Alumina fibers based continuous fiber

The first alumina based continuous fiber was produced in 1974 by 3M and is sold under the name Nextel 312. It contains only 62% alumina together with boria and silica. 

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. 

Oxide fibers find uses both as insulation and as reinforcements. Glass fibers, based on silica, possess a variety of compositions in accordance with the characteristics desired. They represent the biggest market for oxide fibers. Unlike other oxide fibers, glass fibers are continuously spun from the melt and are not used at temperatures above 250°C. Short oxide fibers can be melt blown whilst other aluminasilicate and alumina based continuous fibers are made by sol-gel processes. Initial uses for these fibers were as refractory insulation, up to 1600°C, but they are now also produced as reinforcements for metal matrix composites. Continuous oxide fibers are candidates as reinforcements for use up to and above 1000°C. 

The alumina based fibers discussed in section 3.2 possess a range of compositions. They can be short, as with the S affil fibers or continuous, as with the others described. Their properties at room temperature depend on the ct-alumina content and at high temperature, the presence of any second phase (31). The Saffil fiber contains a few percent of silica with the remainder of the composition being alumina in one of its transition phases or as a mixture of transition phases and a-alumina. Table 7 shows the changes in processing of fibers of this type (32).The properties of alumina based fibers areshown in Table 8. Figure 3 shows the tensile curves of a pure a-alumina fiber, the Fiber FP, which had a grain size of 0.5 p,m (23). 

Reinforcements that have been used for CMCs include continuous fibers, discontinuous fibers, whiskers, and particles. Key continuous fibers used in CMCs include carbon, silicon carbide-based, alumina-based, alumina-boiia-sihca, quartz, and alkah-resistant glass. Steel wires are also used. Discontinuous CMC fibers are primarily silica based. Silicon carbide is the key whisker reinforcement. Particulate reinforcements include silicon carbide, zirconium carbide, hafnium carbide, hafnium diboiide, and zirconium diboride. 

Maneeratana, V., Sigmund, W.M. Continuous hollow alumina gel fibers by direct electrospinning of an alkoxide-based precursor. Chem. Eng. J. 137(1), 137-143 (2008)... 

---