MODELING OF A MICROWAVE POSTDISCHARGE NITRIDING REACTOR

In a postdischarge nitriding reactor, reactive species, which have a s hort lifetime, are created by means of a plasma and then sent by conve ction towards the sample which is to be treated. The aim of the model presented here is to optimize the gas flow characteristics (compositio n, flow rate, pressure etc.) in order to obtain a maximum reactivity a round the sample. The experimental reactor used has a very simple geom etry and works with low power (less than 200 W) microwave discharges ( 2450 MHz) in Ar-N2 mixtures for a pressure in the 10-1000 hPa range. T his reactor allowed us to point out the complexity of the different op erating parameters, justifying the development of a predictive model S uch a model was developed with the code PHOENICS. It allowed us to det ermine the effect of the operating parameters on the velocity field, t he temperature field and the atomic nitrogen (the nitriding species) m ass fraction map. The standard operating conditions used for the treat ment of iron samples were chosen as reference conditions. Then several sets of operating conditions were tested, pointing out the extremely important effect of pressure and gas velocity in the reactor on the at omic nitrogen mass fraction.