Boron nitride fiber fabrication

Wider use of fiber-reinforced ceramic matrix composites for high temperature structural applications is hindered by several factors including (1) absence of a low cost, thermally stable fiber, (2) decrease in toughness caused by oxidation of the commonly used carbon and boron nitride fiber-matrix interface coatings, and (3) composite fabrication (consolidation) processes that are expensive or degrade the fiber. This chapter addresses how these shortcomings may be overcome by CVD and chemical vapor infiltration (CVI). Much of this chapter is based on recent experimental research at Georgia Tech. 

Boron nitride (BN) is a versatile ceramic that is found and used in various crystallographic and geometrical forms. Although there are chemical similarities, the conditions for the synthesis and fabrication of each form (hexagonal, cubic, polymorphs of BN, fibers, two-dimensional forms and composites) have different requirements and are... 

Electrically insulating and thermally conductive qualities are important in computer chips fabrication. One approach taken is based on boron nitride fillers which offers these two properties. There is also a need to develop materials which are thermally conductive but electrically insulating in high humidity conditions. Polyurethane composites filled with aluminum oxide or carbon fiber can be used for this application. Figure 19.15 shows the effect of the amount of filler on thermal... 

Fiber reinforced ceramic matrix composites (CMCs) are under active consideration for large, complex high temperature structural components in aerospace and automotive applications. The Blackglas resin system (a low cost polymer-derived ceramic [PDC] technology) was combined with the Nextel 312 ceramic fiber (with a boron nitride interface layer) to produce a sihcon oxycarbide CMC system that was extensively characterized for mechanical, thermal, and electronic properties and oxidation, creep mpture, and fatigue. A gas turbine tailcone was fabricated and showed excellent performance in a 1500-hour engine test. 

The SiOC matrix was prepared using the Blackglas 493-type preceramic resin. The Nextel 312 fabric was an AF-10 5H satin weave (600 denier tows, 275 g/m areal weight). Nextel 312 is the lowest cost ceramic fiber with acceptable strength and high temperature capability that is commercially available. The boron nitride interface layer on the Nextel 312 fibers was produced by the previously described high temperature nitridation process. 

Metallized metal, polymer and carbon. Types la, lb, and Ic, are variants of the solid metal fibers and are distinguished therefrom by a metal layer upon the base fiber s periphery. They are fabricated by electrochemical deposition or grafting of a suitable metal, such as nickel, copper, aluminum, and their alloys, as a thin layer upon the fiber s surface. In general, these variants evolved in attempts to improve upon one, or more, properties of the Type 1 fibers. Applications of metal-on-metal. Type la, are typified by the structures described in 1972 by McNab(26) who used refractory, non conducting, base fibers for example, aluminum oxide and boron nitride, upon which were deposited films of noble metals. McNab s objective was to improve upon the strength and flexibility of Type 1 fibers by selecting a base fiber for its mechanical... 

Seghi, S. Lee, J. and Economy, J. High density carbon fiber/boron nitride matrix composites Fabrication of composites with exceptional wear resistance. Carbon, 2005, 43, 2035-2043. 

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