The CVD Process for Fiber Production

Two fibers are presently produced by CVD on a commercial scale boron and silicon carbide. The production of these two fibers requires a monofilament starter core capable of being heated resistively such as a tungsten or graphite fiber. I l The deposition apparatus is shown schematically in Fig. 19.1. 

Since a core is required, it is not possible to produce fibers with a small diameter and present production diameters are in the range of 100-150 pm, compared to an average of 10-20 pm for solgel derived fibers. Being very stiff with a high Young s modulus 

A new process based on laser CVD does not require a core material and is able to produce fibers with a much smaller diameter. Deposition rate is up to 1 mm/sec. The process is still experimental and is presently being developed for the production of boron, SiC, and Si3N4.1 1 The core-less deposition may be accomplished by impinging the laser beam on the growing end of a retreating fiber in a CVD atmosphere. 

Properties. CVD boron fibers have high strength, high modulus, and low density. Their properties are summarized and compared with SiC fibers and other inorganic fibers in Table 19.2 (data supplied by the manufacturers). 

The reactivity problem can be partially remedied with the use of intermediate coatings (see Sec. 2.5 below). 

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CVD in Fiber, Powder, and Monolithic Applications 467 2.3 The CVD Process for Fiber Production... 

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