Thermal Conductivities of Some Metals in the Solid and Liquid States

Abstract

Thermal conductivities of some metals and eutectic alloys above and below their melting points, 50° to about 400° C.—A guard ring method of measurement was used. A cylindrical rod of the metal, 1.5 cm in diameter and 12 cm long was surrounded by a slate tube and outside that a hollow brass cylinder. Both rod and cylinder were independently heated electrically at the top and cooled by flowing water at the bottom so as to maintain the same temperature gradient in both, as shown by thermocouples. The input of energy into the rod was corrected slightly for heat leakage and divided by the temperature gradient times the area to get the conductivity. The conductivities of tin and cadmium decrease at the melting point by over 1/3 and ½ respectively. For thallium, there is a drop of 1/10 at about 120° C. The temperature coefficients are about the same before and after melting, being -5×${10}^{-5\mathrm{}}$ (Sn), +21×${10}^{-5\mathrm{}}$ (Cd), +8×${10}^{-5\mathrm{}}$ (Th). For the eutectics: $\mathrm{Sn} .92$, $\mathrm{Zn} .08$; $\mathrm{Sn} .62$, $\mathrm{Pb} .38$; $\mathrm{Pb} .87$, $\mathrm{Sb} .13$; $\mathrm{Pb}.\mathrm{} 46$, $\mathrm{Bi} .54$; the temperature coefficients for the liquids are all positive constants and have values at 300° C— from.0011 (Pb—Bi) to.0030 (Pb—Sb)—close to those found for gases at that temperature, indicating that the mechanism is similar in the two cases. Below the melting point the curves vary, one increasing with temperature (Sn—Zn), two decreasing, and one reaching a maximum (Pb—Sb). The sudden decrease on melting varies from 2/3 for (Sn—Zn) and (Pb—Sn) to 1/10 for (Bi—Pb).