• CCPF is a chemistry-driven process that primarily involves gas-solid heterogeneous reactions. It is important to recognize that in CCPF the reaction is not limited to the surface. The conversion develops inward to the core of the fiber via a mechanism unique to each fiber.

• The fibers produced by CCPF are usually of fine diameter, which favors the kinetics of conversion.

• The composition of the product fiber is governed by the precursor fiber and the reactants used in the conversion, offering many new possibilities for exploration.

• Fiber properties can be further improved by post reaction treatment, such as crystallite orientation by hot stretching to improve modulus and strength in the case of BN and the removal fiber kinks also by hot stretching to improve strength in the case of B₄C fiber.

  It must be pointed out that this technology is still in its early stage of development, the examples reported by early researchers having merely laid the groundwork for the technology. Efforts along the following lines may be fruitful:

• Experimental work on various combinations of precursor fibers with a variety of reactants directed at making fibers of interest. The effort will help to define the practical limits of the approach.

• Characterization and application development for the fibers made by this technology. Based on the results of application assessment, scale-up work should be done for selected fibers to provide a realistic basis for assessing costs.

Chemical vapor deposition (CVD) fibers are formed by the deposition on a monofilament substrate of a species generated by a vapor-phase reaction occurring adjacent to or at the substrate surface. In general, the CVD reaction is initiated as a result of the substrate being heated, usually to incandescence. For production fibers the substrate continuously moves through the reaction apparatus or reactor, thus increasing in diameter through the processing, with the CVD fiber product being spooled or taken up downstream of the reaction chamber.

The formation of continuous fibers by the application of CVD technology has proven to be a reliable and routine approach to the production of consistent products such as boron and silicon carbide fibers. CVD processing has a wide range of applicability and flexibility in terms of chemical composition, and is limited only by the availability of volatile reactant molecules that incorporate the species to the deposited.