Morphology and growth mechanism of mullite whiskers synthesized in molten potassium sulfate medium

Mullite powder was prepared using SiO2 and AI2(SO4)3·18H2O as starting materials in molten K2SO4 medium, which were fired at 800°C, 900°C, 1000°C, 1100°C and 1200°C for 3 h, dissolved, separated and dried. The phase composition and crystal morphology of synthesized powders were analyzed by X-ray diffraction (XRD) and Scanning electron microscopy (SEM). The results demonstrated that the synthesized mullite powder was composed of mullite whiskers in nano-scale. At 900°C, mullite began to occur although quartz phase still existed. At 1000°C, the quartz phase completely disappeared, and high purity mullite were obtained. Above 1100°C, the mullite began to decompose. Thus, 1000°C was regarded as the reasonable synthesizing temperature. Meanwhile, the growth mechanism of mullite whisker was discussed based on the theory of crystal growth in liquid-solid systems.