The Temperature Coefficient of the Surface Tension of Liquid Metals

Abstract

The author's approach is based on the conception of ``structure'' of liquids. From rather simple assumptions about the symmetry of configuration of the nearest neighbors the entropy change connected with bringing up N-Avogadro's atoms from the bulk of the liquid into its free surface is estimated and the temperature coefficient of the surface tension is calculated therefrom. Two entropy terms are taken into consideration. The first term ΔSosc is due to the difference in the frequency of oscillation of the atom inside and on the surface, and is calculated from the respective number of neighbors. This term allows the calculation of the lower limit of the temperature coefficient of the surface tension (because the ``unsharpness'' of the free surface is not accounted for). The second term allows us to estimate—again from the number of the nearest neighbors in the bulk and on the surface—the maximal value ΔSconf, to account for the ``unsharpness'' of the surface. The experimental data lie well within the calculated limits and almost coincide with the values calculated from (ΔSosc+½ΔSconf)/A where A is the surface occupied by N-Avogadro's atoms. The influence of the thermal expansion is expressed by the change of A with temperature.