MODELING OF A MICROWAVE POSTDISCHARGE NITRIDING REACTOR

In a postdischarge nitriding reactor, reactive species, which have a short lifetime, are created by means of a plasma and then sent by convection towards the sample which is to be treated. The aim of the model presented here is to optimize the gas flow characteristics (composition, flow rate, pressure etc.) in order to obtain a maximum reactivity around the sample. The experimental reactor used has a very simple geometry 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. This reactor allowed us to point out the complexity of the different operating parameters, justifying the development of a predictive model Such a model was developed with the code PHOENICS. It allowed us to determine the effect of the operating parameters on the velocity field, the temperature field and the atomic nitrogen (the nitriding species) mass fraction map. The standard operating conditions used for the treatment 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 atomic nitrogen mass fraction.