Electro-Static Discharge Ignition of Monolayers of Nanocomposite Thermite Powders Prepared by Arrested Reactive Milling

Abstract

Reactive nanocomposite powders with aluminum as a fuel and copper, bismuth, iron, and molybdenum oxide as oxidizers: 2Al·3CuO, 2.35Al·Bi 2 O 3 , 2Al·Fe 2 O 3 , and 2Al·MoO 3 , were prepared by arrested reactive milling, placed in monolayers on a conductive substrate and ignited by an electro-static discharge (ESD) or spark in air, argon, and vacuum. The ESD was produced by discharging a 2000 pF capacitor charged to a voltage varied from 5 to 20 kV. Emission from ignited particles was monitored using a photomultiplier equipped with an interference filter.Experimental variables included particle sizes, milling time used to prepare composite particles, surrounding environment, and starting ESD voltage. All materials ignited in all environments, producing individual burning particles that were ejected from the substrate. The spark duration varied from 1 to 5 µs; the duration of the produced emission pulse was in the range of 80 -250 µs for all materials studied. The longest emission duration was observed for the nanocomposite thermite using MoO 3 as an oxidizer. The reaction rates of the ESD-initiated powders were defined primarily by the scale of mixing of and reactive interface area between the fuel and oxidizer in composite materials rather than by the external particle surface or particle dimensions. In vacuum, particles were heated by ESD while remaining on the substrate until they Downloaded by [University of Nebraska, Lincoln] at 12:34 13 April 2015A c c e p t e d M a n u s c r i p t 2 began generating gas combustion products. In air and argon, particles initially pre-heated by ESD were lifted and accelerated to ca. 100 m/s by the generated shock wave; the airborne particles continued self-heating due to heterogeneous redox reactions.

Reactive Structural Materials: Preparation and Characterization

“…If used for the same materials, ignition temperatures observed in the laser heating experiments can be compared to those expected from the kinetic trends obtained from thermal analysis and/or from the heated filament experiments. Still higher heating rates, in the range of 10 9 K s −1 are achievable in the experiments using an electrostatic discharge (spark) as an ignition source . An increase in the heating rate can cause a qualitative change in how the reaction propagates .…”