Spectral Emissivity, Total Emissivity, and Thermal Conductivity of Molybdenum, Tantalum, and Tungsten above 2300°K

Abstract

The emissivities and thermal conductivities of high purity arc melted molybdenum and tantalum and powder metallurgy tantalum and tungsten were measured between 2300°K and their respective melting points. A method is presented for the determination of spectral and total emissivities from the determination of brightness temperature at the center of an electrically heated rod as a function of heat flow rate. The method does not depend on the experimental achievement of blackbody conditions. Spectral emissivities were also determined by measurement of brightness temperatures at the respective melting points. Thermal conductivities of electrically heated rods were determined by the Jain and Krishnan longitudinal heat flow method. The spectral emissivities of tantalum and tungsten decrease linearly with increase in temperature. The spectral emissivity of molybdenum is constant. The total emissivities of molybdenum, tantalum, and tungsten increase with increasing temperature. For any of the metals the spectral and total emissivities are closest to each other at the melting point. The melting point of tantalum is significantly lowered by small increase in impurity content. The thermal conductivities of molybdenum, tantalum, and tungsten decrease linearly with increasing temperature. The ranges of spectral emissivity, total emissivity, and thermal conductivity above 2300°K are as follows: ελεTK (cal. cm−1sec.−1∘K−1)Molybdenum0.300.271–0.2850.34–0.32Tantalum0.361–0.3500.288–0.3240.15–0.11Tungsten0.37 –0.360.268–0.3520.38–0.30