TiO2/SiO2复合气凝胶的制备与传热特性

针对SiO2气凝胶红外遮光性能差的问题,以纳米二氧化钛作为掺杂剂,以正硅酸乙酯(TEOS)为原料,采用溶胶-凝胶工艺和非超临界干燥方法制备了不同TiO2掺杂量的纳米孔改性SiO2气凝胶复合材料,研究了pH值和乙醇含量对凝胶时间的影响,并采用SEM、TEM和BET方法分别对凝胶的表面形貌和孔结构进行了分析表征.结果表明,当pH为6时,乙醇/TEOS为8∶1(摩尔比)时,可得到掺杂均匀、完整的TiO2/SiO2凝胶；热处理后的复合气凝胶具有网状纳米孔结构；当掺杂量小于5％时,干凝胶平均孔径为20～50 nm,比表面积均大于1 000 m2/g.通过红外透过率及消光性能比较,TiO2掺杂SiO2干凝胶复合材料的红外光屏蔽功能较纯SiO2气凝胶提高了50％.

Preparation and heat transfer performance of TiO2 / SiO2 composite aerogels

Due to the poor performance of the infrared shading of silica aerogel,sol-gel processing and non-supercritical drying methods were used to synthesize TiO2/SiO2 nano-porous modified aerogels with varying volume content of TiO2 additive.Tetraethoxysilane(TEOS) was used as a precursor and titania was used as the opacifier.The effects of the pH and the content of alcohol on the stability of the gel were investigated,and TG-DTA,SEM,and BET techniques were used to characterize the heat decomposition process,microstructure,and pore structure of the composites.The experimental results show that homogeneous TiO2/SiO2 gel was formed at pH=6 and the optimized mol ratio of ethylene alcohol and TEOS is 8∶1.Nano-porous aerogels can be achieved after heat treatment and the average pore size is 20~50nm with a specific area of over 1 000 m2/g when TiO2 is less than 5%.The infrared transmission and extinction coefficient of the binary aerogels were also investigated compared to the pure SiO2 aerogels,and the results show that SiO2 aerogels doped TiO2 had enhanced the function of the light shield by about 50%.