The self-diffusion of Na was studied at temperatures ranging from 300 to 1200C by using a 22Na radiotracer. It was found that the diffusivity depended upon the temperature and the composition and ranged from 10-11 to 10-5cm2/s. The Arrhenius plots were non-linear over the entire temperature range but could be divided into 3 sections (table 124). One section was below the glass transition temperature, one was between the transition temperature and 700C, and the third was situated above 700C. This behavior suggested a change from a pure jump mechanism in the glass to a mechanism which was governed by the free volume of the glass melt. There were also some indications of the occurrence of a mixed alkali effect whose magnitude varied with temperature and composition.

M.Braedt, G.H.Frischat: Physics and Chemistry of Glasses, 1988, 29[5], 214-8

Table 124

Diffusion of Na in xNa2O-(1-x)Rb2O•3SiO2 Glasses