A MODEL FOR THE ELECTROCHEMICAL-BEHAVIOR OF TIN AND TIC

We have performed simple model calculations for the surface electronic structure of TiN and TiC based on the theory of Miedema for the heat of formation of these compounds. The electronic properties of pure anionic (N- and C-surfaces) and pure cationic (Ti-) surfaces are contrasted. The anionic surfaces have a higher surface energy, and cannot screen external fields as well as the cationic surfaces. Our model suggests that at potentials below the onset of oxidation surface layers enriched in nitrogen (resp. carbon) are formed, which shield the underlying titanium atoms from the external field. At higher potentials the field can penetrate through the anions at the surface and induce the oxidation of the titanium atoms.