Pure carbon graphite is used for seals it will usually be impregnated with other materials that are provided to variously improve the sealing ,by reducing porosity ,improve the wear performance or increase strength. It is widely used, being one of the face pair on the vast majority of mechanical seals, but also found as the most popular material for segmented circumferential seals and for piston rings in dry or marginally lubricated conditions.
It has the advantage of being a comfortable material with good dry running properties, wide temperature range and extensive chemical resistance. It is superior with respect to temperature ,chemical compatibility range and recovery from transient upset ,with the ability to re-establish a carbon transfer film.
Seal carbons are then impregnated to improve the properties. It is very common to impregnate the seals with synthetic resin to convert the porous structure into a low permeable material. Higher duty materials can be impregnated with metal which can provide an increase in the hardness and strength together with improved conductivity. A popular metal impregnated for seal carbons is antimony. It is important for the metal to also have good bearing properties. The temperature limit of the finished carbon component is usually dictated by the manufacturing process and impregnants that may be used. This will be for instance the limit of the resin bonded or impregnated materials and the 'wiping' temperature of a bearing metal. For non-impregnated grades the short-term limit of carbon graphite material is up to 350 Degrees C. and up to 500 Degree C. for graphitized material.