Spectral emissivity of Ta in the red and in green and change in emissivity resulting from change in surface structure induced by heat treatment

The spectral emissivity ελ of tantalum for λ=0.645 μ and λ=0.546 μ has been measured by using a De Vos blackbody in ultrahigh vacuum. Changes of the emissivity with heat treatment are related to changes in surface structure, and the reproducibility of results is demonstrated by making measurements on two different blackbodies of identical construction that have been subjected to similar heat treatment. The data presented are compared to previously published results. It is found that ε0.645μ between 1100° and 1700°K for tantalum that is not heated above 1700°K ranges from 0.420 to 0.411; that ε0.645μ between 1100° and 2400°K for tantalum that is heat treated one hour at 2450°K ranges between 0.394 and 0.370; and that ε0.546μ in the latter temperature interval, also for heat-treated tantalum, ranges from 0.456 to 0.423.