Effect of annealing on microstructure and thermal conductivity of Li2TiO3 and Li4SiO4

Abstract

• The microstructure of Li 2 TiO 3 keeps stable during annealing. • The phase decomposition of Li 4 SiO 4 is observed during annealing. • Li 2 TiO 3 has stable thermal performance, however Li 4 SiO 4 degrades during long-term operation. Li 2 TiO 3 and Li 4 SiO 4 are considered as candidate tritium breeding materials due to its excellent physical, chemical and tritium release performance. Thermal conductivities of solid tritium breeding materials are determined by microstructure, sintering density and surface condition which will change during operation of fusion reactor. A comprehensive understanding of thermal performance of tritium breeding materials is essential due to the extreme operation condition in the fusion reactor. In this work, the microstructure and thermal conductivity was investigated for Li 2 TiO 3 and Li 4 SiO 4 annealed at the corresponding temperature of tritium breeding blanket. SEM (Scanning electron micrography) results presented the stable structure of Li 2 TiO 3 and instability of Li 4 SiO 4 . XRD (X-ray diffraction) and Raman indicated the disorder of the crystal structure. It can be attributed to lithium loss during annealing process. EPR (Electron paramagnetic resonance) showed that there were almost no defects related unpaired electron. It is due to defect recovery at higher temperature, as well as tiny H 2 amount in sweeping gas. There was no obvious change of thermal performance for Li 2 TiO 3 during different annealing time. It is indicated that Li 2 TiO 3 has a good thermal performance to resist heat load. But thermal performance of Li 4 SiO 4 decreased largely after annealing. It is resulted from variation of the structure during annealing process. Based on the present work, it is illustrated that Li 2 TiO 3 has stable thermal performance under annealing condition, however, the thermal performance of Li 4 SiO 4 is not so stable for long service time at higher temperature.