EXAMINATION OF NON-IDEAL EXPLOSIVES

Ryan Rettinger

doi:10.23860/diss-rettinger-ryan-2019

Abstract

As seen in multiple cases, including the 2013 Boston Marathon bombing, improvised explosives compositions may be as simple as a combination commonly-available fuel/oxidizer (FOX) mixtures initiated by an electrically-heated wire. The predictive knowledge of large scale explosive potential of FOX mixtures is incomplete. Predicting explosive potential from laboratory-scale analytical test data is desirable. Herein the explosive properties of fuel/oxidizer combinations (FOX) were measured at both the small scale (2 g) with bomb calorimetry for heat output and closed-vessel dynamic pressure rise and also on the large scale (5 kg) with high speed photography for detonation velocity and with piezoelectric pressure probes for TNT air blast equivalence. Potassium nitrate (KN), potassium chlorate (KC), potassium permanganate (KMnO4), potassium iodate (KIO3), ammonium nitrate (AN), and ammonium perchlorate (AP) were prepared with sucrose (Su) fuel, and KN, AP, and AN were prepared with aluminum (Al) fuel. The results were compared to each other as well as predictions from Cheetah thermochemical code in order to correlate detonation performance, particularly the ideality of detonation performance, with simple laboratory screening tests. Presented here are the results of around 60 explosive experiments which have become the first series of experiments at the URI explosives test facility to successfully field photon Doppler velocimetry (PDV) and ultra-high speed photography. The experiments outlined herein focus on homogeneous improvised explosives, namely hydrogen peroxide (HP) aqueous solutions fueled with ethanol (EtOH). These materials have been chosen as a template system for evaluation with time-resolved detonation diagnostics aimed at screening clandestine non-ideal explosive threat materials for detonable character even, and especially, in configurations below their critical diameter. The ‘galloping’ detonation instabilities of these materials have been captured on camera in the stoichiometric mixture of HP:EtOH in diameters from 1 to 2.6 inches; a steady detonation never formed. Reactive particle velocity waveforms for this mixture were measured by PDV through a PMMA pressure-maintaining window. These materials were subjected to both overdriven and underdriven configurations, and non-steady waveforms have been collected to monitor non-ideal explosives under these conditions i.e. inside the infinite diameter region of a range of different shock loading environments. Several mixtures of HP:EtOH have also been artificially doped with glass microballoons to study the ideality of this mixture in a heterogeneous regime. Successful detonations of heterogeneous HP:EtOH mixtures were observed using as low as 40% HP.

Highlights

Hundreds of years ago, the field of energetic materials began with the invention of a fuel-oxidizer mixture of charcoal, sulfur, and potassium nitrate, which became known as black powder [1]
We have previously reported a series of 11 oxidizers and 13 fuels examined by differential scanning calorimetry (DSC), simultaneous DSC/TGA (SDT), and by open burn
3.1 Photon Doppler Velocimetry (PDV) Results The earliest results were obtained to calibrate the PDV equipment and components; the experiment captured the PDV record of the end-on aluminum surface of a 501 exploding bridgewire detonators (EBWs) detonator being propelled in air

Summary

Introduction

The field of energetic materials began with the invention of a fuel-oxidizer mixture of charcoal, sulfur, and potassium nitrate, which became known as black powder [1]. Homemade explosives (HMEs) often fail these tests because they release too little energy to support detonation in the prescribed tests; they are not recognized as real explosive threats These HMEs will perform as explosive materials if the charge size is increased beyond a configuration-specific size, the critical diameter (Dcr). The critical charge size of many potential threat materials is so large that they are frequently not perceived as threats, when in reality they were tested below Dcr. For example, as dictated by shipping regulations, ammonium nitrate (AN) is not classed as an explosive, rather as DOT 5.1, because it does not propagate detonation at a diameter of 3.65 cm [1]. For non-ideal explosives, a term which describes most homemade explosives (HME), the constraint of performing small-scale testing necessarily means studying these materials in configurations well below their critical diameters (Dcr).

Methods

Results

Discussion

Conclusion