THE REACTION OF NITROGEN WITH DILUTE-SOLUTIONS OF BARIUM IN LIQUID LITHIUM - ELECTRICAL-RESISTIVITY, X-RAY PHASE-ANALYSIS, KINETIC AND THERMAL-ANALYSIS STUDIES

The reaction of nitrogen with liquid lithium containing dissolved bari um which follows a solution-precipitation mechanism has been studied. Initially, nitrogen dissolves in the liquid metal to form an homogeneo us solution; the reaction is first order with respect to nitrogen with an activation energy of 33.6 kJ mol-1. Subsequently, it reacts to for m a precipitate of Li3N; the Li3N crystallisation face is dependent on the barium content of the solution, nitrogen solubility rising with i ncreasing barium content. The ternary nitride, LiBaN, is only formed o n cooling the solution; there is no evidence for Ba2N or Ba3N2 formati on. This behaviour contrasts with that in the corresponding Na-M-N (M = Sr or Ba) systems where the solubility is directly proportional to t he alkaline-earth metal content of the solution and the precipitating phase is the alkaline-earth metal subnitride, M2N (M = Sr or Ba). Anal ysis of the crystallisation fields of Li, Li4Ba, LiBaN and Li3N indica ted they are separated by monovariant curves which fall from the binar y eutectics (Li-Ba, x(Ba) =0.105 and 416K; Li-N, degenerate at 453.5 K , Li3N-LiBaN, unknown) through a quasi-peritectic equilibrium involvin g liquid, lithium, Li4Ba and LiBaN (372 K) to a ternary eutectic point based on liquid, lithium, Li3N and LiBaN (368 K).