A Technique for Measuring Equilibrium Thermodynamic States of Liquid Metals at High Temperatures and Pressures

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Abstract
This paper presents a method for overcoming temperature and pressure limitations inherent in conventional techniques for measuring equilibrium thermodynamic data. The method can be applied to conducting materials that can be resistively heated and that do not dissociate in the liquid phase; and it is thus particularly suitable for investigating pure liquid‐metal thermodynamic data. The technique has been applied extensively to lead at temperatures exceeding 5000 K and at pressures up to 2 kilobars. A cylindrical material specimen 1 mm in diameter and 25 mm long is interposed between two current leads and mounted axially concentric with a high‐pressure cell. After the cell is pressurized with helium, a current pulse from the overdamped discharge of a high‐voltage capacitor bank heats the wire at such a rate that its expansion is nearly isobaric. The energy deposited in a central segment of the sample is computed by integrating the product of the current flowing in the segment with the resistive voltage developed across it. With these data, sample resistance can also be calculated during a major portion of the time that current flows. Because mounting constraints limit sample expansion to the radial dimension, the equilibrium volume is calculated from the expanded diameter, which is measured by means of pulsed x‐radiography.