Analysis of Ignition Sites for the Explosives 3,3′-Diamino-4,4′-azoxyfurazan (DAAF) and 1,3,5,7-Tetranitro-1,3,5,7-tetrazoctane (HMX) Using Crush Gun Impact Testing

Abstract

The handling safety characteristics of energetic materials must be measured in order to ensure the safe transport and use of explosives. Drop-weight impact sensitivity measurements are one of the first standardized tests performed for energetics. They utilize a small amount of the explosive sample and a standard weight, which is dropped on the material from various heights to determine its sensitivity. While multiple laboratories have used the impact sensitivity test as an initial screening tool for explosive sensitivity for the past 60 years, variability exists due to the use of different instruments, different methods to determine the initiation, and the scatter commonly associated with less-sensitive explosives. For example, standard explosives such as 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (HMX) initiate reliably and consistently on the drop-weight impact test, whereas insensitive explosives such as 3,3′-diamino-4,4′-azoxyfurazan (DAAF) exhibit variability in sound levels and the expended material. Herein we investigate the impact sensitivity of DAAF and HMX along with a more detailed investigation of ignition sites using a novel “crush gun” apparatus: a pneumatically powered drop-weight tower with advanced diagnostics, including high-speed visual and infrared cameras. Using this crush gun assembly, the ignition sites in HMX and DAAF were analyzed with respect to the effects of particle size and the presence of a source of grit. The formation of ignition sites was observed in both explosives; however, only HMX showed ignition sites that propagated to a deflagration at lower firing speeds. Finally, the presence of grit particles was shown to increase the occurrence of ignition sites in DAAF at lower firing speeds, though propagation to a full reaction was not observed on the time scale of the test. These results enable a better understanding of how ignition and propagation occurs during the impact testing of DAAF.

Understanding Explosive Sensitivity with Effective Trigger Linkage Kinetics

“…We have computed the rates and specific and molar heats of explosion for a chemically diverse set of 24 organic explosive molecules. The molecules comprise the nitrate ester-based explosives erythritol tetranitrate ([(2 R ,3 S )-1,3,4-trinitrooxybutan-2-yl] nitrate, ETN), its isomer L-ETN, pentaerythritol tetranitrate ([3-nitrooxy-2,2-bis­(nitrooxymethyl)­propyl] nitrate, PETN), and the PETN derivatives 2-((nitrooxy)­methyl)­propane-1,3-diyl-dinitrate (PETN-CH), 2-methyl-2­((nitrooxy)­methyl)­propane-1,3-diyl-dinitrate (PETN-CMe), and 2,2,2-tris­(nitroxymethyl)­ethylamine (PETN-CNH 2 ), the nitramines cyclotrimethylene trinitramine (1,3,5-trinitro-1,3,5-triazinane, RDX), cyclotetramethylene tetranitramine (HMX), erythritol tetranitramine ( N , N ′,N″, N ‴-(butane-1,2,3,4-tetrayl)­tetranitramide, ETNA), and hexanitrohexaazaisowurtzitane (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexazatetracyclo­[5.5.0.0. , 0 , ]­dodecane, CL-20), the nitroaromatic molecules diamino trinitrobenzene (2,4,6-trinitrobenzene-1,3-diamine, DATB), triamino trinitrobenzene (TATB), three isomers of trinitrotoluene (TNT), 2,3,4-TNT, 3,4,5-TNT, and 2,4,6-TNT, 2,4,6-trinitrobenzaldehyde (TNBAL, see Supporting Information), N -Methyl-N,2,4,6-tetranitroaniline (tetryl), 2,4,6-trinitroaniline (TNA), 2,4,6-trinitrophenol (picric acid), hexanitrostilbene (1,3,5-trinitro-2-[(E)-2-(2,4,6-trinitrophenyl)­ethenyl]­benzene, HNS), and 2,4-dinitroanisole (1-methoxy-2,4-dinitrobenzene, DNAN), the nitrimine nitroguanidine (1-nitroguanidine, NQ), the azoxyfurazan 3,3′-diamino-4,4′-azoxyfurazan ((4-amino-1,2,5-oxadiazol-3-yl)-[(4-amino-1,2,5-oxadiazol-3-yl)­imino]-oxidoazanium, DAAF), and the azide erythritol tetraazide (1,2,3,4-tetraazidobutane, ETA) . The structures of the 24 molecules are depicted in Figure .…”

“…While drop weight impact tests are performed routinely by most laboratories, they involve sub-shock impacts on small amounts of material in a contrived geometry that real explosives are unlikely to experience. Furthermore, the results can exhibit significant variability that depends on site-to-site and operator-to-operator differences in testing protocols and the properties of the explosive. ,− Nevertheless, sub-shock drop weight impact sensitivity is known to be strongly correlated with small-scale gap test shock sensitivity. , …”

Sources of Variation in Drop-Weight Impact Sensitivity Testing of the Explosive Pentaerythritol Tetranitrate

“…Figure shows a clear separation in sound levels for the Go’s and No-Go’s, especially when grit paper is used. The tests with the bare anvil exhibit less separation in sound levels, likely due to the lack of reliable ignition sites in the absence of grit, which could result in partial ignitions of the explosive material. , In both cases, changes in the auditory threshold (117 dB, horizontal dotted lines) up or down by, say, 5 dB, would change the estimated E 50 very little. Further, the difference from about 100 to 130 dB (typical No-Go to Go, respectively) should be easily observable, with or without audio equipment.…”

Identifying the Molecular Properties that Drive Explosive Sensitivity in a Series of Nitrate Esters

“…PETN, PETriN, and PEDN generated the expected S-curve behavior (see Supporting Information for an expanded view of PETN and PETriN), with maximum sound levels for PEDN (121–124 dB) that were significantly lower than those of PETN and PETriN (129–134 dB). Most sound levels for PEMN fell below the threshold to be considered a Go, at the approximate sound level expected for an inert material in this test …”