Drophammer

First impression of the impact sensitivity of new compounds can be received by the older drophammer shown in Figure 1.22. By using this drophammer only an impact energy of 30 J can be set.

Figure 1.22 Drophammer (old version).

The recent impact sensitivity tests were carried out according to STANAG 4489 [99]

modified according to instruction [100] _{using a BAM (Bundesanstalt für}

Materialforschung) [101] _drophammer.[102] _{The sample, placed between two flat, parallel,}

hardened steel surfaces, is subjected to an impact by dropping a weight. The impact may result in initiation depending on the sensitivity of the material, weight mass, and its drop height (impact energy). The impact energy is calculated by:

EIS (J) = m (kg) ∙g (9.81 ms–2) ∙ h (m)

Initiation is observed by sound, light effects, smoke, or by inspection. The BAM impact apparatus, known to give fairly reproducible results, is shown in Figure 1.23. Typically drop weights having a mass of 1, 5 or 10 kg are used and the lowest energy required to

create a detonation is recorded. Thus drop-weight and drop-height at which the initiation of the sample occurs are the main parameters determined from impact testing. The drop height at which detonation is observed is thus a measure of impact sensitivity of an explosive. The maximum height in which no explosion was observed has to be confirmed in six independent trials.

Figure 1.23 BAM drophammer.

Table 1.1 Impact sensitivity of selected energetic materials.

Substance Impact energy [J]

Ethylnitrate 1 N2H5ClO4 2 Pb(N3)2 2.5 Lead styphnate 5 Nitroglycerin (NG) 1 Hg(ONC)2 1 PETN 3 RDX 5

1.4.13

Friction Test

The friction sensitivity tests were carried out according to STANAG 4487 [103] _modified

according to instruction [104] _{using the BAM friction tester (Figure 1.24).}[105,106] _The

sample is placed on a rough ceramic plate and a force (created by different weights on the lever) is loaded on the sample trough a stationary pin in contact with the plate. The plate is motor driven trough a complete cycle pass beneath the pin. The test sample is subjected to the friction created by the rubbing of the pin against the plate. Normally the test is run with a pin load of 5 − 10 − 20 − 40 − 60 − 80 − 120 − 160 − 240 − 360 N or values in between depending of the weight and the used groove. Each experiment is evaluated with respect to “no reaction”, decomposition (change of color, smell) or explosion (bang, crackle, spark formation, ignition) and continued, by changing the pin load, until no explosion occurred within six single tests. However, only explosions are evaluated as “positive”. A compound is classified as not friction sensitive if each single test with a friction load of 360 N was evaluated as decomposition or “no reaction”. In this thesis, the classification of impact and friction sensitivities were assigned according to the “UN recommendations on the transport of dangerous goods”.[107]

Figure 1.24 Scheme of the BAM friction tester.

1.4.14

Electrical Spark Device (ESD)

Electrostatic discharge is one of the most frequent and the least characterized causes of accidental explosions of energetic materials. Electrostatic sensitivity tests were carried out using an electric spark tester ESD 2010EN (OZM Research) operating with the “Winspark 1.15 software package”.[108] _{This tester allows to precisely measure both total}

Figure 1.25 OZM small scale electrical discharge device

spark energy discharged into the sample and a fraction of this energy really absorbed by the sample initiating its explosion. This feature allows to determine the true minimum energy sufficient for accidental initiation of the sample. The tester can load the sample with very wide range of spark energies from 1∙10–5 _{to 17 J – allowing to test all}

categories of energetics ranging from extremely sensitive primary explosives to insensitive high explosives. During operation of the instrument, a small amount of the sample is placed on a grounded metal plate anode. The metal plate with the sample is placed on the holder in the instrument, and the desired amount of energy of an electric spark is selected by setting appropriate capacitor and voltage. The energy is calculated by the equation E (J) = ½ C V2 _{with C = capacitance in farads (F) and V = charging voltage}

(V). An electric discharge is performed between the anode with the sample and the discharge needle-electrode above the sample. Initiation is considered to have occurred if either smoke, flame, flash or the characteristic smell of the reaction products is observed.

Table 1.2 Electrical Spark Sensitivity of selected materials.

Substance Electric spark energy [J] RDX 0.15–0.20 HMX 0.21–0.23 TNT 0.46–0.57 TATB 2.5–4.25 PETN 0.19 NQ 0.60 Pb(N3)2 0.005 Human body 0.005–0.02

Annotation: The electrical spark sensitivity strongly dependents on the particle size and shape. As a matter of principle powders are more sensitive than crystalline materials. For appropriate comparison, materials must be sieved before testing.

Figure 1.26 Outdated electrostatic discharge device.

The following Figure 1.27 shows a picture series of a high speed movie clip of the electrical ignition of compound 109 using a tesla coil.

1.4.15

Hot Plate Test

The hot plate test (Figure 1.28) was introduced in the research lab D3.110 to investigate the fast cook up of new compounds in the small scale without direct contact to flames. This test is extremely useful, since it can be performed in the fume hood and can be watched and recorded from safe distance. For this, the energetic material is placed on a copper plate (15 x 15 x 0.25 cm), which is warmed from below using a bunsen burner (distance 5 cm).

Figure 1.28 Two picture series of the hot plate test. A–D: Compound 100 under emission of light, E–H: Compound 90, violent explosion without light emission.