manufacturers. To date, no new or growing market capable of catalyzing the necessary research has been identified.

The production of Si-based ceramic fibers from polymeric precursor is a demonstrated technology, and R&D programs can be identified that are highly likely to improve both fiber properties and fiber cost. Although the organometallic polymer approach to ceramic fibers could be extended to other ceramic systems, these R&D programs are expensive and time consuming and must involve, in addition to the identification of new materials and processes, the scale-up of proposed improvements to show that feasibility can be transformed into commercial reality.

Ceramic oxide fibers can be prepared by any of the processes identified as polymeric, polymer-modified solutions or dispersions, fiber-forming salt solutions, or sol-gel systems, the latter sometimes being used as an all-inclusive term for all of these when applied to the preparation of nonvitreous ceramic fibers by pyrolytic conversion processes.⁹ Most of these fibers have been fabricated by processes that can be categorized generally under "pyrolytic conversion of precursor fibers." Although the information usually provided may disclose the general type of processing by which these fibers are prepared, for example, polymeric or sol-gel (sol is a colloidal dispersion in a liquid medium), details are generally not sufficient for their immediate duplication. The most extensive amount of published information on ceramic fiber processing is in patents, the reference of Bracke et al.² having been cited in Chapter 1. A number of publications over the past several years have provided data on properties of ceramic oxide fibers currently available either commercially or on an experimental basis.^1,9,10

Oxide fibers prepared from the precursor pyrolysis process and that are currently available or under development are listed in Table 3.2 . These fibers are, in principle, desirable for high-temperature applications where the potential for oxidation exists. Except for the NEXTEL Z-11 ceramic fiber of 3M, all of the oxide fibers in the table contain a major A1₂O₃ component. The ZrO₂-SiO₂ fiber is not generally claimed to be of reinforcement grade since its modulus of elasticity is relatively low (76-90 GPa) (11-13 Msi).¹¹ However, fabric made from this fiber does have outstanding resistance to flame penetration, and it may be useful for applications requiring such properties.

Preparation of oxide fibers from polymeric precursors is closely related to the processing of carbon or graphite fibers. However, polymerization of precursors for oxide fibers usually involves hydrolysis of the precursor. Wainer et al.¹² (Horizons, Inc.) prepared polymer precursors for the oxides of

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)