Phase evolution and thermal stability of SrSO4-containing borosilicate glass-ceramics

Abstract

Glass-ceramics are considered as promising candidate for high-level liquid waste (HLW) immobilization. The effects of SrSO₄ content (2‒8 wt%, calculated as SO₃) on the phase composition, microstructure, and thermal stability of borosilicate glass were studied. The results show that the samples with 2‒4 wt% SrSO₄ possess an amorphous structure and no crystals are observed when melted at 1150°C for 3 h. A great quantity of SrSO₄ crystals (∼1 µm) appear and are uniformly distributed in the glass matrix of the sample with 6 wt% SrSO₄ (abbreviated as S6), and the grain size increases with further increasing SrSO₄ content. The SrSO₄ crystal is more thermally stable than Na₂SO₄ crystal in borosilicate glass melts. The SO₃ 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 SrSO₄ along with a small amount of LiNaSO₄ phase at 1050°C‒1150°C. These results suggest that SrSO₄-containing borosilicate glass-ceramics have great potential for the immobilization of sulfur-rich HLW.