Thermal Conductivity of Nickel and Uranium

The thermal conductivity of a metal can be measured at any temperature by a method in which the conductivity of the metal under investigation is compared with the known conductivity of some metal chosen as a standard (1). The rate of heat flow, Q, in a cylindrical specimen of unknown conductivity, is given by the equation Q = - K1AG1, where Ki is the unknown thermal conductivity, A is the cross-sectional area, and G1 = (ΔT/Ax)1 is the temperature gradient. If a cylindrical bar of equal cross-sectional area and known thermal conductivity, K2, is placed in series with the specimen so that the rate of heat flow is the same in both bars, we have Q = -K2AG2, where G2 = (ΔT/ΔX)2 is the temperature gradient in the standard sample. From these two expressions for Q, the unknown thermal conductivity, K1 = (G2/G1)K2, can be found if the temperature gradients in the two rods are measured. In principle, the comparison method is simple but, in practice, complications may arise at high temperatures in providing good thermal contacts, in preventing radial heat losses, and in making reliable temperature measurements. The method has not, therefore, been characterized by high precision at elevated temperatures. The purpose of this investigation was (a) to develop improvements in the apparatus for measuring thermal conductivities of metals at high temperatures by the comparison method, and (b) to determine the thermal conductivities of nickel and uranium in the temperature range 100° C. to 650° C. by the comparison method