Spark plasma sintering of iodine-bearing apatite

The high chemical durability of iodine-bearing apatite makes it strongly prospective for conditioning of radioactive iodine. The synthesis and consolidation of iodine-bearing compounds require low temperatures to avoid iodine volatilization. Spark plasma sintering therefore appears to be a suitable process because of its shorter treatment time and lower sintering temperature compared with other processes such as HUP or HIP. Two alternatives were examined: SPS sintering of iodine-bearing apatite powder and SPS reacting of a stoichiometric lead iodide and lead phosphovanadate powder mixture. The degree of densification and the microstructure of bulk materials in both cases are described and compared. Reactive sintering appears to involve a three-stage mechanism: (i) PbI2 coalescence, (ii) solid-state iodoapatite synthesis and consolidation and, (iii) iodoapatite consolidation in the presence of a liquid phase. The SPS reacted products reveal the finest and most homogeneous microstructure, and a density exceeding 96%.