Diffusion barrier coatings for liquid metal reactors-Part I: liquid metal corrosion

The objective of the series of study is to develop ceramic diffusion-barrier coatings and to characterize the chemical and physical interactions between the coated cladding and coolant metals (liquid lead and sodium) and metallic fuels. In liquid metal cooled fast reactor systems (LMRs), degradation of cladding and structural alloys from liquid-metal exposure poses significant challenges to reactor safety and long-term operation. To mitigate these effects, two zirconia-based coatings were developed: ZrO₂ with Sn metal and ZrO₂ with Sb metal. This Part I focused on corrosion studies of the coatings in both liquid Pb and Na. Corrosion experiments in liquid metals were conducted at 500 °C (SFR) and 600 °C (LFR). Post-exposure characterization shows that both coatings maintain chemical stability and diffusion-barrier performance in liquid lead. In contrast, neither coating remains intact in liquid sodium due to sodium’s strong reactivity with oxygen. Microstructural and phase analyses further revealed the formation of new Pb–Sn intermetallic phases in the Sn-containing coatings, indicating undesirable interactions with lead. In comparison, Sb does not exhibit similar reactivity and promotes the formation of a denser, more compact coating microstructure. These results identify Sb-modified ZrO₂ as the more promising candidate for mitigating liquid-metal infiltration and enhancing coating durability in fast-reactor environments.