Mullite fiber

Mullite fibers Multhiomyan Multiblock copolymers Multi chip modules... 

Ha. J.S. and Chawla, K.K. (1993). Effect of SiC/BN double coating on fiber pullout on mullite fiber/ mullitc matrix composites. J. Mater. Sci. Lett. 12, 84-86. 

This section centers on fiber coatings for non-oxide eomposites in which either the fiber or the matrix is a non-oxide ceramic. Although oxide fiber-reinforced composites have been studied, most of the research available in the literature has focused on SiC fiber-reinforced composites. For example, mullite (3Al203-2Si02) fiber-reinforced SiC matrix composites have been fabricated by CVI (chemical vapor infiltration). However, SiC fiber-reinforced SiC matrix (SiC/SiC) composites are superior for the following reasons (1) mullite fiber-reinforced composites do not improve resistance to oxidation, one of the major factors limiting the use of non-oxide composites and (2) SiC fibers have mechanical properties superior to those of mullite fibers. This section will be concerned primarily with SiC fiber-reinforced ceramic composites, which offer the best oxidation resistance of any non-oxide fiber at high temperatures (particularly above 1,100°C [2012°F]). 

Ceramic fibers consisting of mullite and alumina mixtures have demonstrated creep strengths considerably greater than the creep strengths observed in single-phase alumina or mullite fibers (Chapter 3). The mechanism by which multiphase... 

Richards, E.A., C.J. Goodbrake, and H.G. Sowman. 1991. Reactions and microstructure development in mullite fibers. Journal of the American Ceramic Society 74(10) 2404-2409. ... 

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. 

Various precursors can be used to prepare mullite fibers by dry or wet spinning. An often-used precursor is a mixture of a silica and an alumina sol. The silica sol is prepared by hydrolysis/condensation of TEOS or Si(OC2Hs)4 that, in turn, had been prepared in an alcohol-... 

The aluminum-chelated alkoxide can also be used unhydrolyzed, in a mixture with prehydrolyzed TEOS [51]. This mixture is concentrated under reduced pressure and the fibers are dry [49] [51] or wet spun [48]. Mullite fibers were prepared from a single phase precursor [52], whereby the alumina source was a viscous solution of aluminum formoacetate. After concentration, the dope was dry spun, yielding fibers which contained orthorhombic mullite after firing at 1250°C. Mullite fibers can also be prepared from another single phase liquid precursor, a mixture of an alkoxysilane, such as tetramethoxysilane or ethyl silicate, and an aluminum chlorohydrate polyol complex, such as the 1,2- dihydroxypropane complex, Al2(0H)5CI-H20-CH3CH(0H)CH20H[46]. 

In this equation, A is a constant, Q is the apparent activation energy, R is the gas constant, G is the shear modulus, and p and n are the inverse grain size and stress exponents, respectively. The values of n and Q, measured for the fibers considered here, are listed in Table VI. The high values of n suggest that creep deformation is rate controlled by an interface reaction-limited grain boundary diffusional process [78], Mullite fibers are more resistant to creep than a-alumina fibers. For example, the strain rate of the Nextel 480 mullite fiber at 1200 C is almost two orders of magnitude lower than that of the Nextel 610 a-alumina fiber [55]. 

S. Al-Assafi, T. Cruse, J. H. Simmons, A. B. Brennan and M. D. Sacks, Processing of fine-diameter continuous mullite fibers, Ceram. Trans., 46,65-72 (1994). 

Sayir, A. and Farmer, S.C. (1995) Directionally solidified mullite fibers. In Ceramic Matrix Composites — Advanced High Temperature Structural Materials, Mater. Res. Soc. Proc., 365, pp. 11-21. 

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]. 

FIGURE 18.18 SEM image showing fiber pullout on the fracture surface of AIP04-coated alumina/mullite fiber/Al203 CMC, hot pressed at 1250°C for 1 h. 

The continuous mullite fibers were first made by heat-treating the gel fibers spun from the sol prepared by hydrolyzing the stochiometric mixture of TEOS and acac-modified AIP (Tucker, 1990). The amorphous gel fibers were crystallized to mullite fibers above 1000°C. Thereafter, several cost-effective sol-gel methods of the mullite fiber formation have been developed. In one method, the mixture of silica sol and alumina sol prepared from aluminum salts were spun with the aid of polyethylene oxide (PEO) (Bhattacharya, 1996a). In others the stoichiometric mixture of inexpensive alumina sources (nitrate, acetates. 

Tsai M.T. Hydrolysis, condensation offorsterite precursor alkoxides modification ofthe molecular gel structure by acetic acid. J. Non-Cryst. Solids 2002d 298 116-130 Tucker D.S., Sparks J.S., Esker D.C. Production of continuous mullite fibers via sol-gel processing. Ceram. Bull. 1990 69 1971-1974... 

Zhou XB, Qiu F, Penchal Reddy M, Han YH, Lee J, Huang Q. Comparative study of conventional and microwave sintered mullite fibers a structural study. Advances in Applied Ceramics Structural, Functional and Bioceramics 2015 114 139-43. 

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