Study of Alkali-Metal Vapor Diffusion into Glass Materials

Abstract

To investigate nanodispersion of alkali metals into glass materials, potassium vapor diffusion is conducted using SiO2 glass under well-controlled temperature conditions. It is found that potassium vapor significantly diffuses into the bulk of SiO2 glass with less precipitation on the surface when the host material is kept at a temperature slightly higher than that of the guest material. Positron annihilation spectroscopy reveals that angstrom-scale open spaces in the SiO2 matrix contribute to potassium vapor diffusion. The analysis of potassium concentration obtained by electron probe microanalysis (EPMA) mapping with Fick's second law yields an extremely low potassium diffusion coefficient of 5.1×10-14 cm2 s-1, which arises from the overall diffusion from open spaces of various sizes. The diffusion coefficient attributable to angstrom-scale open spaces is thus expected to be less than ∼10-14 cm2 s-1. The present findings imply that angstrom-scale open spaces play an important role in loading alkali metals into glass materials.

Nanoparticle formation in nanoporous structures and applications

“…The exposition of a dielectric surface of SiO 2 to an atomic alkali vapor, and the adsorption of the latter on the surface, causes the growth of randomly distributed atomic layers [126].…”