Hydrophobic Silica Aerogels by Ambient Pressure Drying

Abstract:

Silica aerogels have been prepared through sol-gel process by polymerization of TEOS in the presence of NH₄F and NH₄OH as catalysts. The solvent present in the gel is replaced by ethanol followed by a non-polar solvent such as n-hexane prior to solvent modification step. Gels are made hydrophobic by treating them with HMDZ to prevent rupture during drying, which has been confirmed by FTIR. Gels are then washed and dried carefully in a PID controlled oven at atmospheric pressure. The ageing duration and solvent exchange combinations are optimized to yield crack-free gels prior to drying. Aerogels are characterized for density, specific surface area, pore volume, pore size, thermal stability and contact angle. Hydrophobic, high surface area (570 m2/g), low density (0.07 g/cm3) silica aerogels are synthesized by using optimized mole ratio of precursors and catalysts. Silica aerogel granules (1-3 mm) as well as monoliths (Ф~35 mm) could be produced through ambient pressure drying of gels.

• Periodical: Materials Science Forum (Volumes 830-831)
• Pages: 476-479
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.830-831.476
• Online since: September 2015
• Authors: Srinivasan Nagapriya*, M.R. Ajith, H. Sreemoolanadhan, Mariamma Mathew, S.C. Sharma
• Keywords: Aerogel, Ambient Pressure Drying, Sol-Gel

References

[1] J.L. Gurav, D.Y. Nadargi, A. Venkateswara Rao, Effect of mixed Catalysts system on TEOSbased silica aerogels dried at ambient pressure, Appl. Surf. Sci. 255 (2008) 3019-27.

DOI: 10.1016/j.apsusc.2008.08.059

[2] Brinker & Scherer, Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing, Academic Press, (1990).

[3] Rao et al, Rapid reduction in gelation time and impregnation of hydrophobic property in the tetraethoxysilane based silica aerogels using NH4F catalyzed single step sol-gel process, Journal of Alloys and Compounds 480 (2009) 689-695.

DOI: 10.1016/j.jallcom.2009.02.027

[4] R.K. Iler, The chemistry of Silica, Wiley, new York, (1979).

[5] A. Parvathy Rao, A. Venkateswara Rao, Microstructural and physical properties of the ambient pressure dried hydrophobic silica aerogels with various solvent mixtures, J. Non-Cryst. Sol. 354 (2008) 10-18.

DOI: 10.1016/j.jnoncrysol.2007.07.021

[6] A. Parvathy Rao, A.V. Rao, Improvement in optical transmission of the ambient pressure dried hydrophobic nanostructured silica aerogels with mixed silylating agents, J. Non-Cryst. Sol. 355 (2009) 2260-2271.

DOI: 10.1016/j.jnoncrysol.2009.07.016

[7] A. Parvathy Rao, A. Venkateswara Rao, G.M. Pajonk, Hydrophobic and physical properties of the ambient pressure dried silica aerogels with sodium silicate precursor using various surface modification agents, Appl. Surf. Sci. 253 (2007) 6032-6040.

DOI: 10.1016/j.apsusc.2006.12.117