纳米莫来石粉体的合成及其表征

SYNTHESIS AND CHARACTERIZATION OF NANOSIZED MULLITE POWDER

以异丙醇铝和正硅酸乙酯为主要原料,采用溶胶-凝胶-超临界流体干燥技术(sol—gel—supercritical fluid drying)制备了n(Al2O3):n(SiO2)为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粉体。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)及物理吸附分析仪等手段研究了经不同温度处理后样品的显微形貌、比表面积、微孔孔容分布及物相变化等规律。TG—DSC分析表明:在煅烧过程中,气凝胶的大部分质量损失(15.98％)在700℃左右已完成,在DSC曲线上450℃和1 105℃时存在2个因结构重整晶化的放热峰和850℃时存在1个非晶化的吸热峰;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,在1 015℃左右开始形成莫来石,在1 100～1 200℃期间就已完全转变成莫来石,1 200℃可得晶粒发育良好的纳米莫来石粉体;TEM和物理吸附分析仪测试结果表明:1 100℃和1 200℃所得纳米莫来石的微粒大小分别为30 nm和50 nm左右,比表面积分别为138.91 m2/g和95.81m2/g。

Nano-sized mullite powder was synthesized through a method of sol-gel-SCFD (supercritical fluid drying) and the middle temperature calcination by using aluminum-isopropoxide and tetraethyl orthosilicate as starting materials. The microstructure of the alumina-silica binary aerogel and calcined nano-sized materials was investigated by means of thermogravimetry-differential scanning calorimeter (TG-DSC), transmission electron microscope (TEM) and X-ray diffractometer (XRD). The TG analysis shows that most mass loss of the aerogel (15.98%) happens at about 700°C. In the DSC curve there exist two exothermic peaks at about 445°C and 1015°C due to the crystallization of Si-O-Al-O in the diphase gels and a small endothermic peak at about 805°C indicating the decomposition of structural water molecules. According to the results of TG-DSC, XRD and TEM, the initial temperature for the mullitization of Al2O3-SiO2 in gel is about 1015°C and the formation of mullite is performed at the range of 1100-1200°C. The size of nano-sized mullite powder calcined at 1100°C and 1200°C is 30 nm and 50 nm, and the specific surface area is 138.91 m2/g and 95.81 m2/g respectively.