Abstract: Polycrystalline mullite fibers were prepared by sol-gel method, using aluminum powders, hydrochloric acid and silica sol as raw materials, water as solvent. The aggregation state of Al³⁺ was measured by ²⁷Al NMR. The pyrolytic decomposition patterns of mullite fibers were assessed by heating samples to different temperatures and characterizing the products by thermogravimetric analysis (TG), differential thermal analysis (DTA), X-ray diffractometry (XRD), and Fourier transform infrared spectroscopy (FT-IR). The micrograph of mullite fibers were observed by means of Scanning Electron Microscope (SEM). The results of ²⁷Al NMR show that Al³⁺ ions aggregate in the PAC sol in the form of Al₁₃ with Keggin structure. TG/DTA analyses show the exotherm at 970℃ can be attributed to the formation of mullite phase and weight loss of the mullite fibers in the heat treatment reaches 48.24%. XRD and FT-IR analyses show that phasepure mullite can be formed at 1000℃ with no other intermediate. After heat-treated at 1250℃, the mullite crystalline fibers with diameter of 3-5μm, grain size of 240nm and tensile strength of 1.1GPa are obtained.

Key words: sol-gel method, mullite, crystalline fiber