Effect of Sol-Gel Processing Parameters on Optical Properties of TMOS Silica Aerogels
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- Venkateswara Rao, A., Pajonk, G.M., Haranath, D. et al. Journal of Materials Synthesis and Processing (1998) 6: 37. doi:10.1023/A:1022607125715
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To optimize and produce silica aerogels with high direct transmittance and low diffusive values, systematic and detailed experiments were carried out on the effect of sol-gel processing parameters on optical properties of silica aerogels. A series of aerogel samples of different molar ratio combinations was optically examined in the UV–visible–NIR range by a spectrophotometer equipped with an integrating sphere. The overall transmittance of the aerogels in the visible range varied from 75 to 93% depending upon the molar ratio combination. The most relevant parameter being studied was the direct/hemispherical transmittance ratio (τ). The best value of τ obtained for an aerogel in the present study was about 93% with a molar ratio of 1 TMOS: 12 MeOH:4 H2O:3.5 × 10−3 NH4OH, respectively. Apart from visible transparencies, solar energetic transparencies of some silica aerogels were also measured and reported. These optical data, together with the porosity measurements, allowed us to improve the process of fabrication of low-diffusing aerogel material. The experimental results are discussed considering the percentage of porosity and heterogeneity generated in pore size distributions due to the variation of sol-gel processing parameters.