Effect of changing the rare earth cation type on the structure and crystallization behavior of an aluminoborosilicate glass

TL;DR

This study investigates how changing the type of rare earth cation affects the crystallization behavior of aluminoborosilicate glass, with minimal impact on structure but significant effects on crystallization patterns and phases.

Contribution

It provides new insights into the influence of different rare earth ions on crystallization behavior in nuclear waste immobilization glasses.

Findings

Little effect on glass structure from RE cation variation

Significant impact on crystallization behavior and phases

Heterogeneous RE-rich silicate phase observed for low ionic radius REs

Abstract

An aluminoborosilicate glass, containing high amount of rare earth (RE) accordingly to the following composition 50.68 SiO2 - 4.25 Al2O3 - 8.50 B2O3 - 12.19 Na2O - 4.84 CaO - 3.19 ZrO2 - 16.35 RE2O3 (wt.%), is currently under study for the immobilization of nuclear waste solutions. In this work, we wanted to investigate the effect of changing the RE cation type on the glass structure and on its crystallization behavior. For this purpose, a glass series was elaborated in which the nature of the RE is varying from lanthanum to lutetium. In this glass series, only little effect was observed on the glass structure. On the contrary, a strong impact was put in evidence on the crystallization behavior through different heat treatments. A slow cooling of the melt at 1^/circC/min, revealed significant crystallization of apatite Ca2RE8(SiO4)6O2 in sample containing rare earths with ionic radii close to that of calcium. Another heat treatment consisting of successive nucleation and growth stages, performed to force the crystallization in the bulk and reduce any surface crystallization effect, put in evidence the existence of a strongly heterogeneous second rare earth rich silicate phase for samples containing RE with low ionic radius (from Y to Lu).