FACTOID #53: If you thought Antarctica was inhospitable, think again - its land area is only ninety-eight percent ice. Reassuringly, the other 2% is categorised as "barren rock".
Pyrolytic carbon is a material similar to graphite, but with some covalent bonding between its graphene sheets. 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 hearts and prosthetic heart valves. Blood vesselstents, 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 brittleness and the large amount of permanent deformation which a stent undergoes during expansion. Material is the substance or matter from which something is or can be made, or also items needed for doing or creating something. ... Graphite (named by Abraham Gottlob Werner in 1789, from the Greek γραφειν: to draw/write, for its use in pencils) is one of the allotropes of carbon. ... A United States soldier demonstrates Foosball with two prosthetic limbs In medicine, a prosthesis is an artificial extension that replaces a missing part of the body. ... Thrombosis is the formation of a clot or thrombus inside a blood vessel, obstructing the flow of blood through the circulatory system. ... An artificial heart is a device that is implanted into the body to replace the original biological heart. ... In anatomy, the heart valves are valves in the heart that prevent blood from flowing the wrong way. ... The arterial system The blood vessels are part of the circulatory system and function to transport blood throughout the body. ... In medicine, a stent is an expandable wire mesh tube that is inserted into a hollow structure of the body to keep it open. ... Heparin (also known as calciparine {United States, United Kingdom, Canada}, liquaemin{United States}, calcilean/hepalean/heparin leo {Canada}) is an injectable anticoagulant, nowadays usually made synthetically. ... For other uses of Brittle, see Brittle (disambiguation). ... In physics and materials science, plasticity is a property of a material to undergo a non-reversible change of shape in response to an applied force. ...
In its pure glassy (isotropic) synthetic forms, pyrolyticgraphite and carbon fiber graphite is an extremely strong, heat-resistant (to 3000C) material, used in reentry shields for missile nosecones, solid rocket engines, high temperature reactors, brake shoes and electric motor brushes.
Pyrolyticgraphite has excellent biocompatibility, and is used in medical equipment to prevent adhesion of blood clots.
Care must be taken that reactor-grade graphite is free of neutron absorbing materials such as boron, widely used as the seed electrode in commercial graphite deposition systems-- this caused the failure of the German's World War II graphite-based nuclear reactors.
Preferably, the particulate graphite is pyrolyticgraphite, is at least partially oriented in the polymer matrix, constitutes from about 25 to 35 weight percent of the composite and has an average particle size of from about 50 to 100 microns when used with such as carbon dioxide lasers, while the polymer matrix is silicone rubber.
Pyrolyticgraphite is an essentially pure graphite formed by a vapor phase deposition process in which a hydrocarbon gas is pyrolyzed in a high temperature vacuum furnace and the resulting carbon deposited on a planar surface with the basal planes of the deposited carbon oriented parallel to this surface.
By "a dispersion of oriented particulate graphite" is meant a dispersion of particulate graphite in which the graphite particles are aligned with their a-b planes substantially parallel both to each other and to the major surface of the composite material comprising the particles.
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