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|Directionally solidified eutectic and off-eutectic mullite zirconia fibres
|Carvalho, R. G.
Pires, M. S.
Fernandes, A. J. S.
Silva, R. F.
Costa, F. M.
GROWN AL2O3-ZRO2(Y2O3) EUTECTICS
|ELSEVIER SCI LTD
|Eutectic and off-eutectic mullite-zirconia fibres were grown by LFZ (laser floating zone) directional solidification. The microstructure of the mullite-zirconia eutectic fibres varies from planar coupled eutectic (1 mm/h pulling rate) through mullite columnar growth with coarse zirconia inclusions (10 mm/h pulling rate) to faceted mullite eutectic dendrites, which enclose a dispersion of fine zirconia fibrils (100-500 mm/h pulling rates). Near-equilibrium conditions determine the crystallization of monoclinic zirconia and the absence of any amorphous phase, whereas for higher speeds the tetragonal structure is retained and a residual liquid is kept after the eutectic solidification. Similar structural and morphological characteristics are displayed by the mullite-rich off-eutectic composition added to the development of prismatic crystals of mullite primary phase. In opposition, heavy constitutional supercooling takes place in the case of the zirconia-rich off-eutectic fibres, where equiaxed zirconia dendrites soon form as a primary phase, leaving a non-equilibrium mixture of alumina and sillimanite as interdendritic constituent. (C) 2012 Elsevier Ltd. All rights reserved.
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|Directionally solidified eutectic and off-eutectic mullite-zirconia fibres_10.1016j.jeurceramsoc.2012.09.032.pdf
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