Carbons fibers

Carbon fiber is produced from several different organic polymers, but polyacrylonitrile has many advantages as a starting material. It is easily spun into fibers, and the chemistry of its pyrolysis reactions favors aromatization as a pathway to graphite-like structures. The process is outlined in reaction sequence (5). 

Pyrolysis can be considered as a three-step process. The first step (stabilization) takes place when poly(acrylonitrile) fibers are heated at 200-300 °C in air. This initiates oxidation and the formation of cross-finks. The second phase (known as carbonization) 

An alternative starting material for carbon fiber production is pitch—a complex mixture of fused polyaromatic hydrocarbon clusters that can also be melt-spun into fibers. 

The pyrolytic formation of carbon fiber provides an introduction to the conditions and temperature programming that is required for the formation of ceramics that contain silicon, boron, aluminum, and other elements. 

Carbon fiber is available in mat form, typically 0.2,0.5,1, and 2 oz./yd.. It is also available in a 0.5 oz./yd. mat as a blend with 33% glass fiber. Other blends are also available such as 25% carbon filler—75% glass fiber, and 50% aluminized glass— 50% carbon fiber. 

Carbon fibers are also available in continuous roving and as chopped fibers in sizes 1 /8-2 in. 

The carbon fiber mat, either alone or supplemented with a ground carbon or graphite filler, provides in-depth grounding systems and static control in hazardous areas where static sparks may result in fires or explosions. 

Carbon fibers are not directly spun but are the product of a complicated aftertreatment. Nowadays, most carbon fibers (90%) are produced from an acrylic precursor. Cellulose rayon is no longer applied as a precursor. Production from pitch has been developed, but is still a small-volume business. 

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Aerospace struetwes made of composite. As part of the evaluation of the developed ultrasonic spectroscopy system the NSC software was tested on ultrasonic resonance spectra from composite panel samples. Spectra were collected with four different types of damages, and from flawless samples. The damages included a small cut in one of the carbon fiber... 

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%. 

Fig. XVII-31. (a) Nitrogen adsorption isotherms expressed as /-plots for various samples of a-FeOOH dispersed on carbon fibers, (h) Micropore size distributions as obtained by the MP method. [Reprinted with permission from K. Kaneko, Langmuir, 3, 357 (1987) (Ref. 231.) Copyright 1987, American Chemical Society.]...

Thus far the importance of carbon cluster chemistry has been in the discovery of new knowl edge Many scientists feel that the earliest industrial applications of the fullerenes will be based on their novel electrical properties Buckminsterfullerene is an insulator but has a high electron affinity and is a superconductor in its reduced form Nanotubes have aroused a great deal of interest for their electrical properties and as potential sources of carbon fibers of great strength... 

PVDFmonofilament [FLUORINECOMPOUNDS,ORGANIC - POLY(VINYLIDENEFLUORIDE)] (Volll) -carbon fibers in [CARBON AND GRAPHITE FIBERS] (Vol 5)... 

Carbon-Carbon Composites. Carbon—carbon composites are simply described as a carbon fiber reinforcement in one or many directions using a carbon or graphite matrix material (see Composite materials). 

For nosetip materials 3-directional-reinforced (3D) carbon preforms are formed using small cell sizes for uniform ablation and small pore size. Figure 5 shows typical unit cell dimensions for two of the most common 3D nosetip materials. Carbon-carbon woven preforms have been made with a variety of cell dimensions for different appHcations (27—33). Fibers common to these composites include rayon, polyacrylonitrile, and pitch precursor carbon fibers. Strength of these fibers ranges from 1 to 5 GPa (145,000—725,000 psi) and modulus ranges from 300 to 800 GPa. 

Acrylonitrile (AN), C H N, first became an important polymeric building block in the 1940s. Although it had been discovered in 1893 (1), its unique properties were not realized until the development of nitrile mbbers during World War II (see Elastomers, synthetic, nitrile rubber) and the discovery of solvents for the homopolymer with resultant fiber appHcations (see Fibers, acrylic) for textiles and carbon fibers. As a comonomer, acrylonitrile (qv) contributes hardness, rigidity, solvent and light resistance, gas impermeabiUty, and the abiUty to orient. These properties have led to many copolymer apphcation developments since 1950. 

Acryhcs and modacryhcs are also useflil industrial fibers. Fibers low in comonomer content, such as Dolan 10 and Du Font s PAN Type A, have exceptional resistance to chemicals and very good dimensional stabihty under hot—wet conditions. These fibers are useflil in industrial filters, battery separators, asbestos fiber replacement, hospital cubical curtains, office room dividers, uniform fabrics, and carbon fiber precursors. The exceUent resistance of acryhc fibers to sunlight also makes them highly suitable for outdoor use. Typical apphcations include modacryhcs, awnings, sandbags, tents, tarpauhns, covers for boats and swimming pools, cabanas, and duck for outdoor furniture (59). 

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