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Jomar Thonstad - One of the best experts on this subject based on the ideXlab platform.

  • A Novel Method for Investigating Solutions of Aluminum in Molten Cryolite
    Metallurgical and Materials Transactions B, 2012
    Co-Authors: Ernest W. Dewing, Trond E. Jentoftsen, Odd-arne Lorentsen, Geir M. Haarberg, Jomar Thonstad
    Abstract:

    In chronopotentiometric work on Fe^2+ in a Cryolite melt (Jentoftsen et al . in Metall. Mater. Trans. B , 2012, vol. 43B, pp. 869–74), after depletion of Fe^2+ at the surface of the iron cathode was complete, continuing electrolysis produced a solution of Al in Cryolite, provided that the time was less than a few hundred milliseconds. Potential–time curves indicate a diffusion-controlled, 2-electron reduction to form monovalent aluminum.

  • Determination of sulphur species in solidified Cryolite melts
    Chemical Papers, 2012
    Co-Authors: Marta Ambrová, Pavel Fellner, Jana Jurišová, Jomar Thonstad
    Abstract:

    Solidified Cryolite melts containing a known amount of Na_2SO_4 (0–713 mg kg^−1 SO _4 ^2− ), Na_2S, FeS, and CdS (0–400 mg kg^−1 S^2−) together with industrial electrolyte samples were tested for the content of sulphate and sulphide ions by ion chromatography. Added and analytically determined contents of sulphate and sulphide were compared and processed by means of linear regression analysis. It was found that the method of ion chromatography yields satisfying results (uncertainty below 1.1 %) and that it is especially suitable for the determination of low content of soluble sulphate or sulphide in solidified Cryolite electrolytes. The method can be used for the estimation of insoluble sulphide content in Cryolite melts as well. Results of industrial samples analysis showed that the content of sulphate and sulphide in the samples is influenced by their treatment before the analysis.

  • Solubility of AlPO4 in Cryolite melts
    Thermochimica Acta, 2006
    Co-Authors: Elke Willam Thisted, Geir Martin Haarberg, Jomar Thonstad
    Abstract:

    Abstract The solubility of aluminium orthophosphate in Cryolite melts was determined. Part of the binary phase diagram of the system Na 3 AlF 6 –AlPO 4 was investigated. The eutectic point was determined to be at 43.7 mass% (or 57.2 mol%) AlPO 4 and (696 ± 1) °C. It is suggested that in pure molten Cryolite melts the orthophosphate ion dissociates partly into a metaphosphate ion and an oxide ion.

  • content of sodium and lithium in aluminium during electrolysis of Cryolite based melts
    Journal of Applied Electrochemistry, 1998
    Co-Authors: Vladimir Danielik, Pavel Fellner, Jomar Thonstad
    Abstract:

    The content of sodium and/or lithium in polarized and nonpolarized aluminium in contact with Cryolite melts was determined in a laboratory cell. The Cryolite-based melts contained 0 to 20mass% excess AlF3 and 0 to 2.5mass% LiF. The cathodic current density ranged from 0 to 0.5Acm−2. The lithium content in aluminium increases linearly with increasing concentration lithium fluoride in the␣melt. It also increases with increasing cathodic current density and decreasing Cryolite ratio. On the other hand the sodium content decreases with increasing concentration of LiF in the melt. This effect is more notable at higher current densities.

  • On the behaviour of tin-containing species in Cryolite–alumina melts
    Journal of Applied Electrochemistry, 1997
    Co-Authors: J. H. Yang, Jomar Thonstad
    Abstract:

    Tin oxide (SnO2) dissolves in Cryolite–alumina melts forming tetravalent tin species, but under reducing conditions it is reduced to divalent tin and, further, to metallic tin. Freezing point depression data for SnF2 and SnO in molten Cryolite (Na3AlF6) corresponded to the formation of one and two new particles, respectively. By anodic dissolution of tin into Cryolite-alumina melts divalent as well as tetravalent tin was formed, depending on current density and composition. During electrolysis of SnO2-based oxygen-evolving anodes, the condensate above the melt contained both divalent (SnF2) and tetravalent (SnO2) tin species.

Mansoor Barati - One of the best experts on this subject based on the ideXlab platform.

  • charge transport properties of Cryolite silica melts
    Electrochimica Acta, 2012
    Co-Authors: Samira Sokhanvaran, Sridevi Thomas, Mansoor Barati
    Abstract:

    Abstract Electrodeposition of silicon from a Cryolite based electrolyte at a relatively low temperature is a promising approach to generate high purity silicon. In order to obtain fundamental data pertaining to electrowinning of silicon from Cryolite–SiO 2 melts, charge transport properties of the melt such as conductivity and electronic and ionic transference numbers were measured. Each property was determined for a range of temperatures and SiO 2 contents. It was found that addition of silica to Cryolite generally decreases the transport rate of charge carriers. The temperature on the other hand had a positive effect on the electronic and ionic conductivities. The variations arise from the structural changes in the melt, particularly formation of complex ions involving Na, Si, and Al.

  • Charge transport properties of Cryolite–silica melts
    Electrochimica Acta, 2012
    Co-Authors: Samira Sokhanvaran, Sridevi Thomas, Mansoor Barati
    Abstract:

    Abstract Electrodeposition of silicon from a Cryolite based electrolyte at a relatively low temperature is a promising approach to generate high purity silicon. In order to obtain fundamental data pertaining to electrowinning of silicon from Cryolite–SiO 2 melts, charge transport properties of the melt such as conductivity and electronic and ionic transference numbers were measured. Each property was determined for a range of temperatures and SiO 2 contents. It was found that addition of silica to Cryolite generally decreases the transport rate of charge carriers. The temperature on the other hand had a positive effect on the electronic and ionic conductivities. The variations arise from the structural changes in the melt, particularly formation of complex ions involving Na, Si, and Al.

George Kaptay - One of the best experts on this subject based on the ideXlab platform.

Samira Sokhanvaran - One of the best experts on this subject based on the ideXlab platform.

  • charge transport properties of Cryolite silica melts
    Electrochimica Acta, 2012
    Co-Authors: Samira Sokhanvaran, Sridevi Thomas, Mansoor Barati
    Abstract:

    Abstract Electrodeposition of silicon from a Cryolite based electrolyte at a relatively low temperature is a promising approach to generate high purity silicon. In order to obtain fundamental data pertaining to electrowinning of silicon from Cryolite–SiO 2 melts, charge transport properties of the melt such as conductivity and electronic and ionic transference numbers were measured. Each property was determined for a range of temperatures and SiO 2 contents. It was found that addition of silica to Cryolite generally decreases the transport rate of charge carriers. The temperature on the other hand had a positive effect on the electronic and ionic conductivities. The variations arise from the structural changes in the melt, particularly formation of complex ions involving Na, Si, and Al.

  • Charge transport properties of Cryolite–silica melts
    Electrochimica Acta, 2012
    Co-Authors: Samira Sokhanvaran, Sridevi Thomas, Mansoor Barati
    Abstract:

    Abstract Electrodeposition of silicon from a Cryolite based electrolyte at a relatively low temperature is a promising approach to generate high purity silicon. In order to obtain fundamental data pertaining to electrowinning of silicon from Cryolite–SiO 2 melts, charge transport properties of the melt such as conductivity and electronic and ionic transference numbers were measured. Each property was determined for a range of temperatures and SiO 2 contents. It was found that addition of silica to Cryolite generally decreases the transport rate of charge carriers. The temperature on the other hand had a positive effect on the electronic and ionic conductivities. The variations arise from the structural changes in the melt, particularly formation of complex ions involving Na, Si, and Al.

Sergei V. Devyatkin - One of the best experts on this subject based on the ideXlab platform.

  • Electrochemical Behavior of Titanium, Silicon and Boron Oxides in Cryolite-Alumina Melts
    2010
    Co-Authors: Sergei V. Devyatkin, Alexander Pisanenko, A.yu. Sarychev
    Abstract:

    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:

  • Physical, Chemical, and Electrochemical Behavior of Boron Oxide in Cryolite-Alumina Melts
    Russian Journal of Applied Chemistry, 2002
    Co-Authors: Sergei V. Devyatkin, George Kaptay
    Abstract:

    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.

  • Chemical and Electrochemical Behavior of Titanium Diboride in Cryolite-Alumina Melt and in Molten Aluminum
    Journal of Solid State Chemistry, 2000
    Co-Authors: Sergei V. Devyatkin, George Kaptay
    Abstract:

    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 .