Investigation of the electrode/electrolyte interface for the Cu+ ion solid electrolyte N,N′-dimethyl-triethylene diamine-copper(1) bromide

The Cu⁺ ion solid electrolyte 47Cu Br·3(CH₃)₂ C₆H₁₂N₂Br₂ was prepared by hot-pressing and characterised by X-ray analysis and electrical measurements. Novel cell arrangements were used to study the electrochemical behaviour of interfaces between this electrolyte and copper metal and also between this electrolyte and two well known solid solution electrodes (SSEs) for copper, Cu₂Mo₆S_7.59 and Cu_1.8S. The behaviour of the electrolyte/copper interface was correlated with scanning electron microscope (SEM) examinations showing the growth of copper dendrites at the interface. Results from the electrolyte/SSE interfaces showed that there is no interfacial polarisation and that the electrode polarisation is controlled solely by the diffusion of Cu⁺ ions in the SSE. These experiments allowed estimates of the chemical diffusion coefficient for Cu⁺ ions in each material to be made.     

Mechanism of film growth of pulsed electrodeposition of nanocrystalline copper in presence of thiourea

This article reports the effect of addition of small amount of thiourea on mechanism of film growth, levelling and grain refinement of pulsed electrodeposition of nanocrystalline copper on stainless steel substrate using simple aqueous acidic copper sulphate solution prepared from 0.25 M CuSO₄·5H₂O and 0.5 M H₂SO₄. The amount of thiourea used in the electrolyte is 0 and 36 mg/l. The results indicate the change in morphology of the deposits with addition of thiourea leading to dendrite free copper deposits. The growth mechanism of the copper deposition is found to change from Volmer–Weber type to Frank-Vander Merwe type making the deposits smoother when deposited with thiourea addition. A small amount (36 mg/l) of thiourea addition leads to decrease in the average grain size of copper from 1160 nm to 14 nm. The results clearly reveal the formation of nanocrystalline copper by addition of thiourea with three orders of magnitude reduction in grain size as compared to the sample deposited without thiourea. Preferential segregation of sulphur (present in thiourea) along the grain boundaries of nanocrystalline copper is shown by energy filter imaging using ultra high resolution transmission electron microscope (TEM), thereby restricting the growth of copper grains during pulsed electrodeposition.     

New ternary molten salt electrolyte based on alkali metal triflates

A novel molten salt electrolyte composed of lithium triflate (CF₃SO₃Li, LiTf), sodium triflate (CF₃SO₃Na, NaTf), and potassium triflate (CF₃SO₃K, KTf) has been prepared and characterized by thermogravimetry/differential thermal analysis (TG/DTA), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry. TG/DTA shows that the electrolyte was thermally stable when the temperature was under 400 °C. Its thermal stability gradually decreased with increase of LiTf concentration. The ionic conductivity of molten salt electrolyte has been evaluated by EIS and its value exceeds 10⁻² Scm⁻¹ in the temperature range from 230 to 270 °C. The electrochemical window of the electrolyte at the molar ratio of 0.5/1/1 is about 4.7 V at 250 °C. This electrolyte with low melting point exhibits promising characteristics for high-temperature lithium batteries.     

An electrochemical study of copper diffusion in non-stoichiometric copper sulphide

The diffusion of copper in hexagonal chalcocite (Cu₂S) is not very well-known. In this work electrochemical cells with natural polycrystalline chalcocite working electrodes have been studied by electrochemical impedance spectroscopy (EIS) over a large frequency range at equilibrium potential. To study this phenomenon between 120 and 160°C a solid electrolyte RbCu₄Cl₅ has been used. The impedance spectra present two distinct regions. At high frequencies the general shape of the diagram in the Nyquist plane is a depleted are of a circle. Changes in electrolyte resistance, interfacial capacitance and transfer resistance have been studied as a function of temperature. At low frequencies, a diffusion impedance is observed attributed to the mobility of copper vacancies. Diffusion coefficients, with an activation energy of 1.7 eV, have been deduced from the impedance diagrams (4.7·10⁻⁵cm² s⁻¹ at 130°C). These results are compared with those obtained with orthorhombic chalcocite between 30 and 60 °C by EIS and using an electrochemical cell with a cupric liquid electrolyte. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

Hydrogen sensor based on oxide proton conductors and its application to metallurgical engineering

Galvanic cell-type hydrogen sensor for high temperature use is now available thanks to the discovery of oxide-type proton conducting solid electrolyte such as acceptor-doped perovskite-type oxides. In order to develop the practically functional hydrogen sensor based on these electrolytes, the electrochemical properties of these oxides should be understood as a function of hydrogen and oxygen potentials at the temperature range where the sensor is to be used. In this review, the properties of indium-doped calcium zirconate (represented by the composition CaZr_0.9In_0.1O_3–δ) known as, among these oxides, the most chemically stable and mechanically strong were explained briefly on the basis of the thermodynamics of the crystal imperfections. Then the structure of hydrogen sensor for molten aluminum and that for molten copper, which were designed to make the best use of the properties of the electrolyte for the respective process conditions, were shown. Lastly, the performance of these sensors examined in the laboratory scale and the practical industrial conditions was overviewed. Paper presented at the 9th EuroConference on Science and Technology of Ionics, Rhodes, Greece, Sept. 15 – 21, 2003.     

Homogeneity range of cubic high temperature cuprous sulfide (digenite)

Within the homogeneity range of the cubic cuprous sulfide Cu_2?δS the sulphur fugacity was measured as a function of composition and temperature using direct (silica gauges) and indirect (H₂S/H₂) methods. The experiments were performed between 789 and 1321 K and in the whole field of compositions from copper-rich to the sulphur-rich boundary of the homogeneity range.The experimental data are interpreted by a combination of the thermodynamics of mixed phases and the point defect theory. The results show that Cu_2?δS is essentially a mixture of Cu₂S and CuS. Other defects than CuS dissolved in Cu₂S, e.g. copper interstitials, are present in small amounts at high temperatures and low sulphur fugacities. These results are in close agreement with data from the literature, derived from metallurgical, DTA, thermobalance and electrical conductivity measurements.     

Energetics of defect formation and interaction in pyrrhotite Fe1−xS and its homogeneity range

Sulphur fugacities in equilibrium with Fe_1?xS (pyrrhotite) were measured at different temperatures in the range 820–1374 K by direct (silica gauges) and indirect (H₂S/H₂) methods. The results give direct evidence of the boundaries of the homogeneity range and can be interpreted in terms of iron vacancy formation and interaction and of an additional defect, e.g. iron on sulphur sites. The homogeneity range of Fe_1?xS is calculated as a function of temperature from the energetic parameters of the defects and the sulphur fugacities limiting the existence region of this phase.Fe_1?xS exists with positive values of x except at the eutectic with iron (1261 K) where x is 0±0.0001.     

Sulphur transformation during pyrolysis of an Australian lignite

Transformation of various sulphur forms, including inherent and added pyrite, sulphates (CaSO₄ and FeSO₄) and organic sulphur, during pyrolysis of an Australian lignite was studied using TGA, TGA-MS and a fixed bed reactor, supplemented by sulphur form analysis. It was shown that hydrogen sulphide (H₂S) and a small quantity of sulphur dioxide (SO₂) were released during the pyrolysis of the pyrite-lignite blend. However, only SO₂ was detected during the pyrolysis of the lignite with high pyrite content. Inorganic matter was found to help retaining some of the inorganic sulphur, including pyrite, in the char. Inherent sulphates decomposed at much lower temperatures than the added sulphates, releasing SO₂ rather than H₂S. The inherent sulphates in the lignite were dominated by iron sulphates which started to decompose and release SO₂ at around 500 K and all sulphate had been decomposed at 1073 K. The retention of organic sulphur in the high organic sulphur lignite was higher than in its acid washed lignite sample, due to the interaction between inherent inorganic matter with the organic sulphur retaining the organic sulphur in the solid phase. SO₂ was the only sulphur gas produced during pyrolysis of acid washed lignite. A comprehensive mechanism of sulphur transformation during pyrolysis of lignite was proposed.     

Range of homogeneity and defect model for Bi2S3

Sulphur pressure measurements inside and at the boundaries of the homogeneity range of Bi₂S₃ were performed as a function of composition and temperature. From the results and literature data a defect model of this substance is deduced. Important defects are singly charged sulphur vacancies and neutral sulphur atoms on bismut sites (antistructure defects). The range of homogeneity is calculated from this model. Bi₂S₃ exists with both sulphur deficit and sulphur excess of up to about 0.002 atoms sulphur per mole of Bi₂S₃. The phase diagram Bi-S is confirmed.     

Effect of magnesium addition on the wetting of alumina by aluminium

In this report the wetting behaviour between polycrystalline alumina substrates and molten aluminium doped with magnesium as a wetting agent has been studied using the sessile drop technique. The time required for equilibrium attainment is investigated. To explore the formation of possible phases at the interface, electron microscopic studies along with EDX analysis have been employed. It is found that magnesium reduces the time and temperature required for equilibrium in the Al/Al₂O₃ system. The Al-7 wt% Mg and Al-10 wt% Mg alloys can wet alumina at temperatures as low as 900 °C. It is also found that molten aluminium doped with magnesium can wet polycrystalline alumina at temperatures below 1000 °C. A thin reaction layer was observed at the Al-Mg/Al₂O₃ interface in the present study.     

Estimation of the homogeneity range of MoS2

The sulphur pressure as a function of composition and temperature has been investigated in MoS₂ with both large and small concentrations of stacking faults. This was done by stepwise annealing with H₂ and analyzing the gas phase. The composition variability seems to be affected only by the concentration of stacking faults. There is no evidence for a homogeneity range of MoS₂ which is free from stacking faults, i.e. this homogeneity range is smaller than 8 × 10^-5 moles S per mole of MoS₂ at temperatures between 1173 and 1373 K. Values of the S₂ pressure in equilibrium with a mixture of Mo₂S₃ and MoS₂ agree with the phase diagram proposed in the literature.     

Copper diffusion in copper sulfide: a systematic study

Copper sulfide Cu_2−xS is a model mineral for chalcogenides because of the existence of a non-stoichiometric compounds series in the range Cu₂S - CuS in which properties change with x. For this reason, we have studied the influence of the mineral composition on the diffusion in this solid. Electrochemical Impedance Spectroscopy (EIS) applied to Cu_2-xS/cupric sulfate electrolyte was the main investigation technique. It enabled us to work at the equilibrium potential at which the composition is fixed and known. Changing the composition by electrochemically removing (or adding) a known amount of Cu, we were able to determine the chemical diffusion coefficient of copper in the composition range (from x=0 to 0.066). In this work, we present the results obtained in the chalcocite and djurleite phases. These results were compared to other values reported in the literature. From this systematic study we discuss various diffusion mechanisms. Our observations support that in chalcocite and djurleite Cu diffuses via a vacancy mechanism. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

利用电子顺磁共振和紫外/可见吸收光谱研究熔融KNO3-NaNO2-NaNO3盐分解过程中的超氧负离子

On account of excellent thermal physical properties, molten nitrates/nitrites salt has been widely employed in heat transfer and thermal storage industry, especially in concentrated solar power system. The thermal stability study of molten nitrate/nitrite salt is of great importance for this system, and the decomposition mechanism is the most complicated part of it. The oxide species O₂^2- and O₂^- were considered as intermediates in molten KNO₃-NaNO₃ while hard to been detected in high temperature molten salt due to their trace concentration and low stability. In this work, the homemade in situ high temperature UVVis instrument and a commercial electron paramagnetic resonance were utilized to supply evidence for the formation of superoxide during a slow decomposition process of heat transfer salt (HTS, 53 wt% KNO₃/40 wt% NaNO₂/7 wt% NaNO₃). It is found that the superoxide is more easily generated from molten NaNO₂ compared to NaNO₃, and it has an absorption band at 420-440 nm in HTS which red shifts as temperature increases. The band is assigned to charge-transfer transition in NaO₂ or KO₂, responsible for the yellow color of the molten nitrate/nitrite salt. Furthermore, the UV absorption bands of molten NaNO₂ and NaNO₃ are also obtained and compared with that of HTS.     

Origin and Distribution of Sulphate in Surface Waters of the Mansfeld Mining District (Central Germany)—A Sulphur Isotope Study

Abstract

In the Mansfeld region (Central Germany) copper mining contributed to an enormous pollution of the environment. Metal- and sulphate-bearing sediments and leachates emerge from the former copper smelters and mining waste heaps, spread along local rivers and finally reach the Saale river. A sulphur isotope study on water and stream sediments was performed along the River “Böse Sieben” and from its tributaries to determine the different sulphur sources. Four major sulphur sources exist in the area: metal sulphide mineralisations (Kupferschiefer), metalliferous sulphidic flue dust, slag, and anhydrite and gypsum of Permian and Triassic age. We obtained δ³⁴S(SO₄)-values in water samples varying from +4‰ to ?18‰ CDT, clearly reflecting the input of sulphate from different sources. Sulphate from the oxidation of sulphidic mining residues is restricted to the mining area and cannot be traced for more than 5 km downstream. The major source for sulphate is the dissolution of gypsum and anhydrite. The sulphur isotope composition in dissolved and sedimentary adsorbed sulphate differs only slightly from each other. Microbial dissimilatory sulphate reduction can not be excluded in the shallow sediment layers.     

Preparation of Cu 2 O nanoparticles dispersed in NH 2 -terminated polyethyleneoxide matrix

Small Copper (I) oxide, Cu₂O, nanoparticles dispersed in diamine-terminated polyethyleneoxide (PEO-NH₂) matrix have been successfully prepared by vacuum evaporation of copper onto the molten PEO-NH₂. The obtained composite were characterized by TEM, electron diffraction, TG-DTA and FT-IR spectroscopy. The stable composite, in which the Cu₂O nanoparticles are stabilized through interaction between NH₂ chain end groups of PEO molecules and Cu₂O nanoparticles was obtained when the samples were heat-treated at 110 ^° C. The mean size of the Cu₂O nanoparticles increased from 2.5 to 3.5 nm in diameter upon increasing the amount of initial Cu deposition. The obtained composite material having a waxy texture was soluble in many solvents without aggregation and can be handled as a simple chemical compound for starting material in various applications. Received 29 November 2000     

Decomposition of the hexagonal copper hydride at high pressure

The process of decomposition of hexagonal copper hydride has been observed in situ in a diamond anvil cell (DAC) using the energy dispersive X-ray diffraction (EDXRD) method. The presence and intensity of diffraction lines of the hexagonal CuH_0.8 phase have been taken as a probe for the decomposition process. The intensity of diffraction lines decreases abruptly in the vicinity of 8.4 GPa, indicating complete decomposition of the hydride. The determined value of decomposition pressure is equal to 8.4±0.6 GPa. The standard Gibbs energy of formation of 54.0±1.3 kJ mol⁻¹ (H₂) calculated for copper hydride has been compared with the result obtained from calorimetric studies. The large discrepancy between the two values suggests that the decomposition pressure does not describe ‘true’ equilibrium conditions in this system.     

The phase composition of tin-nickel electrodeposited alloys

It was studied the tin phase composition of the electrodeposited alloys produced at different temperatures and current densities from an acid chloride/fluoride electrolyte and an acid chloride bath. Mössbauer spectra were consistent with a Ni₃Sn₄ intermetallic compound, dissolved tin, and a Cu?Sn intermetallic compound formed at the interface of the copper substrate.     

The influence of pressure on the electrical conductivity of molten zinc chloride and its Mixtures with potassium chloride

Abstract

The electrical conductivities of molten ZnCl₂ and its mixtures with KCl were measured as functions of pressure, temperature, and composition. The measuremkents were performed in an internally heated pressure vessel in which the melts were contained in open quartz glass cells. The addition of KCl to molten ZnCl₂ causes a large increase of the conductivity at all pressures and temperatures. With increasing pressure the conductivity increases in pure molten ZnCl₂ and in mixtures rich in ZnCl₂ and decreases in mixtures with more than 30 mol% of KCl.     

Segregation and adsorption of sulphur on Ni50Fe50(100) alloy: Studies of the surface composition and structure and of the effects on the passivation

The surface composition of Ni₅₀Fe₅₀(100) alloy was studied and the segregation and adsorption of sulphur were investigated by AES, LEED and radiotracer (³⁵S) techniques. Ion etching produces a surface composition identical to the matrix composition (Ni:Fe=1:1). In the temperature range 300–600°C iron segregates on the surface and nitrogen was detected. Heating to higher temperatures (>600°C) also causes the segregation of iron as well as the segregation of sulphur. The durface reaches a stable composition that does not depend on further changes of the temperature in the range 25–800°C. It consists of an almost complete monolayer of iron segregated on the alloy. The segregation of sulphur leads to the formation of a c(2×2) structure. A sulphur coverage of 45 ng cm^-2, consistent with the c(2×2) structure, was measured by the radiotracer method after chemisorption in gaseous H₂S/H₂ mixtures at 550° and 200 Torr. This sulphur monolayer is stable in a range of p_H2S/p_H2=7.4 × 10^-5-6×10^-4. Above this pressure, a preferential sulphidation of iron is observed. The effects of sulphur on the anodic dissolution and passivation of the alloy in acid solution were studied. Adsorbed sulphur promotes the dissolution and delays the passivation. When the alloy is doped with sulphur, bulk sulphur accumulates on the surface during the dissolution of Ni and Fe. This anodic segregation leads to the formation of an adsorbed layer of sulphur, followed by the growth of a sulphide which blocks the formation of the protective oxide film.     

Structures and magnetic properties for electrodeposited Co ultrathin films on copper

The formation of Co films on polycrystalline copper in diluted sulphuric acid was investigated by employing cyclic voltammetry (CV), atomic force microscopy, and in-situ magneto-optic Kerr effect (MOKE) techniques. By comparing CV measurements in the pure supporting electrolyte (11 mM K₂SO₄/1 mM H₂SO₄) and the cobalt sulphate solution (10 mM K₂SO₄/1 mM H₂SO₄/1 mM CoSO₄), peaks from voltammetric cycling for copper dissolution, readsorption of dissolved copper ions, cobalt bulk dissolution and oxidation of hydrogen could be resolved. As the electroplating time increases, the size of the Co clusters increases and the deposition of Co corresponds to island growth. The first hysteresis loop occurs at a Co thickness of 0.33 nm in the longitudinal configuration. For films thinner than 7 nm, the Kerr intensity increases linearly because the Curie temperature of the film is well above 300 K.