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, xBa= 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).