Reaction of nitrogen with stirred and unstirred liquid lithium

Abstract

The rates of reaction between nitrogen and liquid lithium at 400° have been studied by following changes in pressure of gas in a closed system. The liquid metal, contained in steel vessels, was stirred vigorously by an external rotating magnet, and its surface was broken by a baffle. The results are regular and reproducible. The reaction passes through three stages in which the rates follow the rectilinear, logarithmic, and parabolic laws successively, and are independent of pressure. In the absence of stirring, there is no rectilinear stage. When stirred in the presence of nitrogen, liquid lithium spreads over the total internal surface area of the steel containing vessels; reaction rates are therefore influenced by vessel dimensions and results are correlated on this basis. A value of 33 kcal. mole has been determined for the activation energy at the stage in the reaction when the rates obey the rectilinear law, and reaction is not inhibited by surface films. This ‘fresh surface’ value compares with 15·5 kcal./mole for a surface carrying a continuous nitride film. The product has been identified as Li₃N, and possible mechanisms of reaction are discussed.