The reaction of nitrogen with dilute solutions of barium in liquid lithium: electrical resistivity, X-ray phase analysis, kinetic and thermal analysis studies

Abstract

The reaction of nitrogen with liquid lithium containing dissolved barium which follows a solution–precipitation mechanism has been studied. Initially, nitrogen dissolves in the liquid metal to form an homogeneous solution; the reaction is first order with respect to nitrogen with an activation energy of 33.6 kJ mol^–1. Subsequently, it reacts to form a precipitate of Li₃N; the Li₃N crystallisation face is dependent on the barium content of the solution, nitrogen solubility rising with increasing barium content. The ternary nitride, LiBaN, is only formed on cooling the solution; there is no evidence for Ba₂N or Ba₃N₂ formation. This behaviour contrasts with that in the corresponding Na–M–N (M = Sr or Ba) systems where the solubility is directly proportional to the alkaline-earth metal content of the solution and the precipitating phase is the alkaline-earth metal subnitride. M₂N (M = Sr or Ba). Analysis of the crystallisation fields of Li, Li₄Ba, LiBaN and Li₃N indicated they are separated by monovariant curves which fall from the binary eutectics (Li–Ba, x_Ba= 0.105 and 416 K; Li–N. degenerate at 453.5 K, Li₃N–LiBaN, unknown) through a quasi-peritectic equilibrium involving liquid, lithium, Li₄Ba and LiBaN (372 K) to a ternary eutectic point based on liquid, lithium. Li₃N and LiBaN (368 K).