Development of silica- cenosphere aerogel composites for thermal insulation applications

Novel aerogel composites were prepared by sol-gel process and dried by adding 5 to 15 weight percentage of cenosphere to silica aerogel prepared by subcritical drying process. Silica-cenosphere aerogels were calcined at 1200oC, as alpha-cristobalite phase was formed in silica aerogel at 1200 degrees C. At temperatures less than 1200 degrees C only amorphous silica was found in silica aerogel. Microstructural analysis showed spherical shape in different sizes with micro pores in surface of cenosphere and popcorn-like structure in silica-cenosphere aerogels. Effect of cenosphere addition in silica aerogel was studied by FT-IR. The particle size and distribution of prepared aerogels and cenosphere were analysed by particle size distribution analyser. The average particle size of silica aerogel was found to reduce by increased addition of cenosphere. The nitrogen adsorption studies of cenosphere and silicacenosphere aerogels indicated type II isotherm which represents macroporous/nonporous unrestricted monolayer - multilayer adsorption. The powder flow behaviour of the cenosphere and prepared aerogels were found to be strongly dependent on the particle size and distribution. The compressive strength and thermal conductivity of all the samples were found to be dependent on the porosity and bulk density. Among all the samples, lower density and higher porosity was observed in SC15. The silica aerogel recorded the highest strength value and was reduced by the addition of cenosphere except for SC5. The thermal conductivity was also found to be lowered for silica-cenosphere aerogels than pure silica aerogel and was found suitable for thermal insulation application that do not require strength.