Polycrystalline Mullite Fibers Prepared by Sol-Gel Method

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.