INVESTIGATION OF THE DIFFUSION PROPERTIES OF IMPURITIES IN POLYCRYSTALLINE ALPHA-IRON BY MEANS OF AES

The time development of the surface concentrations of impurities such as sulphur, oxygen and nitrogen in high-purity polycrystalline cu-iron samples has been investigated by means of Auger electron spectroscopy (AES) and scanning Auger microscopy (SAM) during linearly increasing the temperature from about 200 to 830 degrees C. The subsequent segreg ation of N and S revealed strong differences in the segregation kineti cs of these elements - especially with respect to the contribution of the dominating transport mechanism (grain-boundary diffusion and bulk diffusion). Assuming an Arrhenius behaviour, the segregation kinetics was used to determine both the pre-exponential factor and the activati on energy of the effective diffusion coefficient of the segregating su lphur. The results are compared with values obtained by other methods and with model calculations performed on the basis of a layer-by-layer segregation model.