Synthesis of phosphate based glass-ceramic waste forms by a melt-quenching process: The formation process

In this paper, phosphate based glass-ceramic waste forms containing monazite CePO4 as crystalline phase were prepared by a melt-quenching process using NH4H2PO4, H3BO3, Fe2O3 and CeO2 as the feed materials and the formation process was analyzed. The results show that, the decomposition of H3BO3 at the heating temperature below 150 degrees C and the reaction between Fe2O3 and NH(4)H(2)PO(4 )to form NH4FeP2O2 occur firstly. Then phosphate phases such as Fe-4(PO4)(2)O, Fe(PO3)(3), FePO4 and CePO4 form below 750 degrees C, and these phosphate phases are continually dissolved into phosphate glass melts at higher temperatures. Finally, CePO4 phase is the only crystalline phase at higher temperatures such as 1100 degrees C due to its good stability and glass-ceramic waste forms with CePO4 as crystalline phase were obtained by quenching and annealing. Moreover, the content of CeO2 between 8 mol% and 14 mol% has insignificantly effect on the formation process. (C) 2019 Elsevier B.V. All rights reserved.