Processes involved in the electrodeposition of rhenium from chloride melts have been studied over the temperature interval from 680 to 970 0C at a cathodic current density of 5 to 250 mA/cm2. It has been found that rhenium is deposited in the form of continuous layers. In addition to that the growth of deposits as separate single-crystal needles has also been noticed. Continuous layers had axial growth textures. The crystallographic direction of the textures is due to electrolysis conditions, such as concentration of oxygen-containing impurities, temperature, melt composition and cathodic current density. When the concentration of oxygen-containing impurities in the melt decreased, electrolysis temperature increased, the average radius of the supporting electrolyte cations became smaller, or cathodic current density diminished, the direction of the growth textures was changing as follows: (1010) →(1120) →(101L) →(0001) →(0001)needles. The microhardness of the deposits in this series is 900 to 250 kg/mm2. The growth of deposits on textured rhenium substrates and single crystals having different orientations, including bent substrates, was studied. It has been found that the epitaxial growth is virtually unlimited in depth if the orientation of the substrate coincides with the growth texture under given conditions. If the substrate orientation deviated from the growth texture, the epitaxial growth was nearly absent. Kinetic parameters were measured using the galvanostatic method. The exchange current density was determined over the interval of (0.01-0.1) A/cm2 depending on the concentration of oxygen-containing impurities, cation composition, type of the surface and its condition. The parameter α⋅Z, which was estimated by two methods, was equal to 2.1-3.1. The diffusion coefficient of rhenium ions has been found to be 2.8 ⋅10 −5 cm2/s at 790 0C and 3.5 ⋅10 −5 cm2/s at 840 0C. Galvanoplastic production of rhenium products, such as crucibles, ampoules foils, wire, and intricate articles, was performed
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Silicon nucleation process was invesigated in melt KF-KCl-K2SiF6 on glassy carbon substrates at 675 ºС by chronoamperometric method. Using data of the chronoamperograms the linear dependence I – τ3/2 was constructed. That fact testified the progressive nucleation mode of silicon. As seem from SEM micrographs silicon crystals obtained by a single pulse had different sizes, that also confirmed the progressive nucletion mode.
Increasing concerns on global warming and current environmental issues have directed research attention to the problems of energy saving, alternative energy sources, as well as to the improvement of the efficiency of existing chemical current sources. A particular focus is currently concentrated on solar energy use. High-purity silicon plates are employed as details in solar cells. Over the past ten years researchers have sought to create silicon nanomaterials able to significantly improve the efficiency of lithium-ion electrochemical batteries and photovoltaic cells. It is a common knowledge that the principle industrial method for producing high-purity silicon is based on vapor deposition; for example Siemens process [1]. However, it has a number of drawbacks in terms of power consumption, costly reagents, and sophisticated equipment. The development of a low-cost production process for solar and nanocrystalline silicon seems therefore an interesting research task. An alternative approach to the production of silicon is electrodeposition from molten salts containing silicon ions [2-7]. This method can be applied to obtain both coherent covers and Si-nanostructures, such as nanopowders and nanofibres.
Silicon and silicon-based materials find extensive applications in metallurgy, microelectronics, and other emerging industries. The field of use of synthesized silicon varies based on its morphology and purity. This study employs voltammetry, galvanostatic electrolysis, and scanning electron microscopy to examine the impact of KI surfactant (in mol %) to 66.5KF–33.3KCl–0.23K2SiF6 melt at 750°C on the electrowinning kinetics of silicon ions and the morphology of silicon deposits formed on a glassy carbon electrode. The findings demonstrate that the addition of potassium iodide to the KF–KCl–K2SiF6 melt at a concentration of 2 mol % induces changes in interfacial tension at the boundary between the glassy carbon, melt, and atmosphere. Consequently, the wetting of the glassy carbon with the melt decreases, leading to a reduction in the actual working surface area and, consequently, a decrease in cathode current while maintaining current density. Taking into account this effect and employing an algebraic estimation of the influence of the melt meniscus shape, it is postulated that the addition of KI does not significantly affect the kinetics of the cathode process. Nevertheless, the impact of KI addition on the morphology of electrodeposited silicon is mentioned. During the electrolysis of the KF–KCl–K2SiF6 melt, fibrous silicon deposits with arbitrary shapes are formed on the glassy carbon electrode, whereas the addition of 2 and 4 mol % of potassium iodide to the melt leads to the agglomeration and smoothing of silicon deposits under the same electrolysis conditions (cathode current density: 0.02 A/cm2, electrolysis duration: 2 h). The obtained results indicate the potential to manipulate the morphology of electrodeposited silicon for specific applications in various fields.
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