PARAMETRIC STUDY OF THE DECOMPOSITION OF NH3 FOR AN INDUCTION PLASMA REACTOR DESIGN

The present paper reports a study of the gas mixing and chemical transformation in an induction plasma reactor under atmospheric pressure, and its dependence on the plasma operating conditions. For this purpose, the thermal dissociation of ammonia into nitrogen and hydrogen was chosen because of the relative simplicity of the reactions involved and its use in a number of studies on plasma synthesis of ultrafine nitride ceramic powders using ammonia as nitriding agent. A hot-wall reactor configuration is investigated in which ammonia is injected radially through multiple orifices into the gases at the exit nozzle of an induction plasma torch. Concentration mapping in the mixing zone was carried out, using a VG-MicroMass-PC 300 D quadrupole mass spectrometer, for different plasma power levels, in the range 13-24 kW. A 3-point injection mode is used with the injection ports oriented upstream at 45 degrees to the touch axis. This allows uniform mixing of the injected gas in the plasma jet. A systematic study of the effects of plate power and ammonia and plasma gas flow rates on the mixing and dissociation of NH3 in the reactor is reported The results are analyzed and discussed from the viewpoint of their use for optimizing the design of induction plasma reactors, to be applied to the vapor-phase synthesis of ultrafine silicon nitride powders.