LAUSR

Abstract Density functional theory and ab initio thermodynamics studies are performed to investigate the interaction of oxygen, nitrogen and hydrogen molecules with hexagonal close packed Ti (0001) surfaces. The system is modeled as a slab where the concentration of the adsorbed atoms is systematically increased and the most favorable configuration is determined based on total energy comparisons. Varying tendencies are observed for the ground state structures of oxygen, nitrogen and hydrogen adsorption. Oxygen and hydrogen atoms are found to be adsorbed on the surface with increasing concentration and tend to migrate to interior layer only after surface saturation. However, nitrogen prefers to migrate into the interior layers. For all elements, the favorable position in the interior layers is the octahedral interstitial site. Taking into account the partial pressure of oxygen, nitrogen and hydrogen and the effect of temperature, we develop surface phase diagrams that display stable surface configurations. Our studies provide an atomic insight into the structure of the surface scale, passivation effects, and surface tension of Ti for advanced powder manufacturing processes and applications in catalysis.