Why can coke materials such as petroleum coke be converted into graphite, and what conditions are required for conversion? Understanding this problem is instructive for mastering the graphitization production process of graphite sheets.
Graphite is crystalline carbon, while general coal is amorphous carbon - amorphous carbon. Here we further introduce the differences in microstructure between the two.
It can be seen by observing natural graphite with an electron microscope that graphite is a multi-layered laminated crystal of hexagonal ring-shaped sheets between carbon atoms. There is a certain arrangement order between the middle layers of the lamellar body of this crystal. One corner of the hexagonal ring in the upper layer of lamellar body is located at the center of the hexagonal ring of the adjacent layer of lamellar body. The first layer is completely symmetrical with the third layer, and the second layer is completely symmetrical with the fourth layer. The adjacent layers are completely symmetrical with each other. The distance is 3.354 Angstroms (Note Angstrom is the unit for measuring the wavelength of visible light waves, which is equal to one hundred millionth of 1 centimeter, that is, A=10_8 centimeters). The distance between two adjacent carbon atoms in each hexagonal ring structure of the sheet body is 1.42 Angstroms.
From a chemical point of view, readily graphitizable carbons such as petroleum coke and pitch coke are complex organic polymer compounds with aromatic hydrocarbon condensed rings as the basic structural unit. Due to the different coking temperatures, the molecular weights of these polymer compounds are also different.
They have common characteristics, that is, the higher the coking temperature, the greater the molecular weight, and the polymer compounds with aromatic hydrocarbon condensed rings as the basic structural units first develop in the plane direction when forming macromolecules. At the calcination temperature, although this polymer compound with aromatic hydrocarbon condensed rings as the basic structural unit continues to merge in the plane direction, the molecular weight becomes larger and larger, and elements such as hydrogen, oxygen, and nitrogen gradually decrease.
However, there is no regular overlapping arrangement among many planar macromolecules. Although some are already entering an arrangement state, the distance between the layers of planar macromolecules is large, so they do not exhibit the physical properties of natural graphite.