Reactions and Microstructure Development in Mullite Fibers |
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Authors: | Elizabeth A Richards Chris J Goodbrake Harold G Sowman |
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Affiliation: | Ceramic Technology Center, 3M Company, St. Paul, Minnesota 55144 |
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Abstract: | Microstructural and compositional changes during heat treatment of sol–gel-derived mullite fibers with additions of 2 wt% B2O3, 2 wt% P2O5, 2 wt% Cr2O3, and (1 wt% P2O5+ 1 wt% Cr2O3) were compared with those of undoped mullite fibers. For all compositions the sequence of phase development was the crystallization of a spinel phase (?-Al2O3 or Al–Si spinel) from amorphous material, followed by the formation of mullite at higher temperatures. Differential thermal analysis showed that additions of B2O3 and P2O5 increased the temperature of spinel formation and that B2O3 significantly decreased the temperature of mullite formation. After 1 h at 1200°C, the size of mullite grains in fibers that contained B2O3 was less than 1000 Å the grains in fibers of other compositions were 6000 to 12000 Å. After 60 h at 1400°C, fibers modified with B2O3 had a grain size less than 2000 to 3000 Å the grains in fibers of other compositions were 6000 to 12000 Å. B2O3 was the most volatile additive. |
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Keywords: | mullite fibers sol–gel nanocrystalline microstructure |
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