Boron-carbon filament

An important breakthrough in the development of advanced composites came in the late 1960s the invention of boron and carbon filaments in the United States, the United Kingdom, and Japan. These fibers were soon incorporated into some of the earliest... 

Silicon CarbidG Fibers. Silicon carbide (SiC) filaments are produced by a CVD technique. The y3-SiC is obtained by the reaction of silane and hydrogen gases with the carbon filament being the substrate for deposition. The SiC fibers have mechanical and physical properties equal to those of boron, and can be used at higher temperatures than the present boron fiber when available in production quantities. CVD SiC fibers are primarily used for reinforcing metal and ceramic matrices. Alternatively, SiC fibers can be made from a polycarbosilane precursor which is meltspun at 350°C. The final form is obtained by pyrolyzing the fiber at 1200°C in an inert environment. 

Boron Trichloride. Boron trichloride is prepared commercially by the chlorination of boron carbide (equation 15). Direct chlorination of boric acid or a sodium borate in the presence of carbon is an alternative method. Most of the boron trichloride produced is converted to filaments of elemental boron by chemical vapor deposition (CVD) on tungsten wire in a hydrogen atmosphere. Numerous laboratory preparations of boron trichloride have been reported. One of the most convenient is the halogen exchange reaction of aluminum chloride with boron trifluoride or a metal fluoroborate. 

Boron fibers are produced by chemical vapor deposition (CVD) onto a substrate filament (e.g. tungsten or carbon) and thereby consist of two components. They exhibit both metallic and nonmetallic properties, which is to be expected for pure boron due to its position in the periodic table. 

GE reported the discovery of natural semiconducting diamond in 1952 [31]. Presently, hot filament CVD and microwave plasma assisted CVD (MPACVD) produce polycrystalline or diamond carbon (DLC) films at 1-10 pm/h on a variety of substrates. However, true epitaxial growth presently is not routinely achievable at this time. Diamond substrates also are not readily available making large area lattice matched depositions a problem. Typieal substrates are Si, sapphire and even copper. Boron is an effective p-type dopant, but there is no successful n-type dopant, although As, Li, O, P and Sb have been tried. 

High-modulus graphite and carbon fibers, aramid fibers and ECPE fibers are playing a more and more important role in RPs. Boron filaments, with outstanding tensile strengths, are usually used in the form of prepreg tapes and have been primarily evaluated for the aerospace and aircraft industry. 

FIGURE 1-6 Single filament of boron nitride-coated Nippon Carbon Nicalon non-oxide ceramic fiber. Nonoxide fibers discussed in this report include polycrystalline SiC fibers and multiphase (amorphous or crystalline) fibers consisting of B,C,N,Ti, or Si. Current manufacturers include Bayer, Dow Corning, Nippon Carbon, Textron, Tonen, and Ube. Source Dow Coming Corporation. 

Fibrous reinforcement in popular usage is almost synonymous with fibreglass, although other fibrous materials (carbon, boron, metals, aramid polymers) are also used. Glass fiber is supplied as mats of randomly oriented microfibrils, as woven cloth, and as continuous or discontinuous filaments. Hand lay-up is a versatile method employed in the construction of large structures such as tanks, pools, and boat hulls. 

Boron/tungsten fiber applications include the use of filaments and of boron/tungsten fiber reinforced prepreg tape, aluminum matrix composites, and boron/graphite structures. The major applications for these structures are found in the aerospace market and about 25% in sporting goods markets [36]. SiC/carbon fiber reinforced products include aluminum, titanium, and ceramic matrix composites. Major applications for these structures are also found in the aerospace market, minor uses in the industrial market [37]. 

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