Alumina zirconia fibers

Figure 6.5 (a) Microstructure of an alumina fiber. TEM. (b) Microstructure of an (alumina+zirconia) fiber. SEM. The white particles are zirconia. 

Coated abrasives consist of a flexible backing on which films of adhesive hold a coating of abrasive grains. The backing may be paper, doth, open-mesh cloth, vulcanized fiber (a specially treated cotton rag base paper), or any combination of these materials. The abrasives most generally used are fused aluminum oxide, sol—gel alumina, alumina-zirconia, silicon carbide, garnet, emery, and flint... 

A sol-gel method is used to produce silica-stabilized alumina (Saffil) and calda-stabilized zirconia fibers. The flow diagram for Saffil fiber is shown in Fig. 

Since the initial introduction of laser diffraction instrumentation in the 1970s, many different applications to panicle si/e aniilysis have been reported. Ihese have included measurements of si/e distributions of radioactive tracer particles, ink particles used in photocopy machines, zirconia fibers, alumina particles, droplets from electronic fuel injectors, crystal growth particles, coal powders, cosmetics, soils, resins, pharmaceuticals, metal catalysts, electronic materials, phoiugraphic emulsions, organic pigments, and ceramics. About a dozen instrument companies now produce LALLS instruments. Some I.AI.LS instruments have become popular as detectors for size-exclusion chromatography. 

FIGURE 8. A comparison of the creep rate of the Nextel 650 and PRD-166 fibers, both of which are composed of a-alumina and zirconia, the Nextel 720 which is composed of a-alumina and mullite and the pure a-alumina Fiber FP. (Reprinted, from reference 12, "Mechanical and Microstructural Characterization of Nextel 650 Alumina-Zirconia Fibres , with kind permission of Elsevier). 

The creep of alumina based fibers can be reduced by adding a second phase. For example, the steady state creep rate of a PRD-166 a-alumina/t-ZrOa (Y) fiber is about one order of magnitude lower than that of the single phase a-alumina fiber (Fiber FP) [78]. This effect is thought to be related, at least at low temperatures (T<1100°C), to the fact that the dispersed zirconia particles at grain boundaries limit the mobility of intergranular dislocations [67],... 

Farmer, S.C., Sayir, A. and Dickerson, P.O. (1993) Mechanical and microstructural characterization of directionally solidified alumina-zirconia eutectic fibers. In Symposium Proceedings of In-Situ Composites, Science and Technology, pp. 167-182. TMS, Warrendale, PA. 

Oxide fibers include glass fibers, mullite fibers, zirconia fibers and alumina fibers. Of these, a-alumina-based fibers have been used intensively for ceramic matrix composites. Fiber FP, manufactured by Du Pont in 1979, was the first wholly a-alumina fiber produced [34]. At present, Almax (Mitsui Mining Material Co. Ltd., Japan) and Nextel 610 (3M Co., USA) are commercially available a-alumina fibers. Almax contains 99.5% alumina and has an elastic modulus of 330 GPa, and Nextel 610 has a tensile strength of 2.4 GPa and an elastic modulus of 380 GPa [35]. 

In addition to the single fiber formation, the alumina and/or zirconia fiber mats having web-like microstructure were produced by using the centrifugal spinning technique (Venkatesh et al., 1999 Chatleijee et al., 2002a). 

The process competes with the traditional method of fiber production in which the precursor material is melted, usually in an arc furnace, then drawn through spinnerets and spun or impinged by high pressure air. The melt-spin process is not well suited to materials with high melting points such as zirconia, silicon carbide, or pure alumina. 

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