Preparation of mullite whiskers from coal fly ash using sodium sulfate flux

Mullite whiskers were prepared in sodium sulfate flux using coal fly ash. The stability of mullite whiskers was affected by the heat treatment temperature. The main phase in the samples sintered at 950 and 1000 °C was mullite. Only alumina and sodium aluminosilicate were obtained under sintering at 1200 °C. The mullite whiskers were obtained under sintering at 1000 °C; with an aspect ratio of > 25 and about 0.06–0.3 μm in diameter.