CHARACTERIZATION OF SIO2, RF AND CARBON AEROGELS BY DYNAMIC GAS-EXPANSION

Three different types of aerogel, i.e., silica (SiO2), resorcinol-form aldehyde (RF) and carbon aerogels were investigated with respect to sk eletal density, gas transport and adsorption at room temperature using a new dynamic gas expansion (DGE) method. The skeletal densities dete rmined by DGE for the SiO2, RF and carbon aerogels are (2000-2600 +/- 200), (1550 +/- 25) and (2190 +/- 25) kg/m(3), respectively. These val ues are about a factor of 1.3 higher than the skeletal densities deriv ed from liquid nitrogen (LN(2)) adsorption or scattering data. This ef fect is probably due to micropore adsorption. For ail aerogels investi gated, the He and N-2 transport studied in the pressure range below 0. 1 MPa was found to be dominated by molecular diffusion. While for virg in and sintered SiO2 samples the diffusion coefficient, D, scale with density as rho(-0.9) and rho(-1.28), the scaling exponent derived for both RF and carbon aerogels is about - 1.4. The mmol/g er adsorption o f the samples deduced from N-2-DGE is characterized by a monolayer cap acity, n(m), of (1.5 +/- 0.5) mmol/g and Langmuir parameters, B, of (3 .2 +/- 1.0) x 10(-7) and (18 +/- 8) X 10(-7) Pa-1 for the RF and the c arbon aerogels, respectively, Investigation of one of the RF samples b y CO2-DGE yields n(m) = 1.6 mmol/g and B = 45 X 10(-7) Pa-1. In sinter ed SiO2 aerogels the ratio n(m)B/(S/m), with S/m the specific surface area, was found to take 3 common value for all samples of 5.2 X 10(-10 ) mmol/(Pa m(2)).