Surface tensions of some binary fused salt systems

The surface tensions of eight pure fused salts---NaNO3, KNO3, AgNO3, LiCl, NaCl, PbCl2, and ZnCl 2---and nine binary mixtures---NaNO3-KNO3, AgNO3-NaNO3, AgNO3-KNO3, NaCl-KCl, PbCl2-LiCl, PbCl2-NaCl, PbCl2-KCl, PbCl 2-RbCl, and PbCl2-CsCl---were measured by the maximum bubble pressure method. Surface tension showed essentially linear variation with temperature in all cases. As would be expected, large differences were found between the surface tensions of the pure fused salts. The higher surface tension of molten AgNO3 compared to NaKO3 was explained in terms of differences in the polarizability of the metal ions in the melts. The low surface tension of ZnCl2 was assumed to result from extensive association in this melt;The surface tension isotherms of the systems NaNO3-KNO 3 and NaCl-KCl were found to exhibit small negative deviations from ideality. The greater negative deviations from ideality which were found in the systems AgNO3-NaNO3 and AgNO3-KNO 3 were attributed to polarizability differences between the metal ions. The limited data suggested that in binary mixtures of fused salts with a common anion, the deviations of the surface tension isotherms from ideality increase as the differences between the sizes of the replacing cations increase;Actual minima were observed In the surface tension isotherms of the systems PbCl2-KCl, PbCl2-RbCl, and PbCl2-CsCl; no minima were observed in the systems PbCl2-LiCl and PbCl2-NaCl. These minima were attributed to the presence of complex ions or other surface active aggregates in these melts. Other physical measurements strongly support the existence of complex ions, very likely anionic complexes of lead, in the system PbCl2-KCl;The trend in the character of the PbCl2-alkali metal chloride surface tension isotherms was shown to be in accord with the fact that any anionic complexes in these melts would be more stable in the presence of large cations with low polarizing power than in the presence of small ions with large polarizing power;Further evidence for complexing in the PbCl2-alkali metal chloride melts was the presence of a yellow color in those melts whose surface tension isotherms exhibited minima; no yellow color was observed in the PbCl 2-LiCl and PbCl2-NaCl systems. This yellow color which persisted in the solid state at high temperatures was found to increase in intensity with increase to the size of the alkali metal ion;It was pointed out that there is no reason to assume that the complexing in those melts consists only of discrete ions. It was proposed that there are also local aggregations of ions whose structures resemble the structure of the solid state