A new rapid and economical one-step method for preparing SiO2 aerogels using supercritical extraction

作者：Wu, Xiaodong; Shao, Gaofeng; Liu, Sijia; Shen, Xiaodong^*; Cui, Sheng^*; Chen, Xiangbao

来源：Powder Technology, 2017, 312: 1-10.

DOI：10.1016/j.powtec.2017.01.067

• Rapid supercritical extraction
• Silica aerogel
• Heat treatment
• Pore structures
• Thermal conductivity

Monolithic silica aerogels (SiO2) are prepared using the tetraethylorthosilicate (TEOS) as precursor via a rapid supercritical extraction method (RSCE). The effect of heat treatment on the textural and physical characteristics of RSCE-samples are compared with those of the other two conventional supercritical extraction method, i.e. the alcohol supercritical extraction (ASCE) and CO2 supercritical extraction (CSCE). This new RSCE method offers many distinct advantages. The precursor recipe employs TEOS, ethanol, water, diluted hydrochloric acid to catalyst hydrolysis, and ammonia to accelerate the condensation rate. One advantage is the relative simplicity of this method: liquid precursors are poured into the supercritical ethanol drying apparatus following the hydrolysis of the TEOS and the solutions are directly sent to the supercritical extraction point of ethanol without previous aging and solvent exchanges procedures as would be the case for conventional aerogel. Thus, it is much more cost saving and it produces little waste during the overall fabrication. The total fabrication rime from mixing the precursors to taking out can be shortened to as low as 6 h, which is much less time consuming than the conventional ones (usually ca. 4-7 days). All the as-dried SiO2 samples derived from different methods are essentially amorphous, and SiO2 crystallization first occurs for the ASCE sample at 1100 degrees C. The average pore diameters of the as-dried ASCE, CSCE and RSCE samples are 12.70 nm, 14.97 nm and 13.80 nm, respectively, which is consistent with the results of transmission electron microscopy (TEM) analysis. The specific surface area of the as-dried RSCE silica aerogel may reach 915.9 m(2)/g after 700 degrees C, which is larger than the other two samples. The thermal conductivities of the different fiber reinforced RSCE SiO2 aerogel composites are ca. 0.027 W m(-1) K-1, comparable to the ASCE and CSCE aerogel composites. The RSCE method can also be well applied to the fabrication of aerogels based on other precursor recipes.

• 出版日期2017-5-1
• 单位中国航发北京航空材料研究院; 南京工业大学