Effect of Phase Separation on Helium Migration in Sodium Silicate Glasses

Helium permeability, diffusion, and solubility were measured in sodium silicate glasses containing 0 to 40 mol% Na 2 O. These properties appear to depend on the substructure of the glass, since definite inflections occur in the curves of diffusivity and solubility vs composition at the boundaries of the two‐phase region. Similar inflections occur for the activation energy for diffusion and enthalpy of solution at the phase boundaries. These effects are explained by use of a two‐component diffusion model within the miscibility gap and a one‐component model in the single‐phase region.