Thermal properties of carbon aerogels

Abstract The thermal diffusivity, a, of various carbon aerogel samples with different [resorcinol]/[catalyst] ( R C ) ratios and bulk densities was determined from room temperature to about 700°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, cp(T), and the sample density, ϱ: λ = aϱcp. Values between λ = 0.35 W m−1 K−1 (ϱ = 381 kg m−3) and λ = 2.75 W m−1 K−1 (ϱ = 984 kg m−3) at 700°C were derived. The thermal conductivity was found to be proportional to ϱ2.2. The sound velocities were determined from ultrasonic measurements and the microcrystallite size, Lα, using Raman scattering. A phonon mean free path, l, was calculated from the sound velocities. Both Lα (≈ 20 A) and l (≈ 16 A) were found to be independent of density.