Abstract
AbstractEfforts have been made to develop long term sustainable materials for use above 900°C in the SO3/SO2 environments utilized in Nuclear Hydrogen Production Systems. In this study, the surface of Hastelloy X was serially modified by evaporative SiC coating, ion beam mixing (IBM), additional coatings, and final ion beam hammering (IBH). Subsequent heating above 900°C results in no peeling-off of the SiC coating layer in spite of the huge difference in their coefficients of thermal expansion (CTE). It was also found that ion beam hammering (irradiation) suppresses the vacuum sublimation of the low density (∼40% of bulk) ceramic film (bulk materials begin to sublime at ∼ 750°C in a vacuum of 1.5×10−5 torr). The sublimation rate is ≤ 30% of the bulk rate after an annealing at 950 for 2 hrs but is decreased to ≤10% of the bulk rate after irradiation with 70 keV ions to a total dose of 1×1017 N ions/cm2. Further irradiation (up to 4×1017 N ions/cm2) does not further decrease the rate. Both an immersion test in 98% sulfuric acid and the potentiodynamic polarization test suggest that the surface modified Hastelloy X has a greatly prolonged life time in the corrosive sulfuric acid atmosphere, suggesting the serial surface modification process is applicable to the thermo-chemical system for the nuclear hydrogen production.
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