Filament, continuous boron

Attempts to produce boron fibers in a pure state have been frustrated by the brittleness of the material, which has hindered the manufacture of continuous filaments. Currently boron fibers are produced by chemical vapor deposition (CVD) in which boron is deposited by reducing BCI3 in a hydrogen-containing atmosphere at 1127 to 1177°C, according to the overall reaction ... 

Boron itself has been used for over two decades in filament form in various composites BO3/H2 is reacted at 1300° on the surface of a continuously moving tungsten fibre 12/tm in diameter. US production capacity is about 20 tonnes pa and the price in about 80(. The primary use so far has been in military aircraft and space shuttles, but boron fibre composites are also being studied as reinforcement materials for commercial aircraft. At the domestic level they are finding increasing application in golf shafts, tennis rackets and bicycle frames. 

Boric oxide is used to produce many types of glass including low-sodium, continuous filaments for glass-belted tires, and fiberglass plastics. It also is used to make ceramic coatings, porcelain enamels and glazes. Also, the compound is used as an acid catalyst in organic synthesis and to prepare several other boron compounds. 

The first continuous filaments were rayon, and these, as well as polyacrylonitrile (PAN) fibers, have been pyrolyzed to produce graphite fibers. High-modulus reinforcing filaments have also been produced by the deposition of boron atoms from boron trichloride vapors onto tungsten or graphite filaments. 

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. 

A third way to toughen plastics is to add fibers, to make composite materials (3). Fibers in use today include glass, boron, graphite, or other polymers. These may be chopped or added as continuous filaments. With continuous filaments, the fibers carry most of the mechanical load, while the polymeric matrix serves to transfer stresses to the load-bearing fibers and to protect them against damage (31-34). Thus, a controlled amount of adhesion between the fibers and the matrix is required. 

In a design permitting unsuitable metals, they may be replaced with next-generation filament-wound composites (e.g. continuous), glass, graphite, boron, beryUium, titanium alloy, steel, carbon, silicone filament, or strip unidirectional, bidirectional, multi-directional (see Figure 9.50). 

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