Eco-friendly design of complex refractory aggregates as alternatives to the magnesia-chromite ones

Besides the good performance of electrofused magnesia-chromite aggregate (EMCA) in ceramic refractories, the generation of toxic Cr⁺⁶ after working conditions is driving its urgent replacement. Aiming at optimizing the search towards eco-friendly options, this work applied multiple electron-microscope-based techniques to assess its key microstructural features. BSE/EDS imaging coupled with thermodynamic calculations (CALPHAD) indicated that these aggregates were comprised of a periclase matrix where spinel precipitates (d₅₀ ≈ 15μm) were embedded, inducing microcracking due to the thermal expansion mismatch. EBSD technique highlighted its pattern, revealing a good fit with {110} planes, which agrees with the Zener-Stroh crack mechanism. Designing concepts of compositionally complex ceramics were applied to find eco-friendly EMCA alternatives. From the 154 simulated systems, the four most promising ones were experimentally produced and characterized. Although kinetics aspects must be addressed, Cr-free EMCA-inspired microstructures were obtained, highlighting that this design approach can be used to support the development of novel raw materials.