Carbon from isotropic pitch

Characterization of Pore Distribution in ACF Prepared from Isotropic Pitch-Based Carbon Fiber... 

The oxidation reaction starts at a temperature that depends on composition, structure, and microtexture. For example, the oxidation of carbon fibers derived from isotropic pitch precursor fibers in flowing air starts at about 400°C whereas that of the mesopitch based UHM fibers starts at a higher temperature [64]. At a given temperature, the variation of the weight loss, AJmo, as a function of time is linear, to a first approximation, within a rather large domain of weight loss [65-66]. This property is used to characterize the oxidation rate with a kinetic constant, k, defined as ... 

Korai Y, Ishida S, Watanabe F, Yoon SH, Wang YG, Mochida I, Kato I, Nakamura T, Sakai Y, Komatsu M, Preparation of carbon fiber from isotropic pitch containing mesophase spheres. 

The.se fibers are sometimes referred to as isotropic carbon fibers, since they are made from isotropic pitch. These pitches are prepared from high boiling fractions of petroleum feedstocks, usually heavy slurry oils produced in catalytic cracking of crude oil. 

Carbon fibers from isotropic pitch Isotropic pitch or a pitch-like material, such as molten polyvinyl chloride, is melt spun at high strain rates to align the molecules parallel to the fiber axis. The thermoplastic fiber is then rapidly cooled and carefully oxidized at a low temperature (<100 °C). The oxidation process is rather slow, so as to ensure stabilization of the fiber by cross-linking to make it infusible. However, upon carbonization, relaxation of the molecules takes place, producing fibers with no significant preferred orientation. This process is not industrially attractive due to the lengthy oxidation step, and because only low-quality carbon fibers with no graphitization are produced. These fibers are used as fillers in various plastics to form thermal insulation materials. 

The acrylic-based carbon fibres can be engineered to have high modulus (HM) or high tenacity (HT), or a balance between these two properties, and are available in numerous grades. The pitch-based carbon fibres fall into two classes those made from fibres spun from isotropic pitch, which have relatively low strength and modulus, and those... 

Fibers produced from pitch precursors can be manufactured by heat treating isotropic pitch at 400 to 450°C in an inert environment to transform it into a hquid crystalline state. The pitch is then spun into fibers and allowed to thermoset at 300°C for short periods of time. The fibers are subsequendy carbonized and graphitized at temperatures similar to those used in the manufacture of PAN-based fibers. The isotropic pitch precursor has not proved attractive to industry. However, a process based on anisotropic mesophase pitch (30), in which commercial pitch is spun and polymerized to form the mesophase, which is then melt spun, stabilized in air at about 300°C, carbonized at 1300°C, and graphitized at 3000°C, produces ultrahigh modulus (UHM) carbon fibers. In this process tension is not requited in the stabilization and graphitization stages. 

Low density, carbon fiber-carbon binder composites are fabricated from a variety of carbon fibers, including fibers derived from rayon, polyacrylonitrile (PAN), isotropic pitch, and mesophase pitch. The manufacture, structure, and properties of carbon fibers have been thoroughly reviewed elsewhere [3] and. therefore, are... 

A recently developed adsorbent version of ORNL s porous carbon fiber-carbon binder eomposite is named carbon fiber composite molecular sieve (CFCMS). The CFCMS monoliths were the product of a collaborative researeh program between ORNL and the University of Kentueky, Center for Applied Energy Researeh (UKCAER) [19-21]. The m.onoliths are manufactured in the manner deseribed in Section 2 from P200 isotropic pitch derived fibers. While development of these materials is in its early stages, a number of potential applieations can be identified. 

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. ... 

Mochida, I., Ku, C., Yoon, S., and Korai, Y. (1999). Anodic performances of anisotropic carbon derived from isotropic quinohne pitch. Carbon, 37, 323-1. Wu, Y., Fang, S., and Jiang, Y. (1999). Effects of nitrogen on the carbon anode of a lithium secondary battery. Solid State Ionics, 120, 117-23. 

Pitch as a precursor material is cheaper than PAN as a precursor fiber, but the conversion of pitch into mesophase pitch and subsequent fiber formation is complex and costly. When a pitch is not transformed into a mesophase and is spun as an isotropic liquid, the resulting carbon fibers have extremely poor mechanical properties. These considerations explain why more than 90% of today s carbon fibers are fabricated from PAN based precursors. Processes for fabricating carbon fibers from PAN or pitch based precursor fibers differ in important aspects, but also share important commonalties (Figure 2). Finally, the carbon yield from PAN based precursor fibers is 50%, that from mesophase pitch is 70-80%, and that from rayon is 25%. 

Mesopitch based carbon fibers exhibit a variety of microtextures depending on the structure of the specific precursor fiber and the spinning conditions. Mesopitch based fibers prepared from 100% mesophase pitch have a more homogeneous microtexture than those prepared from mixtures of anisotropic and isotropic pitches. Further, disturbing the flow pattern of the... 

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