关键词: SiO₂-Al₂O₃气凝胶, 溶胶-凝胶法, 常压干燥, 热处理, 热稳定性

Abstract: To improve the performance of SiO₂-Al₂O₃ aerogels and expand their application field at high temperatures,SiO₂-Al₂O₃ composite aerogels were prepared by the sol-gel method followed by ambient pressure drying,adopting ethyl orthosilicate as the silicon source,aluminum chloride hexahydrate as the aluminum source,water and ethanol as the solvent,and trimethylchlorosilane/n-hexane as the modifier.The effects of n(Si)∶n(Al) (2∶1,1∶1,1∶2,1∶3 and 1∶4) on the gelling time,microstructure,specific surface area and thermal conductivity of the composite aerogels were studied.On this basis,the SiO₂-Al₂O₃ composite aerogels were heat treated at different temperatures (600,800,1 000,1 100 and 1 200 ℃) for 2 h,and then characterized and analyzed by SEM,XRD,BET,TG-DSC,and FT-IR.The results show that:(1)when n(Si)∶n(Al)=1∶3,the SiO₂-Al₂O₃ composite aerogel has the best performance,the gelling time is 7.64 min,and the specific surface area is 397 m²·g^-1;(2)SiO₂ in the composite aerogel inhibits the crystal transformation of Al₂O₃,and the gel network formed by Al—O—Si bond improves the strength,thermal stability and high temperature thermal insulation performance of the aerogel;(3)when n(Si)∶n(Al)=1∶3,after the heat treatment at 1 200 ℃,α-Al₂O₃ is not detected in the SiO₂-Al₂O₃ composite aerogel,and the porous structure still maintains intact,and its thermal conductivity at room temperature is 0.053 W·m^-1·K^-1。

Key words: SiO₂-Al₂O₃ composite aerogel, sol-gel method, ambient pressure drying, heat treatment, thermal stability