Pyrolytic carbon applications

Fluidized-bed CVD was developed in the late 1950s for a specific application the coating of nuclear-fuel particles for high temperature gas-cooled reactors. PI The particles are uranium-thorium carbide coated with pyrolytic carbon and silicon carbide for the purpose of containing the products of nuclear fission. The carbon is obtained from the decomposition of propane (C3H8) or propylene... 

The pores of the silica template can be filled by carbon from a gas or a liquid phase. One may consider an insertion of pyrolytic carbon from the thermal decomposition of propylene or by an aqueous solution of sucrose, which after elimination of water requires a carbonization step at 900°C. The carbon infiltration is followed by the dissolution of silica by HF. The main attribute of template carbons is their well sized pores defined by the wall thickness of the silica matrix. Application of such highly ordered materials allows an exact screening of pores adapted for efficient charging of the electrical double layer. The electrochemical performance of capacitor electrodes prepared from the various template carbons have been determined and are tentatively correlated with their structural and microtextural characteristics. 

Biomedical. Heart-valve parts are fabricated from pyrolytic carbon, which is compatible with living tissue. Such parts are produced by high temperature pyrolysis of gases such as methane. Other potential biomedical applications are dental implants and other prostheses where a seal between the implant and the living biological surface is essential. Plasma and arc-wire sprayed coatings are used on prosthetic devices, eg, hip implants, to achieve better bone/tissue attachments (see Prosthetic and biomedicaldevices). 

LTI pyrolytic carbon is one of the very few synthetic materials generally accepted as suitable for long-term blood contact applications (1 ). Although a number of hypotheses have been formulated with respect to the blood tolerability of materials, a general theory or mechanism is not yet available. Nyilas, et al., ( ) have shown that in certain situations the local hemodynamics can play a predominant role, while in most cases the solid-blood interfacial properties have been shown to be equally important (2, 3). It is assumed that understanding the plasma protein adsorption processes on solids used for blood-contact applications will lead to a better understanding of solid-blood interactions (, 2, ... 

Endo M., Takeuchi K., Kobori K., Takahashi K., Kroto H.W. and Sarkar A. (199S), Pyrolytic carbon nanotubes from vapor-grown carbon fibers. Carbon, 33,873-881. Hagg May-Britt (1998), MEMBRANES IN CHEMICAL PROCESSINCi A Review of Applications and Novel Developments, SEPARATION AND PURIFICATION A/E77/ODS, 27(1), 51-168. 

If biomass is subjected to the ASTM D 3172 procedure for determination of fixed carbon, chemical transformation of a portion of the organic carbon in biomass into carbonaceous material occurs as described here. All of the fixed carbon determined by the ASTM procedure is therefore generated by the analytical method. Furthermore, the amount of fixed carbon generated depends on the heating rate used to reach biomass pyrolysis temperatures and the time the sample is subjected to these temperatures. Nevertheless, such analyses are valuable for the development of thermal conversion processes for biomass feedstocks. But application of the ASTM procedures to biomass might more properly be called a method for determination of pyrolytic carbon or coking yields. In the petroleum industry, the Conradson carbon (ASTM D 189, differ-... 

Small glassy carbon articles such as crucibles, boats or tubes are utilized under conditions in which high purity and temperature stability are required. Glassy carbon can be used, as with pyrolytic carbon, in prosthetic devices in human medicine. Furthermore the matrix in all carbon composites can consist of glassy carbon rather than pyrolytic graphite. The application fields are the same as those mentioned in Section 5.7.5.1. 

Elemental carbon is usually handled in three forms graphite, diamond, and amorphous carbon. Graphite and amorphous carbon have been extensively used in electrochemistry because of their high electrical conductivity, chemical stability, versatility, and low cost. For electrochemical applications, such materials can be manufactured in bars, powders, and fibers or can even form conducting composites when appropriate binders are used. A number of carbon-based materials, such as pyrolytic carbon, carbon blacks, activated carbons, graphite fibers, whiskers, glassy carbon, etc., have been used in electrochemistry for decades (Yoshimura and Chang, 1998). 

Finally, we addressed the complex problem of carbon corrosion, which is particularly relevant for PEMFC durability and thus commercialization of PEMFC technology. Carbon supports with an ordered crystalline structure, such as graphi-tized carbons, CNTs, and CNFs, as well as pyrolytic carbons of the Sibunit family hold out hope for the development of CLs with higher durability. More systematic studies are required to unveil the complex influence of the structure and morphology of carbon supports on the performance of the CLs and eventually, to develop a new generation of structurally ordered tailored materials for PEMFC applications with enhanced catalytic activities, low noble metal contents, and high dmabilities. 

Ely, J., Haubold, A., Bokros, J. and Emken, M. (1994), New Unalloyed Pyrolytic Carbon with Improved Properties for Implant Applications, XXI Congress European Society for Artificial Organs, Oct. 20-22, Barcelona Spain. Also US Patent 5 514 410. 

Cardiac valves with components fabricated from low temperature isotropic carbons (pyrolytic carbon) are successfully used clinically [23]. These materials are appropriate for such applications as mechanical valves which require long-term chemical inertness, smoothness, and wear-resistance. The reasons for the marked improvement in the performance (reduced thrombosis and thromboembolic stroke rates) of these newer vs. older style heart valves are not entirely understood, but are undoubtedly multifactorial and related to improved patient management and valve design, as well as to the nature of the carbon surface. The specific benefits conferred by pyrolytic carbons with respect to blood cell and protein interactions, resulting in a very low frequency of clinical complications, remain to be defined. The use of carbon coatings has been proposed for other devices, i.e., vascular grafts, although such devices have not yet been used clinically. 

Carbon in its various forms such as pyrolytic carbon, glassy carbon, carbon fiber, carbon fiber reinforced composites, and activated carbon has been a potential and important material in medical science and in medicinal applications. This is due to its properties such as good biocompatibiUty, nontoxicity, no immune reaction with the body, low density, chemical inertness, low coefficient of friction, elastic modulus similar to that of bone, and high adsorption capacity. Some of these applications of carbon materials have been discussed elsewhere" and are beyond the scope of this book. In this section we shall look into some of the medicinal applications based on adsorption by active carbons. Adsorbent carbons in the form of charcoal and activated carbons have been in use for medicinal and health applications for centuries and have been listed in the pharmacopoeia as antidotes and intestinal adsorbents. 

The meyor applications of pyrolytic carbon deposited by fluidized bed are found in the production of biomedical components such as heart valves and in the coating of uranium carbide and thorium carbide nuclear-fuel... 

Biomedical applications require a material with good strength, fatigue-resistance, high erosion resistance, chemical inertness, and compatibility with blood and tissues. Isotropic pyrolytic carbon meets these criteria and is used extensively in biomedical devices such as heart valves and dental implants where Its performance is superiorto other forms of carbon such as pyrolytic graphite or vitreous carbon.PSJ... 

Another fiber coating application is found in fiber optics. An isotropic pyrolytic-carbon coating is applied on optical fibers to improve the abrasion and fatigue resistance, and bending performance. ... 

Pyrolytic carbon or graphite is used to density carbon-carbon structures by infiltration as described in Sec. 2.6 above. Applications include reentry heat shields, rocket nozzles, aircraft disk brakes, and other aerospace components. This topic is reviewed in more detail in Ch. 9. 

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