(655e) Combustion Regimes for Spark Ignited Nanocomposite Thermites

Combustion Regimes for Spark Ignited Nanocomposite Thermites

Ian Monk and Edward L. Dreizin

New Jersey Institute of Technology, Newark NJ 07102

Abstract

Four nanocomposite thermite powders prepared by arrested reactive milling, 2Al-3CuO, 2.35Al-Bi2O3,

2Al-Fe2O3, and 2Al-MoO3, were ignited by Electro Static Discharge (ESD). The powder was placed in

monolayers and in layers of 0.5 mm thickness and the effect of the layer thickness on its ignition and

combustion was studied. Using a 32-channel photomultiplier tube (PMT) coupled with a spectrometer

operating in the visible light wavelength range as well as a single PMT filtered at 568 nm, time-

dependent emission traces were recorded for the ignited materials in the wavelength range of 374.1 -

641.0 nm. Ignition delays, temporal positions of peak emission, emission peak widths, were obtained

directly from the recorded traces. The peak durations were interpreted to represent the particle burn

times. Time dependent temperatures were calculated using the recorded 32-point spectra. The

spectra were curve-fitted using Planck’s black body emission equation, considering temperature as an

adjustable parameter. The Planck’s fits were typically good for the decaying portions of the recorded

emission traces, while substantial discrepancies between the recorded spectra and the anticipated gray

body emission pattern were detected prior to the emission peak. Despite these discrepancies, the

temperatures inferred from both parts of the recorded emission traces, before and after the emission

peaks, matched with each other well. Ignited particles were captured and examined using scanning

electron microscopy (SEM).

Previously, it was reported that nanocomposite thermite powders placed in monolayers ignite and burn

as individual particles, essentially without any delay following ESD. The powders placed in 0.5-mm thick

layers were observed to ignite in two distinct regimes. In one regime, observed for 2.35Al-Bi2O3 and 2Al-

Fe2O3 powders, ignition resulted in combustion of individual particles occurring without a delay, similarly

to what observed for monolayers. For 2Al-3CuO and 2Al-MoO3, ignition occurred with delays and

resulted in a much longer and brighter cloud combustion event. Cloud combustion was occasionally

observed for 2.35Al-Bi2O3 when higher spark energies were used, but was never achieved in this work for

2Al-Fe2O3. Specific temporal characteristics of the emission pulses generated by cloud combustion were

analyzed and compared for different powders. Effect of inert gas (N2, Ar, He) on the cloud combustion

dynamics was studied for different materials. Interaction between ignited particles was found to play an

important role in the observed cloud combustion events.