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

Three different types of aerogel, i.e., silica (SiO2), resorcinol-formaldehyde (RF) and carbon aerogels were investigated with respect to skeletal density, gas transport and adsorption at room temperature using a new dynamic gas expansion (DGE) method. The skeletal densities determined by DGE for the SiO2, RF and carbon aerogels are (2000-2600 +/- 200), (1550 +/- 25) and (2190 +/- 25) kg/m(3), respectively. These values are about a factor of 1.3 higher than the skeletal densities derived from liquid nitrogen (LN(2)) adsorption or scattering data. This effect is probably due to micropore adsorption. For ail aerogels investigated, 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 virgin 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 of the samples deduced from N-2-DGE is characterized by a monolayer capacity, 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 carbon aerogels, respectively, Investigation of one of the RF samples by CO2-DGE yields n(m) = 1.6 mmol/g and B = 45 X 10(-7) Pa-1. In sintered 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)).