The electrical impedance responses of protective oxide scales on stainless steels that are immersed in molten lead-bismuth-eutectic alloy at temperatures up to 600??C

摘要

This research explored the electrical impedance responses of oxide scales on stainless steel, when the steel was immersed in molten lead-bismuth-eutectic alloy (LBE) at high temperatures (up to 600??C). LBE is a candidate coolant for future fast-neutron-spectrum nuclear reactors and for accelerator-driven nuclear systems, in which the LBE can also act as the spallation target. Stainless steels, out of which such systems are usually fabricated, oxidize in the molten LBE. This research used small-amplitude AC signals to measure the electrical impedances of these oxide layers, as a function of time, temperature, oxygen content of the LBE, and applied DC bias. DC voltages that were apparently generated by the oxide layers themselves were also observed. The resistances were one or more orders of magnitude greater than the published resistances of pressed, sintered pellets of similar oxide material, but they showed a similar Arrhenius dependence on temperature. The resistances declined significantly with reducing levels of oxygen and with applied DC bias, also exhibiting rectifying properties. The capacitance was much less variable. The cumulative result of the research has laid a foundation for the technique of making impedance measurements in LBE and other liquid metals; the technique could be used in the future for further scientific investigations of oxidation in LBE and for engineering applications of in situ monitoring of the oxidation.