Synthesis of an alumina enriched Al2O3-SiO2 aerogel: Reinforcement and ambient pressure drying

Abstract

An alumina enriched Al2O3-SiO2 aerogel was successfully synthesized using an inexpensive inorganic aluminum salt Al(H2O)9(NO3)3 as the precursor and tetraethoxysilane (TEOS) as the framework reinforcing agent via a sol-gel process followed by ambient pressure drying. In order to show the enhanced effect of TEOS on aerogel, its structure and properties were detected by FESEM, TEM and BET. Furthermore, FTIR and Raman spectra were collected to explain the enhancement mechanism of TEOS to Al2O3-SiO2 aerogel at the molecular level. The FTIR spectra showed that some AlOSi and AlOSiOSiOAl bonds gradually formed during the reinforcement process. These long AlOSiOSiOAl chains supported and strengthened the alcogel skeleton and effectively avoided potential shrinkage and cracking during the ambient pressure drying process. In addition, Raman spectra supported this conclusion by verifying that AlOSi and SiOSi bonds were present. Moreover, the Raman spectra indicated that with the increase of the Si/Al mole ratio from 0 to 3.0, the primary gel skeleton of AlOAl bonds was gradually transformed to SiOSi bonds. When the Si/Al mole ratio was greater 3.0, SiOSi bonds became the primary bonds in the final aerogel.