抄録
The kinetic theory and the theory of lattice defects have laid a solid fundation for treating the diffusion mechanism in gaseous and solid phases, whereas diffusion phenomena in the liquid state, especially in high temperature melts, remain unaccounted for in many respects. This lack of understanding is due to the limited knowledge of liquid structure, experimental difficulties and the paucity of reliable data. The accurate measurement of diffusivities in liquid systems at high temperature is therefore very significant from the theoretical and practical points of view. In order to clarify the relative importance of various factors for the solute diffusion in liquids, diffusion coefficients in dilute Ag–S, Ag–Se and Ag–Te liquid silver-base alloys have been measured by a modified capillary reservoir method in the temperature range from 1000° to 1300°C. Since sulfur, selenium and tellurium are the elements of Group VIa having similar physico-chemical properties but different particle sizes, it is expected that the results of diffusion experiments will provide valuable information on the mechanism of solute diffusion and the relative importance of various factors, particularly the size effect of solute for diffusion.
The results obtained are summarized as follows:
(1) The diffusion data fit to the following Arrhenius type equations within the limits of experimental errors in the temperature range from 1000° to 1300°C.
For the Ag–S system Dc=6.0×10−3exp(−11500⁄RT)cm2⁄sec
Q=11.5±1.0kcal/g-atom
For the Ag–Se system Dc=1.9×10−3exp(−10300⁄RT)cm2⁄sec
Q=10.3±1.2kcal/g-atom
For the Ag–Te system Dc=9.9×10−4exp(−9200⁄RT)cm2⁄sec
Q=9.2±1.8kcal/g-atom
(2)Thediffusivityincreases(D_S>D_Se>D_Te)astheradiusofthediffusingparticledecreases(r_S<r_Se<r_Te).Itappearsthatthesizeofthediffusingparticleisanimportantfactorforthesolutediffusioninliquids.
(3)Apparentactivationenergyforthesolutediffusionmaybeexpressedintermsoftheactivationenergyforsolventdiffusionandthecoulombicinteractionbetweensoluteandsolventions.Thevaluescalculatedareinexcellentagreementwiththeexperimentalvalues.
(4)ThevaluesofD_i/D_sarebestrepresentedbyamodifiedcriticalfluctuationmodelifthevaluesofβaretakenasafunctionofsolute.
