Influence of roughness and composition on the total emissivity of tungsten, rhenium and tungsten–25% rhenium alloy at high temperature

Abstract : Measurements of the total directional and hemispherical emissivity of tungsten, rhenium and tungsten with 25% rhenium samples of various surface states was carried out in two wavelength ranges, 0.6–2.8 and 0.6–40 μm, from 1300 up to 2500 K in high vacuum. A clear trend was identified for the ratio of the 0.6–2.8 μm to the 0.6–40 μm hemispherical emissivity (assumed to be close to the true α/ε ratio, which is the ratio of the solar absorptivity α to the total emissivity ε) as a function of the RMS roughness. This ratio is decreasing with increasing RMS roughness rapidly up to around 1 μm and then tends to stabilize for higher roughness. It suggests that increasing the roughness, starting from a flat surface, will progressively give more weight to the long wavelength range emissivities in comparison to the short wavelength ones. Beside the RMS roughness, a sharp surface structure on a finer scale found on some samples also led to an additional decrease of the α/ε ratio, but these structures are not stable at high temperature and disappear due to a natural high temperature smoothing. Finally our results also show that the α/ε ratio of rhenium is lower than the one of tungsten.
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Submitted on : Friday, July 17, 2015 - 2:36:17 PM
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E. Brodu, M. Balat-Pichelin, J.-L. Sans, J.C. Kasper. Influence of roughness and composition on the total emissivity of tungsten, rhenium and tungsten–25% rhenium alloy at high temperature. Journal of Alloys and Compounds, Elsevier, 2014, 585, pp.510-517. ⟨10.1016/j.jallcom.2013.09.184⟩. ⟨hal-01178141⟩

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