To obtain the melt cast booster explosive formulation with high energy and low critical detonation diameter, melt cast explosives were designed by 3,4-bis(3-nitrofurazan-4-yl)furoxan (DNTF)/2,4,6-trinitrotoluene (TNT)/glycidyl azide polymer-energetic thermoplastic elastomer (GAP-ETPE)/nano-1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX)/Aristowax. Furthermore, the impact sensitivity, small scale gap test, rheological properties, propagation reliability, and detonation velocity were measured and analyzed. The results show that when the mass ratio of DNTF/TNT/GAP-ETPE/nano-HMX/Aristowax is 34.2/22.8/2/40/1, not only does it indicate excellent rheological property but it has a brilliant safety performance as well. Moreover, it can propagate the detonation waves successfully in the groove at 0.7 mm × 0.7 mm. When the charge density in the groove is 1.70 g·cm−3, its detonation velocity can reach 7890 m·s−1.
With the development of Micro Electromechanical System (MEMS) initiation technique, ammunition system has increasingly tended to be miniaturized, complicated, and intelligent. This requires booster explosives to possess low critical detonation diameter to meet explosive reliability in the small size channel [
The flow characteristic of melt cast explosive offers the applied possibility to the complex and micro channel. Nevertheless, the traditional melt cast carrier TNT cannot be used alone in the micro channel for its limitations of energy, sensitivity, and critical detonation diameter. To improve the energy of melt cast explosive, 3,4-bis(3-nitrofurazan-4-yl)furoxan (DNTF), which possessed high energy, low melting point, and low critical detonation diameter, was added into TNT by Xi’an Modern Chemistry Research Institute [
DNTF and TNT were purchased from Gansu Yinguang Chemical Industry Co. Ltd. of China; nano-HMX granules (80–130 nm) were provided by North University of China [
First, GAP was put in a vacuum drying oven (−0.08 MPa) and then dried at 100°C. Second, GAP (10.00 g) and warmed MDI (2.02 g) were placed in a 100 mL, three-necked, round-bottomed flask. Together they reacted at 60°C while stirring. After 2 hours, warmed BDO (0.48 g) was introduced into the mix. Third, DMF was used to dissolve the product for the next 2 hours. Finally, the solution was put into the vacuum oven (−0.08 MPa) at 90°C for 7 days and then GAP-ETPE binder was obtained.
PerkinElmer Spectrum 100 FT-IR spectrometer, which was made by PerkinElmer in the US, was used to characterize GAP-ETPE. The sample was carried out in a KBr pellet by a MCT detector at a stand-off distance of 5 m using a mid-IR supercontinuum light source. It was measured in 4000–400 cm−1 wave number range with a 4 cm−1 resolution.
DNTF/TNT was selected as melt cast carrier and the mass ratio of them is 60/40 [
Formulations of melt cast explosive used in this experiment.
Samples | Contents (%) | ||||
---|---|---|---|---|---|
DNTF | TNT | GAP-ETPE | Nano-HMX | Aristowax | |
1 | 28.2 | 18.8 | 2 | 50 | 1 |
2 | 34.2 | 22.8 | 2 | 40 | 1 |
3 | 40.2 | 26.8 | 2 | 30 | 1 |
4 | 46.2 | 30.8 | 2 | 20 | 1 |
The ERL type 12 drop hammer apparatus was used for conducting the impact sensitivity test according to the GJB 772A-97 standard method 601.3 [
The small scale gap test was carried out according to test method of safety for booster explosive GJB-2178.1A [
Schematic cross section of the experimental arrangement used to small scale gap test.
The R/S Plus rheometer, which was manufactured by Brookfield Ltd. of USA, was used to test the rheological properties of melt cast formulations by constant rotation measurement unit. The testing conditions were temperature, 80°C; shearing rate, 2 s−1; measure points, 60; testing time, 60 s.
The booster explosives were injected into the grooves of 0.7 mm × 0.7 mm. The detonation reliability test was conducted for the charge according to Figure
Diagrammatic sketch of propagation reliability test.
The detonation velocity in groove booster explosive was measured using the probing method. The sensor probe was installed onto the surface of the charging groove, and the distance of test points was controlled with vernier caliper. The detonation propagation time was measured by oscilloscope.
The FT-IR spectrum of GAP-ETPE was illustrated in Figure
FT-IR spectrum of GAP-ETPT.
The detonation velocities of samples were estimated by EXPLO5 v6.01 computer program [
Results of detonation velocity estimation.
Samples | Density (g⋅cm−3) | Detonation velocity (m⋅s−1) |
---|---|---|
DNTF | 1.937 | 9502 |
TNT | 1.654 | 7241 |
HMX | 1.905 | 9234 |
ETPE | 1.293 | 6645 |
Aristowax | 1.090 | 6451 |
1 | 1.830 | 8647 |
2 | 1.821 | 8562 |
3 | 1.813 | 8485 |
4 | 1.804 | 8409 |
Under mechanical impact and shock waves action, most of the mechanical energy of the explosive transfers to thermal energy firstly. Due to the asymmetry of the mechanical impact and shock waves, instead of acting on the whole explosive, the thermal energy only concentrates on the local scope and forms hot spots. The explosive at the hot spot has thermal decomposition in the first place and releases heat at the same time, which prompts the decomposition speed acceleration of the explosive. If the hot spot number formed in the explosive is enough and the size is large enough, after the hot spot temperature rises to the bursting point, the explosive will be stimulated at these spots and have explosion. Finally, it causes the explosion of partial or even the whole explosive. The impact sensitivity and small scale gap test results of samples are demonstrated in Table
Impact sensitivity and small scale gap test results of samples.
Samples | Impact sensitivity, H50 (cm) | Small scale gap test, |
---|---|---|
Raw DNTF | 25.3 | 100 |
Raw TNT | 149.6 | 0 |
Nano-HMX | 47.3 [ | 15 |
1 | 58.6 | 0 |
2 | 50.2 | 0 |
3 | 48.3 | 0 |
4 | 47.3 | 10 |
The influence of nano-HMX content on viscosity of booster formulations was shown in Figure
Influence of nano-HMX content on viscosity of booster formulations.
The propagation reliability test is an important factor to determine a new booster explosive. Formulation 2 turns out well in the sight of energy output, sensitivity, and viscosity. The result of propagation reliability test of formulation 2 is shown in Figure
Groove charge and postdetonation aluminum witness plates: (a) groove charge and (b) detonation propagation.
A booster explosive based on DNTF/TNT/GAP-ETPE/nano-HMX/Aristowax with the mass ratio 34.2/22.8/2/40/1 has been prepared successfully by a melt cast process. First, the booster explosive exhibits good sensitivity properties, for its drop height is 50.2 cm and it has passed the small scale gap test. Second, this booster shows good flow ability in that its viscosity is less than 2500 Pa·s. Finally, the critical detonation diameter of this melt cast booster formulation is less than 0.7 mm and when the density of the charge is 1.70 g·cm−3 (93.4% theoretical maximum density), its measured detonation velocity can reach 7890 m·s−1. By virtue of these outstanding properties, the melt cast booster explosive is expected to be a candidate filled in the complex and micro channel. By adjusting the formulations the booster explosive with higher energy, less sensitivity, and lower critical detonation diameter may be obtained.
The authors declare that they have no competing interests.