沉淀剂对Al_2O_3-SiO_2气凝胶的影响

Effect of precipitants on Al_2O_3-SiO_2 aerogel

以AlCl3.6H2O和TEOS(Tetraethyl Orthosilicate)为主要原料,分别用NH4OH和(NH4)2CO3作为沉淀剂,采用Sol-Gel法结合真空冷冻干燥技术制备出两种Al2O3-SiO2气凝胶,使用TG-DSC、XRD和BET等技术分析了两种气凝胶在热处理过程中的变化。结果表明:用NH4OH作沉淀剂所获气凝胶为一种双相凝胶,其未经热处理时结构中含有AlOOH物相,热处理过程中首先生成过渡相铝硅尖晶石,再生成莫来石。而用(NH4)2CO3为沉淀剂时所获的气凝胶是一种单-双相混合凝胶,其DSC曲线在831.4℃处存在着由于Si-O-Al-O键断裂吸热而产生的吸热峰,热处理过程中铝硅尖晶石与莫来石同时生成。

Two Al2O3 -SiO2 aerogels were prepared with Sol- Gel and Vacuum Freeze Drying （VFD） methods using AlCl3 · 6H2O, TEOS （Tetraethyl Orthosilicate） as main starting materials and NH4OH and （ NH4 ）2CO3 as precipitants. TG - DSC,XRD and BET were used to analyze the transformation of the two aerogels during firing process. The results showed that the NH4OH added specimen became a diphasic aerogel,in which AIOOH phase was found when unfired. During its firing process,Al-Si spinel was generated at first and then converted into mullite. However, the （NH4）2CO3 added specimen became a aerogel with both diphase and monophase,and an endothermic peak at 831.4 ℃ was observed at its DSC curve due to the collapse of the Si - O - AI - O bonding structure. During its firing process,Al - Si spinel and mullite formed simultaneously.