The corrosion of copper as a tool in the investigation of the reaction kinetics

The copper electrode reaction kinetics have been studied in acid CuSO, solutions. Dissolved oxygen was used to remove the reaction intermediate Cu⁺ from the electrode. This shifted the equilibrium potentials of the two partial reactions in an opposite direction allowing a somewhat unusual interpretation of impedance measurements. The charge transfer resistance of the Cu²⁺ → Cu⁺ reaction was always higher than that of the Cu⁺ → Cu reaction. In the neighbourhood of the open circuit potential an additional “surface step” in the latter reaction made it rate-controlling. The slow diffusion of cuprous ions was manifested in an inductive impedance component in this region.     

“Anionic effect” in copper plating from sulfate aqueous-ethanolic electrolyte containing cyclic polyester

It is shown that, in contrast to aqueous electrolytes, where the electrode process is promoted by the electroreduction of activated surface complexes of Cu²⁺ with SO ₄ ^2– anions, in aqueous-ethanolic electrolytes, it is promoted by sulfate complexes of copper(II) formed in the solution bulk and needing dissociation prior to the discharge. In the presence of cyclic polyester, the discharging complex species have to permeate through the barrier layer at the cathode surface. The layer consists of ethanol molecules and electroneutral associates of sulfate ions with Cu²⁺ cations containing crown-ester molecules in the coordination sphere. As a result, the electrode reaction is considerably inhibited with an increase in the concentration of SO ₄ ^2– anions (anionic effect), and tribotechnical characteristics of copper coatings are significantly improved.Translated from Zashchita Metallov, Vol. 41, No. 2, 2005, pp. 162–167.Original Russian Text Copyright © 2005 by Kuznetsov, Skibina, Geshel, Loskutnikova, Kuznetsova.     

Effects of copper ions on dissolution mechanism of marmatite

The dissolution mechanism of marmatite in the presence of Cu²⁺ was intensively studied by experiments and density functional theory (DFT) calculations. Leaching experiments showed that Cu²⁺ accelerated marmatite dissolution at high temperatures (above 55 °C), but the trend was reversed at low temperatures (below 45 °C), which may be because the reaction mechanism between Cu²⁺ and marmatite changed from surface adsorption to bulk substitution with increasing temperature. The substitution reaction caused more zinc atoms in the marmatite crystal lattice to be released and enhanced the electrochemical reactivity, while the adsorption of copper ions at low temperatures would passivate marmatite, thus inhibiting the reaction process. DFT calculations showed that the energy of the substitution reaction was more negative than that of the adsorption reaction at high temperatures, which further verified the proposed mechanism.     

Reaction Rate Study of the Dissolution of Cuprite in Sulphuric Acid

The rate of reaction of cuprite was measured in a series of sulphuric acid solutions, from which oxygen had been excluded, at various concentrations and temperatures. The overall reaction Cu₂O + H₂SO₄ → Cu⁺⁺ + Cu^o + H₂O + SO₄⁼ may be explained quantitatively by two simultaneous rate reactions involving not only H⁺ but also the hydrolytic adsorption of H₂SO₄. The results indicate the importance of considering surface mass balance relationships associated with heterogeneous surface reactions.     

Redox active thin films of polymeric metal-free octacyanophthalocyanine

Octacyanophthalocyanine is found to undergo oxidative polymerization under electrochemical conditions at 1.6 V. The polymer was characterized by infrared and UV-Vis spectra. The polymer-coated electrode undergoes a reversible electrochemical process when cycled in various electrolytes. The coated film acts as an ion exchange membrane specific to cations. This was proved by electrochemically trapping Fe(Phen)₃²⁺ ions and monitoring the cyclic voltammetric response of the incorporated cations.     

The Role of Cu(I) in the Process of Forming Cu2–xS Coatings by a Chemical Route

The interaction of the Cu₂O adsorbed with Na₂S_n (n = 1–4), during formation of the Cu_2–xS coatings has been investigated by cyclic voltammetry.

The summarized reaction of this process has been shown to correspond to the equation:

Na₂S_n + Cu₂O_ad + H₂0 → Cu₂S_ad + (n–1)S^o + 2NaOH,

where S^o/Cu=(n–1)/2. Such a stoichiometry of reaction can be explained by the formation of an intermediate—the adsorbed polysulphide of Cu(I)—and by its subsequent decomposition into Cu₂S and S^o.

When a thicker coating is being formed, i.e., when the surface being coated is repeatedly immersed into an ammoniate solution of Cu(I) and S^o fully bounded:

S^o_ad + 2 Cu⁺ → CuS + Cu²⁺.

At the same time due to different solubility products (L=2.5·10^?48 and 6.3·10^?36 for Cu₂S and CuS respectively), an exchange

CuS_ad + 2(1–x)Cu⁺ → Cu_2–xS_ad+ (1–x)Cu²+ occurs.

After formation of Cu²⁺, parallel processes characteristic for the interaction of Cu(II) with Na₂S_n start to take place, during which S^o is also formed.     

Microstructures and interfacial behavior of zirconia/stainless steel joint prepared by pressureless active brazing

ZrO₂ ceramic/stainless steel joints were fabricated by pressureless brazing with Ag–Cu filler metals and TiH₂ powders. The microstructures and elemental distributions of the joint cross-section as well as the reaction products at the ceramic/filler interface were analyzed using SEM, EDS, XRD and XPS. The results showed that there existed three zones with a distinguished difference in microstructure crossing the brazing interlayer. A double-layer structure including a reaction layer and a sublayer was formed at the ZrO₂/filler interface, where Ti⁴⁺, Ti²⁺ and Zr²⁺ were located based on the XPS spectra. It is further found that Ti originated from TiH₂ coating diffused into the whole interlayer. The high activity of neonatal Ti caused the reactions of Ti/ZrO₂ and Ti/Cu, resulting in the interfacial phases such as Ti₃Cu₃O, CuTi₃ and Zr.     

Investigation of the Interaction Between Cu2-x S +So Coatings and Pd(II) Ions by Cyclic Voltammetry and X-ray Photoelectron Spectroscopy

The interaction between Pd²⁺ ions and Cu_2-xS coating formed by three cycles and containing ~30 at.% of elementary S has been investigated by the methods of cyclic voltammetry and photoelectron spectroscopy (one cycle of coating formation includes treatment of the surface with Cu(I)+Cu(II) ammoniate solution, hydrolysis of the adsorbed copper compounds and sulphidation of copper oxygen compounds in Na₂S_n solution). After exposure of such a coating to Pd²⁺ ions (1.7 mM PdCl_2’ pH-2), an exchange as well as a redox interaction between the coating components and Pd²⁺ ions has been shown to occur. Due to this the amount of copper in the coating decreases from 2 to 4 times and that of sulphur from 1.5 to 5 times. The coating modified in such a way has been found to contain up to 75 at.% of palladium, ~90% of it being in a metallic state.

It has been determined that at the beginning S^o is bound into a soluble compound:

2Pd²⁺ + S^o + 3H₂O → 2Pd^o + H₂SO₃ + 4H⁺.

The Cu₂S present in the coating is considered to interact with Pd²⁺, with the formation of Pd⁰ and CuPdS_2’, while CuS reacts most likely according to the reaction:

CuS + 3Pd²⁺ + 3H₂O → 3Pd^o; + H₂SO₃ + Cu²⁺ + 4H⁺.

The Cu_2-xS +S^o coating formed on a dielectric and modified with Pd²⁺, contrary to the initial Cu_2-xS +S^o coating, can be plated with copper from any electrolyte for copper deposition.     

Influence of high concentration Zn2+ on floatability of sphalerite in acidic system

The influence of high concentration Zn²⁺ on the floatability of sphalerite in an acidic system was investigated via flotation experiments, zeta potential measurements, contact angle measurements, and X-ray photoelectron spectroscopy. The results indicated that Zn²⁺ was adsorbed on the sphalerite surface and a Zn-hydroxyl complex was formed at a pH of 4 and a Zn²⁺ concentration of 4×10⁻² mol/L. The zeta potential increased and the contact angle decreased from 84.80° to 36.48°, strongly inhibiting the floatability of sphalerite. When S²⁻ or Cu²⁺ activator was used alone, sphalerite was not activated after Zn²⁺ was adsorbed, and its contact angle did not change significantly. However, by using a combination of S²⁻ and Cu²⁺ activators, its floatability was realized after Zn²⁺ adsorption. This result was attributed to the removal of the Zn-hydroxyl complex on the surface of sphalerite by S²⁻. After this removal, Cu²⁺ was adsorbed on the sphalerite surface to form a Cu₂S·S⁰ hydrophobic film.     

通过水性还原法用NaBH4制备纳米铜颗粒过程中反应参数对制备过程的影响（英文）

通过水溶液还原法制备纳米铜颗粒,研究了不同反应条件对制备纳米铜的影响。制备纳米铜的最优条件是:当溶液 pH为12、温度为 313K、1%的明胶作为分散剂时,将0.4mol/L NaBH4加入含有 1.2mol/L 氨水的0.2mol/L CuSO4溶液中。此外,进行了一系列实验来模拟反应进程。结果表明,氨水能改变反应进程。当溶液 pH为10时,氨水将Cu2+转化为铜氨络合物,然后被 NaBH4还原为铜颗粒。当溶液pH为12时,氨水将Cu2+转化为氢氧化铜,然后被 NaBH4还原为铜颗粒。     

Deep removal of copper from cobalt sulfate electrolyte by ion-exchange

SP-C was applied for the removal of Cu²⁺ from simulated cobalt sulfate electrolyte containing Co²⁺ 50 g/L and Cu²⁺ 0.5–2.0 g/L. Experimental conditions included pH of 2–4, temperature of 20–60 °C and contact time of 10–40 min. The investigation demonstrated that SP-C had recommendable efficiency in adsorbing Cu²⁺ from the electrolyte with 25- to 100-fold of Co²⁺. The optimal adsorption conditions of SP-C were pH of 4, contact time of 30 min and ambient temperature. The study also showed that the loaded resin could be effectively eluted with 2.0 mol/L H₂SO₄ solution at a contact time of 40 min; the peak concentration of Cu²⁺ in the eluate was about 35 g/L. The sorption characteristics of Cu²⁺ by SP-C could be described by Langmuir isotherm and the pseudo second-order kinetic equation. Infrared spectra showed that nitrogen atoms in the functional group coordinated with Cu²⁺ to form coordination bands.     

Modification of iron particles with copper for their subsequent use in tribosystems

It was previously shown that lubricating suspensions that contain Fe mesoparticles and OS-20 or ENB 904 surfactants decrease the wear of friction surfaces. However, iron particles are readily oxidized by air. Therefore, the aim of this work is to modify the surface of Fe particles with a copper shell using a transmetallization reaction for the subsequent use in tribosystems. This reaction occurs via an electrochemical mechanism. The rate of the first stage of the modification of iron with copper expressed in electrical units is close to the limiting current density of the electroreduction of Cu²⁺. It occurs as long as Cu²⁺ ions are present in the solution or as long as Fe particles are not destroyed. Surfactants decrease the rate of transmetallization and can destroy iron particles. However, the modification of Fe particles directly in oil occurs at such concentrations of Cu²⁺ that provide the modification of 10% of the particles present in the system. This method for the modification of iron has no effect on the size of the resulting particles.     

The passivation of dilute Cu(Hg) in alkaline solutions

The anodic oxidation of dilute Cu(Hg)-pool electrodes (maximum mole fraction of Cu = 0.031) in aqueous solutions of Na₃PO₄ and NaOH pH range 10.5–12.2, yielded a series of potential-time transients that are found to correspond to the formation of Cu₂O, CuO and Cu(OH)₂ at the higher pH value, and Cu₂O and two soluble species, believed to be CuO²- and HCuO₂-, at the lower pH value. No sign of processes involving Hg appeared even at a mole fraction of Cu as low as 10⁻⁴. Theoretical calculation based on a model of competition between species of Cu and Hg for the available OH- predicts that the electrode should behave electrochemically as pure Cu down to a Cu activity of ca. 10⁻¹². For both anodic and cathodic processes i-τ−1/2 plots are found linear, proposing the applicability of the law τ = ai⁻ⁿ, with n = 2.     

X-ray absorption spectroscopy of electrochemically oxidized Cu exposed to Na2S

Copper surfaces have been investigated by X-ray absorption spectroscopy after electrochemical oxidation and subsequent exposure to sulfide solution. Oxide surface layers on bulk copper surfaces were electrochemically grown in an aqueous NaOH solution at two different potentials and the resulting chemical composition was investigated using X-ray absorption spectroscopy. At both potentials the resulting surfaces consisted largely of Cu₂O. At the more strongly oxidizing potential, an admixture of Cu²⁺-containing phases – mostly Cu(OH)₂ – was detected. Sulfide exposure of both surfaces was found to completely reduce the surface from Cu²⁺ to Cu¹⁺ and resulted in the formation of Cu₂S with an admixture of Cu₂O.     

铜离子对银电解的影响

采用电导率仪测定不同Cu2+浓度下AgNO3溶液的电导率,应用扫描伏安法研究Cu2+对阴极极化的影响,通过恒电流电解精炼研究Cu2+浓度对电解银粉含铜量的影响。结果表明:AgNO3溶液的电导率随着Cu2+浓度的增加而逐渐升高;Cu2+对银的析出具有抑制作用,随着其浓度的增加银的析出电位负移;电解液Cu2+浓度超过21.3 g/L时,银粉铜含量便会超标;银电解液中的Cu2+浓度在10~20 g/L范围时,对银粉中其他杂质元素Bi、Fe、Pb、Te的析出具有抑制作用。     

嗜酸氧化亚铁硫杆菌（ATCC 23270）浸出黄铜矿过程中的EPS、Cu2+和Fe3+的相互作用机制（英文）

采用超声-离心方法提取嗜酸氧化亚铁硫杆菌(ATCC 23270)胞外多聚物(EPS)、EPS中的Cu2+、Fe3+离子,研究生物浸出黄铜矿过程中Cu2+、Fe3+和EPS的相互作用机制。结果表明:与Fe3+离子相比,Cu2+离子可刺激细菌产生更多的EPS;当Cu2+离子浓度从0.01mol/L增加到0.04mol/L时,EPS中Fe3+/Cu2+质量比从4:1降低到2:1;从1%黄铜矿的无铁9K介质中提取的EPS中铜铁含量是从含0.04mol/LCu2+离子的9K介质中提取的量的2倍。在生物浸出黄铜矿过程中,黄铜矿表面结合黄铁钾钒的EPS层减弱了Cu2+、Fe3+离子的迁移,逐渐成为离子扩散壁垒。     

Heat-field-stimulated decomposition reaction in Cu2ZnSnS4

Thermal stability is essential for the potential solar cell material Cu₂ZnSnS₄ (CZTS) in achieving a satisfactory photovoltaic device performance. Although the loss of Sn from CZTS has been reported, the basic decomposition mechanism of a CZTS system has not been well established yet, especially with regard to the role of active Cu¹⁺ ions. This paper not only provides a deeper understanding of the change of Sn species, which includes an equimolar–isobaric vaporization mode transition and a solid–vapor phase transition in a self-generated atmosphere, but also reveals the oxidation state alternation (Cu¹⁺/Cu²⁺) and transfer mechanism of Cu species through carefully designed experiments and a reaction kinetic study. Cu ions are unexpectedly found to be active in affecting the degradation reaction by valance alternation and ion movement upon the application of a heat field to balance the derivation caused by a non-uniform temperature gradient. As a result, a Cu–Zn separation appears, with Cu accumulating near the hot area and Zn near the cold area. A decomposition reaction model of CZTS under a directional heat field is proposed to describe the elemental and electronic state change in atomic scale, and a perfect match is obtained between the model and the experimental results. This paper paves a way to solve the thermal stability issue of Cu₂ZnSnS₄.     

Characterization of Cr（Ⅵ） resistance and reduction by Pseudomonas aeruginosa

The experiments were conducted to evaluate the Cr(VI) resistance and reduction by Pseudomonas aeruginosa. After this bacterium tolerated 40 mg/L Cr(VI), the growth of cells was observed. The bacterial growth was obviously lower than the controls over 24 h and the binary cell fission was observed in cell morphology by scanning electron microscope. P.aeruginosa was found to be able to reduce Cr(VI) although Cr(VI) had toxic effects on the cells. The results demonstrate that Cr(VI) is reduced from 40 mg/L to about 18 mg /L in 72 h. The value of pH drops from 7.02 to around 5.65 after 72 h. A significant increase in the value of redox potential occurs during Cr(VI) reduction and Cr(VI) reduction can be observed over a range of redox potential from +3 mV to +91 mV. Both of SO₄²⁻ and NO₃⁻ have no effect on Cr(VI) reduction. The presence of Zn²⁺ has a notable inhibitory effect on Cr(VI) reduction while Cu²⁺ substantially stimulates Cr(VI) reduction. In the presence of Zn²⁺, Cr(VI) decreases from 40 mg/L to only 26–27 mg/L, whereas Cr(VI) drops to 1–2 mg/L after 48 h in the presence of Cu²⁺.     

Effect of Sulfide Ions on the Anodic Dissolution of Copper in Acetate Media

It is voltammetrically found that a covering film forms on copper in S^2–-ion-containing acetate media. It follows from thermodynamic equilibria, crystallographic parameters, and x-ray spectra of the metal and its compounds that the overall anodic process is composed of two separate processes and yields Cu₂S and Cu₂O. The reaction order in S^2– ions (log i/log C _i)_{E = const}is 0.37. Possible stages of the electrode process are suggested.     

Co‐effect of bis(cyclohexanone) oxalyldihydrazone and copper(II) ion on the corrosion of cold rolled steel in 0.5 M hydrochloric acid solution

Effects of bis(cyclohexanone) oxalyldihydrazone (BCO) and copper(II) ion (Cu²⁺) on the corrosion of cold rolled steel (CRS) in 0.5 M hydrochloric acid (HCl) solution were investigated using Tafel polarization curve and electrochemical impedance spectroscopy (EIS) at 20 °C. Results elucidate that the inhibition efficiency increases with increase in BCO concentration, and the addition of 10^?5 M Cu²⁺ significantly enhances the inhibition efficiency of BCO. Polarization curve results elucidate that the single BCO acts as a mixed‐type inhibitor while the combination of Cu²⁺ and BCO acts as cathodic inhibitor. Ultraviolet and visible spectrophotometer (UV–Vis) results show that BCO molecules do not interact with Cu²⁺ and Fe²⁺ in 0.5 M HCl solution. Atomic force microscope (AFM) result indicates that a protective layer forms on CRS surface after immersion in 0.5 M HCl containing BCO in the absence and presence of Cu²⁺. The adsorption of BCO is found to follow the Langmuir adsorption isotherm in the presence and absence of Cu²⁺. The mechanism of typically chemical adsorption is proposed via the value of free energy of adsorption (ΔG) in the presence of BCO and Cu²⁺.