Phase evolution and thermal stability of SrSO ₄ ‐containing borosilicate glass‐ceramics

Abstract Glass‐ceramics are considered as promising candidate for high‐level liquid waste (HLW) immobilization. The effects of SrSO ₄ content (2‒8 wt%, calculated as SO ₃ ) on the phase composition, microstructure, and thermal stability of borosilicate glass were studied. The results show that the samples with 2‒4 wt% SrSO ₄ possess an amorphous structure and no crystals are observed when melted at 1150°C for 3 h. A great quantity of SrSO ₄ crystals (∼1 µm) appear and are uniformly distributed in the glass matrix of the sample with 6 wt% SrSO ₄ (abbreviated as S6), and the grain size increases with further increasing SrSO ₄ content. The SrSO ₄ crystal is more thermally stable than Na ₂ SO ₄ crystal in borosilicate glass melts. The SO ₃ retention in the glass‐ceramics has no obvious change when the temperatures are lower than 1050°C, and then decreases obviously with further increasing temperature. A white phase separation layer appears on the surface of glass‐ceramic, which is mainly composed of SrSO ₄ along with a small amount of LiNaSO ₄ phase at 1050°C‒1150°C. These results suggest that SrSO ₄ ‐containing borosilicate glass‐ceramics have great potential for the immobilization of sulfur‐rich HLW.