The Surface Tension of Liquid Metals

Abstract

The author is opposed to the generally established opinion that the surface tension of liquid metals is abnormally high (as compared with that of non-metallic liquids) and that the metallic character (the presence of free electrons) is the main cause of the ``high'' surface tension of metals. He shows that this opinion is due to the fact that specific surface tensions (ergs per cm2) are compared and that the influence of temperature is not accounted for. Total surface energies σM—T(dσM/dT)—where σM=σspec×A is the surface tension referred to the surface A occupied (in monomolecular layer) by N-Avogadro's molecules—are of the same order of magnitude. The author expresses the opinion that the main cause of the surface tension of all liquids, whether metallic or not, is the same, viz., the total surface energy is determined by the amount of energy required to bring the molecules or atoms (and electrons) from the bulk of the liquid to its free surface while enlarging the surface area. He shows that in organic liquids showing no dipoles this energy can be calculated directly from the heat of vaporization at absolute zero and from the configuration of nearest neighbors. In the case of metals, the change of kinetic energy of electrons must be considered in addition. The author shows that the latter must contribute a negative term to the total surface energy. In fact, liquid metals show lower surface energies than might be expected from their heats of vaporization and from the configuration of their nearest neighbors (Fig. 1). A short review of the recent electron theories of the surface tension of liquid metals is given.