Pyrolytic carbon 1953299 223658011 2008-07-05T03:17:37Z Leonard G. 46238 refine image title {{Refimprove|date=February 2008}} [[Image:Pyrolytic_graphite.jpg|thumb|right|250px|Sheets of pyrolytic carbon]] '''Pyrolytic carbon''' is a [[material]] similar to [[graphite]], but with some [[covalent bond]]ing between its [[graphene]] sheets as a result of imperfections in its production. Generally it is produced by heating a hydrocarbon nearly to its [[decomposition temperature]], and permitting the graphite to [[crystal]]lise (pyrolysis). One method is to heat [[synthetic fiber]]s in a [[vacuum]]. Another method is to place seeds or a plate in the very hot gas to collect the graphite coating. [[Image:Diamagnetic graphite levitation.jpg|190px|thumb|right|Pyrolytic carbon levitating over permanent magnets]] ==Physical properties== Pyrolytic carbon samples usually have a single [[cleavage (crystal)|cleavage]] plane, similar to [[mica]], because the graphene sheets crystalize in a planar order, as opposed to graphite, which forms microscopic randomly-oriented zones. Because of this, pyrolytic carbon exhibits several unusual [[anisotropy|anisotropic]] properties. It is more [[thermal conductivity|thermally conductive]] along the cleavage plane than graphite, making it one of the best planar thermal conductors available. It is also more [[diamagnetic]] against the cleavage plane, exhibiting the greatest [[diamagnetism]] of any room temperature solid (by weight). It is even possible to [[magnetic levitation|levitate]] reasonably pure and sufficiently ordered samples over [[Neodymium magnet|rare earth permanent magnets]]. ==Applications== * It is used nonreinforced for [[missile]] [[nosecone]]s, and [[ablation|ablative]] (boiloff-cooled) [[rocket motor]]s. * In fiber form, it is used to reinforce plastics and metals (see [[Carbon fiber]] and [[Graphite-reinforced plastic]]). * [[Pebble bed reactor|Pebble bed]] [[nuclear reactor]]s use a coating of pyrolytic carbon as a [[neutron moderator]] for the individual pebbles. * Used to coat graphite cuvettes (tubes) in [[Graphite Furnace Atomic Absorption]] furnaces to decrease heat stress, thus increasing cuvette lifetimes. Pyrolytic carbon is used for several applications in electronic thermal management: thermal interface material, heat spreaders (sheets) and heat sinks (fins) * It is used to fabricate grid structures in some high power [[vacuum tubes]]. ===Biomedical applications=== Because blood clots do not easily form on it, it is often advisable to line a blood-contacting [[prosthesis]] with this material in order to reduce the risk of [[thrombosis]]. For example, it finds use in [[artificial heart]]s and [[artificial heart valve]]s. [[Blood vessel]] [[stent]]s, by contrast, are often lined with a polymer that has [[heparin]] as a pendant group, relying on drug action to prevent clotting. This is at least partly because of pyrolytic carbon's [[brittle]]ness and the large amount of [[plasticity (physics)|permanent deformation]] which a stent undergoes during expansion. Pyrolytic carbon is also in medical use to coat anatomically correct orthopaedic implants, a.k.a. [[replacement joint]]. In this application it is currently marketed under the name "pyrocarbon". These implants have been approved by the FDA for use in the hand for metacarpophalangeal (knuckle) replacements. They are produced by two companies: Ascension Orthopedics <ref>{{cite journal | author=Cook, et al. | title=Long-term follow-up of pyrolytic carbon metacarpophalangeal implants | journal=J Bone Joint Surg Am. |year=1999 | pages=635–48 | volume=81 | issue=5 | pmid=10360692}}</ref> and Nexa Orthopedics. == Footnotes == <div class="references-small"> <references /> </div> == External links == ====Biomedical applications==== * [http://www.azom.com/details.asp?ArticleID=1463 Pyrolytic Carbon for Biomedical Applications] [[Category:Carbon forms]] [[Category:Levitation]] [[Category:Refractory materials]]