Pyrolitic Graphite List
Pyrolitic graphite is a kind of carbon material obtained by chemical vapor deposition. The crystal structure of pyrolitic graphite is composed by stacked hexagonal layers that are consisted of carbon atoms. However, the crystal structure of pyrolitic graphite is not perfect and does not have three-dimensional ordering. Instead, the layers are only parallel stacked, which is called "chaotic layer stacking" structure. The deposition surface of pyrolitic graphite has the appearance of cauliflower-like pattern, and it is composed of numerous small bubbles. When observed under a microscope, it can be seen that the section is composed of many cones. Pyrolitic graphite is a highly anisotropic material. When the test directions change, the mechanical properties, thermal properties, magnetic properties and the others are very different. Pyrolitic graphite has good chemical stability and it is very stable to water, organic solvents and most acids and bases.
Figure 1. A picture of pyrolitic graphite.
Applications:
- Space technology fields: With the advantages of light weight, excellent mechanical strength at high temperature and erosion resistance against high-speed airflow, pyrolitic graphite can be used as the throat lining of rocket nozzle. However, in order to make use of the advantages of this material, many factors should be fully considered in the structural design. In addition, pyrolitic graphite has anti-magnetic suspension effect, which can be used as an attitude control damper component of artificial satellites. It should be noted that the materials used for this purpose need to be made into spheres. The spheres should have uniform mass and a certain thickness to ensure sufficient anti-magnetic force.
- Electronics industry field: The application of pyrolitic graphite to electron tube grid is a new stage in the history of high-power electron tube technology. Compared with traditional molybdenum, pyrolitic graphite grid has good mechanical strength at high temperature and lower secondary electron emission coefficient. In addition, pyrolitic graphite has low expansion coefficient and high thermal conductivity and emissivity, which can withstand higher grid power consumption. Furthermore, coating pyrolitic graphite on a high-purity graphite base can improve the quality of the products and extend the life of the base.
- The others: Pyrolitic graphite can also be used in other fields. Pyrolitic graphite can be used as monochromator for X-ray and neutron diffractometer. Pyrolitic graphite plates can be used as discharge chamber materials for argon ion lasers. In addition, depositing a layer of pyrolitic graphite on atomic absorption spectrophotometer by graphite furnace can greatly improve the sensitivity, accuracy and service life of the analysis.
Production processes:
Pyrolitic carbon is deposited by chemical vapor deposition method of high purity hydrocarbon gas on the matrix of 1800℃- 2000℃ under certain furnace pressure. The hydrocarbon gases used mainly include natural gas, propane, acetylene, carbon tetrachloride, toluene and the others, and the types have little influence on the properties of the products. The matrix is graphite. The quality and the surface processing of the graphite have a significant influence on the quality of the pyrolitic graphite. The heating method mainly includes direct heating method and indirect heating method. The equipment and operation of direct heating method are relatively simple, and it is suitable for laboratory. The indirect heating method is widely used in industry, and it can be divided into resistance and induction heating.
Reference
- Zhangxiong Wu, Wei Li, Yongyao Xia, Paul Webley and Dongyuan Zhao, Ordered mesoporous graphitized pyrolytic carbon materials: synthesis, graphitization, and electrochemical properties[J]. Journal of Materials Chemistry, 2012.
