以廉价的铝粉、工业盐酸和酸性硅溶胶为主要原料, 通过溶胶凝胶法制备了多晶莫来石纤维. 采用27Al NMR测试了聚合氯化铝溶胶中Al3+的聚集状态, 采用XRD、FT-IR、SEM和TG-DTA等手段表征了不同热处理温度下莫来石纤维的物相组成、纤维形貌以及纤维的热分解特性. 27Al NMR结果表明, Al3+主要以Keggin结构的Al13形态存在于聚合氯化铝溶胶中. 具有24个活性Al-OH键的Al13聚阳离子易与硅溶胶中的Si-OH发生失水缩聚反应, 生成具有长链结构的纺丝溶液. XRD、FT-IR和TG-DTA结果表明, 纤维热处理到950℃时开始结晶, 到1000℃可获得单一的莫来石晶相, 整个过程的纤维失重在48.24％. 经1250℃热处理, 获得的莫来石纤维的直径为3～5μm, 晶粒尺寸约为240 nm, 拉伸强度为1.1GPa.
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 phasepure 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.
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