caa a22 4500 463223551 CHVBK 20180405153219.0 cr unu---uuuuu 170326e20071001xx s 000 0 eng 10.1007/s10853-007-1788-2 doi (NATIONALLICENCE)springer-10.1007/s10853-007-1788-2 Effect of solvent exchanging process on the preparation of the hydrophobic silica aerogels by ambient pressure drying method using sodium silicate precursor [Elektronische Daten] [A. Parvathy Rao, A. Venkateswara Rao, G. Pajonk, Poonam Shewale] Experimental results obtained on the preparation of hydrophobic silica aerogels by ambient pressure drying method using the sodium silicate precursor with the variation of solvent exchanging process, are reported. The silica hydrogel was prepared by passing the 1.12 specific gravity sodium silicate through the Amberlite (TM) 120 Na+ resin and addition of 1M ammonium hydroxide to silicic acid. The gel was kept in an oven for 3h to strengthen the gel. Solvent exchange was carried out with ethanol and hexane for 36h each followed by 24h silylation using 20% hexamethyldisilazane (HMDZ) in hexane. Unreacted HMDZ was washed with hexane by keeping the gel in hexane for 24h. Solvent was decanted and the gel was dried for 24h by keeping the gel at 50°C for 6h, at 150°C for 12h and at 200°C for 6h. The low density (0.06g/cm3), highly porous (96.9%), highly hydrophobic (contact angle of 160°), low thermal conductivity (0.07W/mK) aerogels were obtained for the process of three times exchange with ethanol and three times exchange with hexane in 36h each, followed by silylation with 20% HMDZ in hexane and two times washing with hexane in 24h. FTIR studies showed the increase in the intensity of the Si-H and C-H bands of the aerogels with the increase of solvent exchanging times because of increase in silylation for more times of solvent exchange processes. It was found from the TG-DTA studies that the hydrophobicity of the aerogels retained up to the temperature of 325°C. Water absorption studies show that the aerogels were remained hydrophobic up to 4months when the aerogels were placed over the water as well as for up to 60h in a 90% humid atmosphere. SEMs of the aerogels reveal that the pore sizes of the silica network increased, so the percentage of optical transparency decreased with the increase in exchange times with ethanol and hexane. Springer Science+Business Media, LLC, 2007 Parvathy Rao A. Air Glass Laboratory, Physics Department, Shivaji University, 416004, Kolhapur, Maharashtra, India aut Venkateswara Rao A. Air Glass Laboratory, Physics Department, Shivaji University, 416004, Kolhapur, Maharashtra, India aut Pajonk G. Laboratoire Des Materiaux et Procedes Catalytiques, Universite Claude Bernard, Lyon1, 43 Boulevard Du11Novembre 1918, 69622, Villeurbanne Cedex, France aut Shewale Poonam Air Glass Laboratory, Physics Department, Shivaji University, 416004, Kolhapur, Maharashtra, India aut Journal of Materials Science Springer US; http://www.springer-ny.com 42/20(2007-10-01), 8418-8425 0022-2461 42:20<8418 2007 42 10853 https://doi.org/10.1007/s10853-007-1788-2 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s10853-007-1788-2 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Parvathy Rao A. Air Glass Laboratory, Physics Department, Shivaji University, 416004, Kolhapur, Maharashtra, India aut NATIONALLICENCE 700 1- Venkateswara Rao A. Air Glass Laboratory, Physics Department, Shivaji University, 416004, Kolhapur, Maharashtra, India aut NATIONALLICENCE 700 1- Pajonk G. Laboratoire Des Materiaux et Procedes Catalytiques, Universite Claude Bernard, Lyon1, 43 Boulevard Du11Novembre 1918, 69622, Villeurbanne Cedex, France aut NATIONALLICENCE 700 1- Shewale Poonam Air Glass Laboratory, Physics Department, Shivaji University, 416004, Kolhapur, Maharashtra, India aut NATIONALLICENCE 773 0- Journal of Materials Science Springer US; http://www.springer-ny.com 42/20(2007-10-01), 8418-8425 0022-2461 42:20<8418 2007 42 10853 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer