Is Pyrolytic Graphite Used in House Insulation?

Formation of Pyrolytic Graphite

• Pyrolytic graphite is produced by chemical vapor deposition or CVD. Hydrocarbon gases such as liquid benzene or methane are heated in the presence of a heat-resistant form of mandrel. For pyrolytic graphite production, this form is usually made of commercial or sintered graphite. The gas molecules are broken up by the hot surface of the heated form. This process is called pyrolysis. Carbon molecules are deposited from the pyrolyzed gas as a thin film over the form. Sometimes, many layers are deposited. Depending on how the pyrolytic graphite is to be used, it can be left as a coating on the form, or it can be removed and further treated.

Thermal Conductivity

• Pyrolytic graphite sheets are used as a heat sink in electronics because of high thermal conductivity. The conductivity is twice as high as copper and three times as high as aluminum. Sheets can be bent or cut to fit into small spaces. They are used in products like personal computers, mobile phones, DVD players, digital cameras and optical communications devices, because they conduct heat away from where it is generated. The thermal conductivity of pyrolytic graphite is what first drew attention to this material in the 1950s as a possible heat shield material when the Intercontinental Ballistic Missiles were being developed. Pyrolytic graphite is used for temperature resistant brakes and clutch plates in aircraft and also as shielding and cladding in rockets.

Anti-magnetic Properties

• Pyrolytic graphite demonstrates an anti-magnetic property. It is termed a diamagnetic material, because it repels magnetic fields. A thin piece of a pyrolytic graphite sheet can be suspended a few millimeters above a set of four neodymium magnets. The sheet seems to float or levitate, and needs no energy source, remaining there indefinitely. However, the graphite sheet changes position if external disturbances occur. This technology is incorporated into sensing devices that detect tilt or vibrations.

Other Uses

• A coating of pyrolytic graphite renders items non-reactive to other molecules, so it can be used to coat nuclear fission particles in nuclear reactors as well as in nuclear reactor guiding tubes for fuel rods. Medicine uses a pyrolytic graphite coating on implants, such as joint replacements and other prosthetic devices, and in implanted devices, such as heart flaps and valves. Dental implants also receive pyrolytic graphite coatings.