Surfaces Carbon Fiber

Formation of the transcrystalline structure also depends on the geometry of the chain and the fiber surface. Carbon fibers and polyamides are a good match. This makes the chain arrangement on the surface of the fiber very precise and thus the resultant composite is very strong. ... 

Poly(indole) has found applications as an organic polymer coating. The performance of layered semiconductors has been shown to be improved by the electropolymerization of layers of poly (indole) on the defective sites of the surface. Carbon fibers may be coated with poly(indole) by electropolymerization. More recently, poly(indole) has been employed for the polymer coating for a glucose sensor [125]. 

Carbon Composites. In this class of materials, carbon or graphite fibers are embedded in a carbon or graphite matrix. The matrix can be formed by two methods chemical vapor deposition (CVD) and coking. In the case of chemical vapor deposition (see Film deposition techniques) a hydrocarbon gas is introduced into a reaction chamber in which carbon formed from the decomposition of the gas condenses on the surface of carbon fibers. An alternative method is to mold a carbon fiber—resin mixture into shape and coke the resin precursor at high temperatures and then foUow with CVD. In both methods the process has to be repeated until a desired density is obtained. 

More than 95% of current carbon fiber production for advanced composite appHcations is based on the thermal conversion of polyacrylonitrile (PAN) or pitch precursors to carbon or graphite fibers. Generally, the conversion of PAN or pitch precursor to carbon fiber involves similar process steps fiber formation, ie, spinning, stabilization to thermoset the fiber, carbonization—graphitization, surface treatment, and sizing. Schematic process flow diagrams are shown in Eigure 4. However, specific process details differ. 

There are two mechanisms of PAN-based carbon fiber oxidation dependent on oxidation temperature ((67,68). At temperatures below 400°C, oxygen diffuses into the fiber and attacks at pores resulting in significantly increased fiber surface area. At higher temperatures impurities catalyze the oxidation reaction. 

SSIMS has been used in the TOP SSIMS imaging mode to study very thin layers of organic materials [3.32-3.36], polymeric insulating materials [3.37], and carbon fiber and composite fracture surfaces [3.38]. In these studies a spatial resolution of ca. 80 nm in mass-resolved images was achieved. 

Mochida, I., Kawano, S., Hironaka, M., Kawabuchi, Y., Korai, Y., Matsumura, Y. and Yoshikawa, M., Kinetic study on reduction of NO of low concentration in air with NHj at room temperature over pitch-based active carbon fibers of moderate surface area, Langmuir, 1997, 13(20), 5316 5321. 

The structure of CBCF is shown in the SEM micrograph in Fig. 4. The crenellated surface of the rayon derived carbon fibers is clearly visible, as is the phenolic derived carbon binder. The preferred orientation of the fibers (resulting from the slurry molding operation) is obvious in Fig. 4, and imparts considerable anisotropy to the material. The molding direction is perpendicular to the plane of the carbon fibers in Fig. 4. 

Fig. 15. Mesopore surface area as a function of pore diameter obtained from mercury intrusion data for PAN derived carbon fiber porous monoliths [28].

Fig. 2. Results of interfacial shear strength measurements of the same fiber/matrix systems using four different micro-mechanical tests during a round-robin program involving 12 different laboratories, (a) Results for untreated, unsized carbon fibers, (b) Results for carbon fibers with the standard level of surface treatment. Redrawn from ref. [13].

Fig. 9. The effect of voids due to poor wetting on adhesive strength, (a) The zippering effect of voids aligned in the plane of shear, (b) Macro-voids in the resin formed during the manufacture of a carbon fiber reinforced prepregs. (c) Micro-voids caused by axial crenulations along carbon fiber surfaces.

The segregation process of graphite on the surface of a metal particle is similar to that proposed by Ober-lin and Endo[35] for carbon fibers prepared by thermal decomposition of hydrocarbons. Flowever, the... 

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