Experimental investigation on synergistic slow oxidation and rapid combustion of micron-sized iron and aluminum powders for energy storage application

The investigation into the individual application of iron and aluminum as carbon-free fuel sources has been extensively explored and holds significant promise. However, there remains a gap in understanding synergistic effects achievable through the blending of these two fuels, as well as a need for comparative analyses between the slow oxidation and rapid combustion processes of these fuels to complement each other. This research proposes blending micron aluminum and iron powders to analyze their slow oxidation and rapid combustion features under diverse atmospheric conditions and heating rates, using thermogravimetric methods, kinetic calculations, and in-flow experiments. The research blending micron iron and aluminum powders to analyze their slow oxidation and rapid combustion features under diverse atmospheric conditions and heating rates, using thermogravimetric methods, kinetic calculations, and in-flow experiments. The findings reveal that the combination of aluminum and iron powders promotes oxidation, resulting in increased weight gain and heat flux rate compared to individual metals. Moreover, the triggering temperature rises from 545 to 652 °C with an increase in aluminum powder content. As heating rates increase, characteristic parameters T1, T2, and Hpeak2, rise for both fuels. However, aluminum powder tends to decrease Ti, while iron powder slightly increases it due to differences in oxide layers. The slow oxidation of aluminum and iron powders conforms to different models, yielding distinct oxidation patterns. The apparent activation energy of aluminum decreases from 258.4 to 238.7 kJ·mol−1 with rising heating rates, while that of iron exhibits a lower increase and remains lower than aluminum providing insights into combustion initiation conditions. Combustion initiation is contingent upon the concentration of metal powder and oxygen, with both aluminum and iron powders combustion being enhanced and subsequently attenuated with increasing excess air ratio. However, due to differing reactivity and surface passivation layers, the excess air ratio required for aluminum powder combustion (1.2–2.4) exceeds that of iron powder (1.3–1.7). The research elucidates the mechanisms underlying the slow oxidation of iron and aluminum fuels, delineates suitable combustion conditions, and furnishes new empirical and theoretical underpinnings for the oxidation characteristics of mixed iron-aluminum fuels, thereby advancing metal-fueled energy storage technologies.