Oxidative passivation of Fe–Cr–Al steels in lead-bismuth eutectic under oxygen-controlled static conditions at 700° and 800 °C

Abstract

Lead-bismuth eutectic (LBE) is a candidate heat transfer fluid for fast nuclear reactors and for concentrating solar power energy systems, due to its low melting point and beneficial thermophysical properties. Increasing the maximum operating temperature beyond 600 °C, can increase thermal efficiency of power conversion. However, LBE causes liquid-metal corrosion in many solids used as structural materials at high temperatures, due to increasing solubility of their constituents. A way to mitigate this issue is to establish a controlled oxidative passivation, by maintaining a desirable oxygen concentration in liquid LBE to promote formation of protective oxide scales on structural materials. In this study, the corrosion behavior of three Fe–Cr–Al alloys in LBE at 700 and 800 °C has been tested in two different oxygen concentrations. It was found that oxygen concentration of 1 × 10−6 wt% in LBE at both temperatures promotes formation of protective scales in all tested candidates. At 700 °C, these scales are more compact and well-adhered to bulk in all candidates. At 800 °C, lower-Al-containing candidates develop a thinner but adherent scale containing various oxides, while scales in higher-Al-containing candidates contain mostly Al-oxide and suffer more breaking and spalling off. However, oxygen concentration of 2 × 10−7 wt% proves to be insufficient for protective scales formation in all three Fe–Cr–Al alloys.