High-temperature containers and other free standing products: Containers and other free standing parts are produced by depositing the pyrolytic carbon or graphite onto a graphite mandrel. After the deposition is completed, the mandrel is removed, usually by machining.
It is difficult to deposit pyrolytic graphite in shapes have sharp radii without interlayer delaminations. These delaminations are caused by the stresses generated by the considerable differences in the thermal expansion in the ab and c directions which can overcome the low interlaminar shtrength. These delaminations do not occur with isotropic pyrolytic carbon.
Common applications of pyrolytic graphite are:
– Boats, and crucibles for liquid-phase epitaxy.
– Crucibles for molecular-beam epitaxy.
– Reaction vessels for the gas-phase epitaxy of Ⅲ-Ⅴsemiconductor materials such as gallium arsenide.
– Trays for silicon-wafer handing.
Free-standing isotropic pyrolytic carbon ias a material of choice for solid propellant rocket nozzles. Because of its strength, hardness, and isotropic nature, it is able to withstand the mechanical erosion which is the dominant failure mechanism above 3200C.
Resistance-heating elements: Because of its good electrical characteristics and refractoriness, pyrolytic graphite is used extensively for high-temperature resistance-heating elements. In combination with pyrolytic boron nitride, it provides an integrated heating system in which the graphite is the resistive element and PBN the insulating substrate. Bothe materials are produced by CVD. The product is used as a source heater in metal evaporation and semiconductor epitaxy, as a substrate heater in thin-film deposition, as a melt heater for crystal growth, and in other applications.
Nuclear applications: Isotropic pyrolytic carbon exhibits excellent stability under neutron irradiation. This, coupled with its high strength, dense isotropic structure, and impermeability to gases, makes it the material of choice for the coating of nuclear fission particles to contain the fission products. The coating is produced in a fluidized bed.