Kinetics of nitridation of calcium

Abstract

The kinetics of the reaction of nitrogen with sintered, evaporated calcium films has been studied between 23 and 200°C using a constant-pressure technique. The results are consistent with a modified Mott & Cabrera theory of thin film formation, the rate being controlled by the mobility of the calcium ions through the nitride lattice under the influence of the potential difference set up between the metal and chemisorbed nitrogen at the nitride surface. The rate depends directly on the first power of the pressure suggesting a reversible adsorption to form a ‘surface complex’, N - 2 . The linear dependence of activation energy on the inverse thickness of the nitride layer is verified and the critical temperature determined. In addition, an estimation of the fraction of the total number of metal sites per unit area interface from which the metal ion penetrates the nitride layer has been made.