硅含量对Al2O3-SiO2气凝胶结构和性能的影响

研究了硅含量对Al2O3-SiO2气凝胶结构和性能的影响.结果表明,随着硅含量的增加,Al2O3-SiO2溶胶的凝胶时间逐渐延长,气凝胶密度逐渐增大.其结构逐渐由多晶勃姆石向无定形SiO2过渡.Al2O3-SiO2气凝胶同时含有Al-O、Si-O以及Al-O-Si结构,600 ℃煅烧后的物相为无定形γ-Al2O3和SiO2,1 200 ℃煅烧后为莫来石相.当硅含量为6.1wt%～13.1wt%时,适量的硅抑制了Al2O3-SiO2气凝胶的相变,其1 000℃的比表面积(339～445 m2·g-1)高于纯Al2O3气凝胶(157 m2·g-1).SEM分析表明,硅元素的加入改变了Al2O3气凝胶的结构形貌,随着硅含量的增大,Al2O3-SiO2气凝胶逐渐由针叶状或长条状向球状颗粒转变.

Effect of Silica Content on Structure and Properties of Al2O3-SiO2 Aerogels

The effect of silica content on structure and properties of Al_2O_3-SiO_2 aerogels was investigated. The results show that with the increase in silica content, the gelation time of the sol is prolonged, the density of aerogel is increased, and the structure is changed from crystal boehmite to amorphous silica. Al_2O_3-SiO_2 aerogel is constituted of Al-O, Si-O and Al-O-Si network. Aerogels convert to amorphous γ-Al_2O_3 and SiO_2 after 600 ℃ calcination, and transformed to mullite at 1 200 ℃. When silica content is 6.1wt%～13.1wt%, as a result of the suppression of the phase transformation, Al_2O_3-SiO_2 aerogels have larger surface area (339～445 m~2·g~(-1)) than pure alumina aerogel (157 m~2·g~(-1)) at 1 000 ℃. SEM shows that the microstructure of Al_2O_3 aerogel is changed by the addition of silica. With the increase in silica content, the shape of aerogel particle is changed from acicular or clubbed into spherical.