This study investigates prospective materials for carbon-free electrodes in the fused-salt electrolysis of primary aluminium. Specifically, novel metal-ceramic composites, based on AISI 316L steel (60%) and recycled MgO (40%) from former refractory lining components, are examined with a focus on their thermo-mechanical properties. For the fabrication of this material, the powder metallurgical technique of Spark Plasma Sintering (SPS) is of particular interest due to its potential to yield a dense microstructure with low porosity. A pre-oxidation of the steel-MgO composite material was proven to induce a protective layer capable of withstanding contact with molten aluminium melt while also exhibiting electrical conductivity [1,2].

The mechanical properties at high temperatures (800-1100°C) are investigated for steel-ceramic composites containing either fresh or recycled MgO reinforcements to determine whether the recycled nature of the particles has an influence on the thermo-mechanical performance. Quasi-static compression tests have already indicated that composites with recycled MgO particles exhibit a higher compressive strength than their counterparts containing fresh ceramic reinforcements. Insights into time-dependent properties of the different composite variants are obtained through stress-relaxation tests and creep investigations. In order to assess temperature-dependent failure mechanisms, such as a decreased tendency for ceramic particle cracking during compression at higher temperatures, microstructural investigations using a scanning electron microscope are conducted. The discussion also includes the impact of impurities, which arise from the interaction of the refractory linings with melts or slags, on the thermo-mechanical behaviour of the composite material.

In summary, this study examines how replacing fresh MgO reinforcements with a recycled alternative impacts the thermo-mechanical properties of a potential carbon-free electrode material based on a novel steel-ceramic composite.

References
[1] S. Yaroshevskyi, С. Weigelt, P. Malczyk, V. Roungos, J. Hubalkova, T. Zienert, B. Kraft, S. Wagner, C.G. Aneziris, Open Ceramics, 2023, 16, 100458.
[2] P. Malczyk, T. Zienert, F. Kerber, C. Weigelt, S.-O. Sauke, H. Semrau, C. Aneziris, Materials, 2020, 13, 4737.