Electrochemical behavior of some copper alloys in sulfuric acid solutions

In this article, the corrosion behavior of Cu? Fe and Cu? Al? Fe was studied in H₂SO₄ solutions in the absence and presence of different concentrations of some inorganic additives, Na₂MoO₄, K₂Cr₂O₇, KIO₃, and Na₂B₄O₇. The techniques of measurements used were open‐circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy. The polarization measurements indicated that the corrosion current, I_corr, of Cu? Fe is less than that of Cu? Al? Fe. The investigated additives in H₂SO₄ shifted E_corr to more positive values and increases I_corr. Impedance measurements indicated that Nyquist plots for Cu? Fe may be regarded as a semi‐circle in early stages of immersion and tends to be a part of semi‐circle with elapse of time and a well‐defined inductive loop appears. In case of Cu? Al? Fe, the Nyquist plots tends to be semi‐circle or depressed semi‐circle. The values of R_p for Cu? Fe are higher than those for Cu? Al? Fe. On the other hand, the values of C_dl for Cu? Fe are lower than those obtained for Cu? Al? Fe. The presence of these additives in H₂SO₄ solutions decreases the values of polarization resistance (R_p) and increases the values of corrosion current density (I_corr) and capacitance of double layer (C_dl).     

Electrochemical behavior of titanium‐tantalum alloys in sulfuric acid solutions

Titanium exhibits a good corrosion resistance in oxidizing acids and neutral media but it is severely attacked in reducing acids. On the contrary, tantalum presents an excellent resistance in both oxidizing and reducing acids, but its high cost limits its use to very aggressive conditions. The titanium‐tantalum alloys are promising materials for use in reducing acids, due to their lower cost and density when compared to tantalum, and their higher corrosion resistance when compared to titanium. Titanium‐20, 40, 60 and 80 wt% tantalum alloys were prepared by arc‐melting and their microstructures were characterized by scanning electron microscopy and X‐ray diffractometry. Their electrochemical behaviors were studied in 20 to 80 wt% sulfuric acid solutions at room temperature, using open‐circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. Different behaviors were observed depending on the tantalum content and acid concentration. A clear tendency of increase in corrosion resistance with the increase of tantalum content is observed, especially in 80 wt% sulfuric acid solutions.     

Anodic oxidation of Ag-Cu alloys in sulfuric acid solutions when reaction products are unstable

Based on the impedance models of porous layer, anodic behavior of silver as a component of Ag-Cu alloys in aqueous sulfuric acid solutions is analyzed. It is shown that, in order to adequately describe the electrochemical process, chemical decomposition of superficial passivating silver-sulfate layer should be taken into account. Decomposition rate constants of the layer on silver-copper alloys of diverse composition are calculated. Original Russian Text ? A.V. Noskov, E.P. Grishina, A.M. Pimenova, 2008, published in Fizikokhimiya Poverkhnosti i Zashchita Materialov, 2008, Vol. 44, No. 4, pp. 374–377.     

Corrosion behavior of niobium, tantalum and their alloys in boiling sulfuric acid solutions

The corrosion resistance of niobium, tantalum and Nb-20, 40, 60 and 80 wt% Ta alloys in boiling 20, 40, 60 and 80 wt% H₂SO₄ solutions is studied using the mass-loss technique. The corrosion rates of all materials increase with acid concentration and diminish initially with time. After nearly 200 h, the corrosion rates stabilize due to superficial oxide formation. The corrosion resistance increases with tantalum content. A preferential dissolution of niobium from the Nb-Ta alloys is noted. Recrystallization heat treatments reduce slightly the corrosion rates. The anodized materials are more corrosion resistant than the untreated ones during the first 200 h, but behave similarly for longer exposure times.     

SERS spectroscopy studies on the electrochemical oxidation of single-walled carbon nanotubes in sulfuric acid solutions

Surface-enhanced Raman scattering (SERS) and cyclic voltammetry (CV) were used to investigate oxidation–reduction processes of single-wall carbon nanotube (SWNT) films deposited on Au supports in 0.5 M H₂SO₄ solutions. In the potential range (0; +1000) and (0; +1500) mV versus saturated calomel electrode (SCE), the oxidation–reduction reactions of SWNT films are quasi-reversible and irreversible, respectively. Anodic polarization of SWNT films until +1000 mV versus SCE produced compounds similar to the bisulfate intercalated graphite. Regardless of excitation wavelength, i.e. 1064 or 676.4 nm, variation in the Raman spectra exhibited a decrease in the intensity of the bands associated with the radial breathing mode (RBM) situated in the 120–240 cm⁻¹ spectral range. Also an increase in the intensity of the D band is accompanied an up-shift of this band. A gradual decrease of the Breit–Wigner–Fano component was observed at λ_exc=676.4 nm. Partial restoration of the Raman spectra was achieved by a subsequent alkaline solution treatment. Potentials higher than +1000 mV versus SCE resulted in SWNTs breakage and fragments of different length were formed such as closed-shell fullerene. This was observed in the SERS spectrum by: (i) the disappearance of the RBM band, (ii) the increased D-band shifted to ca. 1330 cm⁻¹ and (iii) the appearance of a new band at 1494 cm⁻¹, frequently observed also in the Raman spectrum of fullerenes on the type C₇₀, C₈₄, C₁₁₉, as well as in its derivative compounds (e.g. C₆₀O, clathrates, etc.). Appearance and increase in the intensity of the Raman band at 1494 cm⁻¹ as result of an anodic polarization of the SWNT film in solution of H₂SO₄ 0.5 M in 1-butanol is a further evidence of the nanotubes breakage.     

Relation between individual properties of alloy components and anodic behavior of multicomponent alloys in acidic environments: I. Active dissolution and passivation of Fe-Cr alloys in sulfuric acid solutions

The active dissolution and passivation of Fe-Cr alloys are analyzed with the use of concepts of the appearance, operation, and blockade of active dissolution sites on the actual metal surface. General regularities of the effect of chromium on the rate of the anodic process at the change in the alloy composition and electrode potential are considered. The less noble, but easily passivable chromium component provides a dual effect on the anodic behavior of the binary alloys; it stimulates the anodic reaction at the low content in the alloy and suppresses the process at the high content. The principally different electrochemical properties of the alloy components result in the step-by-step passivation of the alloy with an increase in the potential, which is reflected by regular breaks in perfect anodic curves.     

High-temperature inhibitor of steel corrosion in sulfuric acid solutions

A new high-temperature (up to 140°C) inhibitor of steel corrosion in sulfuric acid, IFKhAN-92, that yields Z = 99% at a content of at least 1 wt % was developed. To enhance the protective effect of IFKhAN-92 at an elevated temperature, KI additions may be used. IFKhAN-92 was shown to be effective in hindering electrode reactions on steel. The high efficiency of this catalyst in H₂SO₄ solutions is most likely conditioned by the specific adsorption of IFKhAN-92 molecules on a metal surface.     

Effects of acidity,temperature and surfactants on electrochemical behavior of V~(5+) ion in sulfuric acid solutions

1　INTRODUCTIONSeveralredoxcouplesincludingCe4 +/Ce3+,Mn3+/Mn2 +,Co3+/Co2 +andV5+/V4 +etchaveat tractedmuchattentioninindirectelectrosynthesisofsomeorganiccompoundsandinmediatedelectro chemicaloxidationofbenzene ,aniline ,phenolandchlorinatedorganicsetc[17] .Electrochemicalbehav ioroftheredoxcoupleCe4 +/Ce3+hasbeenstud ied[8,9] .Beingstrongandselectiveoxidizingagents ,vanadiumsalts ,comparedwithcoppersalts ,weremoreefficienttocatalyzetheoxidationoftoluenetobenzaldehydeviaelectrochemica…     

Impedance of NiSi electrode in sulfuric acid in the active anodic dissolution range

Anodic behavior of NiSi electrode in 0.5 M H₂SO₄ in a potential range of active dissolution is studied. A conclusion about the selective dissolution of nickel from nickel silicide at a small anodic polarization (up to 0.15 V) is drawn based on the impedance data. The solid-phase diffusivity of nickel and the thickness of the diffusion zone are estimated.     

The inhibition of the dissolution of iron in sulfuric acid by halide ions

The dissolution rate of mild steel in 1 N H₂SO₄ without and with different additions of Cl^?, Br^? and I^? has been measured. Analysis of the results indicates that halide ions adsorbed on the metal surface inhibit the dissolution reaction. Adsorption occurs according to the Frumkin isotherm.     

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.     

Regularities of electrochemical dissolution of Cu 62 Zn alloy in chloride solutions

The pattern of the electrochemical ionization and passivation of Cu 62 Zn brass in chloride solutions with different compositions is studied. The electrochemical dissolution of Cu 62 Zn alloy is shown to be controlled by ionization of the copper component in the alloy. The dissolution selectivity of the brass Cu 62 Zn components and the modification of the surface of the alloy during electrochemical etching in chloride solutions are studied. The uniform electrochemical dissolution of α-brass in an acid medium was found to occur in the presence of chlorine ions and an Fe³⁺ oxidizing agent.     

Corrosion behavior of iron-aluminum alloys and its composite steel in sulfuric acid

The corrosion behavior of an iron-aluminum alloy with bcc structure and a composite of an iron-aluminum and a steel was studied in H₂SO₄ solution. The corrosion resistance deteriorates with increasing aluminum content of an iron-aluminum alloy. XPS measurements showed a magnetite formation on the corroded surface and a preferential corrosion of iron. The corrosion resistance for the composite of an iron-aluminum alloy and a CrMo steel is comparable to that of a CrMo steel. This implies that a corrosion-resistant composite is achievable by controlling the aluminum content of the Fe-Al alloy without the additives.     

To the Tafel slopes at the anodic dissolution of iron in sulfuric electrolytes

Based on the hypothesis of the reversibility of an iron electrode, one can relatively easily explain the experimentally obtained Tafel slopes without multistage complex schemes involving hypothetic intermediate iron hydroxo compounds. On the other hand, the coincidence of the experimental slope with the slope following from the relation derived may be considered as a proof of the reversibility of the iron electrode. The Tafel slope is reproducible both on the clean and partially passivated iron surface. Original Russian Text ? Yu.P. Vishnevskaya, D.A. Tkalenko, M.V. Byk, V.A. Rupp, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 5, pp. 540–542.     

Electrically-conductive fibers of polyaniline spun from solutions in concentrated sulfuric acid

The preparation of solutions of polyaniline in concentrated sulfuric acid is described. The solutions were characterized by viscosity measurements and by ultraviolet(u.v)-visible spectroscopy. Polyaniline was successfully processed into monofilaments and films from these solutions. In contrast to previous reports, polyaniline derived from sulfuric acid displays sharp X-ray reflections, indicative of a significant degree of crystallinity. The electrical conductivity of as-spun, washed and dried fibers was in the range 20 – 60 S/cm.     

Contribution of electrochemical dissolution during pickling of low carbon steel in acidic solutions

An electrochemical cell coupled with ICP-OES chemical analysis was used to explore the role of chemical and electrochemical reactions in pickling of low carbon steel in acidic media. Impedance spectroscopy was used to highlight scale properties. Dissolution of hematite is shown to be mainly of chemical nature, whereas the dissolution of magnetite and wüstite is both chemical and electrochemical. Initially, chemical dissolution of the scale dominated. The electrochemical reactions included oxidation of magnetite and wüstite and reduction of ferric ions formed by chemical dissolution. After the electrolyte reached the steel substrate, electrochemical dissolution of the iron was the main reaction.     

Quantum chemistry study on the effect of Cl ion on anodic dissolution of iron in H2S-containing sulfuric acid solutions

The effect of Cl⁻ ion on the anodic dissolution of iron in H₂SO₄ solutions containing low H₂S level has been studied by electrochemical polarization curve measurements. The total energy and binding energy of the competitive adsorption for Cl⁻ and HS⁻ ions have been calculated with CNDO/2 method, as well as the net charge distribution of iron atoms at an anodic potential. The results showed that certain concentration of Cl⁻ ion inhibit the anodic reaction of iron accelerated by HS⁻. However, when Cl⁻ ion reached saturated adsorption, it began to promote the anodic reaction of iron due to the increased negative charge of iron atoms.     

黄铜矿与斑铜矿在酸性细菌培养基中的电化学溶解对比(英文)

采用电化学测试和X射线光电子能谱(XPS)测试分析黄铜矿与斑铜矿在酸性细菌培养基中的电化学溶解过程。斑铜矿直接氧化反应比还原反应更容易发生,但黄铜矿既难被氧化,又难被还原。斑铜矿具有更高的氧化速率,从而比黄铜矿更容易被溶解。铜蓝(CuS)是黄铜矿与斑铜矿溶解过程的中间产物。因此,斑铜矿的溶解途径主要为直接氧化过程,中间产物铜蓝(CuS)可能限制其进一步溶解。黄铜矿的溶解途径包含了还原-氧化过程,其中,黄铜矿首先被还原为与斑铜矿类似的中间产物,再进一步被氧化,并产生铜蓝(CuS),而黄铜矿的最初还原过程是其溶解过程的主要限制步骤。     

The effect of focused ultrasound on the electrochemical passivity of iron in sulfuric acid

Focused ultrasound was used to study passivity of pure iron in 2 N H₂SO₄. Ultrasonic waves were used to depassivate a passive surface film and influence the subsequent repassivation process. A curved piezo-electric transducer produced high frequency (1.58 MHz) ultrasonic waves which created cavitation at the focal point. Acoustic focal intensities up to 3.4 kW cm^?2 were generated. Low frequency (20 kHz) ultrasound was produced with a commercial sonicator equipped with an exponential microhorn. At high focal intensities (above 1.5 kW cm^?2) a single (100 ms) pulse of ultrasound produced depassivation; at low intensities continuous ultrasonic exposure was required. In all cases, the induced depassivation was followed by precipitation of a metal salt film upon the metal surface before the oxide film formation.     

The electrochemical dissolution of cobalt in carbonate-bicarbonate solutions from EIS and steady polarization data

The cobalt electrodissolution process in carbonate-bicarbonate containing solutions 8.9 ? pH ? 10.5 covering relatively wide ranges of ionic strength, pH, and hydrodynamic conditions, has been investigated using electrochemical impedance spectroscopy (EIS) and steady polarization data. To distinguish the competing stages of the metal electrodissolution mechanism a cobalt rotating disc electrode was utilized. The proposed mechanism model consists of the formation of adsorbed Co(I) intermediate species followed by mass-transport contributions of soluble Co(II) ions as final products. The coherence of the proposed mechanisms with EIS and steady polarization data is presented.