Effect of the real iron crystal structure on the segregation of sulphur

The kinetics of the segregation of sulphur in monocrystalline iron a-Fe 111.has been studied using the AES method. The segregated sulphur originated from bulk contamination. Segregation has been studied at temperatures of 730 and 820 K. The results of the studies are discussed taking into account the real mosaic structure of the monocrystalline sample of iron. The adsorption sites for the segregating sulphur could be located on the surface but also in the defects of the monocrystalline sample. At lower temperatures segregation occurs only from defects open to the surface. If the defects are empty, segregation does not occur. At higher temperatures segregation from the bulk to the surface occurs via defects. The ratio of the number of adsorption sites in the defects of the crystalline lattice to the number of adsorption sites on the surface has been determined from kinetic measurements as ND: NS(1 : 2. The value of y DGDyDGS.rRT varies between 1 and 4 depending on the concentration. The variations are caused by the inhomogeneity of the adsorption sites in defects. q1998 Elsevier Science B.V. All rights reserved.