Measurements of comparative apparent thermal conductivity of large monolithic silica aerogels for transparent superinsulation applications

Large monolithic crack-free transparent silica aerogels were prepared by a patented sol-gel route, and then directly washed and dried with supercritical CO2. In order to characterise as precisely as possible the apparent thermal conductivity of such superinsulating materials, two methods were developed (so-called hot-band and micro-fluxmeter techniques) and the results obtained at room temperature and atmospheric pressure were compared with the standard hot-wire measurements under the same conditions. A reproducibility study showed no large deviations between the thermal conductivities obtained by these different techniques. This leads to the conclusion that aerogels prepared in this way present a good thermal and optical compromise (low thermal conductivity, high light transmission, and no significant radiative heat transport component at room temperature) and can be considered as transparent superinsulating materials.