Reduction Characteristics of Iodate Ion on Copper: Application to Copper Chemical Mechanical Polishing

Potentiodynamic and potentiostatic polarization, and the rotating disk electrode technique were used to study the reduction characteristics of iodate (IO₃ ^–) ion on copper (Cu). Depending on the relative concentrations of IO₃ ^– and H⁺ two pH regimes were observed. The cathodic current in the first regime (pH > ,3) was controlled by H⁺ diffusion from the solution to the metal surface. In the second regime (pH > 3 and up to 10^–2 m IO₃ ^– concentration) the cathodic current was found to be under mixed control, involving reaction control via the electrochemical reduction of IO₃ ^– and transport control via the diffusion of I₂(aq). It was concluded that IO₃ ^– was an effective oxidant for Cu chemical mechanical polishing (CMP) with strongly acidic (pH < 3) slurries but it was not convenient reagent as an oxidant for Cu CMP with weakly acidic (pH > 3) slurries.     

The electrochemical behaviour of copper in alkaline solutions containing sodium sulphide

The electrochemical behaviour of copper in NaHCO₃ solution (pH 9) and NaOH solutions (pH 14) in the presence of sodium sulphide (10^–3 to 5×10^–2m) was investigated by using rotating disc electrode and rotating ring-disc techniques, triangular potential scanning voltammetry and potentiostatic steps. When the potential increases from –1.2V upwards, copper sulphide layers are firstly formed at potentials close to the equilibrium potentials of the Cu/Cu₂S and Cu/CuS reversible electrodes. When the potential exceeds 0.0 V (NHE), the copper oxide layer is electroformed. Pitting corrosion of copper is observed at potentials greater than –0.3 V. The charateristics of copper pitting are also determined through SEM optical microscopy and EDAX analysis. There are two main effects in the presence of sodium sulphide, namely, the delay in the cuprous oxide formation by the presence of the previously formed copper sulphide layer and the remarkable increase of copper electrodissolution when the potential exceeds the cuprous oxide electroformation threshold potential. These results are interpreted on the basis of a complex structured anodic sulphide layer and on a weakening of the metal-metal bond by the presence of adsorbed sulphur on the copper surface.     

Electrochemical investigations of pitting corrosion behaviour of type UNS S31603 stainless steel in thiosulfate-chloride environment

The pitting corrosion behaviour of type UNS S31603 stainless steel (316L SS) in 0.01, 0.05 and 0.1 M thiosulfate ion (S₂O₃ ^2–) in the absence and presence of various concentrations of chloride ion (Cl^–) was studied using the cyclic potentiodynamic polarization method. The influence of major factors which affect pitting corrosion such as pH and temperature, were also investigated. It was found that both the pitting potential (E _pit) and the repassivation potential (E _rp) decreased with increase in Cl^– concentration and solution temperature and a more pronounced difference in E _pit values for various concentrations of S₂O₃ ^2– in 1.0 M Cl^– was obtained at lower temperatures. The effect of pH on E _pit, E _corr and E _rp values for different concentrations of S₂O₃ ^2– in the presence of 1.0 M Cl^– was also determined.     

Kinetics of Sn electrodeposition from Sn(II)–citrate solutions

The influence of solution chemistry on the electrodeposition of Sn from Sn(II)–citrate solutions is studied. The distribution of various Sn(II)–citrate complexes and citrate ligands is calculated and the results presented as speciation diagrams. At a SnCl₂·H₂O concentration of 0.22 mol/L and citrate concentration from 0.30 mol/L to 0.66 mol/L, SnH₃L⁺ (where L represents the tetravalent citrate ligand) is the main species at pH below about 1.2 and SnHL⁻ is the main species at pH above about 4. Polarization studies and reduction potential calculations show that the Sn(II)–citrate complexes have similar reduction potentials at a given solution composition and pH. However, the Sn(II)–citrate complexes become more difficult to reduce with higher total citrate concentration and higher solution pH. Nevertheless, SnHL⁻ which forms at higher pH is a favored Sn(II)–citrate complex for Sn electrodeposition due to better plated film morphology, likely as a result of its slower electroplating kinetics. Precipitates are formed from the Sn(II)–citrate solutions after adding hydrochloric acid (to lower the pH). Compositional and structural analyses indicate that the precipitates may have the formula Sn₂L.     

Use of a rotating cylinder electrode in corrosion studies of a 90/10 Cu–Ni alloy in 0.5 mol L−1 H2SO4 media

The corrosion of 90/10 Cu–Ni alloy in deaerated 0.5 mol L^–1 H₂SO₄ containing Fe(III) ions as oxidant and benzotriazole as inhibitor was studied using a rotating cylinder electrode (RCE). Nonselective dissolution was observed in all experimental conditions investigated. In the absence of Fe(III) ions, the anodic process is diffusion controlled while cathodic process is charge transfer controlled. In contrast, with Fe(III) ions as oxidant, the cathodic process is controlled by diffusion and the anodic process is under charge transfer control. These conclusions were obtained from measurements of open circuit potential as a function of the RCE rotation rate as previously verified for the RDE. Inhibition efficiency evaluated from weight loss and calculated from polarization curves showed good agreement.     

Anodic oxidation of copper cyanide on graphite anodes in alkaline solution

The anodic oxidation of copper cyanide has been studied using a graphite rotating disc with reference to cyanide concentration (0.05–4.00 M), CN:Cu mole ratio (3–12), temperature (25–60 °C) and hydroxide concentration (0.01–0.25 M). Copper had a significant catalytic effect on cyanide oxidation. In the low polarization region (about 0.4 V vs SCE or less), cuprous cyanide is oxidized to cupric cyanide complexes which further react to form cyanate. At a CN:Cu ratio of 3 and [OH^–] = 0.25 M, the Tafel slope was about 0.12 V decade^–1. Cu(CN)₃ ^2– was discharged on the electrode and the reaction order with respect to the predicted concentration of Cu(CN)₃ ^2– is one. With increasing CN:Cu mole ratio and decreasing pH, the dominant discharged species shifted to Cu(CN)₄ ^3–. Under these conditions, two Tafel slopes were observed with the first one being 0.060 V decade^–1 and the second one 0.17–0.20 V decade^–1. In the high polarization region (about 0.4 V vs SCE or more), cuprous cyanide complexes were oxidized to copper oxide and cyanate. Possible reaction mechanism was discussed.     

An α-K3PMo3W9O40 film loaded with silver nanoparticles: Fabrication, characterization and properties

A composite film consisting of the mixed-addenda Keggin-type polyoxometalate α-K₃PMo₃W₉O₄₀ (PMo₃W₉) and silver nanoparticles (AgNPs) was fabricated on quartz, silicon, and ITO by the layer-by-layer self-assembly method. The regular growth of the multilayer film was monitored by UV–vis spectroscopy, and the morphology was measured by atomic force microscopy (AFM). The multilayer film embedded by AgNPs exhibited the photo-luminescence ascribed to electronic transitions from excited states to d levels of the silver nanoparticles. The composite film also showed electrocatalytic activity towards reduction of NO₂⁻, H₂O₂, ClO₃⁻, BrO₃⁻, and IO₃⁻ attributed to tungsten-centered and molybdenum-centered redox processes of PMo₃W₉.     

Passivation and pitting corrosion of tin in gluconate solutions and the effect of halide ions

The passivation and pitting corrosion of tin in sodium gluconate (SG) solutions was studied by using potentiodynamic and cyclic voltammetric techniques. Some samples were examined by X-ray and SEM. The effect of the concentration of gluconate ion, pH, potential scanning rate, successive cyclic voltammetry, switching potential and progressive additions of halide ions on the passivation and pitting corrosion of a tin anode was discussed. The data obtained show that low concentrations of SG have an inhibition effect on the pitting corrosion of tin in neutral media. The pitting corrosion of tin increases with increasing SG concentrations due to the formation of soluble tin-gluconate complex. The critical pitting potential depends on the gluconate ion concentration, pH and scan rate. Two cathodic peaks are observed in the cathodic polarization curve, corresponding to the reduction of the dissolved pitting corrosion products. The critical pitting potential shifts progressively to more negative values with increasing halide ion concentration. In all experiments, the aggressive action of halides decreased in the order Cl^–>Br^–>I^–.     

Electrochemical behaviour of copper in neutral aerated chloride solution. I. Steady-state investigation

The electrochemical behaviour of a Cu rotating disc electrode in neutral aerated NaCl solution was investigated in the cathodic and anodic ranges and at the corrosion potential. In the cathodic range, where the reduction of oxygen takes place, reduction peaks allow the identification and quantitative evaluation of insoluble corrosion products (CuCl and Cu₂O). In the anodic range Cu is dissolved, most likely as CuCl ₂ ^– . A new mechanism for the anodic dissolution is proposed after comparing our data with previously published mechanisms. Corrosion currents were found to decrease with time and to be a function of the rotation rate of the electrode. Both the mixed kinetics of the anodic partial reaction and diffusion through a porous layer seem to be relevant in controllingl _corr.     

A voltammetric study of galena immersed in acetate solution at pH 4.6

The electrochemistry of galena in an acetate solution at pH 4.6 has been studied through the use of linear sweep voltammetry. Analysis of the voltammograms for anodic limits as high as 845 mV indicates that S⁰ is the sulphur-bearing species generated during the oxidative dissolution of galena. Furthermore, interpretation of the electrochemical data on the basis of thermodynamic considerations indicates that galena interacts with the acetate electrolyte and that Pb(CH₃COO)₂(aq) is also produced during anodic oxidation. When the scan direction is reversed in the cathodic direction, the oxidation products are removed by two reduction reactions when the solution is quiescent: the recombination of Pb(CH₃COO)₂ and S⁰ to form PbS and the reduction of S⁰ to H₂S. In a stirred solution, only the second reaction is possible. Experiments conducted in the presence of 10^–3 or 10^–2 M lead acetate indicate that the presence of dissolved lead tends to inhibit the dissolution process. Furthermore, metallic lead can begin to deposit on the galena surface when the potential drops below about –330 mV SHE. The data also agree most closely with thermodynamics when Pb(CH₃COO)₂ is considered to be the aqueous species involved in the deposition and dissolution of metallic lead.     

Effects of Zn and Pb as alloying elements on the electrochemical behaviour of brass in borate solutions

The electrochemical behaviour of brasses with various Zn content (5.5–38) and brass (Cu–38Zn) with different Pb content (1.3–3.3) in borate solution, pH 9.0, was investigated. The effects of applied potential and the presence of aggressive Cl^– ions were also studied. Different electrochemical methods such as open-circuit potential measurements, polarization techniques and electrochemical impedence spectroscopy (EIS) were used. Increase in zinc content decreases the corrosion rate of brass in borate solution exponentially. Long immersion of leaded brasses and alloys with different Zn content improves their stability due to the formation of a passive film. The passive film formation under open-circuit and potentiostatic conditions proceeds via dissolution–precipitation mechanism. The addition of a low concentration of Cl^– ion (0.01 M) to the borate solution increases the corrosion rate of Cu–38Zn due to dezincification. Increase in Cl^– ion concentration (0.01–0.2 M) decreases the corrosion rate of the brass exponentially due to formation of insoluble CuCl. For Cl^– ion concentrations >0.2 M the corrosion rate of the brass increases again due to the formation of the soluble CuCl₂ ^– complex.     

Influence of different anions on the behaviour of aluminium in aqueous solutions

The influence of chloride, sulfate and perchlorate anions on the behaviour of native oxide layers on aluminium is investigated using electrochemical techniques. Due to its influence on the open circuit potential and the cathodic side of the polarization curve the oxygen concentration has been carefully controlled. Two kinds of attack on a commercially pure aluminium (99.5 wt %) have been observed. In all the investigated 0.5 M Cl^–, 0.5 M ClO^– ₄ and 0.5 M SO^2– ₄ aqueous solutions the metal is corroded around the iron and silicon containing precipitates, but only in Cl^– and ClO^– ₄ solutions is crystallographic pitting observed. Comparison with high purity aluminium (99.99 wt %) shows that pitting corrosion is not influenced by the presence of impurities in the aluminium alloys, but by the presence of anions in solution. The pH and/or oxygen concentration determine whether or not the pitting potential coincides with the corrosion potential.     

Electrochemical properties of Composites based on Nanocrystalline Anatase (TiO2) and Copper compounds (CuBr, CuO)

The electrochemical properties in aqueous solution of composite materials made from nanocrystalline anatase TiO₂ with CuBr and CuO are reported. CuO–TiO₂ composite samples are prepared by a novel route based on oxidation of CuBr–TiO₂. The corrosion of CuBr–TiO₂ composite electrodes prevents a detailed electrochemical analysis. The data on CuO–TiO₂ composites are consistent with the presence of a surface layer of TiO₂ nanoparticles. A Mott–Schottky analysis gives a flat-band potential of –0.5 V/NHE (pH = 6) and a low carrier density of 10¹⁴cm^–3.     

Photo-Fenton degradation of 17β-estradiol in presence of α-FeOOHR and H2O2

A novel photocatalyst, α-FeOOH-coated resin (α-FeOOHR), was prepared and applied for the photodegradation of natural estrogen 17β-estradiol (E2) in presence of H₂O₂ under the relatively weak UV irradiation. The continuing loading of ferric oxide on resin was achieved by in situ hydrolysis of Fe³⁺ in alkaline solution. The effects of initial pH, catalyst loading, oxidant concentration and iron leaching on the photodegradation of E2 were investigated. The batch photodegradation experiment showed that high removal efficiency of E2 and fairly good mechanic stability could be obtained by the spherical photocatalyst α-FeOOHR in aqueous solutions. The photodegradation efficiencies slightly decreased with the increase of initial pH in the wide pH range of 3–11. Increase of oxidant and catalyst will enhance photodegradation efficiencies thus lead to increase the Ferric leaching. Neglected iron leaching showed the stability of the loaded α-FeOOH withstanding the oxidation. X-ray photoelectron spectrum (XPS) shed light on the surface activity change of photocatalyst and heterogeneous catalytic essence of this process.     

AC impedance spectroscopy as a technique for investigating corrosion of iron in hot flowing Bayer liquors

The flow-induced corrosion of iron, in spent Bayer liquor at high temperatures, was investigated using a rotating cylinder electrode (RCE) in an autoclave facility. A temperature range of 100–230 °C and equivalent pipe velocities in the range 0.84–3 m s^–1 were used. AC impedance technique was applied to monitor in situ the entire corrosion process. Corrosion rates measured by a.c. impedance expressed as average 1/R _p were in good agreement with those obtained by weight loss measurements. The results suggest that a.c. impedance is a suitable method to monitor the corrosion process of steels exposed to flowing Bayer liquor at higher temperatures.     

Electrochemical behaviour of copper in neutral aerated chloride solution. II. Impedance investigation

A.c. and EHD impedance measurements were performed on a Cu rotating disc electrode immersed in neutral aerated NaCl and the results were compared with simulated curves according to the kinetic model developed in Part I. The agreement is good over the whole anodic range and at the corrosion potential. A slowing down of the mass transport rate is explained by diffusion through a surface layer (Cu₂O) at the corrosion potential and for the close anodic range. It is confirmed that, on the cathodic plateau, the interface may be considered as uniformly accessible for the cathodic partial reaction of oxygen reduction. However, at less cathodic potential a surface layer effect due to CuCl must also be taken into account. Diffusion coefficients for both O₂ and CuCl ₂ ^– were determined by EHD impedance.     

Corrosion of Mild Steel in low Conductive Media simulating Natural Waters

The corrosion of a mild steel was examined in two aerated neutral aqueous solutions, defined as reference solution (0.2 g L^–1NaCl) and as -solution (1.3 g L^–1NaCl + 0.63 g L^–1NaHCO₃ + 0.27 g L^–1Na₂SO₄). Their composition was chosen on the basis of the physical and chemical properties of certain natural waters. The solutions simulated the least (reference solution) and the most (-solution) aggressive waters of the Sebou river in Morocco, as determined after a four-year examination (1991–94), at 13 pump stations located along the river. Various experimental methods were used to determine the corrosion mechanism. Cathodic range voltammetry using a rotating disc allowed the kinetics of oxygen reduction process to be determined. Since the conductivity of the solutions were low, the potential was corrected for ohmic drop estimated through the high frequency limit in the Nyquist diagrams (electrochemical impedance spectroscopy) as well as the current interrupter method. After correction, the polarization curves revealed a diffusion plateau attributed to dissolved oxygen reduction. At the plateau, a two-step mechanism was derived involving oxygen diffusion through the hydrodynamic layer and through a porous inner layer formed by the corrosion products. This inner layer could not be observed by SEM, but both EIS and EHD (electrohydrodynamic impedance) confirmed the presence of a thin porous dielectric layer. At the open circuit potential, the corrosion rate was determined by the diffusion rate of dissolved oxygen in the -solution, and by charge transfer in the reference solution. This shows that the corrosion mechanism strongly depends on the electrolyte and its conductivity.     

Comparative study of the potentiodynamic behaviour of aluminium at low potentials in barrier layer and in pore-forming electrolytes

The potentiodynamic behaviour of a 99.9995% aluminium electrode in several barrier layer and pore-forming electrolytes at a temperature of 25° C, with sweep rates in the range 1–200 mV s^–1 and potentials between –2.00 and 3.00 V (versus SCE), has been studied. In the anodic sweep the potential of zero current,V _j=0, depends on the pH of the electrolyte and corresponds to a corrosion potential (the cathodic and anodic reactions coexist). In the 0.5 M H₃BO₃-borax solution (pH=6.3) and afterV _j=0, the current density increases in a convex form, approaching a steady-state value. For this electrolyte and the potential ranges studied, the anodic charges corresponding to the anodic sweep are independent of the sweep rate and are associated with the formation of a barrier layer oxide. In the neutral 0.50 M propanedioic acid solution (pH=7.0) and the potential ranges studied, the anodic charges are much greater than those corresponding to the H₃BO₃-borax solution, and metal corrosion combined with a solvent effect of the electrolyte is found. The greatest anodic charges are found for the H₂SO₄ solution (pH=1.0); the anodic current increases rapidly in the potential ranges studied due to pore initiation. The cathodic and anodic behaviour of aluminium depend strongly on the electrolyte employed, basically through the effect of the electrolyte on the oxide film and through the pH of the solution.     

Wear of graphite anodes during electrolysis of add sulphate solutions

Graphite electrodes were prepared by mixing calcined coke and coal tar pitch. They were pressed under 250 kg cm^–2 and heat treated up to 2800° C. Rectangles measuring 70 mm x 40 mm x 8 mm were anodically polarized under galvanostatic and potentiostatic conditions. Electrolyses were conducted at 10–50 mA cm^–2 for periods ranging from 10–120 hours in Na₂SO₄ solutions acidified with sulphuric acid to various pH values. The wear of graphite anodes increased with decreasing bath temperature, increasing acid concentration, decreasing pH of the electrolyte and increasing current density. A model is suggested which assumes that corrosion takes place via the formation of a lamellar crystal compound with the formula (C ₈ ⁰ O)(OH)₃HSO ₄ ^– ·2H₂SO₄.The compound is unstable at higher temperatures when corrosion is effected by oxidation of graphite by atomic oxygen. The formation of the carbon ions was found to be a necessary precondition for the formation of the complex.     

Removal of nitrogen from wastewater for reusing to boiler feed-water by an anaerobic/aerobic/membrane bioreactor

The innovative process anaerobic/aerobic/membrane bioreactor (A/O/MBR) was developed to enhance pre-denitrification without the energy consumption of the recirculation pump for reusing wastewater to boiler feed-water. The performance of this bioreactor was investigated. Firstly, the septic tank wastewater with low ratio of COD/TN was disposed by a dynamic membrane bioreactor (DMBR). It was found that, although the high concentration of NO₂⁻–N in the effluent implied the potential ability of DMBR to realize shortcut nitrification and denitrification, the effluent of single DMBR was difficult to reach the criteria of reusing to boiler feed-water. Then, the process A/O/DMBR in disposing the septic tank wastewater was studied. The results indicated that this process not only accomplished the removal of 91.5% COD, 90.3% NH₄⁺–N and 60.2% TN, but also successfully realized pre-denitrification without additional recirculation pump. At last, based on the A/O/DMBR, a pilot plant A/O/MBR was built to dispose the municipal raw sewage. In the stable operation period, the average removal efficiencies for COD, NH₄⁺–N, TP and turbidity reached 90%, 95%, 70% and 99%, respectively. During the tested HRT run of 9.0 h, the effluent of COD, NH₄⁺–N, TP and turbidity was about 10 mg/L, 3 mg/L, below 1 mg/L and 1.2 NTU, respectively, which reached the criteria of the boiler feed-water in China.