Total Hemispherical Emissivity of Potential Structural Materials for Very High Temperature Reactor Systems: Alloy 617

Total hemispherical emissivity of Alloy 617 was measured for applications in very high temperature reactors with apparatus based on ASTM Standard C835-06. The emissivity data were obtained for the following surface conditions: (1) as-received (rolled sheets) from manufacture, (2) sandblasted with aluminum oxide beads, (3) oxidation in air at temperature of 1153 K, and (4) coated with graphite powder. For the as-received Alloy 617, emissivity increased from 0.26 to 0.34 over the temperatures 593 K to 1164 K. Sandblasting Alloy 617 with alumina beads increased the emissivity to 0.46 to 0.73 in the temperature range 600 to 1300 K (emissivity increased further when higher grit size beads were used). The oxidation of Alloy 617 gave a slight increase in emissivity from 900 to 1250 K with larger increases above 1100 K. Coating of graphite onto as-received and 60-grit sandblasted increased the emissivity by roughly 0.12 and 0.20, respectively, over the measured temperature range.