1. Metal crucible production process Neodymium fluoride as a raw material in the production cycle is short of calcium reduction process, product quality and stability. Regardless of whether the reduced or steamed calcium ingots are to be carried out in an intermediate frequency furnace, the equipment investment is high. If the problem of extremely difficult filtration in the wet production process of barium fluoride is solved, the cost of barium fluoride is lower than the cost of barium oxide, and this method necessarily shows its vitality. In order to adapt to electrolysis using barium chloride as a raw material, it is preferable to add magnesium to lower the melting point of the cathode product to be carried out below the melting point of the crucible, thereby reducing the volatilization loss of the chloride electrolyte. This is beneficial for rare earth plants with cesium chloride production capacity. Allegedly this method can satisfy the production of neodymium-iron-boron Nd production requirements. Because of the high oxygen content, when establishing the national standard of cockroaches, it is considered that it is necessary to set a standard product. Experts also believe that chloride is easy to absorb moisture, and the durability of electrolysis is poor, and harmful chlorine gas is released, which is a disadvantage. Thus uncompetitive, individual manufacturers neodymium chloride as raw materials, electrolytic neodymium iron alloys, for self-production of NdFeB, consistency produced by neodymium-iron alloy composition difference. Using cerium oxide as a raw material and fluoride as an electrolyte, molten metal is used to produce metal ruthenium. Because of the high boiling point of the fluoride, the electrolysis can be awakened above the melting point of cerium. The equipment has low investment in equipment and simple process. The technology of the research institutes has been introduced in many places in China. As a result, there have been more productions than sales, competitive exports, loss sales, and shoddy situations, resulting in some units unable to survive. Second, the production of oxide electrolysis (1) Equipment Oxide electrolysis is equipped with a voltage regulator and a rectifier to provide electrolytic DC power. The rectifier is silicon rectified with a maximum output voltage of 36 volts and a current of 3000 amps. There is also a 72 volt output, and two electrolyzers are electrolyzed in series. This not only complicates the main circuit, but also causes difficulties in operation due to different furnace operation conditions, but the advantage is that the temperature rises quickly. We also encounter difficulties in heating in production practice, mainly due to poor conductivity of the electrolyte, and the composition of the electrolyte is easily solved. Otherwise, the temperature is raised, and the electrolysis effect will not be good. The normal electrolysis current of the electrolyzer is more than one thousand ampere and two thousand ampere. The former produces about 30 kilograms of metal per day, and the latter produces up to 50 kilograms per day. (2) Raw materials and electrolytes The cerium oxide is obtained by calcination of oxalate, which can meet the requirements of the national standard. It is proved that the carbon and chloride roots not specified in the national standard must be strictly controlled. If the caustic soda exceeds the standard due to storage, the effect of the solution is not affected. Precipitation with ammonium bicarbonate, burning the obtained cerium oxide, the effect of the solution is not good. The electrolyte uses a NdF 3 -LiF system with different compositions. The fly in the ointment of this electrolyte is that the solubility of NdO 3 is small, about 4%, which brings difficulties to the operation. It is a meaningful foundation work to seek a multi-component electrolyte with a large solubility for Nd 2 O 3 . Barium fluoride and lithium fluoride used as electrolytes tend to cause Si in the metal bismuth to exceed the standard, and quality management should be strengthened. The preparation of NdF 3 is divided into wet method and fire method. If the cesium fluoride can be prepared by wet method directly or slightly pretreatment from the stripping solution, the problem of extreme filtration is breakthrough, and the stripping solution is precipitated with oxalic acid. After calcination to form cerium oxide, and then using a wet method to form cesium fluoride, the production cost will be much lower. Although the preparation of cesium fluoride by fire method is higher and the quality is better, large and medium-sized enterprises are preparing to adopt this method. (3) Electrolyzer and electrode materials The electrolysis cell and anode are processed with graphite . At present, there is no better material than graphite. The cathode is made of molybdenum rod, and the metal crucible is inevitably containing a trace amount of molybdenum. Some manufacturers have changed the use of tungsten rods because of the user's requirements for molybdenum. The product is bound to contain trace amounts of tungsten. NdFeB showed trace amounts of molybdenum or tungsten-containing magnetic influence, as a cathode material is niobium has become the best choice. Because bismuth boron contains a small amount of bismuth, it has a good effect on its performance. (four) electrode process The cerium oxide dissolved in the electrolyte produces ionization: Nd 2 O 3 = 2Nd 3+ + 3O 2- Cathodic process: Nd 3+ +3e=Nd Anode process: 2O 2- -4e=O 2 Oxygen reacts with graphite immediately at high temperature: O 2 +2C=2CO↑ Side reactions can also occur, and they are minimal in quantity. The metal deposited on the cathode is collected in the lower crucible, and the ingot is periodically taken out. The graphite anode should be replaced regularly, and the structural size is adopted to make the processing volume small, the cost is low, the replacement is convenient, and the conductivity is good, which is an actual trick. (5) Operation Operation of furnace, furnace, electrolysis, metal, packaging and other aspects. According to the relationship between the anode and the cathode and the need of heat balance, after the furnace is built, it should be fully roasted before starting. It can be added with pre-melted electrolyte or DC arc furnace. The former requires the addition of chemical equipment, while the latter does not require chemical equipment, but it has an effect on the electrolyte and the electrode is also damaged. In the normal electrolysis stage, electrolysis is maintained within a prescribed temperature and current range, and the desired raw materials are uniformly added. When the electrolysis reaches a sufficient amount of metal in the crucible, the metal ingot is manually removed using a titanium or stainless steel spoon. For a furnace of metal, use several spoons alternately to minimize the contamination of the spoon with metal. According to the national standard, the metal ingot should be less than one kilogram to make the metal easily detach from the metal mold. Not only the form of the mold should be paid attention to, but also the metal is in the expanded state after the ingot is in the expanded state. The electrolyte that is carried out is returned to the electrolytic cell. The electrolyte in the furnace is added to a predetermined liquid level to carry out the next stage of electrolysis. After the product has passed the analysis, it will be packaged into the warehouse. Wrap the metal block in a plastic bag and wrap it in paper. Some manufacturers use a composite plastic bag for vacuum packaging, but the bag may be damaged during handling. Third, some views a. The quality of metal bismuth has been issued the national standard. The relative purity of strontium is two grades of 99% and 95% respectively. Each grade is mainly divided into three grades according to the carbon content. The carbon content of grade A is not more than 0.05%, the carbon content of the B grade is not more than 0.10%, and the carbon content of the C grade is not more than 0.15%. At present, the domestic manufacturers B grade products are about 70%-80%, the rest are mainly C grade products, A grade products are very few, only some manufacturers claim that the products contain less carbon. NdFeB manufacturers generally do not analyze the carbon content of metal ruthenium, but they all hope that the lower the carbon content, the better. So far, there has been no report on the effect of metal lanthanum on the properties of strontium iron and boron. A research unit has done some work in this area, but it has not been published. In the process of NdFeB production, the process itself has carbonation. The conclusion is that the carbon content of the metal ruthenium is about 0.08%, and it is also believed that the NdFeB is not contained in the carbon, but it has an adverse effect on the magnetic properties. The user's pros and cons of the metal crucible is mainly based on whether the permanent magnet material with good performance can be produced. An in-depth and scientific understanding of the quality of metal bismuth, how to further reduce the carbon content remains to be explored. b. Market problems Metal ruthenium is mainly used as raw material for NdFeB (about 30% ammonium). According to relevant information, the domestic production capacity of NdFeB is 800 tons/year. Due to the poor export situation, domestic promotion and application is not enough, the actual annual output is less than 100 tons, making the production capacity of metal bismuth far exceed the demand. Actively promoting the application is extremely important for the production of metal bismuth. Some township and village enterprises, in terms of sales advantages, sell metal crucibles at a low price in order to survive in a limited market. In particular, enterprises with poor power supply conditions, unstable sources of raw materials, and poor quality assurance systems are more difficult to maintain after the tax exemption period. If there is competition, there will be survival of the fittest. The market is weak and the competition is more intense. c. The direction of production improvement to improve quality, reduce costs, improve production conditions, is the improvement direction of metal bismuth production. To do this, we must work hard from the following aspects. 1 The raw material yttrium oxide must not only meet the requirements of the national standard, but also must provide appropriate regulations for the carbon and chlorine content; 2 the silicon content of the electrolyte must be controlled; 3 select the best cathode material; 4 improve the structure of the graphite anode ; 5 to reduce the carbon content of the product; 6 to achieve continuous quantitative feeding; 7 to achieve economies of scale.
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