Structural features and crystallization of Na2O-Cs2O-B2O3-SiO2 glasses for radioactive waste immobilization

Abstract

Borosilicate glasses have long been the preferred form for immobilizing high-level radioactive wastes. However, a significant drawback of glass-matrices involves the low rate of loading with radionuclides. One of the approaches to solving this problem envisages a multiphase glass system with crystalline inclusions. The present work aims to study model borosilicate glasses and glass-ceramics containing Cs atoms serving as a radionuclide simulator. Two approaches for the synthesis of glass-ceramics were used: directed crystallization, and pressing followed by annealing. The structure of initial borosilicate glasses and glass-ceramic samples obtained by these means was studied using Raman spectroscopy. An X-ray diffraction analysis was applied to identify crystalline phases. The morphology and composition of the crystalline phase was evaluated using scanning electron microscopy. The obtained results showed that the structure and properties of the synthesized glass-ceramic material is determined by the composition of initial glasses. Due to the ratio of modifying cations in glasses at a constant boron-to-silicon ratio, the crystalline phases identified in glass-ceramics are significantly affected by the anionic structure. The formation and growth of crystals was also established to be dependent on the technological scheme of synthesis.