The natural graphite can be devided into two kinds,one is natural flake graphite powder,and another one is aphanitic graphite powder,the classification is according to the crystallization morphology. The crystal diameter of the graphite >1μm is called natural flake graphite, and it can be seen the crystal structure by naked eye or ordinary microscope;and another type with the crystal diameter of the graphite <1μm,and it’s hard to see the crystal structure under the microscope,so it’s called aphanitic graphite powder,and most aphanitic graphite powder sharp as the earth,so it is also called amorphous graphite.
According to the size of the scale,the flake graphite powder can be classified as different grade,the particle size>+0.3mm,+0.18mm and+0.15mm,it’s called large scale graphite powder,and the size below 0.15mm,it’s called fine scale graphite. The application and value of the large scale graphite is better than the fine graphite,so the industrial utilization value is better.
The dense bulk graphite is evolved from the coalfield,the ore is black colour,and the sharp is dense block. The main composition is graphite,and except for the graphite ,there will be some quartz, mica, limonite, pyrite and some clay minerals. And the fixed carbon is different,from 60%~80%,the lowest is 15% and the highest is 90%. It’s the main types of the aphanitic graphite.
The degree of crystallization,scale size is important to the process performance, industrial value and the use. So the economic value of the flake graphite is higher than the aphanitic graphite,for example,most graphite crucible is made from the large scale graphite,because the strength of the large scale graphite is higher, and the thermal resistance is better,so the service life of the crucible is longer. The fine size graphite powder is hard to process the expanded graphite,the expanded graphite must be made from the large scale graphite powder. However,the aphanitic graphite can be used in the lithium battery,and the performance is better than the large scale graphite powder.
Except for the degree of crystallization,the fixed carbon content is also important to the property of the graphite powder. The content >80% is widely used,and the content <80% can be only used as the casting paint. The fine size high purity graphite can be used as lubricant,but the content of the fixed carbon need to be >99%,the particle size is 2~10μm. The graphite powder used as pencil need a fixed carbon >95%, the particle size should be <10μm,it should be the natural flake graphite.