Pb17Li and lithium: A thermodynamic rationalisation of their radically different chemistry

Abstract

The contrasting chemistry of Pb17Li and lithium is attributed to their lithium activities. PbLi alloys exhibit marked negative deviations from ideality owing to ‘chemical short range order’, giving γ Li = 7.26 × 10 −4, a Li = 1.23 × 10 −4 and G Li = −57.8 kJ mol −1 in Pb-17Li at 773 K. This G Li value is sufficiently negative to prevent the reaction of Pb17Li with gaseous hydrogen and nitrogen to form LiH and Li 3N but not with oxygen containing gases to form Li 2O. Similarly, nitride and carbide ceramics are compatible with Pb-17Li but oxide ceramics are liable to degradation. In contrast, unit activity liquid lithium reacts with all the gases and, depending on their free energy of formation, some of the ceramics. Wherea, dissolved oxygen is corrosive in Pb-17Li, giving LiCrO 2, dissolved nitrogen adopts the corrosive role in lithium giving Li 9CrN 5. The instability of LiH in Pb-17Li renders tritium extraction facile; this contrasts with lithium for which tritium extraction is difficult owing to LiH formation.