Low-Melting CaCl2-NaCl-Al2O3 Electrolyte for Direct Electrochemical Reduction Solid Al2O3

Abstract

Abstract:The electrical conductivity and density of the low-melting CaCl 2 -NaCl-Al 2 O 3 systems at 550°C~800°C ranges were respectively measured by the Continuously Varying Cell Constant Technique, ac-techniques and Archimedes method. The materials were applied as the electrolyte for the direct electrochemical reduction solid Al 2 O 3 at 550°C ~800°C. The materials were composed of 71wt.%~87wt.%CaCl 2 (corresponding NaCl), NaCl and Al 2 O 3 (without and saturated). The results showed that additive Al 2 O 3 decreased the electrical conductivity of the materials, and resulted in the increase of activation energy of conductance. The functional relationship between the electrical conductivity and temperature was linear, and conformed to the Arrhenius equation. Increasing the CaCl 2 content decreased the electrical conductivity of the materials, but the density was increased. Increasing the CaCl 2 , the decrease scope of the electrical conductivity was small and the increase trend of the density was slowed down, the influence of increasing the content of CaCl 2 in systems on the direct electrochemical reduction solid Al 2 O 3 process is smaller. The temperature was a decisive factor on the electrical conductivity of the electrolytes and electrolysis process.

Compatibility Issues of Yttria‐Stabilized Zirconia Solid Oxide Membrane in the Direct Electro‐Deoxidation of Metal Oxides

“…). Addition of yttria in salt perhaps decreases the electronic conductivity in salt, preventing the electrochemical reduction of zirconia and thereby microchannels are not developed inside the membrane.…”

Compatibility of SiC--and MAX phase-based ceramics with a KNO3-NaNO3 molten solar salt

“…Similar to SiO2, Grambalova et al [33] reported that K + -and Na + -based molten salts interact chemically with Al2O3. Treatment of Al2O3 with a CaCl2-NaCl containing electrolyte leads to the electrochemical reduction of Al2O3, which becomes stronger at higher concentrations of NaCl [36]. Lee et al [37] reported that the native aluminium oxide film on Al dissolves faster in contact with more basic solutions that contain more Na + salts.…”

Electrolytic Reduction of Solid Al2O3to Liquid Al in Molten CaCl2

“…Meanwhile, electrolytic reductions of various kinds of solid oxides in CaCl 2 and/or CaCl 2 -based molten salts have been investigated by many researchers in the last two decades. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Fray et al reported the direct electrolytic reduction of TiO 2 pellets in a CaCl 2based melt, known as the FFC Cambridge process. [1][2][3][4][5][6] This process has the potential to replace the conventional Kroll process for producing Ti metal, owing to its simple system and relatively low temperature.…”

“…For the electrochemical reduction of Al 2 O 3 , there have been several studies conducted in CaCl 2 -based melts. [13][14][15][16][17] Yan investigated the reduction of Al 2 O 3 tube using a Nb box-type cathode in molten CaCl 2 -NaCl at 1173 K. 13 In this study, Al-rich Al-Ca alloy droplets with 84.9-98.4 at%Al was obtained. Yan and Fray also reported the electrochemical reduction of Al 2 O 3 in CaCl 2 -LiCl at 973 K and CaCl 2 -NaCl at 1173 K. 15 They reported that calcium aluminate was formed as an intermediate product during the electrolysis.…”

“…Yan and Fray also reported the electrochemical reduction of Al 2 O 3 in CaCl 2 -LiCl at 973 K and CaCl 2 -NaCl at 1173 K. 15 They reported that calcium aluminate was formed as an intermediate product during the electrolysis. Xie et al 14,16 also reported that Al droplets were obtained by the electrochemical reduction of Al 2 O 3 in molten CaCl 2 -NaCl at 823 K 14 and at 1073 K. 16 However, the purity of Al droplets was not clear. In all above studies, because they used a two-electrode system, the reaction mechanism, including the relations between the electrode potential and the formation phase, has not been clarified yet.…”