Ignition of Nanocomposite Thermites by Electric Spark and Shock Wave

Abstract

Nanocomposite 8Al ⋅ MoO3 thermite particles were prepared using arrested reactive milling and ignited using two experimental techniques. In spark ignition, a monolayer of powder was placed on a conductive substrate and heated in air by a pulsed electrostatic discharge. In shock ignition, an individual particle was targeted by a miniature, laser‐driven flyer plate accelerated to a speed in the range of 0.5–2 km s−1. In both experiments, time‐dependent optical emission produced by the ignited material was monitored and recorded. The heating rates achieved in the present experiments are on the order of 109−–1011 K s−1. These ignition methods result in a very fast combustion with characteristic burn times reduced by 1–3 orders of magnitude compared to the burn times measured previously for the same material ignited in the CO2 laser beam, where it was heated at a much lower rate of about 106−–107 K s−1. Ignition delays observed in both shock and spark ignition experiments are close to each other and vary in the range of 120–200 ns. The times of characteristic rapid increase in the optical emission of the ignited particles are also close to each other for the two experiments; however, these times are somewhat shorter (less than one μs) for the spark ignition tests compared to few μs observed for the shock initiated particles. Preliminary ideas enabling one to interpret the present results are discussed. This work establishes an approach for systematic studies of high rate ignition and respective combustion of nanocomposite reactive materials.

Physiochemical Characterization of Iodine (V) Oxide Part II: Morphology and Crystal Structure of Particulate Films

“…Such environments vary broadly as well, ranging from a gentle mixing, stirring, or coalescence processes [38], to more intense milling [39], swaging, [40] or sonication processes [12,41]. Of all of these, sonication is one of the most commonly used, versatile, and significant in that it physically pulverizes solid constituents, typically in a liquid-solid slurry, into smaller fragments of a more uniform size and simultaneously increases the degree of intermixing when multiple components are present.…”

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

“…The lack of difference in the peak position, peak width, and the total burn time between fine and coarse particles can be understood considering that, as suggested earlier (Shaw et al 2014), the burn time of these nanocomposite particles ignited by the ESD is likely controlled by heterogeneous reactions within the particles rather than reactions involving the external particle surface. In other words, the reaction is initiated before the scale of mixing between aluminum and metal oxide inclusions can be substantially changed, despite aluminum melting.…”

“…It was also reported that different ignition regimes, involving individual burning particles or aerosolized powder clouds, were observed when the thickness of a metal powder layer struck by ESD varied (Williams et al 2012). Most recently, ESD ignition of reactive nanocomposite thermite powders prepared by Arrested Reactive Milling (ARM) (E.L. Dreizin and Schoenitz 2009) was studied (Shaw et al 2014;Williams et al 2014b). …”

“…100 nm; they are of interest as potential additives to solid propellants (Stamatis et al 2010), reactive structural materials (Stamatis et al 2011), and components of other energetic formulations. It was reported that two distinct spark-initiated ignition regimes were observed for nanocomposite thermites using Al as a fuel and CuO and MoO 3 as oxidizers: monolayers of composite particles ignite within 100-200 ns after the spark discharge onset producing multiple individually burning particles (Shaw et al 2014), whereas thicker powder layers ignite following a substantial (~ 0.1-5 ms) delay after the spark discharge and generate burning powder clouds (Williams et al 2014b). In addition to vastly different ignition delays, the burn times observed for individual particle and cloud combustion were very different.…”

Shock compression dynamics under a microscope

“…We have studied several different types of RM using our laser flyer plate apparatus, including nano-Al + Teflon [27] and Al + MoO 3 [28]. Our latest study of the emission from shocked RM uses as an example the Al + CuO nanothermite reaction.…”