Diagnostic and modeling of N-2-H-2 discharges for iron nitriding

The production of N and H atoms has been studied in DC and HF N-2-H-2 flowi ng discharges and post-discharges in connection with nitriding of iron subs trates. Experimentally, the N and Il atoms have been detected by emission s pectroscopy and Laser Induced Fluorescence (LIF). A strong increase of the main gas atom density (N or H) was found when a small amount of a second ga s (H-2 or N-2) was added. This increase in N or H atom densities Is interpr eted by a model describing the kinetics in the reactive gas volume and on t he surface of the reactor walls (pyrex tube). In particular, it is shown th at the destruction probabilities of N and H atoms on the tube wall are redu ced by a factor of about 2 as a few % of H-2 or Na is introduced into Na or H-2. Correlations are established between the density of N and II atoms an d the thickness and quality of iron nitride layers growing on iron substrat es located within a reactor and placed in the post-discharge of a N-2-H-2 H F flowing discharge. Under the conditions of maximum N and H atom density, thick epsilon-Fe2N1 - x layers without iron oxide superficial sublayer have been found on the iron surface.