(716c) Experimental Study of Ignition of Magnesium Powder by Electro-Static Discharge

Ignition sensitivity of powders to electro-static discharge (ESD) stimulation is commonly tested to assess the safety of powder handling. However, the go/no-go criteria for ignition are often qualitative and poorly defined. The mechanisms of powder ignition by electric spark remain unclear. This research has two objectives. First is to understand the mechanism of powder ignition by electric spark. Second is to develop a laboratory technique for quantitative assessment of powder reactivity using electric spark as an ignition stimulus.

The current research is primarily experimental while a heat transfer model describing interaction of the electric spark and a powder bed is also being developed. A commercially available apparatus for ESD ignition sensitivity testing is used. It is equipped with additional diagnostics for measurements of the discharge current, voltage and optical emission in real time. The optical emission is filtered to separate the signals produced by the spark plasma (primarily UV part of the spectrum) and by the heated material. The discharge energy is being adjusted by selecting a specific capacitor, charging the capacitor to a specific voltage, and by adding a series resistor. Experiments were performed with powders of elemental Al (two size fractions), Mg, and with nanocomposite powders prepared by Arrested Reactive Milling with bulk compositions 2B+Ti and 8Al+3CuO. Experiments investigating the spark ignition mechanism used primarily Mg powder for which the mechanism of thermal ignition is relatively well established.

The optical emission pulse produced by the igniting powders was processed to establish the ignition delay, the amplitude of the emission signal and the integrated signal intensity. The results of these optical measurements were correlated with the pressure measurements obtained in constant volume explosion experiments with the same powders.

The results of this study will be presented and discussed in the paper.