China is rich in rare earth resources. At present, rare earth molten salt electrolysis is used for large-scale industrial production of rare earth metals and their alloys. Graphite refractories have been widely used in rare earth metal electrolysis. The rare earth molten salt electrolysis method is mainly divided into two major systems, one is the rare earth chloride system; the other is the rare earth oxide-fluoride system.
When using rare earth chloride electrolysis, usually dehydrated potassium chloride is used as an electrolyte, and the final product is finally obtained through electrolysis-peeling-cleaning and other steps, but this method is gradually eliminated because of its limitations. The main reason is the rare earth chloride The electrolysis method is only suitable for rare earth metals with a low melting point, and has high energy consumption and large device losses. At the same time, a large amount of chlorine gas is produced during the production process, which causes serious environmental pollution.
At present, the rare earth oxide-fluoride system electrolytic preparation of rare earth metals has made great progress: rare earth oxides as solutes, lithium fluoride or barium fluoride as additives, under the action of an electric field, rare earth metal cations move to the cathode and discharge, precipitation Rare earth metal; graphite material is used as the anode, the primary electrolysis product is carbon dioxide, carbon dioxide reacts with the graphite electrode and graphite lining, and the final products are carbon dioxide and carbon monoxide. Rare earth electrolysis cell is the main equipment used for producing rare earth metal by molten salt electrolysis.
At present, the electrolytic cells are all round graphite cells, and each has advantages and disadvantages: the bottom of the electrolytic cell has pits, high current efficiency, but the bottom is easy to accumulate electrolyte and the electrolyte circulation is poor; , The bottom is not easy to accumulate, but the current efficiency is low due to the frequent release of materials. China has become a major producer and supplier of rare earth metals in the world. Large-scale production of rare earth metals has become a demand and a trend. In order to use and develop more 10,000-ampere electrolytic cells in recent years, the device is relatively more complicated in structure than before and requires relatively high material requirements in all aspects.
At present, when using rare earth oxide-fluoride system for electrolysis, the fluoride molten salt will ionize out fluoride ions under high temperature conditions, which is very corrosive to the equipment. Therefore, the choice of the lining of the electrolytic cell and the anode material is extremely important. Traditional industrial refractories are not suitable for rare earth electrolyzers because they are difficult to resist fluoride ion attack. Chen Dehong et al. Studied the application and effect of SiC-Si3N4 complex phase refractories in rare earth electrolyzers. The results showed that SiC-Si3N4 complex phase refractories were severely eroded in the rare earth molten salt, and cracking occurred in the sheet. Corroded by fluoride ions, and silicon carbide can resist fluoride ion erosion in the material system. At present, the most commonly used anode and lining materials are graphite, which has various forms. In addition to considering the excellent electrical conductivity and corrosion resistance of graphite, some additives are added to enhance the strength of graphite and improve the oxidation resistance of graphite. . Graphite has its own relative advantages as a rare earth electrolytic cell lining. However, in the early electrolytic cell accident, the lining structure was damaged due to the oxidation of the graphite material, which led to the occurrence of production accidents. , Increasing production costs and energy consumption, restricting the development of rare earth molten salt electrolysis, therefore, the development of new lining materials is essential.
At present, there are relatively many studies on graphite anode materials, especially in terms of improving the oxidation resistance of graphite anodes and prolonging the service life of graphite anodes. Liu Zhongxing et al. Studied the corrosion process of graphite anode surface and found that the fluoridation corrosion reaction, and the oxidation caused the graphite to corrode seriously; Hou Fusheng et al. Applied an anti-oxidation coating on the graphite anode to improve the oxidation resistance of graphite. However, there are few studies on the lining of electrolytic cells. In view of the current use of graphite lining, a new high temperature resistant material system is urgently needed to support the development of high efficiency, low cost and low energy consumption in the rare earth industry, and the development of new high temperature resistant and resistant Fluoride erosion, good oxidation resistance and high strength materials are particularly urgent.