Surface morphology effects on ignition temperature of single micron-sized Iron particles

Abstract

Micron-sized iron particles are promising energy storage carriers for combustion-based power systems, underscoring the critical importance of understanding their combustion performance and reaction kinetics. In this study, sponge iron particles with diameters ranging from 20 to 65 μm, and specific surface areas 4 to 6 times greater than those of spherical iron particles of equivalent mass, were injected into uniform high temperature environments at varying temperatures. High-speed microscopic imaging was employed to capture ignition frequencies with particle size resolution. Experimental results indicate that a small fraction of sponge iron particles can ignite at an ambient temperature of 880 K. When the ambient temperature increases to 1000 K, over 90% of the particles undergo ignition. Within the temperature range of 900–1000 K, the ignition frequency of iron particles increases with particle diameter and is independent of oxygen concentration. A numerical model based on the parabolic law on the growth of the oxide layer shows good agreement with the experimental results. Theoretical analysis reveals that increasing the specific surface area of iron particles can effectively lower their ignition temperature. Notably, iron particles produced through the hydrogen direct reduction of combusted iron oxide particles in iron fuel cycle, which possess significantly higher specific surface areas, are predicted to achieve ignition temperatures as low as 630 K, making them highly advantageous for combustion applications in power systems.