YTTRIUM ALUMINATE CERAMIC FIBERS VIA PRE-CERAMIC POLYMER AND SOL-GEL ROUTES

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Abstract
Yttrium aluminum garnet (YAG - Y3Al5O12) fibers have been prepared by dry spinning solutions of yttrium and aluminum carboxylate polymers (precursor route) and by dry spinning aqueous oxide sols (sol-gel route). Fibers from aqueous diphasic gels are prepared by mixing a colloidal alumina sol containing 50-nm hydrous alumina with a colloidal yttria sol containing 10-nm yttrium oxide, using polyvinylpyrrolidone as a spinning aid. Fibers by the precursor route are made from spinnable THF solutions of yttrium isobutyrate and aluminum isobutyrate or from aqueous solutions of polymeric aluminum formate and yttrium acetate. The isobutyrate materials decompose between 200-400°C to an amorphous residue. Crystallization occurs abruptly between 875°C and 900°C, forming the YAG phase directly. The formate-acetate also decomposes to amorphous residues, which form YAG at 900°C. In the diphasic gel, YAG forms gradually between 1000 and 1200°C, with intermediate products YAP (YalO3 perovskite) and/or YAM (Y4Al2O9 monoclinic). At 1500°C, single phase YAG is obtained as pore-free fibers with 500 nm grains.