Aluminate fibers

King, B.H., Y. Liu, R.M. Laine, and J.W. Halloran. 1993. Fabrication of yttrium aluminate fibers. Ceramic Engineering and Science... 

M. K. Cinibulk, T. A. Parthasarathy, K. A. Keller, and T. Mah, Porous Rare-Earth Aluminate Fiber Coatings for Oxide-Oxide Composites, Ceram. Eng. Sci. Proc., 21 [4] 219-228 (2000). 

Ca aluminate fiber fiom inviscid melt 37GPa 4... 

The highest modulus of a given substrate is obtained with a single crystal structure. Single crystal CVD-SiC whiskers (578 GPa) have a stiffen more highly ordered, structure than polycrystalline CVD-SiC fibers (190-400 GPa), and sapphire whiskers and fibers (415 GPa) are stiffer than slurry spun polycrystalline alumina fibers such as Fiber FP (380 GPa). Superimposed upon this relationship is a compositional factor. Fiber modulus and structural order generally also decrease with increasing compositional complexity, e.g., silicon carbide is intrinsically stiffer than silicon oxycarbide such as Nicalon, and slurry spun alumina fibers are stiffer than sol-gel or melt spun aluminate fibers. 

Many continuous inorganic fibers can be formed directly from the liquid phase including melts (Chapter 4) and solutions (Chapter 5). Ceramic aluminate fibers are indirectly derived from a viscous liquid phase, which includes dispersions and sol-gels. These fibers as well as carbon fibers and silicon carbide fibers are initially obtained as nonfunctional precursor fibers. Since the final functional fibers are actually derived from solid precursor fibers, they will be covered in Chapters 8 to 10 dealing with advanced inorganic fibers derived from the solid phase. 

This calcium aluminate fiber was evaluated in structural applications but it was not suitable for the evaluation of infrared optical properties because it contained bound water as evidenced by a strong hydroxyl band at 29 jjm in the IR transmission spectra. Hydroxyl-free compositions were made in carbon crucibles [17] by the Davy process [39], i.e., by a procedure [40] by which disposable optical calcium aluminate bulk glasses are prepared for commercial applications in optical windows. 

Table VII. Modulus of updrawn calcium aluminate fibers [4, 6-8,31]...

Figure 12. Straight fiber and frozen Rayieigh waves. The straight cyiindrical fiber represents an inviscid meit spun caidum aluminate glass fiber that had been surface stabilized with particulate carbon. The frozen Rayleigh wave strudure represents a caidum aluminate fiber that was not surface stabilized and solidified while it was in the process of breaking up into droplets and shot...

ESCA anaiysis confirms the presence of oxidized silicon and oxidized iron in the wire surface or skin [51]. The siiica peak gradualiy disappears at a depth of 100 nm, giving way to the peaks of iron and siiicon. Anaiysis with a CAMECA ion analyzer shows that the intensity of Si peaks decreases to naught between 17 and 55 nm from the surface of a 165 pirn diameter steel wire. The results parallel those noted for carbon with aluminate fibers. 

In summary, a typical aluminate fiber is spun between 1500 and 1700°C (Table VIII). Carbon enters into the skin of the still liquid jet. A secondary carbon sheath is obtained when more carbon is present in the reactive propane environment than needed to stabilize the liquid jet, but after the fiber is solidified (<500°C). At higher temperatures it would oxidize (bum off). Thus, only some fibers have a secondary carbon sheath. If it is formed, it results from side growth, a secondary growth mode, that has already been discussed with regard to the growth of carbon whiskers in a carbon vapor environment (Chapter 2.1.1). 

Figure 15. SNMS depth profile of a translucent calcium aluminate fiber. Redrawn from F. T. Wallenberger and S. D. Brown, High modulus glass fibers for new transportation and infrastructure composites and for new infrared uses, Composites Science and Technology, 51,243-263 (1994).

Inviscid melt spun calcium aluminate glass fibers have low strength (0.5-1.1 GPa) and moduli (46-58 GPa). Low strength and low stiffness can be attributed to the random structure frozen into the fibers during rapid solidification. As a result, they are not likely to become composite reinforcing fibers, despite their excellent alkali resistance which they share with quaternary calcium-aluminate fibers [9]. 

The same generic dry spinning process can be used to fabricate the precursor fiber for a carbon fiber from an infusible polymer, such as polyacrylonitrile, for a polycrystalline aluminate fiber from a sol-gel or for a polycrystalline alumina fiber from a slurry. Again, a high temperature curing step is required to convert the as-spun, amorphous precursor fiber into the final functional fiber. In these cases, however, an amorphous polycrylonitrile precursor fiber changes into a carbon fiber, and an amorphous aluminate precursor fiber into a crystalline aluminate fiber. The final functional fiber is therefore directly derived from a solid and amorphous precursor fiber and only indirectly from a liquid phase, i.e., a melt or sol-gel, respectively. 

Alpha alumina, 600, 605-607 Alpha parameter. See a parameter Alumina. See Aluminum oxide Aluminate fiber, 863 Aluminoborosilicate fiber, 863 Aluminoslicate ester, 218 fiber, 863... 

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