Sodium Diffusion in Glass: I, Single-Alkali Silicate

The isotope effect for 22Na/24Na diffusion was measured for three 25-mol% alkali-silicate glasses. A multiple diffusion mechanism wherein the Na ions diffuse both singly (vacancy mechanism) and in pairs (interstitialcy mechanism) provided the best agreement with the experimental data. According to this tentative model, diffusion by Na ion pairs predominates at low temperatures, and the fraction of Na ions diffusing singly increases with increasing temperature. In the glasses investigated, nearly all of the Na ions diffuse singly in the vicinity of the transformation range