Homogeneity of peraluminous SiO2–B2O3–Al2O3–Na2O–CaO–Nd2O3 glasses: Effect of neodymium content

• Peraluminous glasses present a very large domain of homogeneity.
• Enhancement of neodymium solubility compared to peralkaline glasses
• Boron, aluminum and neodymium play synergic roles for network stabilization.
• Above neodymium solubility limit, crystallization and/or phase separation occur.

Considering the interest of developing new glass matrices able to immobilize higher concentration of high level nuclear wastes than currently used nuclear borosilicate compositions, glasses containing high rare earth contents are of particular interest. This study focuses on a peraluminous aluminoborosilicate system SiO2–B2O3–Al2O3–Na2O–CaO–Nd2O3 defined by a peralkaline/peraluminous ratio RP = ([Na2O] + [CaO])/([Na2O] + [CaO] + [Al2O3]) < 0.5. Samples with various contents of Nd2O3 from 0 to 10 mol% were studied using DSC, XRD, SEM, TEM, STEM and EMPA methods. The glasses present a high thermal stability even after a slow cooling treatment from the melt. Only a slight mullite crystallization is detected for low Nd2O3 content (≤ 2.3 mol%) and crystallization of a neodymium borosilicate crystalline phase combined to a phase separation occurred at high Nd2O3 content (≥ 8 mol%). The solubility of neodymium in the presence of aluminum is demonstrated, with higher neodymium incorporation amounts than in peralkaline glasses.