Hydrogen in liquid alkali metals

Abstract

The chemistry of liquid alkali metal-hydrogen solutions has been surveyed. Solubility data for hydrogen (<6 mol% H) and deuterium (<4 mol% D) in liquid lithium are reported, Li-H log S(mol% H) = 3.523 − 2308/T(°K) Li-D log S(mol% D) = 4.321 − 2873/T(°K), and the isotope effect considered. The hydrogen data are used to augment the LiLiH phase diagram and are compared with corresponding solubilities in sodium, potassium and eutectic NaK (78 wt.% K) alloy; data for rubidium and caesium are not available. The nature of the solute species and the concept of solvation in these solutions are also discussed.Investigations of interactions between hydrogen and non-metals in liquid alkali-metal solutions have shown that, whereas hydrogen and nitrogen act independently in lithium at 420 °C, hydrogen and oxygen interact in sodium at 400 °C according to the equilibrium: O2− + H−⇌ OH− + 2e−. Hydrogen-oxygen interactions in the other alkali metals are also considered and are rationalised in terms of the enthalpy changes of the corresponding solid-state reaction. Furthermore, yttrium has been shown to react, rapidly, with hydrogen dissolved in lithium at a relatively low temperature (400 °C) to form a mixture of a solid solution of hydrogen in yttrium and yttrium dihydride according to the reaction: Li(H) + Y → Li + Y(H) + YH2−x.