Other Refractory-Fiber Materials

Other materials besides boron and SiC widi potential for CVD fiber production are being investigated. They include B4C, TiC and TiB2 deposited on a heated core filament, generally by the hydrogen reduction of the chlorides.l ll J Typical properties of the resulting experimental fibers are shown in Table 14.10. Fiber diameter varies from 20-200 pm. 

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With the exception of glass fiber, asbestos (qv), and the specialty metallic and ceramic fibers, textile fibers are a class of soHd organic polymers distinguishable from other polymers by their physical properties and characteristic geometric dimensions (see Glass Refractory fibers). The physical properties of textile fibers, and indeed of all materials, are a reflection of molecular stmcture and intermolecular organization. The abiUty of certain polymers to form fibers can be traced to several stmctural features at different levels of organization rather than to any one particular molecular property. 

Chemical vapor infiltration (CVI) is widely used in advanced composites manufacturing to deposit carbon, silicon carbide, boron nitride and other refractory materials within porous fiber preforms. " Because vapor phase reactants are deposited on solid fiber surfaces, CVI is clearly a special case of chemical vapor deposition (CVD). The distinguishing feature of CVI is that reactant gases are intended to infiltrate a permeable medium, in part at least, prior to... 

Refractory Fibers Recently, zirconia-based insulating material with a low density and a low thermal conductivity has been developed in the form of fibers, paper, felt, board and shaped articles. The material is a cubic zirconia soHd solution stabilized with yttria, and has a maximum usable temperature of >2100 C. The innovative fabrication technique involves the use of an organic precursor fiber as a structural template, impregnated with an aqueous solution of zirconium chloride and yttrium chloride. The metallic salts are deposited within the organic fiber, which can subsequently be burned off by a controlled oxidation. The hollow remainder is then fired at a sufficiently high temperature (800-1300 °C) so as to induce crystallization, after which the oxide particles are sintered to develop a ceramic bond. Other techniques to produce refractory fibers involve phase inver-... 

Modem machining deals with an increasingly wide range of materials which includes, in addition to the traditional metals, high-chromium and nickel stainless steels, titanium, intermetallics, refractory metals, ceramics, glasses, fiber-reinforced composites, and many others. These materials have widely different properties. They react differently to machining and each presents a special machining problem. 

The properties of alumina listed in Sects. 4-10 show the unusual performance of pure alumina, leading to the variety of applications given in Table 1. Practical aluminas with impurities and defects have somewhat degraded properties, but often are superior to many other materials, and have a variety of specialized applications such as refractories, electronic components, and catalyst substrates. In [1] there are articles discussing the future of alumina. There will continue to be incremental improvements in processing methods and properties, leading to expansion of present applications. What really new areas of application of alumina are likely These predictions are speculative, but the most promising new applications of alumina will probably be in electronic circuits, optical components, and biomaterials. Alumina fibers for composites and optics are attractive if they can be made pure, defect-free, and cheap. Because of its excellent properties other unsuspected applications of alumina will undoubtedly be developed. 

In addition to the related mineral interferences, other minerals common in building material may present a problem for some microscopists gypsum, anhydrite, bru-cite, quartz fibers, talc fibers or ribbons, wollastonite, perlite, attapulgite, etc. Other fibrous materials commonly present in workplaces are fiberglass, mineral wool, ceramic wool, refractory ceramic fibers, kevlar, nomex, synthetic fibers, graphite or carbon fibers, cellulose (paper or wood) fibers, metal fibers, etc. 

The lining of anode baking furnaces is made from alumina silica refractories. This type of refractory actually determines the service life of flue walls of the anode baking furnace. The heat insulation layers may be made from lightweight fireclay brick, vermiculite slabs, fiber boards, and other materials... 

A series of man-made inorganic fibers other than glass exist that are nonflammable, heat stable amorphous materials useful in industrial fabric constructions, including refractory materials. These inorganic fibers... 

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