Carbon, isotropic

Acoustic Emission to Model the Fatigue Behaviour of Quasi-Isotropic Carbon-Epoxy Laminate Composites. 

Other Uses. Anisotropic and isotropic carbon are produced from furfural-modified systems glassy carbon is produced primarily from furfuryl alcohol or BHMF resins (78,79). 

The isotropic form has little graphitic characteristic and essentially no optical activity. It is composed of very fine grains without observable orientation and for this reason, it is known as isotropic carbon rather than isotropic graphite. It is often obtained in fluidized-bed deposition, possibly due to continuous surface regeneration by the mechanical rubbing action of the bed. An isotropic structure, observed by transmission electron microscopy, is shown in Fig. 7.4.111]... 

Isotropic carbon is obtained by the pyrolysis of a hydrocarbon, usually methane, at high temperature (1200-1500°C) in a fluidized bed on a graphite substrate.Under these conditions, a turbostratic structure is obtained which is characterized by very little ordering and an essentially random orientation of small crystallites. In contrast to graphite which is highly anisotropic, such a structure has isotropic properties (see Ch. 7). Isotropic carbon is completely inert biologically. Its properties are compared to alumina, another common implant material, in Table 17.8. Notable is its high strain to failure. 

The major biological application of isotropic carbon is in heart valves. The material is performing well and several hundred thousand units have been produced so far. Other applications include dental implants, ear prostheses, and as a coating for in-dwelling catheters. 

Amorphous Isotropic carbon form closely associated with parent liquor, higher in volatile matter than incipient mesophase... 

Fig. 8.7. Damage area of 24 ply quasi-isotropic carbon fiber reinforced composite laminates containing different resin matrices. After Srinivasan et al. (1992).

Sooty carbon isotropic carbon form comprised of approximately spherical particles less than 1. im in diameter, sometimes referred to as combustion black (ASTM D-5061). 

FIGURE 2.43 Optical micrographs of polished cross section of high-density isotropic carbons. (Courtesy of Prof. K. Oshida, Nagano National College of Technology, Nagano, Japan. With permission.)... 

FIGURE 2.44 Relationship between the mechanical properties and average pore area of high-density isotropic carbons. 

The type of analysis done in Section 4.3.3.1.1 for physically activated carbon fibers (activated with C02 and steam) has been extended to ACF prepared by chemical activation with KOH and NaOH, using the same raw material (isotropic carbon fibers [Kureha Chemical Industry Co.]). 

Preparation Conditions and Porous Texture Characterization Corresponding to the Raw and Activated Isotropic Carbon Fibers... 

Carbon fibers are also of interest as replacements for asbestos fibers in friction materials, such as brake shoes (221. This move was initially driven in order to avoid the health hazards associated with asbestos. In comparison to asbestos reinforced brake formulations, isotropic carbon fibers have been shown to provide much higher friction performance and superior wear resistance, together with many advantages in operating characteristics. These advantages translate to other friction materials, such as clutch plates, and to a much broader range of applications in which carbon fibers are used as reinforcing or filler materials in various matrices. Carbon fibers in the forms of mats, felts, and paper insulation also present viable replacements for asbestos fibers. 

G. M. Kimber, A. Vego, T. D. Rantell, C. Fowler, A. Johnson, and F. Derbyshire, Synthesis of isotropic carbon fibers from coal extracts. Proceedings of the Pittsburgh Coal Conference, Pittsburgh, PA, 1996, pp. 553-558. 

Electrode Assembly. This device consists of a specially machined Teflon electrode holder, two disc electrodes (only one is energized), and a clamp machined from acrylic plastic (Figure 3). The electrode discs are of low-temperature isotropic carbon alloyed with SiC (Carbo-metics, Austin, TX). They were originally developed for use in artificial heart valves (14), and are approximately 1.6 cm in diameter and 1.25 mm thick, and have the surface properties of glassy carbon. Treatment of the discs requires only polishing to a high lustre with diamond grinding compounds of 14,000 and 50,000 mesh. 

Isotropic carbon fibers, whose degree of crystalline order is exceptionally low and whose structure is similar to glassy carbon, have the poorest mechanical properties. Their strength is, however, sufficient for their utilization as insulting fibers, filter media and for catalyst support. 

Two categories of pitch-based fiber exist isotropic carbon fiber produced from an isotropic pitch precursor, and an oriented, anisotropic fiber produced from a mesophase pitch precursor. Isotropic fibers were developed from low melting point isotropic pitches The precursor was melt-spun into fibers, which were oxidized to render them infusible, and then carbonized. Their low strengths and moduli make these fibers unsuitable for use in advanced composites. Orientation was accomplished by a hot-stretching process (>2200°C), but it is accompanied by the same processing difficulties encountered in the rayon precursor process. A different approach was suggested by the discovery of carbonaceous mesophase. ... 

Figure 2.8 Raman spectra of various carbon materials vith an approximately decreasing degree of structural order in the following sequence natural graphite (GC2), high surface area graphite (GA2), calcined needle coke (QCA), green needle coke (QVA), isotropic carbon fiber (FCl), and subbituminous coal (CM3). (Reprinted from Ref. [48] with pemussion firom Elsevier.)...

We will not discuss here models for pores in carbons, as this topic is treated in Chapter 5, and elsewhere in specialist [15] or general reviews [106, 107]. For similar reasons, we will not discuss porosity control [44, 108] in detail. However, porous carbons prepared by the template technique, especially the ordered ones, deserve special attention. Ordered mesoporous carbons have been known to scientists since 1989 when two Korean groups independendy reported their synthesis using mesoporous silicas as templates [109, 110]. Further achievements have been described in more recent reports [111, 112]. One might have expected that the nanotexture of these materials would merely reflect the nature of the precursor used, namely phenol-formaldehyde [109] or sucrose [110] in the two first ordered mesoporous carbon syntheses (as is well known, these two precursors would have yielded randomly oriented, isotropic carbon had they been pyrolyzed/activated under more conventional conditions). However, the mesopore walls in some ordered mesoporous carbons exhibited a graphite-like, polyaromatic character [113, 114], as described in Chapter 18. This information was obtained by nitrogen adsorption at low relative pressures, as in classical... 

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