Anomalous Diffusion of Helium and Neon in Low-Density Silica Glass

Abstract

The diffusion properties of low-density non-porous silica glasses (expanded silica glasses) were researched with the aim of searching for the molecular structure of membrane materials intended for the effective separation of helium–neon gas mixtures. It has been shown on a large number (84) of computer models of such glasses that there are molecular structures of silica in which various helium and neon diffusion mechanisms are simultaneously implemented: superdiffusion for helium and subdiffusion for neon. This makes it possible to significantly (by 3–5 orders of magnitude) increase the helium permeability of such glasses at room temperature and maintain a high selectivity for the separation of helium and neon (at the level of 104–105) at the same time.

Characterization of Silicate Glass/Mullite Composites Based on Coal Fly Ash Cenospheres as Effective Gas Separation Membranes

“…Glass-crystalline membranes can have improved gas transport properties due to the purification of the glass phase from the modifier ions [36,37] and the formation of an expanded low-density microstructure [35] during crystallization [21]. It was of interest to determine how the observed differences in the composition and structure of cenospheres would affect the gas permeability and selectivity of glass-crystalline materials obtained from them.…”

“…Even at high temperatures, the αHe/Ne value of silica glass is significantly higher than that of polymer membranes, 150 at 400 • C [34], but the helium permeability is insufficient for industrial use [32,34]. A low-density silica structure (expanded silica glass) can have a higher helium permeability compared with ordinary silica glass and maintain a high selectivity for He-Ne mixture separation [35].…”