In situ Monitoring of the Oxidation of Coated and Uncoated Austenitic Stainless Steels at Temperatures Lower than 600 °C: Part A—Coating Screening

Abstract

The lithium niobate used in an ultrasonic transducer for liquid metal fast nuclear reactors is prone to a reduction leading to a rapid short circuit of the sensor in operating conditions. Oxygen consumption on stainless steel sensor’s walls was suspected to be the cause of the reduction. Impedance spectroscopy monitoring around 600 °C under different O2 partial pressures shows that the reduction limit is above the equilibrium pressure of iron oxides. As the housing material (304L) cannot be easily changed, various coating solutions enhancing the passivation of the steels were investigated. Sol–gel lanthanum coatings show the best behavior when tested by TGA at 800 °C. However, in situ monitoring of the oxygen consumption by an oxygen sensor close to operating condition shows that it was not enough protective.