Mechanical properties of thermally stable cadmium iodoapatite ceramic by reactive spark plasma sintering technique

Abstract

Apatites based materials have been considered as potential waste forms to immobilize the long-lived radioactive iodine isotope. But the thermal instability and phase decomposition at a higher temperature hamper the waste management process. Spark plasma sintering can be a suitable technique compared to conventional sintering processes due to its rapid heating rate, lower sintering temperature and holding time. In this study, we synthesized a highly dense iodine bearing cadmium iodoapatite ceramic pellets by spark plasma sintering (SPS) technique. We successfully consolidated iodoapatite pellets with ~95.5% of theoretical density (TD) without any iodine loss and phase decomposition after low temperature sintering at 350 o C for 15 mins under 100 MPa. The theoretical density, micro-hardness, and yield strength of sintered pellets were investigated for different sintering temperatures of 300 o C, 350 o C, and 400 o C and holding time (15 min) under the pressure of 100 MPa. The densified pellets displayed nanocrystalline grain structures of 30-80 nm size which contributed to enhanced thermal stability and fracture toughness. The X-ray diffraction and EDS analysis also confirms the presence of iodoapatite structures. This advanced fabrication technique using SPS can help to develop thermally durable waste forms and mitigate the challenges to dispose high- level radioactive waste.