PART V - The Surface Tension of Zinc

The surface tension of zinc has been determined by the sessile-drop method in a progvam emphaszzing detailed experimental care. The surface tension oj. the pure metal was measured over a range of ternperature from the melting point (419.6"C) to 540°C. At the melting point, the suvface tension of zinc was found to be: 1) 99.99+ pct Zn - 757.0 5 dynes per cm 2) 99.999+ pct Zn - 761.0 5 dynes per CI 3) 99.9999 pct Zn - 76'7.5 5 dynes pev cna From experiments carried out in a closed, isothermal cell, the temperatuve coejyicient of the surface tension (6y/6T)p, , of zinc xas found not to be negative but to be postiue. A positive tenzperatre coefficient indicates a greater depee of order in the surface than in the body of the lquid. Houlezer, by delibevately inducing continuous zaporization, a temperature coefficient of su)face tension with a negative slope can be produced. The work reported herein was undertaken as part of a larger program of fundamental research on the properties of molten zinc and zinc alloys. This program grew out of a continuing interest at the Mines Branch in the behavior of liquid metals in the foundry and of a desire on the part of the zinc industry for reliable basic data. The work was originally begun in cooperation with the Consolidated Mining and Smelting Co. Ltd., Trail, B.C., and was subsequently continued from 1960 to date in association with the Canadian Zinc and Lead Research Committee and the International Lead and Zinc Research Organization. Although the surface tension of liquid zinc has of course, been measured before, as Table I and Fig. 1 demonstrate, there is not good agreement among the existing values. Such disparities arise because sources of experimental error are insufficiently controlled. This situation places the reader in doubt. One result may be correct within narrow limits—even fortuitously—yet, because there is not agreement between several values, none can be accepted with conviction and all become suspect. It seemed, therefore, in the circumstances, that there was room for further work embodying considerable emphasis on experimental care in order that, within a small margin of error, an accurate value might be obtained. It was in this spirit that the work was undertaken. METHOD The sessile-drop method -as adopted for this work. In this method, when applied to liquid metals at elevated temperatures, the outline of the meridional section through a drop resting freely on a horizontal surface is recorded photographically. Certain parameters