The surface tension is a measure of the cohesive energy of atoms and correlates with the latent heat of evaporation. The surface tension of normal liquids should decrease linearly with temperature and becomes zero at critical temperature, where the dif­ference between liquid and gas phases disappears. In accordance with Eotvcis’ law (cited in Iida and Guthrie27), it can be presented as follows:

s(T) = kaV-2=3(Tc — T) [10]

where Va is the molar volume and ks is a constant, which is about the same for normal LM.

Considering liquid Na, Pb, and Pb-Bi(e) as nor­mal liquids, a linear correlation can be recommended for the description of the temperature dependence of their surface tension:

s(T; p0) = sM,0 — Aff,0 (T — TM,0) [11]

The experimental data on the surface tension of sodium were reviewed by Golden and Tokar,3 Allen,65 Fink, and Leibowitz.22 In 1993, Keene66 reviewed many data on the surface tension of pure metals (including Na and Pb) at normal atmospheric pressure and concluded that the linear temperature dependence is valid for most LM in the tempera­ture range from normal melting to normal boiling
point. The available recommendations on the surface tension of Pb and Pb-Bi(e) were summarized by Sobolev and Benamati.24 The surface tension of liq­uid Na, Pb, and Pb-Bi(e) is well measured at normal atmospheric pressure from temperatures close to their melting points up to 1100-1300 K. In this tem­perature range, a variation of ±(3-6)% exists between values given by different sources. At higher temperatures, the scatter of the experimental results increases significantly. The coefficients of correlation [11] for these LM, recommended in the report34 and adopted in this work, are given in Table 9, and the calculated surface tension of liquid Na, Pb, and Pb-Bi(e) at normal atmospheric pressure is pre­sented in Figure 8 as a function of temperature.