Oxide Fiber Processing

The second ceUulosic fiber process to be commercialized was invented by L. H. Despeissis (4) in 1890 and involved the direct dissolution of cotton fiber in ammoniacal copper oxide Uquor. This solvent had been developed by M. E. Schweizer in 1857 (5). The cuprammonium solution of ceUulose was spun into water, with dilute sulfuric acid being used to neutralize the ammonia and precipitate the ceUulose fibers. H. Pauly and co-workers (6) improved on the Despeissis patent, and a German company, Vereinigte Glanstoff Eabriken, was formed to exploit the technology. In 1901, Dr. Thiele at J. P. Bemberg developed an improved stretch-spinning system, the descendants of which survive today. 

Oxide fibers are manufactured by thermal or chemical processes into a loose wool mat, which can then be fabricated into a flexible blanket combined with binders and formed into boards, felts, and rigid shapes or fabricated into ropes, textiles and papers. The excellent thermal properties of these products make them invaluable for high temperature industrial appHcations. 

Nonoxide fibers, such as carbides, nitrides, and carbons, are produced by high temperature chemical processes that often result in fiber lengths shorter than those of oxide fibers. Mechanical properties such as high elastic modulus and tensile strength of these materials make them excellent as reinforcements for plastics, glass, metals, and ceramics. Because these products oxidize at high temperatures, they are primarily suited for use in vacuum or inert atmospheres, but may also be used for relatively short exposures in oxidizing atmospheres above 1000°C. 

Oxidation catalysis, molybdenum compounds in, 7 7 38 Oxidation chemistry daytime, 77 791-792 in fiber optic fabrication, 77 138-139 nightime, 77 792-793 Oxidation ditch process, in biological waste treatment, 25 905... 

The last quarter of the twentieth century saw tremendous advances in the processing of continuous, fine diameter ceramic fibers. Figure 6.4 provides a summary of some of the important synthetic ceramic fibers that are available commercially. We have included in Fig. 6.4 two elemental fibers, carbon and boron, while we have excluded the amorphous, silica-based glasses. Two main categories of synthetic ceramic fibers are oxide and nonoxides. A prime example of oxide fibers is alumina while that of nonoxide fibers is silicon carbide. An important subclass of oxide fibers are silica-based glass fibers and we devote a separate chapter to them because of their commercial importance (see chapter 7). There are also some borderline ceramic fibers such as the elemental boron and carbon fibers. Boron fiber is described in this chapter while carbon fiber is described separately, because of its commercial importance, in Chapter 8. 

Crystalline oxide fibers represent an important dass of ceramic fibers mainly because of their superior oxidation resistance, being oxides. We describe the processing, structure, and properties of oxide fibers, mainly alumina and some alumina+silica-type fibers. 

High temperature stability of these nonoxide fibers in air is another critical problem. Thermal stability of ceramic fibers derived from polymeric precursors is of special concern mainly because, as mentioned above, they frequently have undesirable phases present in them. Polycarbosilane-derived SiC fibers, such as Nicalon or Tyranno, involve a thermal oxidation curing process as described above and can contain as much as 10 wt % oxygen (Okamura and Seguchi, 1992). Such fibers decompose at temperatures above 1200 C in a nitrogen or argon atmosphere with SiO and CO gas evolution ... 

Asbestos is a fibrous mineral mined from rock deposits. There are approximately 30 types of minerals in the asbestos group. Of the six that have commercial importance, only oneotile, a hydrated silicate of magnesium that contains small amounts of iron and aluminum, oxides, is used in fiber processing. 

The starting point for the suspension process is a finely divided aluminum oxide powder suspended in water. An additive provides the necessary viscosity. Spinning of this finely divided suspension with the help of additives provides raw aluminum oxide fibers, which by calcining and treatment at high temperature is converted into non-porous sintered a-aluminum oxide fibers. 

Although skeletal muscle fibers, particularly of the "fast glycolytic" type, are able to utilize their phospho-creatine (PCr) and glycogen stores for sizable bursts of energy turnover at rates well exceeding that of oxidative recovery processes, these stores are small in... 

Textiles. In the area of textile and synthetic fiber processing, amine oxides have been used as dyeing auxiUaties as well as wetting agents (51,52), as antistatic agents (qv) (53—55), and as bleaching agents (56,57). 

Oxide fibers have been commercially available since the 1970s. Control of the microstructure through careful processing is essential to obtain the desired properties, which for ceramic fibers for sfrucfural applicafions are... 

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