Relationships Between the Impedance of Oxide Scales on Martensitic and Austenitic Steels and Corrosion Rate in Liquid Lead-Bismuth Eutectic Available to Purchase

The impedance properties (resistance and capacitance) of oxide scales on the martensitic/ferritic steel HT-9 and austenitic stainless steel Type 316L (UNS S31603) were examined during immersion in lead-bismuth eutectic (LBE) using a technique similar to electrochemical impedance spectroscopy. These scales were created by preoxidizing the samples in an air/ water vapor environment at 800°C for various times prior to immersion in LBE. Calculation of oxide conductivity for samples immersed in LBE at 200°C for 200 h yielded σ_HT9 ≈ 4 × 10^–7 (Ω × cm)^–1 while σ₃₁₆ ≈ 3 × 10^–8 (Ω × cm)^–1. The influence of temperature alone gave the anticipated Arrhenius behavior with E_a equal to 0.12 eV, which is consistent with an electron hopping in ferrites close to the magnetite composition (such as Fe_x+1Cr_2–xO₄). The influence of temperature during immersion in LBE deviated from Arrhenius behavior (irreversible). Oxide conductivity data for HT-9 were also used to calculate the corrosion rate using Wagner’s oxidation theory. Values of corrosion rate for HT-9 in LBE at 200°C (oxygen saturated) decreased with increasing preoxidation time from 0.97 μm/h (preoxidation time = 36 h) to 0.55 μm/h (preoxidation time = 63 h).