Pore Size Distribution and Apparent Gas Thermal Conductivity of Silica Aerogel

Silica aerogel is a network of short bonded chains of silica particles, which are fused together. Particles of diameters 2-5 nm and pores of diameter 10-100 nm produce a solid-gas matrix in which the volume fraction of the solid can be less than 5 percent. The small pore size effectively limits the motion of gas molecules and hence reduces the apparent gas conductivity to a very low level. In this paper, we establish a model for the determination of the apparent gas conductivity in terms of the pore sizes. We use the method of gas adsorption-desorption to determine the pore size distribution for silica aerogel. The thermal conductivity is measured by using the hot-wire technique and the experimental data are then used to determine the constants C[sub 1] and n[sub 1] in K = K[sub g][sup o]/[1 + (C[sub 1]/P[sup n1]l[sub ch])]0. 8 refs., 3 figs.