CP620, Shock Compression of Condensed Matter - 2001
edited by M. D. Furnish, N. N. Thadhani, and Y. Horie
2002 American Institute of Physics 0-7354-0068-7
THE EFFECT OF VARIATION OF ALUMINUM PARTICLE SIZE AND
POLYMER ON THE PERFORMANCE OF EXPLOSIVES
Diana Woody1 and Jeffery J. Davis2
Combustion Research Branch, Engineering Sciences Division, Research Department; and
"Detonation Sciences Branch, Engineering Sciences Division, Research Department,
Naval Air Warfare Center Weapons Division, 1 Administration Circle, China Lake, CA 93555-6100
Abstract. The Ballistic Impact Chamber (BIG) test was used to measure the effect of particle size upon
performance of the energetic material. Two different particle sizes of aluminum, 20 micron (|um) and
150 nanometer (nm), were added to LX-17 to measure their effect upon hazard sensitivity and
energy/gram output. Also, the effect of the binder on the performance of the mixtures was explored. For
this paper, Viton and Kel-F were compared. The Ballistic Impact Chamber test measures the initial rate
of reaction, time of reaction, the burning reaction, and the energy output during the impact of the
energetic material.
INTRODUCTION
their exothermic output upon impact. The two
binders compared were Viton and Kel-F.
The Ballistic Impact Chamber (BIC) test is a
small-scale instrumented test capable of measuring
sensitivity and energy/gram output. It does so by
measuring the initial rate of reaction, time of
reaction, and the energy output during the impact of
the energetic material. These parameters were used
to discern differences in the reaction due to the
particle size of the aluminum additive.
Previous studies have been performed to
measure the effect upon performance of the
addition of aluminum to explosives (1). The use of
micron-sized aluminum additives has become the
standard for explosive formulation throughout the
Department of Defense (DOD) for enhancing blast.
It has since been observed that particle size
plays a significant role in the exothermic output
from energetic materials (2). In this paper, the effect
of the size of aluminum added as well as the type of
binder added to an explosive has been studied. Two
aluminum particle sizes, 20 um and 150 nm were
used in the LX-17 analog compositions to compare
EXPERIMENT
The BIC test is a closed-volume version of the
simple drop weight test setup. The impact machine
is 2 m high and 0.30 m wide. The distance from the
bottom of the drop weight to the anvil is 1.57 m.
This height corresponds to the free-fall velocity of
5.5 m/s. A laser diode and light meter were used to
trigger the acquisition of the data obtained from the
pressure gauge.
Each sample was a cylindrical disk
approximately 1.25 mm thick and 5 mm in
diameter. The mass of the sample was between 35
to 50 mg. The sample to be tested was placed on
garnet paper (Norton Corp. #01489 garnet A511,
180A grit paper). The garnet paper served to
standardize the anvil surface friction. The sample
and sandpaper were placed in the test cavity of the
BIC. Figure 1 shows the BIC test chamber.
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However, the oxide shell can take up an appreciable
volume of the of a nanosized particle. The oxide
layer of the Al used in this study was measured to
be approximately 14% by weight of the particle.
Thus, the total amount of Al available to react with
the other materials in the nanometer aluminum
composition is less than is available in the micron
Aluminum composition.
Five sets of samples were tested. The baseline
formulation was LX-17. The other two formulations
were analogs of LX-17 containing 20 jim and
150nm aluminum, respectively. Viton was
substituted for Kel-F for two of the mixtures. Ten
sample tests were conducted on each composition;
the results were then averaged. The explosive
compositions are given in Table 1.
RESULTS AND DISCUSSION
FIGURE 1. Ballistic Impact Chamber.
The averaged results of the BIC tests of this
study are shown in Table 2. The total area under the
pressure time curve (Equation (1)) was used to
determine the average pressure released by the hot
gases of the reacting sample. Typical trace of
pressure vs time are shown in Fig. 2 and 3.
Two ports were located at the bottom of
the wall of the cup. One port was connected to a 30cm-long 0.177 caliber gun barrel which held a
0.177 caliber lead airgun pellet (Crossman
Copperhead) weighing 0.51 gram. The second port
was connected to a fast-response pressure gauge
(PCB Piezotronics, Model #113). This gauge
measured the pressure time development of the
reacting gases from the impacted energetic material.
The hot gases generated by the reacting sample
accelerated the pellet along the gun barrel. Work
done on the pellet by the gases was a measure of the
energy released by the impacted energetic material.
The integration of the pressure/time history trace
was used to calculate the energy released by the
sample.
The nanosized aluminum "ALEX" (Argonide
Inc. Lot # A06-24-25R) had a wide particle size
distribution over a range of 50 - 500 nm with a
typical size of 150 - 200 nm. A major concern
when evaluating the contribution of nanosized
aluminum is the oxide layer that exists on the
particle. This oxide layer is typically on the order
of 3 nm thick for all particle sizes. It is present
because of the diffusion of oxygen, which leads to
passivation of the surface of the metal. For micron
sized particles, the 3 nm shell does not significantly
affect the amount of pure metal in the particle.
P= 1/T Jp(t)dt
(1)
where T = tfmai-to
The total energy released from the gases of the
reacting energetic material during impact was
linked to the pressure via:
Energy = (P) x (Volume of Chamber)
(2)
where Volume - 0.0288 cm3
The data was standardized as Energy/gram
where
E/gm = Energy/mass of sample (grams)
(3)
It can be observed from the data that the
addition of both sized aluminums to LX-17
increased the sensitivity measured as dp/dt and
energy output measured as energy/gram. There is a
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TABLE 1. Compositions Used in the BIC Tests.
Explosive
Organic
Metal
Binder
LX-17
TATB/20 um Al/Kel-F
TATB/150nmAl/kel-F
TATB/20 um Al/Viton
TATB/1 50 nmAl/Viton
92.5% TATB
72.5% TATB
72.5% TATB
72.5% TATB
72.5% TATB
0%
20%20umMDX81
20%150nmAl-Alex
20%20umMDX81
20%150nmAl-Alex
17.5% Kel-F
7.5 % Kel-F
7.5 % Kel-F
7.5 % Viton
7.5 % Viton
, , ^
(g/cc)
1.9
1.97
1.97
1.97
1.97
Process
Pressed
Pressed
Pressed
Pressed
Pressed
TABLE 2. Results from the BIC Test.
Material and Composition
Peak Pressure (psi)
67.1
53.4
146.52
63.6
147.5
245.5
LX-17
TATB, Kel-F, and (20 um aluminum)
TATB, Kel-F, and (150 nm aluminum)
TATB, Viton, and (20 um aluminum)
TATB, Viton, and (150 nm aluminum)
PBXN-109 (cast)
Sensitivity
dp/dt
(psi/us)
0.139
3.45
6.73
0.23
0.56
30.2
Energy
(J/gm)
8.05
9.65
20.86
10.59
17.44
37.83
Kel-F mixture containing the 20 jam aluminum. The
increase in sensitivity is significantly lower for both
sized aluminums mixed with TATB and Viton than
that observed in the mixture containing Kel-F as a
binder. Results from PBXN-109 are also shown in
Table 2 for comparison values.
The greater sensitivity observed in the TATB
mixture containing aluminum and Kel-F could be
due to the contribution from the fluorine in the
Kel-F polymer. Shear has been shown to be an
important factor in the reactivity of energetic
materials. Possibly the small size of the fluorine
atom could make the potentially more polar and
fluorine-rich Kel-F more reactive with the
aluminum additive under shear conditions than the
fluorine-deficient Viton.
FIGURE 2. Pressure vs. time trace for LX-17.
CONCLUSIONS
This study has shown that the size of the
aluminum added to an explosive composition can
have an affect upon its energy output and
sensitivity. The smaller aluminum increased the
sensitivity and the energy output of the explosive.
This was shown in the pressure-time traces obtained
from the gases released under closed volume impact
FIGURE 3. Pressure vs. time trace for LX-17 with 150 nm
aluminum added.
greater increase in sensitivity and energy output for
the TATB-Kel-F mixture containing the 150 nm
sized aluminum than that observed for the TATB-
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tests. The substitution of Viton for Kel-F when
adding aluminum to the TATB mixture resulted in a
slightly lower increase in energy output than that
observed for the mixture containing Kel-F. But at
the same time, the sensitivity does not show as great
an increase with the TATB mixture containing
Viton than it does an increase with the more polar
Kel-F polymer.
Further BIC and Differential Scanning
Calorimetry (DSC) studies will be performed to
measure the effect that humidity may have on the
different sized aluminums. This data should give an
indication of which sized aluminum is more
vulnerable to humidity or general cycling events
that may occur upon storage of the material.
ACKNOWLEDGMENTS
This research was performed under the
sponsorship of Tom Loftus, Air Weaponry
Technology Program.
REFERENCES
1.
2.
Woody, D. L., Davis, J. J., and Coffey, C. S.,
"Comparison of Infrared Emissions from Impacted
Aluminum to Non Aluminum Containing Energetic
Materials," in JANNAF
Hazards
Meeting
Proceedings, April 1992.
Woody, D. L., and Davis, J. J., "The Effect of
Particle Size and Porosity on Metal/Metal
Exothermic Reactions Induced by Low Velocity
Impact," in 14th U.S. Army Symposium on Solid
Mechanics Proceedings, edited by K. lyer and
S. Chou, Battelle Memorial Institute, 1997.
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