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.     

Thermodynamic properties of holmium monogermanide

The heat capacity and enthalpy of HoGe is investigated for the first time over a temperature range between 51.62 and 2096 K. The values of heat capacity, entropy, reduced Gibbs energy (J · mole^?1 × × K^?1), and enthalpy (J · mole^?1) are determined at 298.15 K: C °_P(T) = 49.63 ± 0.20; S °(T) = 89.1 ± 0.7; Φ′(T) = 50.9 ± 0.8; H °(T) ? H °(0 K) = 11391 ± 57. Temperature dependences of enthalpy (J · mole^?1) for holmium monogermanide are determined as follows: H °(T) ? H °(298.15 K) = 8.474 × × 10^?3 · T² + 47.13 · T + 226747 · T^?1 ? 15565 and H °(T) ? H °(298.15 K) = 88.91 · T ? 26507, for 298.15–1765 K and 1951–2096 K, respectively. The enthalpy and entropy of HoGe melting are calculated: T_m = 1765 ± 35 K, ΔH_m = 36.3 ± 2.9 kJ · mole^?1, ΔS_m = 20.5 ± 1.6 J · mole^?1 · K^?1.     

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 Ammonia Leaching of Multimetal Sulphides

This paper briefly describes the studies carried out on oxidative ammonia leaching of Cu-Zn-Pb multimetal sulphides. Kinetics of zinc and copper dissolution were studied with ? 200 + 300 mesh BSS fraction and 1% solids in the slurry. It is observed that the dissolution of sphalerite proceeds by a phase boundary reaction model and that of copper via diffusion through product layer in the temperature range of 70-100°C. The rate equations for zinc and copper dissolution are given by:

1 ? (1 ? α)^1/3 = k _Zn[NH₃][pO₂]^1/2

1 ? 2/3α ? (1 2/3α )^2/3 = k^Cu[NH₃]²[pO₂]^1/2

where the symbols have the usual meanings.

Activation energies for zinc and copper dissolution reactions are estimated to be 66.5 and 55.4 kJ/mole, respectively. Activation energy values thus obtained are also comparable to those obtained using a differential approach.

The leaching results obtained with 10% solids using a wide range of particle size (? 140 + 500 mesh) indicate that copper dissolution is chemically controlled in ammonia as well as ammonia-ammonium sulphate medium in the temperature range of 115-135°C. However, at lower temperature (?55°C). the leaching reaction follows a diffusion model. Zinc dissolution data show deviations from the shrinking core model due to high extractions in the initial stages.     

Effect of Sn Grain Orientation on the Cu6Sn5 Formation in a Sn-Based Solder Under Current Stressing

A SnAgCu-based solder stripe between two Cu electrodes is current stressed with a density of 5?×?10⁴?A/cm² at 393?K (120?°C). After current stressing for 24?hours, electromigration induces the Cu dissolution from the cathode-side Cu electrode, leading to the Cu₆Sn₅ formation in the solder stripe. Very interestingly, the Cu₆Sn₅ phase is selectively formed within a specific Sn grain. Electron backscattering diffraction analysis indicates the crystallographic orientations of Sn grains play an important role in the selective Cu₆Sn₅ formation.     

Directional Solidification and Liquidus Projection of the Sn-Co-Cu System

This study investigates the Sn-Co-Cu ternary system, which is of interest to the electronics industry. Ternary Sn-Co-Cu alloys were prepared, their as-solidified microstructures were examined, and their primary solidification phases were determined. The primary solidification phases observed were Cu, Co, Co₃Sn₂, CoSn, CoSn₂, Cu₆Sn₅, Co₃Sn₂, γ, and β phases. Although there are ternary compounds reported in this ternary system, no ternary compound was found as the primary solidification phase. The directional solidification technique was applied when difficulties were encountered using the conventional quenching method to distinguish the primary solidification phases, such as Cu₆Sn₅, Cu₃Sn, and γ phases. Of all the primary solidification phases, the Co₃Sn₂ and Co phases have the largest compositional regimes in which alloys display them as the primary solidification phases. There are four class II reactions and four class III reactions. The reactions with the highest and lowest reaction temperatures are both class III reactions, and are L + CoSn₂ + Cu₆Sn₅  =  CoSn₃ at 621.5 K (348.3 °C) and L + Co₃Sn₂ + CoSn = Cu₆Sn₅ at 1157.8 K (884.6 °C), respectively.     

Detailed assessment of partial thermodynamic quantities of tin in molten Bi-Sn alloys from electromotive force measurements

All the partial thermodynamic quantities, including the activity and activity coefficient of tin,a _Sn and γ_Sn, in the liquid Bi-Sn alloys between 300 °C and 500 °C are assessed in detail from electromotive force (emf) data. The emf values were obtained from a modified molten salt electrolyte concentration cell that had extraordinary stability within +0.005 mV. The composition dependence of γ_Sn did not follow Darken’s quadratic formalism, nor did the alloy behave as a regular solution. The excess partial quantities, ΔˉH _Sn ,ΔˉS _Sn ^xs , and ΔˉG _Sn ^xs , are oscillating across the composition, and the activity curve exhibits double, positive and negative, deviations from Raoult’s law. The a_Sn, γ_Sn, and ΔˉG _Sn ^xs change from positive to negative departure from ideality in the tin-rich region beyond about x_Sn = 0.82. All those partial quantities and γ _Sn ^o , including the β° (the α function of tin) at infinite dilution, are determined accurately by means of Chiotti’s method. ROBERTO CAMISOTTI, formerly Undergraduate Student, Central University of Venezuela. Formerly Assistant Professor, Central University of Venezuela.     

Thermodynamic properties and high-temperature behavior of lanthanum selenides La3Se4-La2Se3

The enthalpy of the La₃Se₄ and La₂Se₃ boundary compositions of the La_3?xSe₄ phase (0 ≤ x ≤ 1/3) at temperatures from 370 to 2260 K is studied calorimetrically. The values obtained are used and the equilibria of the La-Se system are analyzed to establish, for the first time, the temperature-concentration relationships for the thermodynamic properties of La_3?xSe₄ selenides in the homogeneity region at 298 K ≤ T ≤ 2123 K. The enthalpy function (J/mole) of La^3?xSe₄ is given by H(T) ? (298 K) = (3837 · 10³T^?1 ? 85852 + 266.925 · T ? 8.7503 · 10^?2 T² + 3.437 · 10^?5 T³) · e^?0.2869x. The formation and melting enthalpies of La₃Se₄ are determined: Δ_fH °(298 K) = ?1340 ± ± 28 kJ/mole), Δ_mH = 147.5 ± 9.6 kJ/mole. It is shown that the high-temperature stability of different La_3?xSe₄ compositions is strongly dependent on pressure: as pressure decreases and temperature increases, the selenium content is reduced and the composition tends to La₃Se₄.     

Kinetics of the Reaction between CO2—CO and Liquid Copper

Direct determination of the rate of the reaction between CO₂—CO and pure liquid copper in the interfacial reaction regime and an examination of the effect of oxygen has been made by using the ¹⁴C isotope exchange technique. The first order rate constant for the dissociation of CO₂ on clean, oxygen-‘free’ surfaces is found to be described by the equation:

log K⁰(mol/cm².s.atm) = ? 3510/T ? 2.36

between 1150 and 1400°C, to within an uncertainty of +60%. The first order rate constant for the dissociation (k₂) and that for the formation (k₁) of CO₂ on oxygen-doped surfaces are related through the equation:

k1 = k²a⁰

where a_o the oxygen activity in liquid copper with the standard state defined by pCO₂Sol;pCO = 1. Full consistency is found between experiments with ¹⁴C-labelled C0₂ and CO. The effect of a₀ on the rate of dissociation of CO₂ is in agreement with the site-blocking model and the rate constant (k₂) is found to be consistent with the equation:

with a₀ between 0.015 and 50 at 1200°C. In comparison, the magnitude of the reaction rate is significantly greater than those suggested by earlier studies. Possible causes for the discrepancy are discussed.     

Phase formation in the nickel—Zinc reaction couple

Annealing of Ni’MZn reaction couples at 400°C for 1–25 h results in the formation of intermetallic layers of the γ- and δ-phases at the interface between nickel and zinc. The width of the homogeneity region for the γ-phase is 73.0–86.0 at. % Zn, while that for the δ-phase is 87.5–89.0 at. % Zn. The chemical formula for the γ-phase is thus NiZn_3–6, while that for the δ-phase is NiZn_7–8. The γ-phase growth kinetics is described by a parabolic equation x _i ² ’Mx ₀ ² =2k₁t_i (x_i and x₀ are the thicknesses of the layer at times t_i and t₀=0, k₁ is the growth rate constant): k₁=(4.4±0.2)·10^’M14 m²/sec. The δ-phase shows a deviation from the parabolic law since its growth rate constant decreases from 9.6·10^’M14 m²/sec at t=1 h to 6.9·10^’M14 m²/sec at t=25 h. The thickness ratio for the layers in this time interval chages by about 13%.     

The oxidation of thiosulfates with copper sulfate. Application to an industrial fixing bath

This paper presents the transformation of thiosulfate using Cu(II) salts, such as copper sulfate, at pH between 4 and 5. The nature and kinetics of this process were determined. In the experimental conditions employed, the reaction between thiosulfates and Cu(II) ions produces a precipitate of CuS and the remaining sulfur is oxidized to sulfate, according to the following stoichiometry: 1 mol thiosulfate reacts with 1 mol Cu²⁺ and 3 mol H₂O, generating 1 mol copper(II), 1 mol sulfate and 2 mol H₃O⁺. In the kinetic study, the apparent reaction order was ≈ 0 with respect to H₃O⁺ concentration, in the interval 1.0 · 10^? 4–1.0 · 10^? 5M H₃O⁺; of order 0.4 with respect to Cu²⁺ in the interval 0.21–0.85 g L^? 1 Cu²⁺; and of order 0 with respect to S₂O₃^2? in the interval 0.88–2 g L^?1 S₂O₃^2?. The apparent activation energy was 98 kJ mol^? 1 in the interval 15–40 °C. On the basis of this behavior an empirical mathematical model was established, that fits well with the experimental results. The thiosulfate transformation process using copper(II) sulfate was applied to an industrial fixing bath that proceeded from the photographic industry; after this, the resulting effluent contained less than 10 mg L^? 1 of thiosulfates.     

Cathodic deposition of copper in the presence of aqueous sulfurous acid,bivalent aquacobalt ion,or both using a stainless steel cathode and a graphite anode

A study on cathodic deposition of copper in acidic aqueous sulfate solution has been carried out using a stainless steel cathode and a graphite anode. The individual and the combined effects of added [H₂SO₃·aq] and [Co²⁺·aq] on cathode potential, current efficiency, crystal orientations, and deposit morphology have been investigated and are compared. The maximum decrease of ≿50 pct in cathode potential is more pronounced in the presence of ≿10.25 g/L of H₂SO₃ alone in the electrolyte than that (≿30 pct) in the presence of ≿100 ppm of added Co²⁺ (aq) alone; however, the presence of added Co²⁺ (aq) along with H₂SO₃ (aq) does not cause further decrease in cathode potential in comparison to that observed in the presence of only H₂SO₃ (aq) in the electrolyte. The current efficiency is found to decrease in the presence of [H₂SO₃·aq] in the range of 1.32 to 30.75 g/L or in the presence of added [Co²⁺·aq] in the range of ≿10 ppm to 600 ppm, while the decrease of about 4 pct in current efficiency is more pronounced in the presence of only H₂SO₃ (aq) in the electrolyte, it is about 2 pct in the presence of only added Co²⁺ (aq) in the same electrolyte. The addition of Co²⁺ (aq) to the electrolyte containing H₂SO₃ (aq) does not alter the current efficiency (94 pct) of copper at the cathode. The linear sweep voltammetry (LSV) method was used to study the effect of added [H₂SO₃·aq], [Co²⁺·aq], or both, on the copper deposition at the cathode. The presence of each of these two additives or both causes a depolarization effect; the extent of the depolarization depends on the concentration of H₂SO₃ (aq), Co²⁺ (aq), and the current density. X-ray diffraction (XRD) data suggest that there is a change in the order of the preferred crystal orientations (viz., from the (220) plane in the absence of added H₂SO₃ (aq) and Co²⁺ (aq) to the (111) plane in the presence of added H₂SO₃ (aq) and Co²⁺ (aq) in the electrolyte solution) due to a change in the preferred plane of relative crystal growth. Results of scanning electron microscopy (SEM) indicate that cathode deposits of better surface morphology due to small-sized crystallites are found in the presence of added H₂SO₃ (aq)+Co²⁺ (aq) in the electrolyte solution. 1000 ppm=1.0 g/L=1.0 × 10⁻³ kg dm⁻³     

The kinetics of the exchange of cobalt(II) ions between NaCl and Na2O-SiO2-Fe2O3 melts in the temperature range 1200 to 1400 K

Studies of the equilibria and kinetics of the Co²⁺ ion exchange in the Na₂O-SiO₂-Fe₂O₃/NaCl system were performed over the 1200 to 1400 K temperature range by measuring the emf of galvanic cells of the following composition: $$( - )Co\left| {\frac{{NaCl - CoCl_2 }}{{Na_2 O - SiO_2 - Fe_2 O3}}} \right.\left| {NaCl - CoCl_2 } \right.\left| {Co( + )} \right.$$ Distribution coefficients α of the Co²⁺ ions between the salt phase and silicate melt are of the l0^?2 order. Differential equations describing the transfer process of the Co²⁺ ions from the salt phase to the silicate phase were solved. The diffusion coefficients D_Co ²⁺ in the Na₂O-SiO₂-Fe₂O₃ melt were determined by substituting the Co²⁺ ion concentration change in fused NaCI into the differential equations. The values of D_Co ²⁺ are about 10^?5 cm²S^?1 and they decrease with decreasing temperature and increasing Fe_?2O_?3 content in slags. The diffusion coefficient of the cobalt (II) ions in slags determined in this way is consistent with that determined by the otating disk method.     

Kinetics of spreading in initial stages in metallic systems with different types of interaction between components. IV. Effect of chemical reaction on the kinetics of spreading in tin—Iron group metal systems

A droplet flowing over onto a plate introduced from above has been used to study the kinetics of spreading and to describe the observable characteristics of spreading of tin on iron, cobalt, nickel, and the intermetallic compounds Ni₃Sn, Ni₃Sn₂ under a vacuum of (2–4)·10⁻³ Pa at 400–1000°C, droplet mass 0.01–0.06 g. We show by a formal kinetic analysis of experimental data that in the low-temperature range (400–500°C) the kinetic regime dominates, and in the high-temperature range (600–1000°C) the inertial—kinetic regime dominates. In spreading of tin on iron, cobalt, nickel, and the intermetallic compounds Ni₃Sn and Ni₃Sn₂, the nature of the interaction corresponds to the phase equilibrium in the studied systems. The results for the kinetics of spreading of tin on nickel and the intermetallic compound Ni₃Sn showed that spreading of the main bulk is preceded by spreading of a precursor film. Deceased. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(402), pp. 65–72, July–August, 1998.     

Solubility of oxygen in Fe–Co melts containing titanium

Solutions of oxygen in Fe–Co melts containing titanium are subjected to thermodynamic analysis. The first step is to determine the equilibrium reaction constants of titanium and oxygen, the activity coefficients at infinite dilution, and the interaction parameters in melts of different composition at 1873 K. With increase in cobalt content, the equilibrium reaction constants of titanium and oxygen decline from iron (logK(FeO · TiO₂) =–7.194; logK(TiO₂) =–6.125; logK(Ti₃O₅) =–16.793; logK(Ti₂O₃) =–10.224) to cobalt (logK(CoO · TiO₂) =–8.580; logK(TiO₅) =–7.625; logK(Ti₃O₅) =–20.073; logK(Ti₂O₃) =–12.005). The titanium concentrations at the equilibrium points between the oxide phases (Fe, Co)O · TiO₂, TiO₂, Ti₃O₅, and Ti₂O₃ are determined. The titanium content at the equilibrium point (Fe, Co)O · TiO₂ ? TiO₂ decreases from 1.0 × 10^–4% Ti in iron to 1.9 × 10^–6% Ti in cobalt. The titanium content at the equilibrium point TiO₂?Ti₃O₅ increases from 0.0011% Ti in iron to 0.0095% Ti in cobalt. The titanium content at the equilibrium point Ti₃O₅ ? Ti₂O₃ decreases from 0.181%Ti in iron to 1.570% Ti in cobalt. The solubility of oxygen in the given melts is calculated as a function of the cobalt and titanium content. The deoxidizing ability of titanium decline with increase in Co content to 20% and then rise at higher Co content. In iron and its alloys with 20% and 40% Co, the deoxidizing ability of titanium are practically the same. The solubility curves of oxygen in iron-cobalt melts containing titanium pass through a minimum, whose position shifts to lower Ti content with increase in the Co content. Further addition of titanium increases the oxygen content in the melt. With higher Co content in the melt, the oxygen content in the melt increases more sharply beyond the minimum, as further titanium is added.     

Thermodynamics of Cobalt Aluminate Formation in Molten Cobalt

The oxygen concentration of liquid cobalt in equilibrium with cobalt aluminate and alumina was measured by suction sampling at temperatures in the range of 1783 to 1873 K. Experiments were made with cobalt of high and low initial oxygen content and with the addition of cobalt aluminate. The Gibbs free energy of the formation of cobalt aluminate in equilibrium with cobalt containing dissolved oxygen and alumina is: Co (l) + (1+x) Al₂O₃ + [O]_{1 wt% in Co} = CoO·(1+x)Al₂O₃ with ΔG° = ‐(226400 ± 8730) + (93.04 ± 4.74) T [J/mol]. The oxygen partial pressure in equilibrium with the dissolved oxygen in molten cobalt was determined by zirconia stabilized with magnesia oxygen sensors. The Gibbs standard free energy of dissolution of oxygen in molten cobalt in the range of 1783 to 1873 K is: 1/2 O₂ = [O]_{1 wt% in Co} with ΔG° = ‐76410 – 2.16 T [J/g·atom].     

Distribution of cobalt between liquid copper and copper silicate slag at 1523 K

The solubility of cobalt in Cu₂O-SiO₂ slags held in silica crucibles and equilibrated with copper-cobalt alloys has been investigated for conditions of varying amounts of cobalt in the alloy charged at a temperature of 1523 K. The solution of cobalt in slag from its alloy is explained by the equation: Co (in alloy) + Cu₂O (in slag) = 2 Cu (in alloy) + CoO (in slag) The average distribution ratio, valid from 0.04 to 0.10 pct Co in the equilibrated metal, is: (Pct Co in slag)/(Pct Co in metal) = 400 ± 50 The results are explained with the help of SEM, X-ray diffraction and EDAX, which indicated that the phase assemblages encountered as charged cobalt is increased are: SiO₂ + melt; Co₂SiO₄ + melt and CoO + Co₂SiO₂ + melt. In the last case, a coherent layer of cobalt silicate was found to have formed on the crucible surface. A tentative phase diagram of the ternary Cu₂O-CoO-SiO₂ system is presented. A change in the equation giving the activity coefficient of cobalt in Co-Cu alloys is suggested to bring calculated activity in agreement with the presence of CoO found experimentally as a separate phase. Ramana G. Reddy, formerly at The University of Utah     

Solvent extraction of base metals by mixtures of organophosphoric acids and non-chelating oximes

The effect of non-chelating oximes on the extraction of several transition and nontransition metals by solutions of organophosphoric acids (H₂A₂) in xylene has been investigated. Synergistic enhancements of extraction of divalent transition metal ions were found with the oximes of aliphatic aldehydes, the enhancements of extraction increasing in the order VO²⁺ < Mn²⁺ < Mn²⁺ < Co²⁺ < Cu²⁺ < V²⁺ < Ni²⁺. Large synergistic effects were also found for copper(I) and silver(I). Among the divalent non-transition metals studied (Mg, Ca, Zn, Cd, Sn, and Pb), only cadmium showed a synergistic effect. No significant synergism was found for any of the trivalent metal ions studied (Fe, Cr, V, Al, Bi, La, Ce, and Nd). The extracted complexes of copper, cobalt, and nickel were shown to be octahedral in structure, with the compositions Cu(HA₂)₂(oxime)₂, Co(HA₂)₂(oxime)₂, and NiA(HA₂)(oxime)₃, respectively, in which HA₂^? acts as a bidentate ligand. Extraction rates were found to be rapid, even for nickel, and complete stripping of metal-loaded organic phases was effected by contact with 0.5 M mineral acid. Some practical applications, such as the recovery of nickel from acidic leach liquors, are envisaged.     

Formation of complex compounds of univalent copper at the Cu<Superscript>0</Superscript>-Cu<Superscript>2+</Superscript> interphase boundary in chloride solutions

Kinetics and a mechanism of formation of compounds of univalent copper at the interphase boundary Cu⁰-Cu²⁺ in the solution containing excess chlorine anions are investigated by the spectrophotometry method. It is shown that the [CuCl₂]^? and [CuCl₃]^2? complex anions are formed during the contact of metal copper with the Cu²⁺ ions. The former ones are characterized by the appearance of the band in the region of 233 nm in the spectra of electron absorption, and the latters ones—in the region of 273 nm. The dependence of intensity of absorption bands on the contact time of the Cu²⁺ ions with copper is used to estimate the kinetic parameters of formation and oxidation of the [CuCl₂]^? and [CuCl₃]^2? ions. A thickness of the reaction layer, in which they are formed, is determined. The formation of the Cu(I) compounds during the contact interaction of copper with the Cu²⁺ ions is confirmed by the results of electrochemical investigations. The mechanism of cathode reduction of copper-containing compounds on a copper electrode is suggested.     

硫氰酸铵-十四烷基三甲基溴化铵微晶吸附体系浮选分离铜

建立了硫氰酸铵-十四烷基三甲基溴化铵微晶吸附体系浮选分离铜的新方法。探讨了硫氰酸铵溶液用量、十四烷基三甲基溴化铵（TTMAB）溶液用量和酸度等因素对Cu²⁺浮选率的影响,讨论了Cu²⁺的浮选分离机理。结果表明,在最佳条件下,由Cu²⁺,SCN^-和十四烷基三甲基溴化铵阳离子(TTMAB⁺)形成的不溶于水的三元缔合物(TTMAB)₂ ［Cu(SCN)₄］被定量吸附在TTMAB⁺与SCN^-作用产生的微晶物质TTMAB⁺·SCN^-表面,且被浮选至水相上形成界面清晰的液-固两相,而Fe³⁺、Co²⁺、Ni²⁺、Cd²⁺、Mn²⁺、Al³⁺等离子仍然留在水相中,实现了Cu²⁺与这些离子的定量分离。据此建立了硫氰酸铵-十四烷基三甲基溴化铵微晶吸附体系浮选分离铜的新方法,进行了合成水样中Cu²⁺的定量浮选分离,浮选率为93.4%～103.6%。