Carbon fibers synthesis

Most of the presently available carbon fibers are synthesized from polyacrylonitrile starting materials. Although several other precursors do exist such as rayon and pitch [18], PAN precursor fibers have the best mechanical properties for structural applications. The technology of carbon fiber synthesis is protected very strongly by carbon fiber producers. However, the basic chemistry of carbon fiber synthesis is known. A brief review is included here. 

THERMAL TREATMENTS FOR PAN-BASED CARBON FIBER SYNTHESIS... 

Carbon fibers formed at higher temperatures (>2000 C) are referred to in the literature as high modulus or type I fibers. Fibers formed at lower temperatures (1000-1600 C) are referred to as low modulus or type II fibers. Recent developments in carbon fiber synthesis have resulted in carbon fibers with a tensile modulus intermediate between type I and II but with a tensile strength similar to type II [25]. These newer fibers have been called intermediate modulus. Many improvements in the processing of PAN fibers are being made. A wide range of mechanical properties is available for specific design applications. 

The synthesis of his[3-(2-a11y1phenoxy)phtha1imides] and their copolymer properties with BMI have been reported (43). These allylphenoxyimide—BMI copolymers provide toughness and temperature resistance when used in carbon fiber laminates (44). 

Cyclopentadiene itself has been used as a feedstock for carbon fiber manufacture (76). Cyclopentadiene is also a component of supported metallocene—alumoxane polymerization catalysts in the preparation of syndiotactic polyolefins (77), as a nickel or iron complex in the production of methanol and ethanol from synthesis gas (78), and as Group VIII metal complexes for the production of acetaldehyde from methanol and synthesis gas (79). 

Regarding a historical perspective on carbon nanotubes, very small diameter (less than 10 nm) carbon filaments were observed in the 1970 s through synthesis of vapor grown carbon fibers prepared by the decomposition of benzene at 1100°C in the presence of Fe catalyst particles of 10 nm diameter [11, 12]. However, no detailed systematic studies of such very thin filaments were reported in these early years, and it was not until lijima s observation of carbon nanotubes by high resolution transmission electron microscopy (HRTEM) that the carbon nanotube field was seriously launched. A direct stimulus to the systematic study of carbon filaments of very small diameters came from the discovery of fullerenes by Kroto, Smalley, and coworkers [1], The realization that the terminations of the carbon nanotubes were fullerene-like caps or hemispheres explained why the smallest diameter carbon nanotube observed would be the same as the diameter of the Ceo molecule, though theoretical predictions suggest that nanotubes arc more stable than fullerenes of the same radius [13]. The lijima observation heralded the entry of many scientists into the field of carbon nanotubes, stimulated especially by the un-... 

Composites fabricated with the smaller floating catalyst fiber are most likely to be used for applications where near-isotropic orientation is favored. Such isotropic properties would be acceptable in carbon/carbon composites for pistons, brake pads, and heat sink applications, and the low cost of fiber synthesis could permit these price-sensitive apphcations to be developed economically. A random orientation of fibers will give a balance of thermal properties in all axes, which can be important in brake and electronic heat sink applications. 

Fig. 1. The synthesis route for ORNL s porous carbon fiber-carbon binder composites.

The direct linking of carbon nanotubes to graphite and the continuity in synthesis, structure and properties between carbon nanotubes and vapor grown carbon fibers is reviewed by the present leaders of this area, Professor M. Endo, H. Kroto, and co-workers. Further insight into the growth mechanism is presented in the article by Colbert and Smalley. New synthesis methods leading to enhanced production... 

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. 

Burchell, T.D., Weaver, C E., Derbyshire, F., Fei, Y.Q. and Jagtoyen M., Carbon fiber composite molecular sieves synthesis and characterization. In Proc. Carbon 94, Granada, Spain, Spanish Carbon Group, 1994, pp. 650 651. 

SYNTHESIS OF ACTIVATED CARBON FIBERS FOR HIGH-PRESSURE HYDROGEN STORAGE... 

Synthesis of Activated Carbon Fibers for High-Pressure Hydrogen Storage... 

The C3 family of materials [11-13] exhibits this chemical stability due to a highly functionalized fraction of sp2 carbon [14-17], but in addition contains a carbon fiber backbone in its second bulk component. Carbon fibers [18-21] are the ordered variant of interlaced ribbons in fibers the anisotropic sp2 basic structural units are oriented in one direction [20] by various mechanisms during synthesis. The result is a high... 

The second set of synthesis steps shown in Fig. 9.2 concerns the preparation of the green body for the C3 formation. Steps 5-8 are related to generating a flat or curved sheet from the carbon fiber and the precursor of the binder phase. This process can be complicated because the final part made from C3 cannot be changed in its form nor can it be interconnected to another C3 part by reasonably affordable techniques suitable for mass production. The quality of the final product is here decided by the homogeneity of the material distribution and the exact shaping. 

Carbon materials used for the commercial synthesis of carbon fluoride include natural graphite, petroleum coke, activated carbon, carbon black and carbon fiber. Experimental carbon materials include residual carbon, exfoliated graphite, fullerenes and other unique carbons and carbon inserts. The degree of graphitization of carbon material varies continuously, so it is not simple to define the exact boundary between carbon and graphite. The product formed... 

In the following sections some examples are given of the ways in which these principles have been utilized. The first example is the use of these techniques for the low temperature preparation of oxide ceramics such as silica. This process can also be used to produce alumina, titanium oxide, or other metal oxides. The second example describes the conversion of organic polymers to carbon fiber, a process that was probably the inspiration for the later development of routes to a range of non-oxide ceramics. Following this are brief reviews of processes that lead to the formation of silicon carbide, silicon nitride, boron nitride, and aluminum nitride, plus an introduction to the synthesis of other ceramics such as phosphorus nitride, nitrogen-phosphorus-boron materials, and an example of a transition metal-containing ceramic material. 

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