Carbon used for mechanical seals are mainly divided as following types:
1) Resin carbon: resin carbon can be divided into hard resin carbon and soft-electronic carbon. The impregnated stuff are: organic resin, inorganic and metals. Talbe 3-27 and talbe 3-28 shows the code and performance of the carbon used for mechanical seals.

2) Hot pressed resin: crush the carbon after it was sintered, use phenolric resin or epoxy resin as the bonding agent，after mixed the carbon and phenolric resin or epoxy resin then press and sinter to make the final product. But it is poor at heat spread, higher coefficient of linear expansion, it can be applied for large scale production, lower costs, maily used in lower burthen mechanical seals such as water cooling pump, household appliance etc.

3) Pyrolytic carbon: the pyrolytic carbon made in China is produced by the process that pyrolytic the hydrocarbon such as propylene at the high temperature，make the carbon steam infiltrate into air hole of porous body of carbon to full in the air hole, that will lead the carbon became high density, less air hole，poor permeability to air. It can be used to the high temperature, strong corrosive environment, but it is not suitable to used in large scale production, so it’s cost will be higher if it is used as the material.