Carbon fiber surface resistivity

Processing. The process requires a monofilament carbon-fiber core which is heated resistively in a tubular glass reactor shown schematically in Fig. 19.1. PI A carbon monofilament is pre-coated with a 1 pm layer of pyrolytic graphite to insure a smooth deposition surface and a constant resistivity. 1 1 SiC is then deposited by the reaction of silane and a hydrocarbon. Other precursors such as SiCl4, and CH3SiCl3 are also being investigated. A fiber cross-section is shown in Fig. 19.2.P1... 

After treating different fuel cells to 100 freeze-thaw cycles (from -40 to 70°C), Kim, Ahn, and Mench [261] concluded that stiffer materials used as diffusion layers improved the uniform compression with the CL, resulting in fewer issues after the freeze and thaw cycles. On the other hand, more flexible DLs failed to improve the compression the CL left open spaces for ice films to be formed, resulting in serious issues after the freeze-thaw cycles. However, even with the stiffer materials tested, such ice films were still evident and caused delamination of the DL and CL, surface damage in the CL, and breakage of the carbon fibers. This resulted in increased electrical and mass transport resistances. 

Ultra-high modulus fibers such as aramid and carbon fibers have been currently utilized for composite material fabrication. Ultra-high modulus polyethylene (UHMPE) fiber is also applicable for composite fabrication because of the light weight in addition to its high modulus, vibration damping, and resistance to chemicals. However, this fiber has drawbacks such as poor interfacial adhesion with the polymer matrix of the composite because of highly hydrophobic nature of the fiber surface. 

PTFE, known under the trade names Teflon and Fluon, is resistant to all chemicals, except molten alkalis and fluorine, and can be used at temperatures up to 250°C. It is a relatively weak material, but its mechanical strength can be improved by the addition of fillers (glass and carbon fibers). It is expensive and difficult to fabricate. PTFE is used extensively for gaskets, gland packings (for example, on valve stems), and demister pads. As a coating, it is used to confer nonstick properties to surfaces, such as filter plates. It can also be used as a liner for vessels. 

Activated carbon fibers have attracted increasing attention in recent years as a better adsorbent than granular activated carbons, because they normally present much higher adsorption kinetics and adsorption capacity. Activated carbon fibers only have micropores, which are directly accessible from the external surface of the fiber. Thus, adsorptive molecules reach adsorption sites through micropores without the additional difiusion resistance of macropores, which is usually the rate-controlling step in granular adsorbents. 

Among the mechanical properties of greatest practical impact on catalysis applications is the attrition and crushing resistance of powdered or granular activated carbons, the most commonly used catalytic carbon materials, versus that of activated carbon fibers (ACFs) or of other, less-surface-active carbons (e.g.. 

A more defective form of sp carbon fibers, carbon nanotubules (CNTbs), grown by pyrolytic deposition of carbon into anodized aluminum oxide (AAO) nanochannels, are also used as nanoelectrode arrays for electrochemical sensors. Small graphitic crystallites are deposited on the inner surface of the nanochannels. Since the crystallites do not extend very long (less than micrometers) and are structurally discontinued, the resistance is orders of magnitude higher than CNFs... 

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