Investigations of the thermal stability of lithium films on boron surfaces

Boronization and lithiumization are used as wall conditioning processes to improve the impurity gettering and fuel recycling in current and future fusion devices including ITER. A combination of these processes is in the scope of experiments such as NSTX-U [1] and TJ-II [2]. Thus, interactions of lithium (Li) and boron (B) surfaces are expected, and an understanding of the Li-B system is necessary. Previous studies on Li-B systems have shown poor Li solubility in B, forming B-rich borides (LiB_x with x>10). Limited interactions at temperatures below 573 K were observed, while melting and decomposition were reported above 800 K and 1200 K, respectively [3,4]. In this preliminary study, we evaluate the characteristics of boron surfaces and the thermal stability of Li films on B surfaces using temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). We used XPS to evaluate the surface chemistry and asses the impurity content of the B and Li-B surfaces, and SEM to evaluate the surface morphology. We studied the thermal stability of the Li films on B surfaces using TDS, as a function of Li surface coverage.

[1] NSTX-U Five Year Plan 2021-2025 [2] F. L. Tabarés, et al., Plasma Phys. Contr. F. 50, 124051 (2008). [3] H. Borgstedt and C. Guminski, Journal of Phase Equilibria. 24,572 (2003) [4] V. Milashius, et al., Inorganic Chemistry Frontiers, 5, 853 (2018)