Porous Glass Matrix for Nuclear Waste Storage — Part I: Preparation and Characterisation of Spinodal Phase Separation

Abstract

We have studied the phase separation behavior by spinodal decomposition of two sodium borosilicate glasses of the following composition (weight %) 8Na₂0-32B₂0₃-60Si0₂ (glass A) and 8Na₂0-27B₂0₃-65Si0₂ (glass B). From photographs of glass samples obtained with a Scanning Electron, Microscope, we have determined the growth of the mean size $\bar{r}$ of the microstructures of the least phase as a function of the time of the thermal treatment (0–100 h) and for different temperatures (580, 600, 620 and 640°C). The results are in agreement with the theory of Lifshitz-Slyozov-Ardell which predict a growth of the microstructures of the least phase through the insoluble phase by a diffusion controlled mechanism such that ${{\bar{r}}^{3}} = {{A}_{o}}t{\kern 1pt} exp( - \Delta E/RT)$. The activation energy △E and the pre-exponential term A_o of the diffusion controlled mechanism are △E = 70 Kcal/mol and A_o = 2.2 10²⁴ Å3/h (glass A) and △E = 92 Kcal/moL and A_o = 2.2 10²⁹ Å3/h (glass B). The curves of the sizes distribution of the microstructures allow us to suggest for the glass presently under study the most adequate thermal treatments for the preparation of porous glass matrix to store nuclear liquid waste materials.