The Response of Nitriding Chemistry to Different Initial Gas Compositions

The response of the kinetics of surface-catalyzed reactions to different initial conditions in a gas nitriding furnace has been studied. The predictions are made under the conditions with both high and low concentrations of ammonia and a process temperature of around 520 °C. Results are presented in temporal variations of gas temperature and concentrations and coverages of surface species. It has been shown that in the composition where NH₃ content is richer, there is a strong possibility of developing substantially higher N_ad coverage and so diffusion into the material. Reducing the ammonia content, which means an increase in the proportion of N₂ in the initial mixture, leads to a quicker saturation of the furnace atmosphere to the desorption of the reaction product, N₂, which eventually suppresses the advance of reaction in the forward direction. Low coverage values of H_ad have proved that the adsorbed hydrogen is the most unstable species on the surface.