• Pitch-based carbon fibers have the long-range potential to yield a substantially lower cost process than PAN-based fibers due to higher theoretical yields and lower carbonization costs. However, the approaches to reduced manufacturing costs for both fibers have some common features: improved precursor operating/capital costs, improved heat transfer processing operations for the conversion of precursor to carbon fiber, and use of larger precursor tows.

• The family of pitch and PAN-based carbon fibers encompasses a broad range of thermal and electrical conductivity. This set of conductivity properties is useful for a number of applications in which electromagnetic properties are at least as important as the mechanical properties of the reinforcing fiber. Currently, the mechanical and electromagnetic properties cannot be independently modified. Further research should be conducted in this area in order to be able to produce carbon fibers with tailored mechanical and electromagnetic properties.

The ability to transform silicon-based organometallic polymers to silicon-based ceramic fibers was recognized in the mid-1970s.⁸ About the same time the desirability of a high-modulus, high-strength, thermo-oxidatively stable, low-conductivity fiber for a variety of aerospace, defense, and consumer applications became apparent. For structural applications above about 1100°C, carbon-fiber-based composites (without special protective treatment) fail due to poor oxidation stability; most bulk ceramics, including the common oxide ceramics, fail due to poor mechanical stability. Nonoxide ceramics (e.g., silicon carbide [SiC] and silicon nitride [Si₃N₄]), are attractive candidates but suffer from low toughness and susceptibility to thermal shock. A method of overcoming these deficiencies is to reinforce the bulk ceramic of choice with thermally and oxidatively stable ceramic fibers. While many matrix systems are available, the technology for converting ceramics to fibers exists only for a small number of systems. Preparation of plastic-matrix fiber-reinforced composites with mechanical properties like those produced by carbon fiber, but with lower electrical conductivity, is also of interest. These considerations have led to a focus on the production of continuous SiC and Si₃N₄ fibers over the past decade. Several of these products are now commercially available through Japanese suppliers, such as Nippon Carbon Company and Ube.

To a first approximation, the technology for the production of Si ceramics from polymeric precusors is analogous to the general process shown in Figure 3.1. As shown in Figure 3.5, after polymerization the polymer is melt spun (other possible fiber-forming processes have not been systematically investigated). Next the resulting fiber is cured through a thermochemical cross-linking step ("preoxidation"), and the stabilized fiber is then fired to

Front Matter (R1-R16)

Executive Summary, Conclusions, and Recommendations (1-8)

1 High-Performance Synthetic Fibers for Composites (9-20)

2 High-Performance Fiber Materials: Applications, Needs, and Opportunities (21-48)

3 Fiber-Forming Processes: Current and Potential Methods (49-102)

4 Important Issues in Fiber Science/Technology (103-108)

5 Important Policy Issues (109-118)

Glossary of Terms (119-126)

Appendix (127-129)