Heat and mass transfer during in-flight nitridation of molybdenum disilicide powder in an induction plasma reactor

The present study reveals some of the important parameters which control the in-flight nitridation of molybdenum disilicide (MoSi2) powders when carried out in an induction thermal plasma reactor. Initially, gradients of temperature, velocity and concentration were evaluated, using an enthalpy probe system, for the plasma flow without injection of MoSi2 powders. Radial profiles were then measured at the torch exit to examine the mass and energy transfer mechanisms occurring under different nitridation conditions. These measurements were performed using an induction plasma torch connected to a 50 kW radio-frequency (r.f.) power supply, the torch being attached to a water cooled cylindrical reactor. The process operating conditions studied were plasma plate power, chamber pressure, sheath gas composition, composition and flow rate of quench gas. The effect of last named parameter on the nitridation of the powders was found to be the most important parameter in the nitridation process. The results show that there is an optimum flow rate value for each type of quench gas and the temperature and concentration mapping demonstrates that the combination of high temperatures and high concentrations of N2 are necessary to reach maximum nitridation levels in MoSi2.