Crystallization Behavior of Hybrid Mullite Fiber Precursors

Glass free fine-grained microstructure is ideal for preparing mullite fibers with good high temperature mechanical properties. Single phase/diphasic mullite hybrid precursor was adopted to adjust crystalline microstructure of mullite fibers without adding any glass formers. The single phase precursor crystallized in situ to form mullite at 980 acting as seed crystals for diphasic components in hybrid precursors to induce the formation of mullite crystals at low temperatures. A series of spinnable hybrid mullite precursors were prepared by mixing single phase and diphasic mullite precursors, and their high temperature crystallization behaviors were investigated by XRD, DSC and SEM, with which optimum formulation of hybrid precursor was determined. The results reveal that hybrid precursor containing 70wt% single phase component has ideal crystalline properties and densification characteristics, with fine grain, uniform, and dense structure. Compared with the pure diphasic mullite precursor, the introduction of 70wt% single phase precursor resulted in an increase in apparent nucleation from 810 12 /cm 3 to 110 15 /cm 3 , and a reduction in grain size from 360 nm to 120 nm after heat-treatment at 1400 for 20 h.