Stress-altered aluminum powder dust combustion

Abstract

Aluminum powder was thermally stressed by annealing and quenching, then the powder was non-uniformly dispersed in air and examined for dust combustion behavior as a function of stress-altering conditions. An explosion chamber with a powder injector, spark gap igniter, pressure sensor, spectrometer, and high-speed camera was used for experimentation. Aluminum powder was annealed to 573 K, held for 15 min, and quenched at a rate of 200 K/min (pre-stressed, PS) or 900 K/min (super-quenched, SQ). The untreated (UN), PS, and SQ Al powders were injected into the chamber, and pressure, temperature, and flame spreading behavior were analysed. SQ Al powder exhibited lower pressurization rates than that of PS Al, which was also lower than that of UN Al. Surface modifications to the stress-altered powders may affect their dispersion and suspension in the air environment, which affects flame spreading and pressurization rate. Specifically, annealing powders caused the removal of surface hydration that had two effects: increased the surface energy of the particles (confirmed with density functional theory calculations) and decreased surface roughness (suggested from previous work revealing loss of a nanostructure at the surface with annealing). These two surface modifications may inhibit powder dispersion such that pressurization rate is reduced compared with UN Al powder.