A chemical theory analysis of the solution thermodynamics of oxygen, nitrogen and hydrogen in lead-rich LiPb mixtures

Abstract

The large non-idealities which are seen in LiPb solution thermodynamics are treated by postulating the existence of stable LiPb molecules in solution and strong surface tension effects around all dissolved impurity compounds. The equilibrium constant for LiPb formation obeys the following temperature dependence: In K eq = −1.44+ 7000 T Formulations which derive from these assumptions are used to calculate cold-trap solubilities for hydrogen, nitrogen and oxygen. The minimum cold-trap concentrations (mole fraction) in LiPb eutectic are 4.8 × 10 −5 for hydrogen, 2.5 × 10 −4 for nitrogen and 5.1 × 10 −6 for oxygen; these values are rather lower than the solubilities observed in pure lithium. The same formulations are used to calculate the Sieverts constants for hydrogen and nitrogen in lead-rich LiPb solution; these results agree with the experimentally observed constants. The surface tension interactions are assumed to equal the sum of the energy required to form a hole in the fluid and the energy which is released when the impurity compound is inserted within that hole. The method used here for estimating the latter energy is, I believe, exceptional in its rigor and its predictive capacity. Its use, however, is limited to liquid alloys of metals which, like LiPb, do not form heterometallic oxides and nitrides.