Effect of mixed Catalysts system on TEOS-based silica aerogels dried at ambient pressure
| Autor: | Digambar Y. Nadargi, A. Venkateswara Rao, Jyoti L. Gurav |
|---|---|
| Rok vydání: | 2008 |
| Předmět: |
Heptane
Oxalic acid Xylene General Physics and Astronomy Aerogel Surfaces and Interfaces General Chemistry Condensed Matter Physics Surfaces Coatings and Films Hexane Solvent chemistry.chemical_compound chemistry Organic chemistry Thermal stability Fourier transform infrared spectroscopy Nuclear chemistry |
| Zdroj: | Applied Surface Science. 255:3019-3027 |
| ISSN: | 0169-4332 |
| DOI: | 10.1016/j.apsusc.2008.08.059 |
| Popis: | In the present paper, the experimental results on the effect of mixed Catalysts system on the physical properties of the TEOS-based silica aerogels, are reported and discussed. The aerogels were produced by the single-step as well as two-step sol–gel process followed by atmospheric pressure drying. In the single-step process, only the NH 4 F was used as a catalyst, whereas in the two-step process, NH 4 F as well as a mixed catalysts, i.e., NH 4 F and NH 4 OH, were used after 12 h of acid (oxalic acid) addition. Effect of various exchanging solvents, viz., xylene, toluene, heptane or hexane and silylating agents, viz., MTMS, TMES, TMCS, HMDSO or HMDZ on the physical properties of the as prepared aerogels were studied. The volume of the NH 4 OH, the molar ratios of MeOH/TEOS and HMDZ/TEOS were varied from 0.2 to 1 ml, and 5.5 to 27.5, 0.34 to 0.9, respectively, by keeping the volume of NH 4 F and the concentrations of NH 4 F and NH 4 OH constant at 0.5 ml, 0.1 and 1 M, respectively. Remarkable results were obtained by using mixed catalyst system, hexane as exchanging solvent and surface chemical modification with 5% HMDZ in hexane. The aerogels were characterized by bulk density, optical transmission, thermal stability and contact angle measurements. The surface chemical modification was confirmed by Fourier Transform Infrared (FTIR) spectroscopy. The microstructural studies of the aerogels were done by Transmission Electron Microscopy (TEM), which revealed highly ramified self-similar polymeric structure in large length scale. The thermal stability of the aerogels were tested using TG-DT analyses. It was found that low bulk density (0.065 g/cm 3 ), superhydrophobic (153°), high thermal stability (380 °C) and high optical transmission (95%) of the as produced aerogels obtained at the molar ratio of TEOS:MeOH:oxalic acid:NH 4 F:NH 4 OH:HMDZ for 1:16.5:0.81:0.62:0.63:0.41, respectively. |
| Databáze: | OpenAIRE |
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