Total hemispherical emissivity of tungsten

Abstract

The temperature variation of the total hemispherical emissivity ε_h of an electropolished surface of 3N8 pure tungsten has been investigated with a transient calorimetric technique in the temperature range 180-1000 K. The experimental data are believed to be the first ever obtained on tungsten below 273 K and also the first ever obtained on electropolished tungsten above 273 K. It is found that the data depart in a significant manner at all temperatures investigated from the theory that assumes a zero relaxation time T for conduction electrons. In the range 180-300 K, ε_h behaves as though T is finite and nearly independent of the frequency. At higher temperatures, ε_h behaves in a manner that indicates qualitatively that t is frequency dependent. Beginning at 600 K, the slope of the ε_h-vs-T graph increases steadily up to 1000 K. This increase is belived to be due to the onset of interband excitations.