Preparation and properties of Ce0.5Nd0.5PO4 monazite ceramics by pressureless sintering and spark plasma sintering (SPS)

LnPO 4 ·nH 2 O rhabdophane/monazite is an important actinide-bearing material in the back end of the nuclear fuel cycle. In this work, using Nd 3+ to simulate trivalent actinides, Ce 0.5 Nd 0.5 PO 4 ·0.667H 2 O rhabdophane was synthesized by the wet-chemistry method in 90 °C and pH = 1 solution. The sintering behavior of associated Ce 0.5 Nd 0.5 PO 4 monazite ceramics was investigated by pressureless sintering and spark plasma sintering (SPS), along with appraising their chemical stability. The results reveal that Ce 3+ is successfully replaced by Nd 3+ in the rhabdophane lattice, and rhabdophane can transform to monazite with a temperature over 750 °C. SPS can compact the ceramic sample at a lower temperature compared to pressureless sintering even if the grain size is smaller. Adding a pre-sintering process of 900 °C before SPS and pressureless sintering will further improve the density and Vickers hardness of ceramics. For the chemical stability of Ce 0.5 Nd 0.5 PO 4 monazite ceramics, Ce is more likely to be leached compared to Nd, and the ceramics prepared by SPS with a pre-sintering process have the lowest normalized leaching rates, associated with the values of 2.03 × 10 −5  g·m −2· d −1 and 0.75 × 10 −5  g·m −2 ·d −1 for Ce and Nd, respectively.