Microwave-sintering preparation, phase evolution and chemical stability of Na1-2Sr Zr2(PO4)3 ceramics for immobilizing simulated radionuclides

Sodium zirconium phosphate (NaZr2(PO4)3, NZP) family ceramics were considered as a potential host matrix for the immobilization of nuclear waste. In this study, the dense Sr-incorporated NZP ceramics with the formula of Na1-2xSrxZr2(PO4)3 (x = 0, 0.1, 0.2, 0.25, 0.3, 0.4, and 0.5) were fabricated by microwave-assisted solid-state reaction method. The phase evolution, densification behavior and chemical stability of the as-prepared samples were systematically investigated by XRD, Rietveld refinement, Raman, SEM-EDS and PCT method. The results demonstrated that Na in the NZP lattice could be substituted by the simulated fission product Sr, and the phase composition gradually changed from NZP to Sr0.5Zr2(PO4)3 (SrZP) with the increase of Sr content. The samples presented high densification and uniform elements distribution after microwave sintering at 1100 °C for 2 h. Moreover, the as-prepared samples exhibited the superior chemical stability. The normalized elemental leaching rate of Sr, Na, P, and Zr were 10−3, 10−4, 10−3, and