Zirconia/garnet multiphase ceramics with high immobilization capacity for Nd confers better physical and chemical stability

Abstract

Multiphase ceramics have a high application potential in the field of nuclear waste immobilization because of the efficient synergy between the individual phases. In this work, zirconia/garnet multiphase ceramics with high efficient and effective immobilization capacity of trivalent actinides were successfully prepared using conventional solid-phase sintering. ZrO₂ doping increases the lattice site available for nuclide substitution and advance the immobilization capacity of the ceramic substrate for nuclide. At the same time, the phase change of zirconia is used to tougher and improve the physical properties of the ceramic waste form. The feasibility of using multiphase ceramics for the efficient immobilization of trivalent actinides was assessed by studying the phase evolution, microstructure, Vickers hardness, and chemical stability of the multi-phase ceramics. Zr_1-xNd_xO_2-x/2/Ca_3-yNd_yZr_3-yFe_y-1Fe₃O₁₂ multiphase ceramics exhibited superior physical or chemical properties compared to most of the multiphase ceramics as well as the previously prepared single-phase calcium garnet ceramic waste forms. The Vickers hardness of all the multiphase ceramic samples ranged between 685 and 730 HV0.5. Under the condition of using simulate Bei Shan groundwater as leaching agent, the normalized leaching rates of Nd is approximately 10⁻6 g·m⁻²·day⁻¹, showing good chemical stability and achieving efficient and effective immobilization of trivalent actinides. The excellent chemical, as well as physical properties of Zr_1-xNd_xO_2-x/2/Ca_3-yNd_yZr_3-yFe_y-1Fe₃O₁₂ multiphase ceramics are expected to make them one of the substrates for more efficient and effective immobilizing of trivalent actinides.