G. Reichenauer et al., CHARACTERIZATION OF SIO2, RF AND CARBON AEROGELS BY DYNAMIC GAS-EXPANSION, Journal of non-crystalline solids, 186, 1995, pp. 334-341
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)).