Crystal boria

Boria-free fibers consist of nanocrystalline ri- or y-transition alumina and are porous when fired at 1000°C. They are fully sintered and crystallized as mullite at 1400°C. B20rmodified fibers are poorly crystallized as transition alumina when fired at 1000°C, display a low specific surface area and transform completely to mullite at 1400°C (density 3.00 glcni). Boria seems to enhance sintering at low temperatures before mullitization, and the boria-modified fibers exhibit a lower mullite grain size. 

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