Mineralogical characterization of Al₂O₃ and MgO powders as possible energy carriers

Europe aims to achieve net-zero emissions by 2050, increasing the demand for efficient, carbon-free energy carriers. Metal powders are a promising alternative to fossil fuels, as energy can be stored by reducing metal oxides and released through metal-air combustion. Metal oxides can be re-reduced in a closed-loop cycle. Iron, Al, and Mg are ideal candidates due to their energy density, availability, and recyclability. Supply-chain and environmental factors, such as Fe abundance, Mg energy density and recycled Al circularity, affect suitability and criticality. This study aims to assess variations of experimental parameters, combustion mechanisms and process optimization for heat production. This will support research on low-carbon energy carriers that are high in energy density, competitive with fossil fuels, sufficiently abundant, and easily recyclable.

For this study, Al₂O₃ and MgO powders were produced in a turbulent burner and a fixed-bed reactor respectively, under different initial conditions, including an excess of Al, water injection to produce hydrogen, or a variation of particle size before the combustion. The effects of these parameters on morphology and chemistry of the samples during oxidation–reduction cycles were then evaluated. The two metals were chosen to compare the influence of the metal type on the overall process. PXRD, SEM-EDXS, and TEM-EDXS techniques were used to identify the phases present in the samples allowing a characterization of their morphology, size, and chemistry, thereby improving the understanding of these processes.