Kinetics of surface segregation

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Abstract
The kinetics of surface segregation, are analysed and illustrated by Auger electron spectroscopy observations of tin segregation to the free surface of iron. The analysis extends the diffusion approach of McLean (1957) by incorporating the effects of surface evaporation and by relaxing the constraint of a linear relation between the solute concentration at the surface and that in the adjacent bulk layer. Parameters are evaluated for the iron-tin system and the importance of the predictions is demonstrated by Auger electron measurement. It is found that marked deviations from McLean's analysis can occur at surfaces and that incorporation of the modifications presented here can lead to improvements in the accuracy of both the measurement of surface segregation levels and the deduction of solute diffusivity data, from the kinetic observations, by factors as high as 2 and 30, respectively. The method is applicable to solute diffusivities in the temperature range down to 450°C in iron.