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 th e in-flight nitridation of molybdenum disilicide (MoSi2) powders when carri ed out in an induction thermal plasma reactor. Initially, gradients of temp erature, velocity and concentration were evaluated, using an enthalpy probe system, for the plasma Row without injection of MoSi2 powders. Radial prof iles were then measured at the torch exit to examine the mass and energy tr ansfer mechanisms occurring under different nitridation conditions. These m easurements were performed using an induction plasma torch connected to a 5 0 kW radio-frequency (r.f.) power supply, the torch being attached to a wat er cooled cylindrical reactor. The process operating conditions studied wer e plasma plate power, chamber pressure, sheath gas composition, composition and Row rate of quench gas. The effect of last named parameter on the nitr idation 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 va lue for each type of quench gas and the temperature and concentration mappi ng demonstrates that the combination of high temperatures and high concentr ations of N-2 are necessary to reach maximum nitridation levels in MoSi2. ( C) 2001 Elsevier Science B.V. All rights reserved.