Polycrystalline fibers oxide

FIGURE 1-7 Tow of 3M Nextel 610 polycrystalline ceramic oxide fibers. Polycrystalline oxide fibers are... 

D. J. Pysher and R. E. Tressler, Tensile Creep Rupture Behavior of Alumina-Based Polycrystalline Oxide Fibers, Cer. Eng. Sci. Proc., 13[7-8], 218-226 (1992). 

Saruhan, B. et al., Cristallization of electrostatically seeded lanthanum hexaluminate films on polycrystalline oxide fibers, J. Am. Ceram. Soc., 83, 3172, 2000. 

Representative properites for polycrystalline oxide fibers consisting of predominantly AI2O3... 

Commercial polycrystalline oxide fibers are produced by spinning and hydrolyzing precursors. First a fiber precursor solution is filtered and concentrated to remove excess solvent, forming a viscous spin dope. Then, continuous filaments are extruded by spinning. The filaments are pyrolyzed to remove volatile components and then heat treated above 800X (1,472°F) to crystallize and sinter the fiber. Polycrystalline oxide fibers are produced in tows of200 to 1,000 fibers with diameters of 10 to 16 pm (0.39 to 0.63 mils). Typical ranges of properties are listed in Table ES-1. 

FIGURE 3-19 Typical creep curves for polycrystalline alumina-based oxide fibers at 1,090°C (1,994 F) in air. 

In the last decade, many new oxide fibers with improved high-temperature performance have been commercialized. The keys to these improvements has been (1) the design of fiber microstructures to reduce the volume of amorphous phases and (2) the development of multiphase polycrystalline fibers. Eliminating amorphous phases prevents rapid, viscous deformation under load at high temperatures. Multiphase polycrystalline microstructures appear to inhibit creep, particularly at elevated temperatures. Examples of developmental fibers with improved high-temperature properties include polycrystalline AI2O3, YAG, and mullite filjers. 

Additional investigation of the layered perovskites (KCa2Nb30io and BaNd2Ti30io) should be limited because of the low probability that these compounds will be stable with available creep-resistant fibers. Layered perovskites may be stable with a creep-enhanced polycrystalline alumina fiber although it has been reported that these coatings are stable with alumina only at moderate temperatures ( 1,250°C [2,282°F]). The simpler chemistry of layered P-aluminas and magnetoplumbites are more likely to be used as coatings for available oxide fibers. 

Pysher, D.J., and R. E. Tressler. 1992b. Tensile creep rupture behavior of alumina-based polycrystalline oxide fibers. Ceramic Engineering and Science Proceedings 13(7-8) 218-226... 

Continuous-length polycrystalline ceramic fibers with non-oxide compositions are currently being developed and used for a variety of low and high-temperature structural applications. Recent literature reviews detail the process methods, properties, and applications for the many non-oxide fiber types that have been developed over the last 30 years [1- ]. 

It seems unlikely that polycrystalline oxide fibers will ever approach the use temperatures of SiC-based or C fibers (> 1500°C). Hence, it can be anticipated that even in long-term use, materials selection for refractory composites will balance the high temperature properties of non-oxide composites versus the superior enviro-thermal durability of oxide composites. 

J. D. BIrchall, The preparation and properties of polycrystalline aluminum oxide fibers, Trans. J. Br. Ceram. Soc., 82,143-145 (1983). 

NEXTEL 312 Ceramic Fibers are continuous polycrystalline metal oxide fibers suitable for producing textiles without the aid of other fiber or metal inserts. Nextel fabrics, tapes and sleevings are exceptional, high temperature products designed to meet the toughest thermal and electrical performance requirements and to offer performance far beyond the useful limits of other high temperature textiles. 

Pysher, D. J., and Tressler, R. E., "Tensile Creep Rupture Behavior of Alumina-Based Polycrystalline Oxide Fibers." Proceedings of the 16th Aimuai Conference on Composites and Advanced Ceramic Materiais, Parti of 2 Ceramic Engineering and Science Proceedings, Voiume 13, Issue 7/8. John Wiley Sons, Inc., 2009. 

Fibrous materials may be naturally occurring or synthetically manufactured by thermal or chemical processes (Fig. 1) (see Fibers, survey). Refractory fibers are generally used in industrial appHcations at temperatures between 1000°C and 2800°C. These fibers may be oxides or nonoxides, vitreous or polycrystalline, and may be produced as whiskers, continuous filaments, or loose wool products. 

Fiber chemistry determines whether the material is an oxide or nonoxide and can also influence its vitreous or polycrystalline physical form. Refractory fibers generally have diameters ranging from submicrometer to 10 )J.m, and lengths, as manufactured, may range from millimeters to continuous filaments. 

The 3M Company manufactures a continuous polycrystalline alurnina—sihca—boria fiber (Nextel) by a sol process (17). Aluminum acetate is dissolved in water and mixed with an aqueous dispersion of colloidal sihca and dimethylform amide. This mixture is concentrated in a Rotavapor flask and centrifuged. The viscous mixture is then extmded through spinnerettes at 100 kPa (1 atm) the filaments are collected on a conveyor and heat-treated at 870°C to convert them to metallic oxides. Further heating at 1000°C produces the 10-p.m diameter aluminum borosihcate fibers, which are suitable for fabrication into textiles for use at temperatures up to 1427°C. 

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