Liyu Chen,Jiaxin Yang,Youjian Yang,Jiangyu Yu,Xianwei Hu,Wenju Tao,Zhaowen Wang
The fluorine salt system is a potential electrolyte for the preparation of metals and alloys from metal oxides via molten salt electrolysis. The solubility of ZrO 2 in KF–AlF 3 –Al 2 O 3 molten salts (KF/AlF 3 molar ratio = 2.1–2.8, Al 2 O 3 content = 0–9 wt%) was measured using the isothermal saturation method in this study. The influence of temperature and electrolyte composition on ZrO 2 solubility was analyzed. The dissolution mechanism of ZrO 2 was then determined based on the analysis of X–ray diffraction and Raman spectroscopy results. The experimental results show that the solubility of ZrO 2 in the 2.4KF–AlF 3 molten salt at 1233 K could reach up to 6.62 wt%. Besides, the solubility of ZrO 2 increase with the increase of temperature, the decrease of KF/AlF 3 molar ratio and Al 2 O 3 content. X-ray diffraction and Raman spectroscopy analyses show that the dissolved ZrO 2 in KF–AlF 3 molten salts existed in the form of [Zr 2 O 2 F 6 ] 2− and [ZrF 6 ] 2− complex ions under melting and cooling conditions, respectively. And the dissolution process of ZrO 2 in KF–AlF 3 molten salts can be described using a mass transfer control model.
In this study, Al–Si alloy, a precursor of the solar-grade silicon , was prepared via the aluminothermic reduction–molten salt electrolysis of SiO 2 in KF–AlF 3 molten salt by employing liquid aluminum as the working cathode. The reaction mechanism of the aluminothermic reduction of SiO 2 in KF–AlF 3 molten salt at 750 °C was determined by thermogravimetry–differential scanning calorimetry. The reaction rate equation for the aluminothermic reduction of SiO 2 in KF–AlF 3 molten salt was: d α dt = 7.156 × 10 24 e − 4.688 × 10 5 RT ( 1 − α ) 1.734 . In 49.4 wt% KF–47.6 wt% AlF 3 –3 wt% SiO 2 molten salt at 750 °C, the Si content in the Al–Si alloy obtained by the aluminothermic reduction–molten salt electrolysis of SiO 2 was 24.53 wt%. Compared with solely aluminothermic reduction of SiO 2 , the current efficiency in the process of the aluminothermic reduction–molten salt electrolysis of SiO 2 was evaluated. The results reveal that the Al–Si alloy is predominantly prepared in the aluminothermic reduction step, while supplemented by electrolysis. The calculated Faradic current efficiency of the proposed aluminothermic reduction–molten salt electrolysis process was 28.4%.
Yifan Zhang,Xianwei Hu,Jiaxin Yang,Liyu Chen,Wenju Tao,Fengguo Liu,Zhongning Shi,Zhaowen Wang
Aluminum-vanadium intermediate alloy is a significant raw material for the fabrication of high-performance titanium alloys . In the present study, the electrochemical behavior of NaVO 3 on a solid molybdenum and liquid aluminum electrode is systematically investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV) in the NaF-KF-AlF 3 molten salt and the formation mechanism of Al-V intermetallic compounds is emphatically analyzed. The results show that the electrochemical reduction of VO 3 − on the solid molybdenum electrode is a multi-step process and low-valence vanadium oxide (V 2 O 3 ) is obtained. In contrast, the electrochemical reduction of VO 3 − to V 2 O 3 on liquid aluminum electrode is through one-step process and the deposition potential is more positive than that on molybdenum electrode owing to the depolarization effect of the liquid aluminum electrode. In addition, Al-V intermetallic compounds are obtained on the liquid aluminum electrode by potentiostatic electrolysis. The reduction process of VO 3 − on the liquid aluminum electrode is described as: the electrochemical process is started by the direct electro-reduction of VO 3 − to V 2 O 3 , which is further converted to Al-V intermetallic compounds under the combined effect of electrochemical and aluminothermic reduction, with the latter playing a dominant role.
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