Thermal Properties of Aerogels

Abstract This chapter provides an insight into the different aspects of heat transfer in aerogels and their thermal properties. In this context, the principal heat transfer mechanisms are discussed and illustrated by exemplary experimental results. Typical thermal conductivity values and radiative properties as well as their dependency on external conditions such as temperature or atmosphere are discussed for different classes of aerogels. The chapter concludes with a brief discussion about the specific heat of aerogels. 

Bavarian Center for Applied Energy Research, Am Hubland, 97074 Wiirzburg, Germany e-mail ebert zae.uni-wuerzburg.de 

Aegerter et al. (eds.). Aerogels Handbook, Advances in Sol-Gel Derived Materials and Technologies, DOI 10.1007/978-l-4419-7589-8 23, 

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To reveal the thermal properties of aerogels, stationary hot-plate measurements are usually employed [45]. In such a measurement two equal aerogel specimens are sandwiched between a hot plate and two cold plates. If the electrical power fed into the hot plate and the temperature difference between the hot and the cold plates, as well as the thickness of the specimens, are known, the thermal conductivity can be derived. For the thermal characterization of opacified aerogels, the faster nonstationary hot-wire method can also be used. In this case a thin platinum wire is embedded into the aerogel specimen and a constant power is delivered into the wire, which also serves as a temperature sensor. From the temperature increase in the wire as a function of time, the thermal conductivity of the aerogel specimen can be determined [49]. 

Hunt, A. J. (1992). Optical and Thermal Properties of Silica Aerogel. In Chemical Processing of Advanced Materials, ed. L. I. Hench and J. K. West. New York John Wiley Sons. 

The main disadvantage of gels is their high porosity. This property may be used to improve the thermal insulation of aerogels, but in most cases it is con-... 

Kim GS, Hyun SH (2003) Effect of mixing on thermal and mechanical properties of aerogel-PVB composites. J Mater Sci 38 1961-1966... 

Hrubesh L, Pekala R (1994) Thermal properties of organic and inorganic aerogels. J Mater Res 9 731-738. 

Since (23.16) is independent of direction, it is rally valid for aerogels with isotropic thermal properties. Many experimentally derived values for the thermal conductivity of aerogels under various conditions are available. Hrubesh et al. discussed the superposition... 

Bock, V., Nilsson, O., Blumm, J. and Fricke, J., Thermal Properties of Carbon Aerogels. Journal of Non-Crystalline Sohds, 1995.185(3) p. 233-239. 

Nilsson, O., Fransson, A. and Sandberg, O. Thermal Properties of Silica AerogeL in First International Symposium on Aerogels. 1985. Wurzburg Springer-Verlag. 

Based on recent developments in the field, it can be stated that aerogels still offer the greatest potential for nonevacuated superinsulation systems and consequently must be considered as an amazing opportunity for sustainable development. This chapter of the handbook bridges the gap between those dealing with thermal insulation properties of aerogel materials in general (Chap. 21) and the various commercial products described in Part XV. 

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