THE EFFECT OF THE REAL CRYSTAL-STRUCTURE OF IRON ON THE BEHAVIOR OF SURFACE CONTAMINANTS

The segregation kinetics studies of sulphur and carbon in iron and the adsorption kinetics of oxygen on iron have been discussed, taking int o account the real structure of the monocrystalline sample. The deviat ion of the kinetics results from the t(1/2) law has been interpreted a s the effect of the presence of the adsorption sites in the defects of the monocrystalline iron sample. The equilibrium between the adsorpti on states of sulphur, carbon and oxygen atoms in the defects and on th e surface has been assumed. For sulphur and carbon atoms, the energeti cally more favourable adsorption sites are in the defects; however, fo r oxygen atoms the adsorption sites on the surface are more favourable . The free energy of the segregation of sulphur and carbon atoms from the defects to the surface has been assumed to be a linear function of the degree of filling of the adsorption sites in the defects. The cal culations of the energies of iron clusters with a contaminant atom hav e been also considered. (C) 1998 Elsevier Science B.V. All rights rese rved.