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Pyrolytic carbon is a material similar to graphite, but with some between its graphene sheets as a result of imperfections in its production.
Pyrolytic carbon is man-made and is thought not to be found in nature.Ratner, Buddy D. (2004). Pyrolytic carbon. In Biomaterials science: an introduction to materials in medicine. Academic Press. p. 171–180. . Google Book Search. Retrieved 7 July 2011. Generally it is produced by heating a hydrocarbon nearly to its decomposition temperature, and permitting the graphite to (pyrolysis).
One method is to heat in a vacuum, producing carbon fibers.
It is used in high temperature applications such as missile , rocket motors, heat shields, laboratory furnaces, in graphite-reinforced plastic, coating nuclear fuel particles, and in biomedical prosthesis.
It was developed in the late 1950s as an extension of the work on refractory vapor deposition of metals.
Pyrolytic graphite forms with controlled mosaicities up to a few degrees.
Pyrolytic graphite is also more diamagnetic (χ = −4×10−4) against the cleavage plane, exhibiting the greatest diamagnetism (by weight) of any room-temperature diamagnet. In comparison, pyrolytic graphite has a relative permeability of 0.9996, whereas bismuth has a relative permeability of 0.9998 (table).
With the easy availability of rare-earth permanent magnets developed in the 1970s and 1980s, the strong diamagnetism of pyrolytic graphite makes it a convenient demonstration material for this effect.
In 2012, a research group in Japan demonstrated that pyrolytic graphite can respond to laser light or sufficiently powerful natural sunlight by spinning or moving in the direction of the field gradient. The carbon's magnetic susceptibility weakens upon sufficient illumination, leading to an unbalanced magnetization of the material and movement when using a specific geometry.
Recently, it has been suggested that pyrolytic carbon may possibly be the explanation for the mysterious 'spokes' in Saturn's rings. Due to the process of Chemical Vapor Deposition methane gas at high temperatures (1400K) may have been converted to pyrolytic carbon. The abundant silicates in Saturn's B ring may have acted as a substrate for the pyrolytic carbon to be deposited on. Since pyrolytic carbon is highly diamagnetic the silicate grains coated in pyrolytic carbon can levitate above and below the ring plane due to Saturn's equatorial magnetic field. When sunlight hits these pyrolytic carbon-coated grains they lose electrons due to the photoelectric effect and become paramagnetic and are pulled back to the main ring structure as they are now attracted to Saturn's equatorial magnetic field. The visibility of the 'spokes'
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Pyrolytic carbon is also in medical use to coat anatomically correct orthopedic implants, a.k.a. replacement joints. In this application it is currently marketed under the name "PyroCarbon". These implants have been approved by the U.S. Food and Drug Administration for use in the hand for metacarpophalangeal (knuckle) replacements. They are produced by two companies: Tornier (BioProfile) and Ascension Orthopedics. On September 23, 2011, Integra LifeSciences acquired Ascension Orthopedics. The company's pyrolytic carbon implants have been used to treat patients with different forms of osteoarthritis. In January 2021, Integra LifeSciences sold its orthopedics company to Smith+Nephew for $240 million.
The FDA has also approved PyroCarbon interphalangeal joint replacements under the Humanitarian Device Exemption.
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