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 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.