Relationships Between the Impedance of Oxide Scales on Martensitic and Austenitic Steels and Corrosion Rate in Liquid Lead-bismuth Eutectic

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 σHT9 ≈ 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 Ea equal to 0.12 eV, which is consistent with an electron hopping in ferrites close to the magnetite composition (such as Fex+1Cr2−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\u27s 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)