Construction and Significance of Chromium Nitride Pourbaix Diagrams based at 298 K (25 oC)

Chromium nitrides such as CrN and Cr 2 N are often used for corrosion and wear resistant applications. Pourbaix diagrams can be used to help gauge the thermodynamic stability of elements and compounds. In this paper, Pourbaix diagrams are constructed for CrN and Cr 2 N using thermodynamical data for species at 298 K (25 o C) and at a concentration of 10 − 6 M for aqueous species. These diagrams are useful indicators for the stable regions in which these compounds can be used. The diagrams show that passive Cr 2 O 3 films form on the surfaces where chromium nitride was present. It is argued that the very presence of Cr 2 O 3 films will degrade chromium nitride and make it much less useful as a wear resistant layer. It is further argued that the presence of nitrogen in solid solution is better for the stability of passive films in stainless steels.