Total hemispherical emissivity of pre-oxidized and un-oxidized Zr-2.5Nb pressure-tube materials at 600 ^oC to 1000 ^oC under vacuum

The emissivity of pre-oxidized and un-oxidized pressure-tube specimens has been measured at high temperatures under vacuum. The emissivity values of un-oxidized tube specimens decreased only slightly from 0.34 at 600 ^oC to 0.30 at 800 ^oC and changed gradually to 0.25 at 1000 ^oC. In comparison, the emissivity of pre-oxidized pressure-tube specimens decreased drastically from 0.70 at 600 ^oC to 0.35 at 800 ^oC, and gradually decreased to 0.25 at 1000 ^oC. The oxide layer of the pre-oxidized tube specimens dissolved into the metal matrix when heated to 700 ^oC and higher. Using these results, 2 linear correlations were obtained for emissivity with the oxide thickness measured by scanning electron microscopy and secondary ion mass spectroscopy analysis. (author)