Kinetics of high-temperature nitridation of tantalum under isothermal conditions

Kinetics of the very initial stages of tantalum nitridation was investigated at high-temperature (T=1500-2500 degree) range under isothermal conditions and nitrogen pressure P_N2=150-600 Torr by electrothermographical method. Process features were investigated by following independent analyses: gravimetric, metallographic and conductometric methods. It was established that Ta₂N nitride phase and solid solution were formed within whole investigated temperature pressure-time range. Also step-by-step formation of solid solution and nitride layer was observed at relatively low nitrogen pressures (150-300 Torr), while at high pressures both processes occurred simultaneously from the beginning of the process. Kinetics of tantalum nitridation does not described by well-known parabolic low under investigated conditions. This is due to features of nitrogen solution in Ta and nitride layer formation and growth for finite size samples, as well as limited supply of nitrogen to the metal surface