Influence of Si on the combustion process of micron-sized iron particles

The use of impure powders in the metal-fuel cycle could reduce powder production costs, enable the valorization of underutilized feedstocks, and limit competition with the steel industry. However, the influence of impurities on the combustion process remains poorly understood. Silicon is one of the potential impurities present in low-cost iron sources, and the objective of this work is to investigate its impact on the combustion behavior of micron-sized iron particles. To this end, an Fe-7Si powder was studied using both single-particle and multi-particle combustion setups, enabling in situ visualization and ex situ microstructural analysis, respectively. In the multi-particle burner, the Fe-7Si powder featured limited conversion efficiency (0.1%-6.2%) in the reference preheating conditions. This efficiency increased at higher preheating temperature (26.3%-39% at 930°C). This suggests that Si significantly affects particle ignition, likely through the formation of a Si-rich oxide layer. Nevertheless, once ignited, particles undergo nearly complete oxidation in the liquid state, reaching magnetite as the main oxide phase. The resulting combustion products consist of dendritic structures. A eutectic phase is also detected in the interdendritic region, with a Si enrichment compared to the dendrites. Its presence arises during solidification after reaching the eutectic point associated with a complete oxidation in the liquid state. In the single-particle burner, particles exhibit a multi-peak luminosity profile characterized by an initial small peak, likely associated with the formation of a silicon-rich oxide layer that limits internal diffusion. This stage is followed by a second luminosity increase during which new oxide spots appear at the particle surface, suggesting the formation of iron oxide penetrating the previously formed oxide layer. Overall, Si increases the combustion time of iron particles and modifies the combustion regime toward an internal-diffusion-limited behavior. However, Fe-7Si particles are still able to burn successfully in the liquid state, provided that ignition is achieved.

Affiliations

UCLouvainSST/IMMC/TFL - Thermodynamics and fluid mechanics

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Bruyr, Z., Ahmad, L., Choisez, L., Gilles, M., Jeanmart, L., Halter, F., & Contino, F. (2026). Influence of Si on the combustion process of micron-sized iron particles. Fuel, 431, 141936. https://doi.org/10.1016/j.fuel.2026.141936 (Original work published 2027)