Oxidation mechanism of refractory Molybdenum exposed to oxygen-saturated lead-bismuth eutectic at 600 °C

•Mo reacts with dissolved oxygen and Pb in liquid LBE to produce a multilayer film.•The dissolved oxygen firstly oxidizes the surface of Mo into a nano-structured MoO2.•An ultra-fined PbMoO4 forms on MoO2, and its outer side can grow into columnar grains.•The columnar PbMoO4 can be further oxidized into blocky Pb2MoO5 layer. The oxidation mechanism of refractory Molybdenum exposed to oxygen-saturated lead-bismuth eutectic (LBE) at 600 °C was investigated. The results show a hierarchical structure of multiple corrosion layers. Specifically, a nanostructured tetragonal MoO2 is the first scale that forms on the Mo substrate, followed by development of an ultrafine-grained tetragonal lead molybdate (PbMoO4) layer. On the top of this ultrafine-grained layer, there is a thicker scale that consists of micron-sized columnar PbMoO4 and its upper part can be further oxidized into blocky monoclinic-structured Pb2MoO5. The formation of these multilayered scales is likely predominated by inward diffusion of oxygen and Pb.