Liquid alloys surface tension measurements

J. Schade, A. McLean, W.A. Miller, in Surface Tension Measurements on Oscillating Droplets of Undercooled Liquid Metals and alloys, ed. by E.W. Collins, C.C. Koch. Proceedings of 115th Annual Meeting of lUS-AIME, New Orleans, 1986, p. 233... 

Surface tension and density of liquid alloys have been studied by Moser et al. (2006). Measurements by maximum bubble pressure and dilatometric techniques were carried out in an extensive range of temperatures on liquid alloys close to the ternary eutectic Sn3 3Ag0 76Cu with different Sb additions, which decrease surface tension and density. The experimental data were discussed in comparison also with values calculated on the basis of different models. 

It has been shown that for a liquid alloy of silver and gold near its melting point, the regular solution model gives surface tensions that correspond well with measured values (48). To calculate the surface concentration and profile of a solid alloy, this model has been applied to the Fe-Cu system (49), account being taken of enrichment in several outer layers. 

For liquid metals (mercury, gallium) or their alloys, one can measure another interfacial quantity, interfacial tension equal to the specific energy of the interface formation, y, at different values of the electrode potential, E[, 17]. At equilibrium the Lippmann equation relates it to the electrode-charge density a, that is, to the charge Q in Eq. (2) per unit surface area ... 

For the application of this equation one has to measure surface energy (surface tension) and its dependence on electrode potential at constant activities of the different components. Precise measurements are restricted to liquid metals like mercury or gallium and their alloys. Classical experiments were made with the Lippmann electrocapillary meter. The measurement of the drop time or the drop frequency of a dropping mercury electrode is easier. 

Unfortunately, the aforementioned equations and others (see Refs. 47 and 48) cannot be universally applied and experimental measurement of surface tension is required. For instance, the surface tension of liquid alloys can have local maxima and minima with changes in composition and temperature as seen in the Au-Sn system shown in Fig. 14. 

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