AUGER-ELECTRON SPECTROSCOPY STUDY OF TIN DIFFUSION AND SURFACE SEGREGATION IN ALUMINUM, IN THE LIMIT OF VERY SMALL CONCENTRATION

Equilibrium surface segregation concentrations have been measured for tin diluted in aluminium with bulk concentrations of about 2 × 10-8 atom per aluminium atom, between 623 and 893 K. MacLean's model fits the experimental results well and gives a segregation energy qseg = -77 kJ mole-1 between 293 K and 623 K, the diffusion coefficient of tin is very small and no further segregation is detectable. The maximum surface enrichment is evaluated to 6.3 × 105. The adsorption energy of tin on aluminium has been estimated to qads = -346 kJ mole-1 with the help of the measured segregation energy and of known values for the tin sublimation energy and for the dissolution energy of tin in aluminium in the limit of small concentrations. Kinetic experiments have been performed between 623 K and 823 K. They are well accounted for by MacLean's analysis for grain boundary segregation, modified for the case of surface segregation. From these experiments, we have obtained a measure of the activation energy for diffusion of tin in bulk aluminium. Q = (130 ± 14.5) kJ mole-1 and an order of magnitude for the corresponding frequency factor D0. The results agree with those obtained by Anand and Agarwala by a radio-tracer technique. © 1979.