Abstract
Activation energies of H2O and H2 diffusions in silica glass were evaluated using a quantum chemical method. In order to mimic diffusion process, an interaction of a molecule with a ring cluster (SinOn(OH)2n: n=4–8) was considered. The molecule was forced to go through the ring, and heats of formation along the pass were calculated using the MNDO-PM3 semi-empirical molecular orbital method. The obtained activation energies for H2O and H2 molecules with 6-membered ring are most close with those of experimental studies for silica glass. Thus the present result suggests that “bottleneck” of diffusion process is due to the passage of the molecules through 6-membered rings in the glass structure. This model can be applied to diffusion of other gas molecules in framework silicate crystals and glasses.
