Superinsulating Silica Aerogels

Even though an entire section of this handbook is dedicated to silica-based aerogels (Part 11), we feel that it is necessary to briefly summarize the basics about their synthesis and 

Even if supercritical drying permits to obtain perfectly monolithic and transparent sihca-based thermal insulators, the process to obtain such crack-free large plates remains stUl too far from industrial large-scale commercialization. This was the initial reason why different processes have been studied to develop subcritical routes to access rapid massive commercialization. Among the various studies, aging of the gels in silica precursor containing solution has permitted to reach room temperature thermal conductivities as low as 

002 W at the laboratory scale [31]. The most efficient routes, however, 

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Silica aerogels, a newly developing type of material, also have been produced as thermal insulations with superinsulation characteristics. The nanometer-size cells limit the gas phase conduction that can take place. The aerogels are transparent to visible light, so they have potential as window insulation. The use of superinsulations at present is limited by cost and the need to have a design that protects the evacuated packets or aerogels from mechanical damage. 

Thermal Insulation. In addition to their low thermal conductivity, as discussed in the section above, silica aerogels can be prepared to be highly transparent in the visible spectrum region. Thus, they are promising materials as superinsulating window-spacer. To take further advantage of its... 

K. Duer, S. Svendsen, Monolithic Silica Aerogel in Superinsulating Glazings, Solar Energy, 63, 259-267 (1998). 

Most commercially relevant superinsulating Si02 aerogels have densities between 80 and 200 kg m. Their thermal conductivity values are dominated by conduction through the solid silica particle network at high densities and a combination of radiation and gaseous conduction through the air inside the pores at low densities. To produce the lowest conductivity materials, it is necessary to find an optimum between those two. It seems apparent that... 

Despite those differences, it appears clear that those two aerogel families present a common huge potential for hybridization with their nanostructured silica homologues, which could lead to, among others, brand new reinforced superinsulating materials. 

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