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Some properties of microcrystalline graphite
Type:News  Time:2011/11/13 20:23:10  Read:

Shen Wanci
Natural graphite is divided into crystalline graphite and microcrystalline graphite, which have different oreforming mechanism. Crystalline graphite is often the metamorphic products of carbon rocks. Crystalline graphite in China is mainly flake graphite, with developed layer structure, and obvious anisotropism. Generally, microcrystalline graphite is the metamorphic products of coal. Because its graphite crystals are fine, ≤1um, each graphite has many crystals with different orientations, with nonobvious anisotropism. At the same time, due to oreforming characteristics, rhombohedral crystals occupy a high proportion in microcrystalline graphite crystal structure, about 20—30%,( flake graphite is commonly 10% ). Therefore, when microcrystalline graphite is used as materials for synthetic diamonds, the conversion rate is higher.
Because microcrystalline graphite has high ore grade, generally c≥50%, microcrystalline graphite in Lutang Plant China can reach 80—90%, the microcrystalline graphite can be used as coating, pencil,steel water carburant directly. Due to oreforming, microcrystalline graphite impurity and ash distribute evenly. Therefore, it is hard to improve grade, and carry chemical purification. After several purifications, its purity could reach 99%.therefore, flake graphite is mainly used in high carbon and high purity graphites.
Recent years, with development of technology, in some occasion, some special superiority of microcrystalline graphite is found. For example,in lithiumion battery cathode materials, mesophase carbon microbeads (MCMB) are prepared by human. The imported MCMB is 30,000 $ /t, and domestic MCMB is 170,000180,000 RMB /t. However, after modification, high purity microcrystalline graphite’s properties are better than MCMB (capacity is 330—350mAh/g,and MCMB is ∽00mAh/g). If flake graphite is used as cathode, due to its anisotropism, the shrinkage rate is high to 10% during charge and discharge period. And it is easy to break and battery life service is short. While shrinkage rate of microcrystalline graphite and MCMB is 3%, so the service time is 3%. In addition, CPT deep graphite emulsion, its some parts can use microcrystalline graphite emulsion only. Moreover, graphite is the main component of stealth coating of military equipments. Due to isotropism , microcrystalline graphite has better photoelectric performance against stealth property. Nuclear energy industry  requires isotropism of graphite, so microcrystalline graphite is the good maerials.
Recent years, Chenzhou refined graphite company and Panshi Hengwei graphite company have developed high temperature putification microcrystalline graphite technology. Adopting 28003050℃ superhigh temperature to evaporate ash and impurity, high purity microcrystalline graphite purity can reach 99%,99.9% and 99.99%. At present, industrialization equipments are designed and produced. It is predicted that largescale products will be produced in 20062007. Guangzhou refined graphite company exhibited the new products in Canton Fair, which attracted foreign attention. The foreigners quoted 99%C,20,000 RMB/t, 99.9%C,40,000 RMB /t,99.99%C,80,000 RMB /t. While ore raw materials are just hundreds of RMB/t.But we should pay attention that, our country’s microcrystalline graphite deserves are not very rich. And recent years, people exploit mines casually and burn graphite as buring coal. Our microcrystalline graphite proved reserves are 50 million tons but recent 20 years, nearly 20 million tons have been exploited, and prospective reserves are only 100 million tons, occupying 1/10 of world total reserves. The exploited amounts are 11.5 million tons every year. If this conditions continue, we will have no microcrystalline graphite resources in several decades, lacking an important strategic resource.
( compararison: China’s flake graphite proved reserves are 170 million tons, and world total amounts are 230 million tons;prospective reserves are 400 million tons,and world are 700 million tons.300,000400,000 tons are exploited every year, and 400,000500,000 tons are exploited in recent years.)
From perspective of resource protection, protection of microcrystalline graphite is very serious. Chinas annual export amounts of microcrystalline graphite (ore and ore processing products) are 250,000350,000 tons( price is only hundreds of yuan every ton). The developed country used microcrystalline graphite for deep processing or strategic reserves. If it is not limited, our country’s strategic resources will run out and the potential enemy will become stronger.
【Some properties of microcrystalline graphite】
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