33 Materials And Processes 331 Ceramic Fibers

The most commonly used fibers in CFCCs are alumina, mullite, and silicon carbide. Silicon carbide fiber is produced by Nippon Carbon, COI Ceramics, Textron, and Ube. COI Ceramics distributes Nippon Carbon's fiber tradename Nicalon. It also produce its own silicon carbide fiber under the tradename Sylramic. Textron manufactures silicon carbide fiber under the tradename SCS. Ube sells silicon carbide fiber under the tradename Tyranno. 3M Corporation produces mullite fibers and alumina fibers under the tradename Nextel.

Nicalon ceramic fiber is a silicon carbide-type fiber manufactured by a polymer pyrolysis process. The fiber is homogeneously composed of ultrafine beta-SiC crystallites and an amorphous mixture of silicon, carbon, and oxygen. It is produced in several grades including those named Ceramic, HVR, LVR, and Carbon-Coated Ceramic. The Ceramic grade is Nippon Carbon's standard product, offering optimum mechanical properties and performance at elevated temperatures. HVR is a low-dielectric fiber that sacrifices some strength in order to achieve low-volume resistivity. The LVR fiber has a low-volume resistivity (high dielectric), once again balancing electrical properties with mechanical strength. The Carbon-Coated Ceramic grade fiber is uniformly coated with pyrolytic carbon to a nominal thickness of 1 nm. It is commonly used to reinforce CFCCs because the carbon coating allows the fiber to slip with the matrix. It is supplied with polyvinyl sizing that, if not desired, is removed by hot water rinsing. Nicalon fiber is available as continuous fiber tow or woven in 5, 8, and 12 harness satin weaves (Tables 3.5 and 3.6).

COI Ceramics Sylramic fibers are 10 ^m in diameter (fibers or fibers derived from a polymer composed of silicon, carbon, oxygen, and nitrogen).

TABLE 3.5 Typical Properties of Nicalon™ Fibers

Grade

Property

Unit

Ceramic

0 0

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