Composite aerogels: mechanical, thermal stability and porosity properties

Silica aerogels were made from tetramethoxysilane (TMOS) with 1 and 10 weight percent of natural and synthetic phases of different morphologies. The second materials used include attapulgite, sepiolite, zeolite Y, zeolite 4A, Li fluorhectorite, and kaolinite (30%). Two different sol-gel preparation routes were used, leading to monolithic or partially monolithic aerogels in most cases. Vickers hardness indentation testing was carried out on these samples and also on pure silica aerogels. Hardness varied from <0.01 to 0.2 GPa for composite aerogels compared to 0.04 to 0.09 GPa for the control samples of silica aerogels. Hardness of the as-prepared aerogels varied greatly even among samples of the same mineral composition suggesting that gelation time, pH, and other factors may have greater effect on hardness than second phase composition. Surface area and pore size measurements of samples after sintering at 600° to 1000°C showed high surface areas and mesopores. Composite silica aerogels containing 1 or 10% zeolite superultrastable Y, 1% attapulgite, or 30% kaolinite densified the least during sintering.