Dense Iodoapatite Ceramics Consolidated by Low‐Temperature Spark Plasma Sintering

Abstract

Pb9.85(VO4)6I1.7, a potential waste form for long‐lived I‐129 immobilization, experiences phase decomposition and thus iodine loss at an elevated temperature above 400°C, presenting a significant challenge for effective management of radioactive iodine. In this work, we report low‐temperature consolidation of dense iodoapatite pellets with above 95% theoretical density by spark plasma sintering (SPS) at temperatures as low as 350°C for 20 min without iodine loss. Microstructure analysis indicates a nanocrystalline ceramic with an average grain size less than 100 nm. Grain growth dominates the sintered microstructure at higher temperatures and longer durations. The dense nanoceramics have significantly‐improved fracture toughness as compared with bulk coarsened grain structures. The effects of sintering temperatures (350°C, 400°C, 500°C, and 700°C) and durations (0–20 min) on microstructure, density, fracture morphology, and mechanical properties including Young's modulus and hardness of bulk samples were investigated. Low temperature densified iodoapatites suggest immense potential of SPS as an advanced materials fabrication technology for the development of waste forms for immobilization of volatile radionuclides including radioactive iodine.