Predicting crack growth rate vs. temperature behaviour of Type 304 stainless steel in dilute sulphuric acid solutions

The coupled-environment fracture model for intergranular stress corrosion cracking of Type 304 stainless steel in boiling water reactor primary (water) heat transport circuits containing relatively pure water has been extended to incorporate the effects of sulphuric acid additions to the coolant and to include thermal activation of the crack tip strain rate. These extensions allow comparisons to be made between theoretically estimated and experimentally determined crack growth rates (CGRs) over a considerable temperature range after calibration at a single temperature. The model predicts, in agreement with experiment, that the CGR passes through a maximum with increasing temperature at a temperature of about 180 °C. The temperature dependence of the CGR is attributed to the competing effects of temperature on the thermally activated processes that occur at the crack tip and the properties (including ECP and conductivity) of the external environment.     

Adsorption of thiophene derivatives on steel in sulphuric acid solutions

Measurements of the corrosion rate of mild steel in 1N H₂SO₄ solution at 25°C with and without addition of thiophene mono-derivatives (1.10^?5–2.10^?2 mole/1.) were performed. Adsorption of these compounds was elucidated. Results show that thiophene and its derivatives are adsorbed on the steel surface according to Parsons and Hill de Boer isotherms. This suggests that the adsorptive properties of the compounds under consideration approach to a physical type. From th eadsorption isotherms some thermodynamic data for the adsorption process (ΔG°_d8, and f) are calculated and discussed.     

The hydrogen evolution reaction on iron corroded in dilute and very dilute solutions of sulfuric acid

Permeation transients for hydrogen, generated by corrosion of iron in dilute solutions of sulfuric acid, were recorded with an improved electrochemical permeation apparatus.The mechanism of the hydrogen evolution reactions is coupled discharge hydrogen recombination for all methods of hydrogen generation, low current anodic polarization, cathodic polarization and corrosion.The experimental hydrogen transient was compared with that predicted theoretically.It is concluded that electrochemical hydrogen permeation is a sensitive tool for investigating processes on metal surfaces which are of engineering importance.     

Magnetic field effects on the electrodeposition of copper from copper sulphate in sulphuric acid

The crystal orientations of electrodeposited copper films were determined by X-ray diffraction analysis and scanning electron microscopy. Polarization curves were determined. Magnetic field effects had little or no effect on the texture coefficients. Current efficiency increased by 2% to 5% compared with that in the absence of a magnetic field; polarizations were smaller. The magnetic field had no effect on the direction of the lines of magnetic force, which depended on the magnetic flux densities. Anodic dissolution in a magnetic field proceeded uniformly and was considerably affected compared with electrodeposition.     

Dissolution of Ti wires in sulphuric acid and hydrochloric acid solutions

Ti wire electrodes were immersed in acidic solutions containing H₂SO₄ and HCl of various concentrations at 353 K to evaluate corrosion rate by measurement of electric resistance change (resistometry). Addition of hydrochloric acid to sulphuric acid solution promoted depassivation of Ti. After depassivation, the immersion potential dropped to the hydrogen evolution potential and a hydride layer was formed on the surface. The hydride layer dissolved continuously in the acidic solution. SEM observation showed that Ti wires dissolved almost uniformly in the early stage and that the dissolution then trace became irregular due to nonuniform growth of the hydride layer. Dissolution rate of a Ti wire was estimated almost accurately by resistometry.     

Stress corrosion cracking of pure copper in dilute ammoniacal solutions

Studies of the stress corrosion cracking (SCC) of 99.999% copper and Cu-Zn alloys containing up to 10 wt%Zn in NH₄OH solution were made with varying concentrations (0.03–0.07 M) and temperatures (40–70°C). Stress corrosion cracking occurs on pure copper and all of the alloys under the condition in which thick tarnish film (Cu₂O oxide film) forms. The path of cracking is transgranular for pure copper and alloys containing < 1.3 wt%Zn, but intergranular for alloys containing > 1.3 wt%Zn. Crack propagation rates and times-to-failure estimated by the tarnish rupture theory, utilizing experimentally determined values of the fracture strain of film and the creep rate of specimens during SCC tests, are in good agreement with those observed under constant load.     

On the electrochemical behaviour of tungsten: the formation and dissolution of tungsten oxide in sulphuric acid solutions

The formation and dissolution of the anodic oxide film of tungsten were investigated in sulphuric acid solution of different concentrations. The dissolution process was found to follow a first order mechanism under different conditions. It seemed that, in highly diluted solutions, the hydrate formation is favoured, whereas in concentrated solutions, the process takes place via the formation of WO₂²⁺. The rate of dissolution was found to increase by increasing the initial current density of formation.     

The electroremoval of copper from dilute waste solutions using Swiss-roll electrode cell

Copper is usually present in concentrations less than 5 g/L⁻¹ in dilute waste solutions. The low concentrations make these solutions unsuitable for the electro-flow owinning processes via conventional electrolysis cells. Unconventional, two-and three-dimensional electrode cells with relatively large cathodic area are essential for such treatment. Different types of cells are mentioned in the literature. Among these cells, the two-dimensional Swiss-roll cell (SR) is considered in this study. The effects of cathodic current densities, initial copper concentrations, free sulfuric acid concentration, the presence of iron and zinc cations, and the rate of flow of the solution on both the cathodic current efficiency and power consumption were studied. Copper was removed from synthetic and industrial mixtures of Cu/Fe/Zn sulfate solutions to less than 5 ppm with power consumptions of 10.326 kWh/kg⁻¹ and 8.61 kWh/kg⁻¹, respectively. The correlation between the SR cell and packed-column cell on such treatment was also considered.     

Corrosion behaviour of copper containing low alloy steels in sulphuric acid

The influence of the addition of Cu on the corrosion resistance of low alloy steel in sulphuric acid was investigated using AC and DC electrochemical methods and a weight loss test, which took place in 10 wt% H₂SO₄ solution at room temperature. The electrochemical measurements indicated that the corrosion rate is suppressed by the addition of Cu due to a higher hydrogen overpotential and prevention of the active dissolution. Surface analyses (XPS, EPMA and SEM) of the corroded surfaces conducted after the immersion test indicated that the rust layer formed on the Cu containing steels was enriched with Cu compounds.     

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.     

Influence of 1,2-diaminoethane on the mechanism of aluminium corrosion in sulphuric acid solutions

The influence of 1,2-diaminoethane (DAE) on aluminium corrosion in H₂SO₄ solutions (pH 3) was investigated. In pure H₂SO₄, rapid uniform corrosion is followed by inhibition due to the formation of stable Al-sulphate binuclear bidentate metal bound surface complexes via a ligand exchange mechanism with two neighbouring sites. Metastable pitting is also observed. DAE acts as a strong corrosion inhibitor for both uniform and localised corrosion, due to the formation of Al-DAE monodentate hydrogen-bond surface complexes either by direct adsorption of the protonated molecule on Al-OH sites or via a ligand exchange mechanism with the proton of an site.     

Effect of Chloride Ions on the corrosion behaviour of iron-nickel alloys in sulphuric acid solutions

The effect of chloride ions on the corrosion behaviour of binary iron-nickel alloys in sulphuric acid solutions has been investigated using polarization resistance and potentiodynamic polarization measurements. A moderate inhibition effect of the chloride ions on the corrosion of these alloys has been found, which depends on the pH of the medium, as well as on the composition and the structure of the alloys investigated. It has been shown that the action of the chloride ions on the partial corrosion reactions is reflected by an inhibition of the cathodic hydrogen evolution reaction and by an activation of the anodic metal dissolution reaction, the first effect being stronger. Using atomic absorption analysis it has been established that no preferentional dissolution of the alloy components in the presence and in the absence of chloride ions occurs during the corrosion of the iron-nickel alloys.     

The anodic behaviour of chromium steel X20Cr13 in organic solutions of sulphuric acid

Anodic polarization measurements have been carried out on X20Cr13 steel in anhydrous solutions of H₂SO₄DMF and H₂SO₄CH₃OH. Anodic films are formed on the steel surface, which inhibit the process of steel dissolution. The films differ through their electrochemical behaviour from passive films formed in water solutions of sulphuric acid. These films are of salt-like and not oxide-like character. The solvent as well as its water content affects the solubility of “salt” films and hence the anodic behaviour of steel in investigated environments.     

Anodic behaviour of stainless steel S43000 in concentrated solutions of sulphuric acid

Electrochemical, AES and XPS techniques were employed to characterize the anodic behaviour of S43000 stainless steel in concentrated sulphuric acid (90.0-96.4 wt.%). Electrochemical experiments showed that passivity is not spontaneous and requires anodic polarization in the acids studied. Rotating cylindrical electrode experiments showed that the corrosion rate is controlled by the mass transfer rate of FeSO₄ from a saturated surface salt. AES and XPS analyses provided evidence that passivity involves the formation of a chromium-rich oxide-hydroxide film. The passivation mechanism and passive state stability are considered to relate to the manner in which undissociated H₂SO₄ molecules participate in the corrosion process. The findings have meaningful implications regarding the development of more corrosion resistant stainless steels for acid service.     

Oxidation of polyacetylene in aqueous solutions containing sulphuric acid and selected supporting oxidants

It has been found that the addition of strong oxidants such as HNO₃, NaNO₂, KMnO₄, K₂Cr₂O₇ and NaIO₃ to an aqueous solution of sulphuric acid greatly facilitates the insertion of HSO₄^? ions into (CH)_x. [CH-(HSO₄)_y]_x formation occyrs even in less concentrated solutions in which sulphuric acid alone does not oxidize polyacetylene. Based on the above observation, a new analytical method for NO₃^? determination has been proposed. The method consists of acidification of any neutral, aqueous solution of a nitrate salt with sulphuric acid to 5.7 M. Although H₂SO₄ of such concentration does not oxideze polyacetylene, in the presence of NO₃^?, doping occurs due to the formation of free HNO₃ upon acidification. The doping reaction results in a significant increase of the electronic conductivity of the polyacetylene, σ. Log σ vs NO₃^? concentration plots are linear over a nitrate concentration range of 2 - 40 mM and can be utilized in chemical analysis. The selectivity of the proposed method is limited. Although the majority of common ions (HSO₄^?, Cl^?, PO₄^3?, etc. …) do not influence the measurements, the presence of other (than HNO₃) oxidants in the solution must be avoided.