Influence of Chemical Additions and Specific Surface Area on Micro-explosion of Burning Iron Particles

Micro-explosions (ME) during combustion of iron strongly affect combustion time, morphology, and oxidation of the final products. These explosions are caused by a sudden release of gas, but its origin (if at all unique) remains unclear. This gas could come from impurity within the particles (e.g., carbon), hydrogen adsorbed on the surface, or a combination thereof. This study investigates how the carbon and hydrogen content, originating from passive hydroxide layer and thus varying with the powders specific surface area, influences the occurrence and intensity of ME in four iron-based powders: pure Fe, Fe-7Si, DRI (Direct Reduced Iron), and Fe-5.2Al 2 O 3 . The particles were ignited in an electrodynamic levitator and observed through high-speed imaging and luminosity measurements. This enabled statistical identification of ME through luminosity evolutions and quantitative assessment of the particle inflation level across powders. The results show that DRI and Fe-5.2Al 2 O 3 particles exhibit the highest ME probability (>90%), correlating with their larger specific surface areas (1.26 and 0.61 m 2 /g) compared to the other powders (