Although domestic and foreign production of high purity graphite production process is similar, but there are still differences, are as follows:
(1) China’s production process is complex, baking and impregnation need to be repeated in order to achieve production targets. This makes the production cost high and the yield is low.
(2) purification methods, purification of graphite methods are mailly flotation, alkali acid, hydrofluoric acid, chlorination roasting, high temperature and so on. Flotation is the use of graphite floatability of the graphite enrichment purification, graphite ore by floatation after the final concentrate grade is usually about 90%. Alkaline purification of graphite is the principle of graphite impurities such as silicates, quartz and sodium hydroxide and chemical reaction, and then washed to achieve the purpose of de-silicon; some, such as metal oxide impurities, leaching with acid, and then filtered , And the washing was separated from the graphite. Alkali acid method can get graphite products with fixed carbon content of 99% or more. Hydrofluoric acid is the use of impurities in graphite and hydrofluoric acid reaction of water-soluble fluoride and volatiles to achieve the purpose of purification. Japan, France and other countries have introduced a patent with ammonium bifluoride or ammonium fluoride and 93% of the carbon content of graphite powder reaction, the fixed carbon content of graphite can be increased to 99.95%. Chlorination roasting method is to add a certain amount of graphite powder reducing agent, in a certain temperature and the specific atmosphere of roasting, and then through the chemical reaction of chlorine, so that the material into a low boiling point of the liquid metal vapor phase or condensed phase Of the chloride and complexes and escape, so separated from the rest of the components, to purify the purpose of graphite. Generally, the purity of the graphite is greater than 98%. The use of high-temperature method is due to the nature of the boiling point of graphite is one of the highest material, melting point (3850 ± 50) ℃, the boiling point of 4500 ℃, while the boiling point of silicate minerals are at 2750 ℃ (quartz boiling point) the following, the graphite of the boiling point of the highest in the nature of the material, The boiling point is much higher than the boiling point of the impurity-containing silicate, thereby removing the impurities. High temperature method is generally heated to 2700 ℃ or more, the carbon content of graphite products can reach more than 99.99%. For each of the above methods, each method has its own advantages and disadvantages, domestic and foreign enterprises select the appropriate purification method., according to their characteristics and purity of raw materials requirements,
(3) different molding technology, at present, the major domestic high-purity graphite production enterprises, mainly used is cold isostatic pressing, cold isostatic pressing graphite powder can be compacted to make the density distribution, anisotropic coefficient is small And other advantages. Foreign enterprises, is used in hot isostatic pressing, it is a process in high temperature and high pressure at the same time, so that the material subjected to static pressure of the technology, not only to improve the compactness of a lot of compact, but also save time and improve efficiency .
(4) different graphitization process, at present, the vast majority of enterprises in China is using Graphite Acheson graphite furnace, while the foreign use more heat within the graphite furnace. Acheson method is characterized by the furnace into the calcined products and resistance material (coke) together constitute the furnace resistance, power after the temperature of 2000 ~ 3000 ℃ to make the roasted graphitization. Because of this furnace is characterized by simple structure, durable, easy maintenance, is currently widely used in China’s industrial graphite furnace. However, this kind of furnace has too much energy consumption, the quality of graphitized products is unstable, uneven, volatile, harmful gas is difficult to recover, dust and other shortcomings, the current industry to use more heat within the series Graphitization furnace. The “inner string” graphitizing furnace is a kind of furnace which does not use the resistance material, and the current flows directly through the electrode column which is vertically connected by several roasting products to produce high temperature to make the calcined product graphitized.
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