溶胶-凝胶法制备多晶莫来石纤维

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 Prepared by Sol-Gel Method

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.