Abstract
Mullite crystallization behavior was studied using two kinds of gels obtained from the same compositional solutions from which mullite precursor fiber is spinnable. The gels were obtained by the following two different procedures: (1) Al(OPri)3 and TEOS were simultaneously added to Al(NO3)3 containing aqueous solution, and (2) Al(OPri)3 was added to Al(NO3)3 containing aqueous solution, then TEOS was added to these solutions. XRD experiments for both gels after heating at 1000°C showed that Al and Si mixing is away from the ideal homogeneity. The gel prepared by the latter procedure had less complete molecular-scale homogeneity of Al and Si mixing than that by the former procedure. Mullite crystal was detected after heating at 600°C in the former and at 800°C in the latter. These mullite particles were presumed to act as nuclei and to increase the crystallization rate at isothermal treatment. The difference of mullite crystallization temperature were interpreted from the differences of changes in radii of gyration for the concentration process of these solutions. The differences of mullite nucleation and growth from the gel specimen obtained by the different processes were attributed to these different solution structures, even though the raw materials had the same compositions.
