Synthesis and sintering of a monazite–brabantite solid solution ceramics using metaphosphate

In order to improve monazite-based ceramics, to be used as actinides waste-form, a procedure for synthesis and sintering of a monazite–brabantite solid solution (ssMB) using metaphosphate La(PO3)3 is described. Using LaPO4, CeO2, ThO2, CaCO3 and La(PO3)3 as precursors, the gaseous emissions are strongly reduced, compared to a process using (NH4)H2PO4. Detailed dilatometric studies show sintering of that product is a two-steps process: coalescence and boundary diffusion. From X-ray diffraction, electron microprobe analyses, SEM observation, dilatometric study and TG–DTA, the reaction scheme is identified and the thermal treatment for synthesis and sintering is optimized to obtain homogeneous, dense, reproducible and well-crystallized pellets of La0.73Ce0.09Th0.09Ca0.09PO4 and La0.91Ce0.09PO4.