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The electrochemical behavior of cobalt and molybdenum oxides in molten carbamide at 135°C has been studied. The potentials and limiting discharge currents of cobalt and molybdenum have been determined by the cyclic voltammetry method. According to the results of the studies, an electrolysis mode for the formation of cobalt–molybdenum coatings has been selected.

Lanthanum silicides (La5Si4, La5Si3, La4Si, LaSi and LaSi2) are metal-like compounds with semiconductor properties. If this were true, it could become technologically important as an infrared detector material [1]. The possibility of electrochemical synthesis of lanthanum silicides from molten salts were investigated in this work. It can be concluded from thermodynamic calculation that silicon discharge from molten salts more positive than La (~ 0.8 V), in this case electrochemical synthesis possible only in two step, first deposited of Si, next step deposition of La onto Si with formation of lanthanum disilicide: I. 2Si + La(III) +3 e = LaSi2 ΔE0 10233 K = ΔG0 1023 K/ (nF) ≈ 0.500 V,where ΔE0 – is potential (V), ΔG0 - is the Gibbs energy of the reaction I. (J), n – is the number of electrons involved in the reaction (in our case, n = 3), F – is Faraday constant. The electrochemical behaviour of the molten salts system NaCl-NaF-LaF3-K2SiF6 was studied by cyclic voltammetry. A glassy carbon crucible served as a vessel for the melt and as an auxiliary electrode; a W wire was used as the working electrode; the measurements were made with respect to glassy carbon reference electrode 1023 K in argon atmosphere. Typical cyclic voltammogram for molten salts system NaCl-NaF-LaF3-K2SiF6 show two step process of electrochemical synthesis of LaSi2at 1023 K in Ar on W working electrode (Fig. 1 .). On the base of thermodynamic calculation and voltammetric investigation, it has been show that lanthanum disilicide can by electrochemical synthesized from a NaCl-NaF- LaF3-K2SiF6 melt at 1023 K in two step. References R.G. Long, M.C. Bost, J.E. Mahan., Appl. Phys. Lett. 5 3, 1272 (1988). Fig. 1. Voltammogram of a NaCl-NaF-LaF3- K2SiF6 melts on a W working electrode, v= 0.1 V/s. Figure 1

The electrodepositions of tungsten and its alloys has been of considerable interest because of usual properties of the metal and alloys. The electrodepositions of W and Co from water solutions and Na2WO4-WO3-CoO at 1023 K were investigated in more works. The possibility of electrodeposition of W-Co alloys from carbamide melts at 408 K has been examined. When studying the electrochemical behaviour of cobalt and tungsten oxides and its compounds (WO3, Li2WO4, Na2WO4, K2WO4) in molten carbamide, it can be concluded that maximum limiting currents are typical of the system (NH2)2CO-Li2WO4. Cyclic voltammograms showed the potentials of deposition of tungsten and cobalt. Layered Co-W coatings on nickel cathodes have been obtained by the electrolysis of the molten system (NH2)2CO-CoO- Li2WO4 at current densities of 5-10 mA/cm2. The cathodic products were analyzed by XRD and JEM-2100F SEM. Fig. SEM of the surface morphology of W-Co coating deposited by electrolysis from (NH2)2CO-CoO- Li2WO4 melt. Figure 1

Nickel silicides are used as Schottky barrier and as ohmic contacts owing to the combination of properties typical of metal (high electrical conductivity) and nonmetal (low heat conductivity) [1]. Nickel silicides are usually produced by the thermal vacuum spraying of nickel on single-crystalline silicon plates [2]. The objective of this work was to examine the possibility of obtaining nickel silicides by electrolysis of molten salts, containing silicon ions, on a Ni cathode. It can be concluded from thermodynamic calculation that silicon discharge depolarization through NiSi2 formation is 0.110 V at 993K: I. Ni + 2Si = NiSi2 The electrochemical behaviour of the system NaCl-NaF-K2SiF6 was studied by cyclic voltammetry. A glassy carbon crucible served as a vessel for the melt and as an auxiliary electrode; a Ni wire was used as the working electrode; the measurements were made with respect to glassy carbon reference electrode 7200С in argon atmosphere. Current-potential curves exhibited, at potentials more positive (~100 mV) than silicon discharge potential, a new irreversible electrochemical process followed by a chemical reaction. Up to 25 mm thick dense NiSi2 layers have been obtained by the electrolysis of a NaCl-NaF-K2SiF6 melt on a Ni plate at 7200С in argon atmosphere at current density of 50 mA/cm2 (Fig. 1.), which was confirmed by X-ray phase analysis. The chemical composition map of metallographic section shows the silicon distributions. On the base of thermodynamic calculation, voltammetric investigation and electrolysis experiments, it has been show that nickel disilicides can by electrochemical synthesized in a NaCl-NaF-K2SiF6 melt at 7200С on a nickel cathode in argon atmosphere. References M. Lawrence, A. Dass, David B. Fraser, Chih-shihWei, Appl. Phys. Lett. 58, 1308 (1991). Y. He, J.Y. Feng, W.Z. Li, Journal of Crystal Growth, 254, 70-74 (2003). Fig. 1. SEM micrograph: cross-section of a Ni cathode after the electrolysis of a NaCl-NaF-K2SiF6 melts at 7200С in Ar atmosphere.

In this work, the interaction of Si, SiC and TiC with a Na2CO3-K2CO3 melt at 7500С on Ar atmosphere and in air was investigated. The optimal process for the fabrication of carbon fibers or nanotubes is interaction between silicon carbide and carbonate melts. It has been show that the modification of carbon materials depends on SiC powder fineness.

The electrochemical behaviour of vanadium oxides in a carbamide- KCl melt at 1200C was studied by cyclic voltammetry. In the (NH2)2CO-KCl melt with additions of trivalent vanadium, an electrochemical process of oxidation of trivalent vanadium to pentavalent one was observed in the anodic region. V2O5 is irreversibly discharged in the (NH2)2CO-KCl melt with reactant adsorbed strongly.

The process of dissolution of titanium, silicon, and boron oxides in carbonate melts is studied. Voltammetric studies are used to show that the most electropositive electrochemical process in molten carbonates is discharge of carbon dioxide dissolved in the melt to elementary carbon. Electrochemical synthesis of carbides in carbonate melts is possible at the potentials more positive by their value than the potential of carbonate decomposition. Interaction of titanium and silicon carbides with carbonate solutions is studied.

Titanium diboride is a promising protective material for the cathodic bottom of aluminium baths [1]. Solubility of TiB2 in molten aluminium at 1300 K is 6×10 wt.% [2]. Equilibrium between liquid aluminium and solid titanium diboride is reached within 10 hours of their contact in a laboratory cell. The solubility of aluminium in titanium diboride at 1300 K is so low, that it could not be measured. The possibility of electrochemical synthesis of titanium diboride on carbon cathodes in situ from cryolite-alumina melts containing titanium and boron oxides was shown in Ref. [3]. This experiment was made in pure cryolite. Industrial Hall-Heroult technology uses synthetic cryolite, containing 0.8 % silica. In electrolysis experiments with synthetic cryolite containing titanium and boron oxides, cathode surface was passivated with silicon – oxygen compounds. The present paper examines the possibility of electrochemical synthesis of ternary compounds Ti-Si-B from cryolite-alumina melts containing titanium, silicon and boron oxides. Electrochemical behavior of cryolite-alumina melts containing titanium, silicon or boron oxides was studied by cyclic voltammetry. Voltammetric investigations were conducted in a Pt crucible with the working electrode of Pt wire and oxygen-platinum reference electrode in air at 1000C. As the boron oxide interaction with molten cryolite yields gaseous boron trifluoride, the bath was stabilized by inserting boron into the melt in the form Al4B2O9 compound, which forms from boric acid and alumina. The titanium dioxide and silica was added to the cryolite-alumina melts. In the system Na3AlF6-Al2O3-Al4B2O9 was observed a three electron irreversible change transfer with formation of insoluble product

The determination of the oxidation state in which vanadium is in metallurgical slag's is an important factor in choosing the optimal conditions for the production of ferrovanadium by the silicothermal method. On the basis of thermodynamic calculations, electrochemical investigations and UV-Vis spectroscopy it has been shown that in vanadium-contain metallurgical slag's vanadium is in the form of V2O3.

Electrochemical synthesis of binary and ternary compounds in the system Ti-Si-B from chloridefluoride melts has been investigated by voltammetry and electrolysis. Electrochemical syntheses of titanium diboride, four titanium silicides (TiSi2, TiSi, Ti5Si4, Ti5Si3), silicon tetraboride and a new ternary compound, Ti5Si3B3, have been found to be one-step processes. The stoichiometry of the deposited compounds has been found to correlate with the bulk concentration of Ti, Si and B ions in the melt.

Metals, semiconductors, and their binary and ternary compounds can be produced by electrolyzing molten salts of the components. For a Ti–Si–B system, reduction potentials of all three elements are close, which significantly alleviates the problem. Using thermodynamic calculations, voltammetric measurements, and electrolysis we demonstrate the possibility of producing metal-like refractory compounds. Binary compounds TiB2, Ti5Si3, and SiB4 and a new ternary compound Ti5Si3B3 are produced electrochemically.

Preparation of aluminum alloys in an aluminum electrolyzer considerably reduces the cost price of the resulting ligatures. Introduction of new oxides into molten cryolite frequently disturbs the electrolyzer operation. The behavior of boron oxide in molten cryolite and the possibility of stabilizing the electrolyzer operation were studied.

Electrosynthesis of zirconium boride from cryolite–alumina melts containing zirconium and boron oxides is studied. A thermodynamic estimate of the synthesis feasibility and cyclic voltammetry data prove that the synthesis involves one stage. Electrolytic ZrB2coatings on nickel are obtained.

Electrosynthesis of hafnium diboride from cryolite-alumina melts containing hafnium and boron oxides is studied. Thermodynamic estimation and voltammetric measurements show this process to occur in one-stage. Hafnium diboride coatings on nickel are obtained by electrolysis.

Powder and coatings of metal-like refractory compounds (MLRC) can be produced by electrochemical synthesis from molten salts. The stoichiometry of the deposited MLRC was found to correlate with the molar ratio of MLRC component ions in the melts. The system Ti–Si–B is of particular interest in terms of electrochemical synthesis since the titanium, silicon and boron potentials in the melt are close together. The electrochemical synthesis has been investigated in the system NaCl–KCl–NaF–K 2 TiF 6 –K 2 SiF 6 –KBF 4 at 700°C. The opportunity of deposition of new ternary compound in the system Ti–Si–B is shown by the electrochemical synthesis from molten salts.

The optimal conditions of electrochemical synthesis of silicon carbide in carbonate melts containing silicon oxide were determined on the basis of thermodynamic calculations and data of cyclic voltammetry.

Titanium diboride is the most perspective material for protection of the cathode lining of aluminum electrolysis cells. One of the possible methods for obtaining a titanium diboride coating is an electrochemical synthesis from cryolite melt containing oxides of titanium and boron. In the present paper the behavior of oxides of titanium and boron in cryolite melt is considered. Coherent coating of titanium diboride has been deposited from the molten system Na 3 AlF 6 -Al 4 B 2 O 9 -CaTiO 3 .

The objective of this work was to study and to develop a method for high-temperature electrochemical synthesis (HTES) of transition metal diboride coating from chlorofluoride melts.

Presented at the NATO Advanced Study Institute, Kas, Turkey, May 4 -14, 2001. Electrochemical synthesis of titanium silicides from chloro-fluoride melts has been investigated by thermodynamic calculation, voltammetry and electrolysis. The electrochemical synthesis of four titanium silicides (TiSi2, TiSi, Ti5Si4, Ti5Si3) was to be a one-step process, the stoichiometry of the deposited silicides being correlated with the concentration of Si and Ti ions in the melt.