Comparative studies on the physical properties of TEOS, TMOS and Na2SiO3 based silica aerogels by ambient pressure drying method

Abstract

In order to compare the various precursors of silica aerogels, three different precursors namely TMOS, TEOS and Na2SiO3 were studied in this paper. The property differences of the aerogels caused by the three precursors were discussed in terms of reaction process, gelation time, pore size distributions, thermal conductivity, SEM, hydrophobicity and thermal stability. It has been found that the gelation time of the silica gel is strongly dependent on the type of precursor used. During the surface modification process, organic groups were attached to the wet gel skeletons transforming the hydrophilic to the hydrophobic which were characterized by Fourier Transform Infrared spectroscopy (FTIR). It has been found that the contact angle of the Na2SiO3 and TMOS precursor based aerogels with water have the higher contact angle of 149° and whereas Na2SiO3 precursor based aerogel has the lower contact angle of 130°. The thermal conductivities of the Na2SiO3 and TMOS based aerogels have been found to be lower (0.025 and 0.030 W m−1 K−1, respectively) compared to the TEOS based (0.050 W m−1 K−1) aerogels. The pore sizes obtained from the N2 adsorption measurements varied from 40 to 180, 70 to 190, and 90 to 200 nm for the TEOS, TMOS and Na2SiO3 precursor based aerogels, respectively. The scanning electron microscopy studies of the aerogels indicated that the Na2SiO3 and TMOS based aerogels show narrow and uniform pores while the particles of SiO2 network are very small. On the other hand, TEOS aerogel show non-uniform pores such that the numbers of smaller size pores are less compared to the pores of larger size while the SiO2 particles of the network are larger as compared to both Na2SiO3 and TMOS aerogels. Hence, the surface are of the aerogels prepared using TEOS precursor has been found to be the lowest (~620 m2 g−1) compared to the Na2SiO3 (~868 m2 g−1) and TMOS (~764 m2 g−1) aerogels.