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 temperat
ure dependence of a could be described by the same equation for all sa
mples. 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. Th
e thermal conductivity was found to be proportional to rho(2.2). The s
ound velocities were determined from ultrasonic measurements and the m
icrocrystallite 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 f
ound to be independent of density.