Multicomponent ceramic fibers

Solution chemistry remains attractive as an inexpensive technique useful for processing ceramics, fibers or coatings, even on a large scale not possible with evaporation techniques. However, the application of these solution techniques to multicomponent systems has rarely been attempted. A better basic understanding of all reaction steps from the solution to the ceramic is needed before a real improvement in the process will be possible. 

TABLE 10-2. MULTICOMPONENT OXIDE GLASS AND CERAMIC FIBERS PREPARED BY THE SOL-GEL METHOD... 

Synthetic polymers have become extremely important as materials over the past 50 years and have replaced other materials because they possess high strength-to-weight ratios, easy processabiUty, and other desirable features. Used in appHcations previously dominated by metals, ceramics, and natural fibers, polymers make up much of the sales in the automotive, durables, and clothing markets. In these appHcations, polymers possess desired attributes, often at a much lower cost than the materials they replace. The emphasis in research has shifted from developing new synthetic macromolecules toward preparation of cost-effective multicomponent systems (ie, copolymers, polymer blends, and composites) rather than preparation of new and frequendy more expensive homopolymers. These multicomponent systems can be "tuned" to achieve the desired properties (within limits, of course) much easier than through the total synthesis of new macromolecules. 

When multicomponent alkoxide solutions, or a single alkoxide and a soluble inorganic salt, are mixed, a multicomponent alkoxide may result. In this way, such complex oxides such as the YBCO superconductor (cf. Section 6.1.2.4) can be formed. Sol-gel processing can also be used to coat fibers for composites and to form ceramics with very fine pore sizes called xerogels. A xerogel commonly contains 50-70% porosity, a pore size of 1-50 nm, and a specific surface area exceeding 100 m /g. 

Several kinds of electro- and/or magneto-ceramics have been formed into thin fibers by the sol-gel method with the aim at the application to sensing elements. In the preparation of strictly stoichiometric double or multicomponent oxides such as LiNbOs, PbTi03 and so on, the intimate mixing of raw materials at molecular level in sols or gels would permit the direct formation of desired compounds without diffusion process of constituent atoms or ions, which is indispensable in the conventional powder route. It is often observed. 

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