Ignition of metal powder layers of different thickness by electrostatic discharge

Metal powder layers of different thicknesses were ignited by electrostatic discharge. Spherical aluminum and magnesium and titanium sponge powder were considered. The powder layer thickness affected initial velocities of the particles ejected by the spark and shapes of the formed dust cloud flames. These effects are important for practical assessments of the fire hazard. Both the powder layer thickness and electrostatic discharge voltage affected the electrical resistance of powder layers. For all powder monolayers, electrostatic discharge caused particle fragmentation and dust cloud flames. Dust cloud flames were produced for all magnesium samples and for 500-μmthick aluminum layers, when the spark's energy exceeded a certain threshold. For thinner aluminum layers, and at reduced spark energy, electrostatic discharge ignition generated single burning particles. Only occasional, individual igniting particles were detected for 30-500-μm-thick titanium layers for which the powder was fused by electrostatic discharge. The temperatures of aluminum and magnesium particles estimated assuming adiabatic heating of the entire powder layer are reasonably high. A similar estimate for titanium yields an unreasonably low temperature, suggesting that only a fraction of the titanium powder layer thickness is effectively heated by the electrostatic discharge current.