Isotropic carbon fiber

PAN-based carbon fibers Isotropic-pitch-based carbon fibers... 

The torsional modulus is shown in Figure 20.22 and appears to be governed by the structure of the microsection increasing in the order— mesophase pitch based carbon fiber < rayon based carbon fiber < isotropic pitch based carbof fiber < PAN based carbon fiber. 

Certain pitches can be spun directly into isotropic pitch fibers with only minor devolitization. Carbonized isotropic pitch fibers cannot be graphitized and develop mechanical and thermal properties that are substantially inferior to those produced by other precursors. However, isotropic pitch fibers are very inexpensive and have found commercial applications in areas that do not require the exceptional mechanical and thermal properties of mesophase pitch-based carbon fibers. Isotropic pitch-based carbon fibers are used in filters, brake pads, activated carbons, and as substrates for chemical vapor deposition (23). Table 3 summarizes properties of isotropic pitch-based carbon fibers. 

The results presented below were obtained using a 2 mm thick carbon fiber reinforced epoxy composite laminate with 16 layers. The laminate was quasi isotropic with fiber orientations 0°, 90° and 45°. The laminate had an average porosity content of approximately 1.7%. The object was divided in a training area and an evaluation area. The model parameters were determined by data solely from the training area. Both ultrasound tranducers used in the experiment had a center frequency of 21 MHz and a 6 dB bandwidth of 70%. 

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. 

Affected by multiple scattering are, in particular, porous materials with high electron density (e.g., graphite, carbon fibers). The multiple scattering of isotropic two-phase materials is treated by Luzatti [81] based on the Fourier transform theory. Perret and Ruland [31,82] generalize his theory and describe how to quantify the effect. For the simple structural model of Debye and Bueche [17], Ruland and Tompa [83] compute the effect of the inevitable multiple scattering on determined structural parameters of the studied material. 

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. 

Isotropic fibrous materials, 11 176-177 Isotropic microporous membranes, 15 798 Isotropic moldings, 23 397 Isotropic pitch-based carbon fibers, 26 734-735... 

Fig. 9.1 Top view on two variants of C3 materials. The carbon fibers (a) themselves exhibit a complex inner microstructure that needs carful optimization for strength and stability. The isotropic filler phase (b) should be free of pores and other weak points caused by uneven distribution in the composite body. The ordered graphitic BSU (c) can provide a very strong but still flexible anchoring of the fibers in the isotropic matrix.

Fig. 6.23. R-curve prediction ( — ) and experimental data (O) for a carbon fiber-epoxy matrix quasi-isotropic [C/ 45°/90 ), laminate. After Wells and Beaumont (1987).

Fig. 6.24. Comparison of notched strength of carbon fiber-epoxy matrix quasi-isotropic [0°/ 45°/90°...

One of the most important properties which control the damage tolerance under impact loading and the CAI is the failure strain of the matrix resin (see Fig. 8.8). The matrix failure strain influences the critical transverse strain level at which transverse cracks initiate in shear mode under impact loading, and the resistance to further delamination in predominantly opening mode under subsequent compressive loading (Hirschbuehler, 1987 Evans and Masters, 1987 Masters, 1987a, b Recker et al., 1990). The CAI of near quasi-isotropic composite laminates which are reinforced with AS-4 carbon fibers of volume fractions in the range of 65-69% has... 

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

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

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... 

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