THERMAL-PROPERTIES OF CARBON AEROGELS

The thermal diffusivity, alpha, of various carbon aerogel samples with different [resorcinol]/[catalyst] (R/C) ratios and bulk densities was determined from room temperature to about 700 degrees C. The temperature dependence of a could be described by the same equation for all samples. The thermal diffusivity was found to vary linearly with density. Thermal conductivity values were calculated using the heat capacity, c(p)(T), and the sample density, rho: lambda = alpha rho c(p). Values between lambda = 0.35 W m(-1) K-1 (rho = 381 kg m(-3)) and lambda = 2.75 W m(-1) K-1 (rho = 984 kg m(-3)) at 700 degrees C were derived. The thermal conductivity was found to be proportional to rho(2.2). The sound velocities were determined from ultrasonic measurements and the microcrystallite size, L(alpha), using Raman scattering. A phonon mean free path, l, was calculated from the sound velocities. Both L(alpha) (approximate to 20 Angstrom) and l (approximate to 16 Angstrom) were found to be independent of density.