Pyrolytic graphite is a new type of carbon material made from hydrocarbons or steam as raw material, which is decomposed at high temperature and precipitated on the surface of substrate. The structure and performance of pyrolytic graphite are directly related to the pyrolysis temperature, where the product of pyrolysis at a temperature of 800-100℃ is called pyrolytic carbon; pyrolysis at a temperature of 1400-2000℃ or a higher temperature is called pyrolytic graphite.
Pyrolytic graphite is a product of high-temperature chemical vapor deposition, and is now mostly heated by medium-frequency induction (or heated by choke-type graphite heater), and the vacuum furnace is the main equipment for manufacturing pyrolytic graphite. Graphite heaters are set up inside the induction ring, graphite sleeve built-in deposition substrate, they are heated by induction.
When starting, the air in the furnace is removed first, and the vacuum degree reaches below 133.3-266.3Pa, and then the electricity is sent to raise the temperature. When the substrate reaches the specified deposition temperature, a mixture of nitrogen and hydrocarbon gases mixed in a certain proportion is fed for pyrolysis. In this process, the vacuum pump continuously pumps out the exhaust gas, while the mixture is constantly rationed input, after a certain period of time after the precipitation, the pyrolysis of carbon layer with a specified thickness is obtained. The whole plant is divided into four systems: gas supply, heating, exhaust and monitoring.
The raw materials for pyrolysis can be natural gas, liquefied petroleum gas, coal gas or benzene and toluene vapor. The dilution carrier can use nitrogen, argon, hydrogen, etc. to control the deposition rate and density. The substrate can be made of refractory metals such as tungsten, molybdenum, tantalum, etc. or lump graphite, and for pyrolytic carbon products for semiconductors and electronics technology, high-purity graphite should be used as the substrate. The substrate must be finely machined and polished to facilitate demolding, and the corners should be rounded as much as possible to reduce the internal stress of pyrolytic carbon.
During the deposition process, the three main parameters, temperature, pressure, and gas flow, should all strive to stabilize. The deposition time, on the other hand, is determined by the desired pyrolysis layer thickness. The optimum choice of these parameters needs to be more dependent on the use and nature of the pyrolyzed graphite.