Room-temperature diffusion in Cu/Ag thin-film couples caused by anodic dissolution

Thin, 100-nm films of first silver and then copper were deposited consecutively onto inert substrates by magnetron sputter deposition. Constant anodic current densities were applied at room temperature to dissolve the outer copper film to varying depths. The 50Cu/50Ag interface, derived from the auger electron spectroscopic concentration-depth profile, initially moved into the copper toward the outer dissolving surface, indicating enhanced diffusion of copper into silver. After longer times at all anodic current densities, the interface reversed and moved back toward the underlying silver-rich layer, indicating that eventually diffusion of silver into copper predominated. The reversal time was inversely proportional to the anodic current density. These effects are explained by anodic formation of subsurface vacancies which migrate as divacancies to the copper/silver interface where they affect interface movements by the well-known Kirkendall mechanism. Calculated diffusivities up to 10⁻¹² cm²/s at maximum anodic current densities of 900 μA/cm² are dramatically above any that are normally observed at room temperature.     

Electrotransport and diffusion of Co,Fe, and Ag in γ-Cerium

Electrotransport mobilities and diffusion coefficients were obtained for radiotracer impurities of Fe, Co, and Ag in Ce. The iron and cobalt moved toward the anode with mobilities of ～10^?3 cm²/v-s in the range of 550° to 650°C. The silver moved to the cathode with mobilities of ～10^?5 cm²/v-s in the range of 600° to 700°C. The, diffusion coefficients obtained fit an Arrhenius equationD=D _o e ^?ΔH/RT with the following parameters: Fe:D _o=3.3×10^?4, ΔH=4.6 kcal/mole Co:D _o=10^?2, ΔH=11 kcal/mole Ag:D _o=1.4, ΔH=28 kcal/mole The results are compared with other rare-earth diffusion data, and the possibility of a substitutional-interstitial diffusion mechanism, is considered.     

The electrochemical oxidation of chalcopyrite in ammoniacal solutions

The anodic dissolution of chalcopyrite in ammoniacal solutions was investigated using electrochemical methods. At low overvoltages, the formation of a copper deficient sulfide layer, Cu_1-xFeS₂ through a charge transfer reaction is proposed based upon the dependence of the rest or open circuit potential on solution composition and the presence of a Tafel region of appropriate slope. In addition, a current peak that occurs at 10⁻⁴ A/cm² is a function of the square root of the voltage scanning speed and is explained in terms of a charge transfer reaction. At larger overvoltages, constant potential experiments and mass balances performed at various anodic potentials indicate that the dissolution is consistent with the overall reaction, CuFeS₂ + 4NH₃ + 9OH^- = Cu(NH₃) ₄ ⁺² + Fe(OH)₃ + S₂O ₃ ⁼ + 3H₂O +9e ^-, although some copper may be released to solution in the cuprous state and some ferrous iron has been identified in the product film. Currentvs time data taken during constant potential experiments were found to obey a linear rate relationship. This was interpreted in terms of the formation of a layer of constant thickness which is corroded at the outer interface at the same rate it is formed at the inner interface.. The model proposed is typical of the corrosion of some metals. An examination of the polarization curves shows the dissolution reaction to be first order with respect to [OH^-]. The lack of dependence on [Cu²⁺] indicates that the catalytic effect of cupric ion during oxygen pressure leaching is related only to the cathodic reduction of O₂ in agreement with the results of previous investigations.     

Electrotransport and diffusion of iron and silver in α-yttrium

The electrotransport mobilities and diffusion coefficients were determined for iron and silver impurities in yttrium. The mobility of iron increased from 1.2 x10^-4 cm²/V-s at 900°C to 7.4X10^-4 cm²/V-s at 1330°C. The silver mobility ranged from 8.1X10^-6 cm²/V-s at 905°C to 6.4 x 10^-5 cm²/V-s at 1095°C. The iron movement was anode-directed, and the silver movement was cathode-directed. The diffusion coefficients obtained fit an Arrhenius equationD = D₀e-ΔH/RT with the following values: Fe:D ₀ = 1.8 x 10^-2 cm²/s ΔH = 85 kJ/mol (20 kcal/mol); Ag:D ₀ = 5.4 x 10^-3 cm²/s ΔH = 77 kJ/mol (18 kcal/mol). A substitutional-interstitial mechanism previously proposed for anomalously high diffusion rates of impurities in cerium and lanthanum is also proposed for yttrium.     

Electrochemical behavior of the dissolution of gold-silver alloys in cyanide solutions

The dissolution behavior of gold and silver from Au/Ag alloys in aerated cyanide solutions has been investigated using rotating disc electrodes. The variables studied included concentration of cyanide, oxygen partial pressure, and rotating speed of the disc. The dissolution potential and the rate of dissolution were obtained in view of the anodic and cathodic current-potential relationships. The results were discussed in terms of the mixed potential theory. The results showed that the dissolution rate of gold and silver from the alloys was partially controlled by chemical reaction but largely controlled by transport of either oxygen or cyanide, depending on their relative concentrations under the experimental conditions employed in this study. The diffusion coefficient of free cyanide, D_cn ^?, was found to be (1.25 ± 0.05) X 10^?5 cm²/s. The diffusion coefficient of oxygen, $D_{O_2 } $ , was calculated to be (1.29 ± 0.02) X 10^?5 cm²/s.     

Studies on the application of copper(I)-ammune sulphate electrolytes in copper electrorefining

The electrolysis of a copper(I)-ammine sulphate electrolyte between copper electrodes has been investigated. A sealed cell and a solution containing 30 g/kg Cu, 95 g/kg NH₃ and 95 g/kg SO₄ were used.Current efficiencies (cathodic and anodic), at current densities over 100 A/m², were higher than 95% and were practically independent of the electrolysis variables (25–55°, 100–500 A/m² and 70–130 g/kg of NH₃ solution).It was shown that at temperatures over 40°C the energy consumption for electrorefining is lower in the copper(I)-ammine electrolyte than in a typical acidic electrolyte.Contributions to the energy consumption from the electrode processes and the resistance of the electrolyte have been determined from the experimental data.     

A Method for the Estimation of the Interface Temperature in Ultrasonic Joining

Ultrasonic joining of copper foil to 1100 aluminum sheet at nominal joining temperatures of 298 K to 413 K (25 °C to 140 °C) for 1.25 second caused significant copper diffusion into the aluminum sheet, indicating very high diffusivity (D) values of 1.54 × 10^?13 to 2.22 × 10^?13 m²/s. The D values reflect high excess vacancy concentrations caused by the rapid plastic deformation in the joining surfaces. A method is presented to estimate the actual values of interface temperature from the diffusion data and expected values of vacancy concentrations. The estimated values of interface temperature were about 390 to 410 deg below the equilibrium melting point of aluminum, and in agreement with reported experimental values.     

Effect of added cobalt ion on electro-deposition of copper from sulfate bath using graphite and Pb–Sb anodes

Effect of added Co²⁺(aq) on copper electro-deposition was studied using Pb–Sb and graphite anodes and a stainless steel cathode. The presence of added Co²⁺(aq) in the electrolyte solution was found to decrease the anode and the cathode potentials. The optimum level of Co²⁺(aq) concentration in the electrolyte, with respect to the maximum saving of power consumption was established. Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) were used to study the influence of added Co²⁺(aq) on the anodic and the cathodic processes in a copper sulfate-sulfuric acid electrolyte. The oxygen-evolution potential is depolarised at lower current densities (≤ 150 A/m²) and attains saturation at [Co²⁺]_o ? 600 ppm; whilst at higher current densities (≥ 300 A/m²) it is depolarised with [Co²⁺]_o ≥ 300 ppm. The presence of Co²⁺ promoted the deposit of a smoother and brighter copper cathode as measured by surface reflectivity. X-ray diffraction (XRD) showed that added Co²⁺ changed the preferred crystal orientations of the copper deposits. Scanning electron microscopy (SEM) indicated that the surface morphology of the copper deposited in the presence of added Co²⁺ has well-defined grains. Analysis of cathode copper deposits found negligible cobalt.     

Kinetics of disilicide layer growth at the interface of tungsten with molten copper, silver, and tin saturated with silicon

The kinetics of WS₂ layer growth at the interface of tungsten with molten metals saturated with silicon is studied. Research is performed at 1200°C using melts based on copper, silver, and tin. It was established that WSi₂ layer growth in these melts obeys a “parabolic” rule but the corresponding growth rate constants differ markedly, i.e., from 3.4·10^?11 m²/sec (melt based on copper) to 1.5·10^?13 m²/sec (melts based on silver and tin). The reasons for this difference are discussed.     

Absorption of gaseous oxygen by liquid cobalt,copper, iron and nickel

An experimental investigation of the rates of oxygen solution in molten cobalt, copper, iron and nickel was carried out using pure oxygen and a constant-volume Sieverts’ method. It was found that the volume of gaseous oxygen which initially reacted with the inductively stirred metals was strongly dependent on the physical nature of the oxide film which formed during the first stage of reaction. The initial temperature of the molten iron, cobalt, and nickel was 1600°C, and for copper was 1250°C. For initial oxygen pressures above the melt of about one atmosphere both molten iron and copper, which formed liquid surface oxides, initially absorbed nearly 20 cm³ (STP) O₂/cm² of melt surface area, while molten cobalt and nickel, which formed solid oxides, absorbed about 6 cm³ (STP) O₂/cm² under the same experimental conditions. For approximately 30 s after the initial reaction between these liquid metals and gaseous oxygen, the oxygen absorption rate was proportional to the square root of the oxygen pressure above the melt, and proportional to the melt surface area, but independent of melt volume. The rate-limiting step for oxygen absorption by liquid iron, cobalt and copper can be described by dissociative adsorption of oxygen molecules at the gas/oxide interface. After 30 s of reaction, the rate of oxygen absorption became less dependent on the oxygen pressure above the melt. This indicated that the rate-controlling step was changing from a surface reaction to growth of the oxide layer by cationic diffusion in the bulk oxide. The oxidation rate of liquid nickel appears to be too complex to be described by models for dissociative adsorption of oxygen molecules at the gas/oxide interface and parabolic growth of the oxide layer. The formation of a thin layer of nickel oxide which allows oxygen to migrate through cracks or grain boundaries may be responsible for the relatively high oxygen absorption rate compared to that of liquid cobalt. R. H. RADZILOWSKI, formerly a Graduate Studient at The University of Michigan     

Study of the mechanism of anodic dissolution of Cu2S

The anodic dissolution of Cu₂S in sulfuric acid solutions was studied under galvanostatic and potentiostatic conditions. The anodic products were studied by mineralogical and X-ray diffraction methods. In every case, the formation of a digenite Cu_1-8S layer is observed at the surface of Cu₂S according to 5Cu₂S → 5Cu_1.8S + Cu⁺⁺ + 2e A copper concentration gradient appears through the digenite layer whose thickness remains constant as soon as a Cu_1.1S layer appears at its own surface according to 3Cu_1.8S → 4Cu_1.1S + Cu++ + 2e If the electrolysis conditions are such that the anodic potential remains low, the next reaction to occur is 10Cu_1.1S → HCu⁺⁺ + 10S + 22e But if under galvanostatic conditions, the current density is high enough at a given temperature to reach the sharp rise in anodic potential, or if under potentiostatic conditions the potential is kept high, two other reactions are possible: 10Cu_1.1S → 10CuS + Cu⁺⁺ + 2e followed by CuS → Cu⁺⁺ + S + 2e Moreover, at high anodic potential, the following reaction occurs also to some extent CuS + 4H₂O ? Cu⁺⁺ + SO₄ ⁼ + 8H⁺ +8e resulting in a decrease in anodic current efficiency for the copper dissolution. From a more practical point of view, it was shown that it is possible to deplete virtually completely the copper content of the anode (residue at less than 0.5 pct Cu)keepingthe electrode potential at a low value (less than +650 mV/ENH). Providing the temperature is high enough (75°C at least), the mean current density remains near to 2 A/dm², a suitable value to obtain good cathodic deposits.     

Diffusion in the titanium-nickel system: II. calculations of chemical and intrinsic diffusion coefficients

Diffusion coefficients in the Ti-Ni system have been calculated by the aid of equations given by Sauer and Freise, and Wagner. Values for the TiNi (50 at. pct Ni) phase were found to be:D ^u (cm²/s) = 0.0020 exp - 142,000/R for the temperature range between 650 and 940°C. The heat of activation, expressed in J/mol, has an accuracy of ±6000. For the β-Ti(Ni) phase containing 6 at. pct Ni the temperature dependence of the diffusion coefficient is expressed by:D ^u (cm²/s) = 0.0688 exp - 141,000/RT. The uncertainty in the energy of activation is ±12000 J/mol. No clear variation of the diffusion coefficient with concentration could be detected. It was found that Ni is by far the fastest moving component in β-Ti(Ni), Ti₂Ni and TiNi (at least in the composition range between 50 and 53 at. pct Ni). Values ofD _Ni/D _Ti have been calculated with an equation derived by van Loo. The significance of the calculated values is critically examined. By means of a practical example it is shown that the calculated ratio of the intrinsic diffusion coefficients can be extremely sensitive to slight variations in the position of the marker interface.Diffusion coefficients in the Ti-Ni system have been calculated by the aid of equations given by Sauer and Freise, and Wagner. Values for the TiNi (50 at. pct Ni) phase were found to be:D ^u (cm²/s) = 0.0020 exp - 142,000/R for the temperature range between 650 and 940°C. The heat of activation, expressed in J/mol, has an accuracy of ±6000. For the β-Ti(Ni) phase containing 6 at. pct Ni the temperature dependence of the diffusion coefficient is expressed by:D ^u (cm²/s) = 0.0688 exp - 141,000/RT. The uncertainty in the energy of activation is ±12000 J/mol. No clear variation of the diffusion coefficient with concentration could be detected. It was found that Ni is by far the fastest moving component in β-Ti(Ni), Ti₂Ni and TiNi (at least in the composition range between 50 and 53 at. pct Ni). Values ofD _Ni/D _Ti have been calculated with an equation derived by van Loo. The significance of the calculated values is critically examined. By means of a practical example it is shown that the calculated ratio of the intrinsic diffusion coefficients can be extremely sensitive to slight variations in the position of the marker interface. This paper is based on a Thesis submitted by G. F. BASTIN in fulfillment of requirements for the degree of Doctor in Technological Sciences.     

Absorption of gaseous oxygen by liquid cobalt, copper, iron and nickel

An experimental investigation of the rates of oxygen solution in molten cobalt, copper, iron and nickel was carried out using pure oxygen and a constant-volume Sieverts' method. It was found that the volume of gaseous oxygen which initially reacted with the inductively stirred metals was strongly dependent on the physical nature of the oxide film which formed during the first stage of reaction. The initial temperature of the molten iron, cobalt, and nickel was 1600‡C, and for copper was 1250‡C. For initial oxygen pres-sures above the melt of about one atmosphere both molten iron and copper, which formed liquid surface oxides, initially absorbed nearly 20 cm³ (STP) O₂/cm² of melt surface area, while molten cobalt and nickel, which formed solid oxides, absorbed about 6 cm³ (STP) 0₂/cm² under the same experimental conditions. For approximately 30 s after the initial reaction between these liquid metals and gaseous oxygen, the oxygen absorption rate was proportional to the square root of the oxygen pressure above the melt, and pro-portional to the melt surface area, but independent of melt volume. The rate-limiting step for oxygen absorption by liquid iron, cobalt and copper can be described by dissocia-tive adsorption of oxygen molecules at the gasJoxide interface. After 30 s of reaction, the rate of oxygen absorption became less dependent on the oxygen pressure above the melt. This indicated that the rate-controlling step was changing from a surface reaction to growth of the oxide layer by cationic diffusion in the bulk oxide. The oxidation rate of liquid nickel appears to be too complex to be described by models for dissociative ad-sorption of oxygen molecules at the gasJoxide interface and parabolic growth of the oxide layer. The formation of a thin layer of nickel oxide which allows oxygen to migrate through cracks or grain boundaries may be responsible for the relatively high oxygen ab-sorption rate compared to that of liquid cobalt. Formerly a Graduate Student at The University of Michigan     

Charge transfer at Fe/FeO(CaF2) electrodes at 1450 ‡C: Exchange current density,electrode capacitance,diffusivity

The kinetics of the electrode reaction Fe = Fe _slag ²⁺ + 2e ^- has been investigated using the single and double pulse techniques. It was found that the exchange current densities are very large increasing from 2 to 10 A cm^-2 in the range of Fe²⁺-concentration from 2 · 10^-6 to 30 · 10^-6 mole cm⁻³. The electrode capacitance increases from 50 ΜF cm^-2 approximately linearly with the square root of Fe²⁺-concentration. An attempt was made to explain the concentration dependent part of the capacitance in terms of a model involving electrosorption of the speciesFe _ad ⁿ⁺ at the slag/iron interface. If the adsorbed iron ions are the intermediates in a consecutive charge transfer mechanism, the rate determining step is the transfer of iron between the adsorbed layer and the slag. On the other hand, it may be possible that the transfer is in one step with adsorption occurring in parallel. Formerly with Max-Planck Institut für Eisenforschung, D-4000 Düsseldorf, Germany     

Effect of electrotransport on the solidification of Sn-Bi alloys

The influence of an electric field upon the stability of a planar interface during solidification of single phase Sn-Bi alloys was studied. Electrotransport of solute, increased temperature gradient due to Joule heating, melting of perturbations on the interface, and Peltier heating effects at the interface were all considered. At current densities of 1275 amp/cm² an effect of the electric field was observed. The effect appears to be due to alteration of the consti-tutional supercooling criterion by electrotransport, but it is somewhat smaller than pre-dicted theoretically. J. C. WARNER, formerly with Ames Laboratory of the U. S. Atomic Energy Commission, Iowa State University, Ames, Iowa 50010,     

Electrode polarization in the DC electroslag melting of pure iron

It is evident from the known ionic properties of the slags used in electroslag melting, that the dc melting process must be accompanied by Faradaic reactions on the slag/ingot and slag/electrode interfaces. The present work has determined the magnitude of the overpotentials resulting from concentration polarization at these interfaces, in the case of pure iron/CaF₂+Al₂O₃, CaF₂+CaO slags using a galvanostatic pulsing technique in an electrolytic cell. The polarization overpotential existing on an electrode in an operating ESR unit has been measured by the same technique. It is found that the potentials observed on the ESR electrode agree well with the results from the electrolytic cell. The primary anodic process is postulated to be the corrosion of iron, leading to an Fe²⁺-saturated layer on the anode surface at sufficiently high current densities. The cathodic process is suggested to be the Faradaic reduction of Al³⁺ or Ca²⁺, to give a concentration of [Al]_Fe or (Ca)_slag in the cathode interface region. This observation is supported by the fact that the cathodic potentials with respect to a C/CO reference electrode are close to those predicted from the reactions: (Al₂O₃)+3C=3CO(g)+2Al(l) or (CaO)+C=CO(g)+Ca(g) At very high current densities both the anodic and cathodic processes may convert to arcs, leading to process instability. The chemical and thermal effects of the overpotentials are briefly discussed and compared with the present results on ESR ingots of pure iron.     

Electrode processes at the glass carbon/LiCl-CuCl-CuCl2 melt interface

The kinetics of the electrode processes occurring at the glass carbon/LiCl-CuCl-CuCl₂ $\left( {N_{CuCl - CuCl_2 } = 0 - 7.5 mol \% } \right)$ melt interface is studied by the coulostatic method, single current pulse chronopotentiometry, and stationary voltammetry at a temperature of 950 K and the atmospheric pressure of chlorine over a melt. The exchange current densities in the molten mixtures are determined by the coulostatic method. These data are used to calculate the transfer coefficient (?? = 0.54 ± 0.06) and the rate constant of the electrode reaction Cu²⁺ + e ^? ai Cu⁺ (k _S = 0.26 ± 0.02 cm/s). The results of stationary voltammetry in the cathode potential region reveal pronounced limiting currents up to the precipitation of metallic copper on an electrode. The experimental data obtained by chronopotentiometry are used to find the transition times for various current densities over the entire concentration range under study. The dependences plotted in the i??^1/2 = f(i) coordinates suggest the presence of a chemical homogeneous reaction preceding the electrode process. The total value of the rate constants of the forward and back reactions is estimated to be ??2. The copper mono- and dichloride concentrations are determined in the concentration range under study.     

The nature of copper electrowon in the presence of iron using sulfur dioxide sparging

The nature of copper electrodeposits obtained under conditions of ferrous oxidation and gas (SO₂ with N₂/air) sparging has been studied using synthetic solutions in the absence of organic inhibitors. The quality of the deposit was improved by increasing the sparging rate and temperature and by decreasing the applied current density and sulfuric acid concentration. The copper deposits were found to contain about 14 μg/g sulfur compared with 5 μg/g in the starter cathode. The texture of the deposits was affected by the rate of gas sparging and applied current density. A pyramidal morphology was observed at current densities in the order of 200 A/m². At higher current densities polycrystalline, unoriented dispersion-type deposits were obtained.     

Influence of titanium content and grain size on hydrogen cracking behaviour of hot-rolled steels

Hydrogen induced cracking was investigated for hot-rolled titanium steels. Aim of the present work was to observe the influence of titanium content and grain size on the cracking behaviour. Three titanium steels (0.12-0.30 % Ti; O.0057-0.0480 % C) and one non-titanium steel (0.0056 % C) were used for the investigation. Various grain sizes were generated by heat treatment at 950, 1050 and 1150 °C; furnace cooling was applied. The specimens were electrolytically charged with hydrogen at various current densities. It was found that cracks are generated at low charging current densities for the investigated steels. The titanium steels showed better performance than the non-titanium steel. It was shown that the charging current density does not correspond to the hydrogen concentration in a steel; the hydrogen concentration in steel B was 3.8 ppm at 1 mA/cm², in steel D it was found to be 15.5 ppm at 0.5 mA/cm². The total hydrogen concentration was found to be influenced by content of precipitates and grain size. It was shown that the percentage of cracked grain boundary area increases with increasing grain size. This increase is linear for the non-titanium steel whilst for the titanium steels a plateau was observed at a grain size diameter of 50 μm.