Pitch carbonization

Mechanical Properties and Stability at Elevated Temperature. One increasingly important characteristic of carbon fibers is their excellent performance at elevated temperatures. Strength tested in an inert environment remains constant or slightly increases to temperatures exceeding 2500°C. Amoco s high modulus pitch carbon fiber P-50 maintains approximately 80% of room temperature modulus at temperatures up to 1500°C, then decreases more rapidly to 30% at 2800°C (64). The rapid decrease in modulus is a result of increased atomic mobiHty, increa sing fiber plasticity. 

Coals mesophase pitch coal chars coal tar pitch carbon mesocarbon microbeads, carbon fibers semi-coke, calcined coke activated carbons premium cokes, carbon fibers, binder and matrix... 

Hamada, T., Nishida, T., Furuyama, M. and Tomioka, T., Transverse structure of pitch fiber from coal tar mesophase pitch. Carbon, 1988, 26(6), 837 841. 

Fig. 2. Schematic representation of basal plane orientation in several types of carbon fibers. (A) Single crystal graphite. (B) ex-pitch carbon fiber. (C) ex-PAN carbon fiber, (D) VGCF.

Yamada, Y., Imamura, T., Kakiyama, H., Honda, H., Oi, S., and Fukuda, K., Characteristics of meso-carbon microbeads separated from pitch. Carbon, 1974, 12, 307 319. 

For rayon fiber based composites (Sections 3 and 4) the fiber and powdered resins were mixed in a water slurry in approximately equal parts by mass. The isotropic pitch carbon fiber composites (Section 5) were manufactured with less binder, typically a 4 1 mass ratio of fiber to binder being utilized. The slurry was transferred to a molding tank and the water drawn through a porous screen under vacuum. In previous studies [2] it was established that a head of water must be maintained over the mold screen in order to prevent the formation of large voids, and thus to assure uniform properties. The fabrication process allows the manufacture of slab or tubular forms. In the latter case, the cylinders were molded over a perforated tubular mandrel covered with a fine mesh or screen. Moreover, it is possible to mold contoured plates, and tubes, to near net shape via this synthesis route. 

Pitch carbon fibres General purpose Aeronautics Aeronautics high modulus... 

Epoxy/pitch-carbon fiber fabric (8-harness satin) 40 379 ... 

A comparative study has been made by optical and electron microscopy of the anisotropic texture of several cokes from caking coals and pitches carbonized near their resolidification temperature. A simple technique made it possible to examine, by both methods, the same area of each sample and to identify the corresponding zones of the two very similar images. The anisotropy observed in polarized light appears in electron microscopy as differences in contrast resulting not from inequalities in electron absorption, but, as revealed by microdiffraction and dark Reid examinations, from diffraction phenomena depending on the general orientation of the carbon layers within each anisotropic area. 

The samples of coals and pitches carbonized up to about 500°C. possess relatively unorganized structures. The carbon atoms are arranged in layers and form large, aromatic-type molecules, approximately plane and including... 

Figure 1. Scanning electron micrograph of fracture surface of a mesophase pitch carbon fiber etched with chromic acid to reveal the radial arrangement of constituent lamellar molecules.

Figure 2. Scanning electron micrograph of a polished surface subsequently etched with chromic acid, of a carbon fiber-pitch carbon composite showing the orientation of a constituent lamellar molecules of pitch carbon parallel to surfaces of the carbon fiber.

Analyses of Pitch. Modern analytical facilities of high-pressure liquid chromatography, gel permeation chromatography, an(j 1 nuclear magnetic resonance and mass spectrometry, associated with 1R and UV spectroscopy enable a total molecular constituent analysis of pitch composition to be obtained. The use of such information could then possibly be the route to prediction of pitch quality on carbonization. It would appear that such an approach would not be successful (ignoring the cost factor for such detailed analysis). The pitch cannot be considered as an assembly of molecules which pyrolyse independently of each other. The pitch carbonizes as a multi-phase system and experience today would indicate the impossibility of predicting all interactions, physical and chemical. 

A major factor to consider in pitch carbonizations is the facility for hydrogen transfer reactions. These stabilize otherwise reactive radical species and permit the growth of mesophase in a fluid of low viscosity. Hydroaromaticity and methylene linkages are able to transfer hydrogen without creating radicals. 

Catalytic cracking bottoms (CCB) is a widely used aromatic feedstock for carbon production, such as aromatic pitch, carbon black and carbon fibers. 

The aromatic pitches produced from CCB-distillate are being developed for pitch carbon fiber production. 

Melting of the carbon precursor a monolithic is heated with a pitch carbon, resulting in penetration of the carbon material into the pores of the monolith structure. During heating, carbonization occurs, solidifying the carbon on the monolith. 

Early Stages of Petroleum Pitch Carbonization—Kinetics and Mechanisms, R. A. Greinke... 

Yoon, S.-H., Korai, Y., and Mochida, I. (1996). Axial nano-scale microstructures in graphitized fibers inherited from liquid crystal mesophase pitch. Carbon, 34, 941-56. 

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