Sol-Gel-SCFD法制备纳米莫来石

以AIP(Aluminum-isopropoxde)和 TEOS(Tetraethyl Orthosilicate)为主要原料,采用Sol-Gel-SCFD(超临界流体干燥)技术制备了n(Al₂O₃):n(SiO₂)=3:2的Al₂O₃-SiO₂二元纳米气凝胶,通过中温煅烧,获得了纳米级莫来石.用热重-差示扫描热量计(TG-DSC)、透射电子显微镜(TEM)、X射线衍射仪(XRD)和物理吸附分析仪(Autosorb)等手段对二元纳米气凝胶和纳米莫来石进行了分析和研究.TG-DSC研究表明,在煅烧过程中,气凝胶的大部分失重(15.98％)在700℃左右已完成,DSC曲线上在445和 1015℃存在的两个放热峰是由于二元凝胶中的Si-O-Al-O结构重整和莫来石化所致,而在805℃处小的吸热峰是由体系中结构水分解所致;借助于 TG-DSC、XRD和 TEM分析手段,可以确定在纳米Al₂O₃-SiO₂二元材料内,莫来石的开始形成温度为1015℃左右.XRD分析表明,完全转变成莫来石温度在1100～1200℃之间,1200℃可得晶粒发育良好的纳米级莫来石;TEM和物理吸附分析仪测试结果表明,1100和1200℃所得纳米莫来石的微粒大小分别为30和50nm左右， 比表面积分别为138.91和95.81m²/g.

Preparation of Nanometer Mullite by Sol-Gel-SCFD Method

Nanometer mullite was prepared through Sol-Gel-SCFD and middle temperature calcination by using aluminium-isopropoxde and tetraethyl orthosilicate as starting materials, the alumina-silica binary aerogel and calcined nanosized materials were investigated by using thermogravimetry-differential scanning calorimeter (TG-DSC), transmission electron microscope (TEM), X-Ray diffractometer (XRD) and specific surface area and porosimetry. TG-DSC indicated the removal of most of the volatiles, i.e. 15.98% up to about 700℃, and in the DSC curve, the existence of two exothermic peaks at about 445 and 1015℃ may be due to the crystallization of Si-O-Al-O in diphasic gels and mullitization, and a small endothermic peak at about 805℃ indicated the decomposition of structural water molecules. The beginning temperature of mullitization of the Al₂O₃-SiO₂ at about 1015℃ in gel was confirmed by TG-DSC, XRD and TEM, XRD results which also showed the formation of mullite at the range 1100-120℃. TEM and surface area and porosimetry results showed that the nanosized mullite calcinated at 1100 and 1200℃ exhibited the sizes of 30nm and 50nm, specific surface area 138.91m²/g and 95.81m²/g respectively.