Impact of chemical diffusion on crystal growth in sodium borosilicate glasses

The link between multicomponent diffusion and crystal growth has been investigated in a sodium borosilicate glass of interest to the nuclear industry. The growth rate of cristobalite, the principal crystal formed in this system, was studied between 700 degrees C and 900 degrees C. The growth rate was found to be linear with time and had an activation energy of 60 ±12 kJ.mol^-1 which is dose to the activation energy of sodium self-diffusion. Analysis of compositions around crystals and in the bulk of the glass revealed compositional gradients assigned to multicomponent diffusion. A diffusive mechanism involving exchange between silicon and boron appears to drive melt compositions near the crystals while in the bulk of the glass, another diffusive mechanism is predominant, consisting of exchange of silicon and sodium, justifying the value calculated for the activation energy of crystal growth. These results were then used for modeling growth rates in our glass. (authors)