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Thermal properties of organic and inorganic aerogels

Published online by Cambridge University Press:  03 March 2011

Lawrence W. Hrubesh  and
Richard W. Pekala
Lawrence W. Hrubesh
Affiliation:
Chemistry and Materials Science Department, Lawrence Livermore National Laboratory, Livermore, California 94551-9900
Richard W. Pekala
Affiliation:
Chemistry and Materials Science Department, Lawrence Livermore National Laboratory, Livermore, California 94551-9900
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Abstract

Aerogels are open-cell foams that have already been shown to be among the best thermal insulating solid materials known. This paper examines the three major contributions to thermal transport through porous materials, solid, gaseous, and radiative, to identify how to reduce the thermal conductivity of air-filled aerogels. We found that significant improvements in the thermal insulation property of aerogels are possible by (i) employing materials with a low intrinsic solid conductivity, (ii) reducing the average pore size within aerogels, and (iii) affecting an increase of the infrared extinction in aerogels. Theoretically, polystyrene is the best of the organic materials and zirconia is the best inorganic material to use for the lowest achievable conductivity. Significant reduction of the thermal conductivity for all aerogel varieties is predicted with only a modest decrease of the average pore size. This might be achieved by modifying the sol-gel chemistry leading to aerogels. For example, a thermal resistance value of R = 20 per inch would be possible for an air-filled resorcinol-formaldehyde aerogel at a density of 156 kg/m3, if the average pore size was less than 35 nm. An equation is included which facilitates the calculation of the optimum density for the minimum total thermal conductivity, for all varieties of aerogels.

Type
Articles
Information
Journal of Materials Research , Volume 9 , Issue 3 , March 1994 , pp. 731 - 738
Copyright
Copyright © Materials Research Society 1994

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