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Structural evolution in sol-gel-derived yttrium aluminum garnet-alumina precursor fibers

: Kruger, R.; Glaubitt, W.; Lobmann, P.

Journal of the American Ceramic Society 85 (2002), Nr.11, S.2827-2833
ISSN: 0002-7820
Fraunhofer ISC ()
structural evolution; water-vapor atmosphere; dense amorphous fiber; amorphous fiber structure; adsorption; transmission electron microscopy; Young's Modul; pyrolyzed fiber; elastic behavior; sintering test; residual C content; organic; micropore; pyrolysis temperature

A sol leading to a eutectic Al/sub 2/O/sub 3/-Y/sub 3/Al/sub 5/O/sub 12/ composition was spun into fibers. These fibers were dried and pyrolyzed between 200 degrees and 850 degrees C in a nitrogen or water-vapor atmosphere. Pyrolysis in nitrogen resulted in dense, amorphous fibers with considerable residual carbon content. In water vapor, fibers also remained amorphous, but organics were almost completely removed. The loss of organics created micropores that grew as the pyrolysis temperature increased. The amorphous fiber structures were examined by nitrogen adsorption, helium pycnometry, and transmission electron microscopy. Young's moduli of the pyrolyzed fibers were measured, and porosities of the fibers were calculated from both nitrogen-adsorption data and elastic behavior. Sintering tests showed the best sinterability for fibers pyrolyzed in water vapor to 385 degrees -500 degrees C.