Flame propagation behaviours in nano-metal dust explosions

Abstract

Flame propagation behaviours in 40nm titanium, aluminium and iron dust clouds were investigated by high-speed photography. 40nm titanium, aluminium and iron dust flames were all characterized by discrete single glowing burning particles with smoothly spherical front. “Micro explosions” caused by the fragment ejection occurred in both 40nm titanium and aluminium particles burning processes. At nano scales, the heat and mass transfer regimes were absolutely different with micro particles, which resulted in different propagation velocities. The average pulsating flame propagation velocities of 40nm titanium, aluminium and iron dust clouds were 0.565m/s, 0.189m/s and 0.035m/s, respectively. From SEM analysis, it was inferred that 40nm titanium, aluminium and iron particles were burnt in liquid, gas, and solid-phase, respectively. From XPS analysis, it was found that N2 played a significant role in titanium particles combustion. 40nm titanium combustion products contained 43% TiO2 (Ti4+), 27% Ti2O3 (Ti3+), 21% TiO (Ti2+) and 9% TiN (Ti3+). While 40nm aluminium combustion products just contained 100% Al2O3 (Al3+), and 40nm iron combustion products contained 49% Fe2O3 (Fe3+), 26% Fe3O4 (Fe3+/Fe2+), 15% FeO (Fe2+) and 10% iron nonoxides. Inerted by nitrogen for preventing nano‑titanium dust explosions was inadvisable.