Aluminosilicates fiber

Aluminosilicate Fibers. Vitreous alurninosihcate fibers, more commonly known as refractory ceramic fibers (RCF), belong to a class of materials known as synthetic vitreous fibers. Fiber glass and mineral wool are also classified as synthetic vitreous fibers, and together represent 98% of this product group. RCFs were discovered in 1942 (18) but were not used commercially until 1953. Typical chemical and physical properties of these materials are shown in Table 3. 

Fig. 2. Thermal conductivity of refractories where ASF = aluminosilicate fiber and ZF = zirconia fiber. See Table 13 for group classifications (5,25).

Silica and aluminosilicate fibers that have been exposed to temperatures above 1100°C undergo partial conversion to mullite and cristobalite (1). Cristobalite is a form of crystalline silica that can cause silicosis, a form of pneumoconiosis. IARC has determined that cristobalite should be classified as 2A, a probable carcinogen. The amount of cristobalite formed, the size of the crystals, and the nature of the vitreous matrix in which they are embedded are time- and temperature-dependent. Under normal use conditions, refractory ceramic fibers are exposed to a temperature gradient, thus only the hottest surfaces of the material may contain appreciable cristobalite. Manufacturers Material Safety Data Sheets (MSDS) should be consulted prior to handling RCF materials. 

Griffith7 chronicled in lively fashion the growth and sudden demise of an extraordinary project of the Monsanto Co. to make phosphate fibers as substitutes for the much maligned asbestoses. The object was to make materials with most of the desirable properties of asbestos, but that would hydrolyze slowly in, say, the alveoli of the lungs to form a soluble and biologically beneficial product (phosphate ions), so avoiding the tendency of insoluble aluminosilicate fibers to remain indefinitely in biological material with the attendant risk of cancer. 

The Nextel series of fibers produced by the 3M Company consists of a variety of aluminosilicate fibers. These contain mainly AljOj+SiOj and some B2O3. The compositions and properties of Nextel 312, Nextel 440, Nextel 550, Nextel 610, and Nextel 720 fibers are given in Table 6.3. Nextel 610 is, of course, the a-alumina fiber described above. The sol-gel manufacturing process used by 3M Co. has metal alkoxides as the starting materials. Metal alkoxides are M(OR)j -type compounds where M is the metal and n is the metal valence, and R is an organic compound. Selection of an appropriate organic group is very important. It should provide sufficient stability and volatility to the alkoxide so M-OR... 

Figure 6.14 A comparison of various polycrystalline alumina and aluminosilicate fibers in the Nextel series. Note the superior creep resistance of the Nextel 720 fiber. 3M data.

Discontinuous Oxide Fibers 1.2.1. Melt-Spim Aluminosilicate Fibers... 

K. Nubian, B. Samhan, B. Kanka, M. Schmucker, H. Schneider, and G. Wahl, Chemical vapor deposition of Zr02 and C/Zr02 on mullite fibers for interfaces in mullite/aluminosilicate fiber-reinforced composites, J. 

Figure 5. Barium aluminosilicate fiber composite (a) powder/fiber (25wt%) mix, and (b) the fracture surface of an isostatically-prcssed and sintered fiber composite.

Generic borosilicate E-glass fibers Aluminosilicate fibers (<30%CeO2) Lead silicate glass fibers (<30%PbO) Niobium silicate fibers (<15%Ni,Os)... 

Kanka, B and Schneider, H., "Aluminosilicate fiber/mullite matrix composites with favorable high-temperature properties." Journal of the European Ceramic SocietylO.S (2000) 619-623. 

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