Low thermalconductive, transparent and hydrophobic ambient pressure dried silica aerogels with various preparation conditions using sodium silicate solutions

• Published in: Journal of sol-gel science and technology Vol. 47; no. 1; pp. 85 - 94
• Main Authors: Rao, A. Parvathy, Rao, A. Venkateswara, Bangi, Uzma K. H.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01-07-2008; Springer; Springer Nature B.V
• Subjects: Aging; Bonding strength; Ceramics; Chemistry; Chemistry and Materials Science; Colloidal gels. Colloidal sols; Colloidal state and disperse state; Composites; Contact angle; Density; Differential thermal analysis; Exact sciences and technology; Fourier transforms; General and physical chemistry; Glass; Heat conductivity; Heat transfer; Hydrogels; Hydrophobicity; Inorganic Chemistry; Isopropanol; Materials Science; Microscopy; Nanotechnology; Natural Materials; Optical and Electronic Materials; Original Paper; Pore size distribution; Porosity; Porous materials; Pressure; Scanning electron microscopy; Silica; Silica aerogels; Silicon dioxide; Sodium silicates; Spectrum analysis; Thermal conductivity; Thermal stability; Transmission electron microscopy; Xylene; Thermal conductivity; Hydrophobicity; Optical transmission; Pore size distribution; Silylation; Sodium silicate; Binary compound; Aerogel; Porous material; Silica; Pore size; Sol gel process; Preparation; Distribution
• ISSN: 0928-0707; 1573-4846
• DOI: 10.1007/s10971-008-1746-8

The experimental results on the preparation of low thermal conductivity and transparent ambient pressure dried silica aerogels with the sodium silicate solution, TMCS silylating agent with methanol, isopropyl alcohol, hexane and xylene solvents, are reported. This study is focussed on the effect of preparation conditions such as varying the number of preparation steps, pH of the hydrosol and hydrogel ageing temperature, for the production of the low thermal conductive silica aerogels and the results are analysed. Density, thermal conductivity, % of optical transmission and contact angle of the aerogels were measured. The Fourier Transform Infrared Spectroscopy (FTIR) studies revealed the presence of Si–C and C–H along with the Si–O–Si and OH bonds and their intensities strongly depend on the processing steps, pH of the hydrosol and gel ageing temperature. The UV–Visible spectra indicated the % of optical transmission of the aerogels decreased with increasing the number of processing steps, increase in the pH of the hydrosol from 3 to 8 and decreased for ageing temperature up to 50 °C. Further increase in temperature >50 °C, the % of optical transmission of the aerogels increased. The TGA-DTA data showed the thermal stability of the aerogels with respect to hydrophobicity is 325 °C. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) analyses revealed the nanostructure of the aerogels. The porosity of the aerogels was studied using the pore size distribution. Silica aerogels with low density (0.051 g/cc), low thermal conductivity (0.049 W/m K), optical transmission (65%), high hydrophobicity (159°) and resistance to humid atmosphere >1 year was obtained in the present studies.