The electrification of high-temperature processes, such as steel casting, can remarkably increase energy efficiency and reduce costs. A material of choice for refractory lining parts like slide plates and stoppers in continuous casting are Al₂O₃-based ceramics, allowing for operation at 1500 °C and above. However, as the large temperature differences between the initially cold part and the liquid result in significant thermal stresses, the parts frequently fail due to thermal shock. Internal resistive preheating would efficiently reduce the thermal gradients but requires sufficient electrical conductivity of the parts. Electrically conductive bulk refractory composites based on Al₂O₃ and refractory metals, like Nb and Ta [1], offer an intriguing combination of thermal shock resistance, fracture toughness and erosion resistance. 

A major concern of the composites is the oxidation resistance of the metal component. Previous scanning electron microscopy investigations of reactions between Al₂O₃ and the metals in sintered composites revealed where different refractory metal oxides evolved [2]. For a more thorough, nanoscale study of interfacial reactions in sintered and magnetron-sputtered model materials, atom probe tomography (APT) and transmission electron microscopy (TEM) results are presented. As model materials, we prepared pure Nb layers on single crystalline sapphire, for which diffusion of O along Nb grain boundaries during a heat treatment led to a reaction at the ceramic-metal interface [3]. Additionally, Nb-Al alloy layers were prepared by co-deposition (Figure 1a and b) and were subsequently heat-treated (Figure 1c) to study oxide formation in the Al-Nb-O system.