Micron and nano iron particles: Experimental investigation of size dependent combustion in ethanol slurries and bimetallic thermite

• The study analyzes distinct combustion behaviors of micron- and nano-sized iron particles technology in ethanol and thermite. • Micron Fe in ethanol forms porous shells, enhancing burning. • Nano Fe enables rapid thermite ignition by strongly reducing activation barriers. • Micron Fe in thermite yields stable, semi-spherical particles suitable for consolidation via FAST/SPS technology. The combustion dynamics and characteristics of dense iron–ethanol slurry droplets containing 30 wt% Fe (in both micron- and nano-sized forms) and Fe-doped Al/Fe 2 O 3 thermites containing 5 wt% Fe (in both micron- and nano-sized forms) are investigated as a function of iron particle size. Single droplet experiments with high-speed imaging and in-situ thermocouple measurements are combined with TGA–DSC and SEM/EDS to link burning behavior to aggregate morphology. In ethanol, micron Fe (10 µm) settles toward the droplet periphery (terminal velocity ∼0.06 mm/s), forming a porous shell that improves O₂ access, raises the peak internal temperature to ∼326°C, and increases the d²-law burning rate to 0.76 mm² s⁻¹ (+10%) while shortening the total burn time. Nano Fe (40 nm) remains more uniformly dispersed (terminal velocity ∼0.04 mm/s) and forms smoother, less-porous aggregates; despite a higher peak temperature (∼266.5°C) and frequent small disruptive events, the burning rate decreases to 0.63 mm² s⁻¹ (–9%) and the total burn time contracts through secondary atomization. These outcomes show that aggregate architecture and settling, not surface area alone, govern heat/mass transfer and apparent burning rate in highly loaded metal fuel droplets. Translating these insights to thermites, adding 5 wt% nano-Fe triggers earlier ignition and rapid energy release, whereas 5 wt% micron-Fe yields more completely reduced, Fe-rich, semi-spherical residues, indicating locally more complete conversion. The work establishes a transport-to-morphology-to-combustion framework for designing metalized fuels and tailoring ignition and energy release in aluminothermic composites.