Pore network connectivity and effective diffusivity of silica aerogels

Silicon–titanium oxycarbide glasses as bimodal porous inorganic membranes

“…D re of the oxycarbide membranes (see Table 1) are close to those estimated for conventional silica or alumina porous supports 22 and are lower than those estimated for silica aerogels. 20 Therefore, these data clearly confirm the possibility of producing silicon-titanium oxycarbide glasses to be used as membranes for liquid and gases.…”

“…If the porosity of the prepared silicon-titanium oxycarbide membranes is taken into account, moderate mass transport properties may be expected. 20 Using the effective medium theory, Burganos and Sotirchos 21 developed a convenient and reliable method for calculation of the effective diffusivity in porous solids. Neglecting Knudsen diffusion coefficient, the effective diffusivity in a porous structure is given by: where ε is the porosity, D the bulk diffusion coefficient, τ the tortuosity factor, and (d 2 ) e and (d 2 ) are calculated from the equations:…”

Facile processing of clays into organically‐modified aerogels

“…The structure of these silica aerogels has been well established and, to some extent, resembles a "string of beads." [20][21][22][23] A limited literature exists in which silica aerogels are combined with organic polymers to produce nanocomposite materials. [24][25][26][27] In none of these studies has the use of clay aerogels been investigated.…”

“…We suspect this agent is the source of interference in aerogel formation. Under conditions that appear to maximize stabilization of Laponite/ water suspensions (Table 1, entries 21,22), aerogel formation was observed as a result of freeze-drying. These Laponite aerogels were not as mechanically robust as those obtained with montmorillonite, likely reflecting the assembly of small disk units rather than longer, continuous sheets.…”

Kinetics of Supercritical Drying of Gels

“…Knudsen gas diffusion and molecular or bulk diffusion are significant diffusion mechanisms that occur in the aerogel pores. Aerogels have a pore size distribution, generally in the mesopore range and hardly in the micropore range, with pores typically ranging from 5 to 100 nm and an average pore diameter between 20 and 40 nm [11,48,50]. Diffusion in mesopores is mostly governed by molecular diffusion since the pore size is at least one order of magnitude larger than the mean free path of gas molecules.…”