| In recent years, rare earth oxide-fluoride cell has been improved and optimized. An increase of cell capacity from3kA to lOkA has been achieved. However, parallel and vertical cathode-anode arrangement currently being used shown many drawbacks such as high energy consumption, pollution and cost. The great economic and social benefits would be obtained if the cell with submerged cathode were popularized in rare earth industry. The cell with submerged cathode haven’t been applied to neodymium electrolysis due to active chemical property of rare earth metals, strong corrosive of rare earth fluoride and low solubility of rare earth oxide in electrolyte. Based on the backgroud above, preparation of new electrode material, application feasibility of ceramic material in neodymium electrolysis cell with submerged cathode, physical and chemical properties of NdF3-LiF melt, and cathodic process in neodymium electrolysis were studied and discussed in this paper. These studies have certain significance for improvement of electrolysis process, directing practical production, and design of reduction cell with submerged cathode.Pure TiB2ceramics and TiB2-Ti ceramics were prepared using vacuum hot pressing technique. Chemical reactions occurred during the sintering process were discussed using X-ray diffraction, SEM-EDX and thermodynamic calculation. Microstructure of the material was observed by SEM-EDX, and the effects of content of sintering additive and sintering temperature on microstructure and relative density were discussed. It is noted that sintering temperature would have little effect on density as the samples become considerable dense. It is clear that Ti powder has a great enforcement effect on sintering, and high dense TiB2-Ti samples could be obtained at lower sintering temperature.Wettability of TiB2-Ti ceramics by NdF3-LiF-Nd203melt at1050℃was studied. Real time images of wetting process were observed with a CCD camera, and the results showed that wetting was a dynamic wetting process with characteristics of reactive wetting. Corrosion resistance of TiB2-based ceramics in NdF3-LiF-Nd2O3was studied at1100℃, TiB2-5wt.%Ti exhibits better corrosion resistance than pure TiB2. Thermal shock resistance of TiB2-based ceramics was studied, the results showed that thermal stress resulting from thermal cycling could weaken strength of materials, and addition of metallic titanium could enhance the thermal shock resistance of TiB2-based ceramics. Application feasibility of Si3N4-SiC in neodymium electrolysis was dicussed in this paper, the results showed that existing Si3N4-SiC was diffcult to resist the corrosion comes from NdF3-LiF-Nd2O3melt due to loose binder phase (Si3N4). The results of electrolytic experiment using Al2O3ceramics as cell material showed that NdAl alloy affecting product quality was produced during electrolysis.The liquidus temperature of NdF3-LiF melt was measured by cooling curve. It is found that liquidus temperatue increases with the increasing mole fraction of NdF3. Dissolution of Nd2O3in NdF3-LiF melt and effect of Nd2O3on liquidus temperatue of NdF3-LiF melt were discussed by theory of coordination chemistry and cryoscopic method. Metal dissolution phenomenon in LiF, NaF and NdF3-LiF-Nd2O3melt was discussed by means of XRD, raman spectrum and transparent quartz cell. Thermal conductivity of NdF3-LiF and NdF3-LiF-Nd2O3was measured by the way of steady-state plate and fitted equations suitable for thermal conductivity and temperature from350℃to650℃were obtained.The cathodic process in neodymium electrolysis of NdF3-LiF-Nd2O3was studied by means of electrochemical method, such as cyclic voltammetry and chronopotentiometry. Small-scale cell with submerged cathode was designed for neodymium electrolysis. Unstability of electrolysis in cell with submerged cathode and formation of slag were discussed, and relevant measures have been proposed. |
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