Characterization of chromia scales formed n supercritical carbon dioxide

Initial experimental work at 700 degrees-800 degrees C is in progress to develop a lifetime model for supercritical CO2(sCO(2)) compatibility for a 30-year lifetime of a >700 degrees C concentrated solar power system. Nickel-based alloys 282, 740H and 625 and Fe-based alloy 25 are being evaluated in 500-h cycles at 1 and 300 bar, and 10-h cycles in 1 bar industrial grade CO2. The alloys showed similar low rates of oxidation in 1 and 300 bar CO2 in 500-h cycles at 750 degrees C. However, in 10-h cycles, alloy 25 showed accelerated attack at 700 degrees and 750 degrees C. Transmission electron microscopy scale cross-sections on alloy 25 after 1000 h at 700 degrees C in sCO(2) and in air only showed a small row of carbides beneath the scale in the former environment. Similar characterisation was performed on alloys 625 and 282 after sCO(2) exposure at 750 degrees C.