Physical properties of sodium silicate based silica aerogels prepared by single step sol–gel process dried at ambient pressure

Abstract

The experimental results on physical properties of water glass (sodium silicate) based silica aerogels prepared by single step sol–gel process, dried at atmospheric pressure are reported. The hydrolysis and condensation reactions of the sodium silicate precursor proceeded with tartaric acid as a catalyst. The hydrogel was vapour passed in order to remove sodium salt from the gel network. Solvent exchange was carried out using methanol and hexane as a solvents. Finally, surface chemical modification of the gel was done using trimethylchlorosilane (TMCS) followed by ambient pressure drying of the gel up to the temperature 200 °C. To get good quality aerogels various sol–gel parameters such as water vapour passing period varied from 0.5 to 2 h, gel aging from 1 to 4 h, Na 2SiO 3/H 2O molar ratio from 3 × 10 −3 to 1.5 × 10 −2, tartaric acid/Na 2SiO 3 molar ratio from 0.3 to 1.9 and TMCS/Na 2SiO 3 molar ratio from 4.8 to 12. The aerogels were characterized by percentage of volume shrinkage, bulk density, porosity and hydrophobicity. The hydrophobicity of the aerogel was confirmed by Fourier Transform Infrared (FTIR) Spectroscopy and contact angle measurements. Microstructural studies have been carried out by Scanning Electron Microscopy (SEM) and nitrogen adsorption BET analysis. From the TGA–DTA studies of the aerogels, it was found that the aerogels were thermally stable up to 470 °C. Low density (∼0.066 g/cm 3), high hydrophobicity (∼145°), high porosity (∼97 %), high pore volume, surface area of 510 m 2/g aerogels have been obtained for Na 2SiO 3:H 2O:tartaric acid (C 4H 6O 6):TMCS molar ratio at 1:166.6:2.5:12 respectively with half an hour water vapour passing.