Transparent monolithic aerogels

The most extensively studied chemical system for aerogel formation is the silica system. The sensational images associated with aerogels— free-standing transparent monoliths insulating a hand from a flame or holding up a brick (Fig. 8.2), are almost all of silica materials. The reason for this lies in the well-developed and facile sol-gel chemistry of silica that lends itself to formation of robust monoliths, as well as the intriguing physical properties and associated applications of such materials (11,13). 

Hu X, Ji S, Littrell K and Risen WM Jr (2000) Transparent monolithic metal ion containing nanophase aerogels. Mater. Res. Soc. Symp. Proc. 581 353-362... 

Ji S (2001) Synthesis and Studies of Transparent, Monolithic Polymer-Sihca Hybrid Aerogel Materials. Ph. D. Thesis, Brown University... 

Figure 45.10 Four optimized transparent aerogel prototypes joined in a test frame for hot box measurements (a), and cross-section of two different approaches for application of the foil rim seal solution (b) for a monolithic aerogel-based evacuated glazing [20].

Aerojet has made organic aerogels with densities of 0.1-0.2 g/mL3 for use in insulators and capacitors.252 Transparent macroporous monoliths have also been made by polymerization of trimethylolpropanetrimethacrylate using toluene, ethyl formate, and other liquids as poro-gens.253 Poly(alkyl methacrylates) have good resistance to outdoor weathering and can be used in windows. 

Figure 18.4. Monolithic metal-containing transparent chitosan-silica aerogels.

Figure 26.8. Hemispherical (black), direct (blue) and diffuse (red) normal transmission of a monolithic silica aerogel shown in Figure 26.7 presenting a transparency ratio %TR = (r — above 90% (as calculated...

TiUotson T.M., Hrubesh L.W. Transparent ultralow-density silica aerogels prepared by a two-step sol-gel process. J. Non-Gyst. Solids 1992 145 44-50 Wang J., Kuhn J., Lu X. Monolithic silica aerogel insulation doped with Ti02 powder and ceramic fibers. J. Non-Cryst. Solids 1995 186 285-290... 

An example of a pure transparent aerc el monolith is presented in Figure 10.1a, while the aerogel monolith sponge-like surface is shown in Figure 10.2a exhibiting nanoscale walls surrounded by pores with dimension of about 20 nm. 

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