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6
Advanced Gun Propellants
CURRENT RESEARCH FOCUS
The status of advanced gun propellants was obtained from presentations to the
committee given by or discussions held with Army and Navy researchers from ARDEC, ARL,
NSWC/IH, and ONR.~-3 In order to meet the requirements of future warfighting concepts that
call for the use of smaller, lighter, more lethal forces with minimal logistics tails, both Army
and Navy researchers recognize the need to develop new and improved gun propellants.
Medium- and large-caliber guns will continue to play a major role in these concepts, but
barrel sizes must be reduced and munitions must be made smaller, lighter, more lethal, and
longer-range. For example, to meet the needs of the Army's Future Combat System, the size
of the main tank gun, currently at 120 mm, must be significantly reduced, but at the same
time muzzle energy must be increased by 25 percent. The Navy will depend more on 5-in.
guns that fire extended-range munitions. To reduce the logistics burden further, gun tube
wear must be reduced. New energetic materials and geometries must be used if these
needs are to be met.
Additionally, health and safety concerns establish needs for environmentally safer, or
"green," munitions that are insensitive to harsh handling and less vulnerable to attack.
Advances in propellants alone cannot meet all of these needs. There must be synergistic
design of the barrels, breaches, recoil systems, munitions, and propellants.
As in the case of new energetic materials research and development, the number of
U.S. researchers actively working on the formulation and development of advanced gun
propellants is a group of fewer than 25 dedicated individuals. Researchers in this area are
concentrated at ARDEC, AR L, NSWC/IH, and a small number of industrial corporations.
Significant research and development efforts in high-performance gun propellants are going
on throughout the world, most notably in Germany and Switzerland. The efforts of foreign
A.B. Forch Horst. 2002. Review of Army Advanced Energetic Materials Programs and Facilities, U.S.
Army Research Laboratory Weapons and Materials Research Directorate. Aberdeen Proving
Ground, Md. May 7.
2 M.N. Maddinec, J. Pertucci, J. Brough, and D. Cichra. 2002. Discussion of advanced energetic
materials at Indian Head. Teleconference with the committee held on May 31.
3 J.M. Goldwasser, ONR. 2001. Presentation to the committee. July 31
28
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AD VANCED G UN PROPELLANTS
29
researchers have led to the development of propellants with reported performance
advantages over currently fielded U.S. propellants—the performance of the former is
relatively flat over a wide temperature range.4
The most promising research in progress for Army applications involves the use of new
layered propellants that use new energetic ingredients. Navy researchers are likewise very
interested in the use of layered propellants to enhance performance, but are also strongly
motivated to find ways to reduce barrel erosion and thereby enhance barrel life. Both Army
and Navy approaches employ advances in propellant-processing technologies that have
matured significantly during the past decades. Additional details of these two research
thrusts are discussed below. It should be noted that no significant research in gun
propellants is being conducted by the lJ.S. Air Force.
CURRENT GUN PROPELLANTS
All those who made presentations on gun propellants noted that over the past 30
years, the basic ingredients in fielded propellants have remained the same. The most
important of these ingredients include nitrocellulose, nitroguanidine, nitroglycerin, and other
nitrate esters. No propellants using new energetic molecules have been fielded. What has
improved during this time period is the processing, formulation, and manufacturing of widely
used, legacy molecules. Examples of uses for these materials are shown in Table 6-1.
TABLE 6-1 Comparison of Formulations (in percentage) for Propellant Materials
Propellant Material
M1
M30A2 Low-Vulnerability
Ammunition (LOVA)
Nitrocellulose 83.11 88.00 27.00 4.00
Nitroglycerine O 0 22.50 0
Nitroguanidine O 0 46.25 0
Cyclotrimethylene trinitramine (RDX) ~ O O 0 76 00
cycl otetra m ethyl e n etetra n itra m i n e ~ H MX)
Dinitrotoluene (DNT)
Dibutylphthalate (DBP) + diphenylamine (DPA)
Diethylene glycol dinitrate (DEGDN)
Ethyl centralite
Potassium nitrate
9.77
5.87
o
o
o
7.82
2.93
o
o
o
o
o
o
1.50
2.75
o
o
o
0.40
o
Other 1.25 1.25 0 19.60
SOURCE: N. Eldredge, Picatinny Arsenal, 2001. Presentation to the committee. December 13.
New, recently fielded U.S. propellants have compositions and performance
characteristics very similar to those of the formulations listed in Table 6-1. For example,
Propulseur d'Appoint a Poudre (PAP 7993) solid propellant (a joint development between
ARDEC and industry) is very similar to M1 but uses an environmentally acceptable plasticizer
to replace dinitrotoluene (DNT). While this propellant shows improvement in the
environmental area, it does not provide any added performance.
4 R.L. Simmons and B. Beat-Volgelsanger.2000. Introduction to NitroChemie El Gun Propellant.
Presentation to 37th JAN NAF Combustion Meeting, Monterey, Calif., November. CPIA Publication
701:201-205.
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30
ADVANCED ENERGETIC MATERIALS
ADVANCED GUN PROPELLANT RESEARCH
The challenge with respect to propellants research and development is to enhance
propellant performance significantly, while taking into account such objectives as reduced
pun tube wear. lower flame temperatures of orooellants. and "soft launch" cacabilitv for
~ . ~ . . . . . . . . . .
smart munitions, among other attributes. Research and development efforts In propellants
have focused on performance, increased survivability, reduced vulnerability and sensitivity,
and enhanced safety during transport and use. Efforts should continue in these areas. To
reduce the size of munitions—thus allowing reductions in casing, barrel, and breach sizes—it
is recognized that focusing solely on propellants will not provide an adequate solution.
Propellant developers will need to work with gun tube designers to increase the size of the
breach relative to smaller gun tubes in order to maintain the volume available within the
casing for propellants. Such cooperative efforts among propellant and gun tube designers
offer potential for improved systems and should continue.
Army Research Activities
To improve propellant performance so that it reaches the goal of increasing muzzle
energy by 25 percent without increasing barrel wear, ARL and ARDEC are currently exploring
energetic formulations based on thermoplastic elastomers (TPEs). These formulations
include the use of new, higher-energy fillers (such as CL-20) and nanostructured energetic
materials. The primary driver for the use of these new TPE-based propellants has been their
excellent performance coupled with relatively low flame temperatures (see Figure 6-1~.
In addition to the advantage just noted, TPE propellant may be used in advanced
layered geometries. Typical layered geometries are shown in Figure 6-2. When propellants
are manufactured in these configurations, a relatively slow burning propellant is used on the
outer layers and a faster-burning composition is used in the center core. Propellant
geometries are tightly controlled to enable the inner-core propellant to begin burning as the
projectile moves down the bore. This allows the pressure to be maintained at a high level for
a relatively long duration and often results in a double hump in the pressure time response,
as shown in Figure 6-3.
4000
3500
3000 _
c 2500
-
LL
2000
NCiNE
f'ropel~ --
-
Adv?nced TRE
.
Pro,oellants
900 1 000 1 1 00 1 200
Im petus f Jig ~
1300 1400
FIGURE 6-1 Calculated impetus and flame temperature for conventional (nitrocellulose ENC]
and nitrate esters LI\IE]) and thermoplastic elastomer (TPE) propellants.
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ADVANCED GUN PROPELLANTS
Disk
Slow Burning
|~: Rate Outer Layer
i/ /
,' ~ \ Strip
/ I' ~
1 ~ ~
h ~ ~ ;~ t ~ ~ ~
~ \\
\\ Fast Burning
Rate Inner Layer Wrap
FIGURE 6-2 Typical layered geometries of TPE propellants.
FIGURE 6-3 Pressure time trace from the firing of a 120-mm gun using layered TPE
propellant.
The use of these layered propellants results in improved energy transfer to the kinetic
energy of the round and hence in higher muzzle energy.5 6 Despite these promising results,
no layered propellants are used in currently fielded systems.
The new propellants under development by the Army have thermochemistry different
from that of traditional nitrocellulose-based propellants. The impact of these differences in
combustion products on gun bore erosion is not known. To begin evaluation of the erosivity
of new propellants, researchers at ARL have been using a subscale erosion tester. It is
anticipated that this device will be very useful in determining comparative erosivity of new
and current propellants.
At the same time, Army researchers are evaluating tantalum coatings or ceramics on
the surface of the barrel bore. To support this effort further, modeling is being done at both
the molecular and the macroscopic level to assess thermochemical reactions and surface
kinetics, respectively; the results are being validated with experimentation.
The advanced layered propellants under development by the Army have exhibited
problems with sensitivity. ARL and ARDEC have initiated a collaborative advanced
technology directive focused on insensitive high-energy munitions.
A key test in assessing the vulnerability of propellants is the pendulum test developed
at ARL. In this test, a shaped charge jet attenuated through a conditioning plate of rolled
homogeneous armor challenges a propellant sample (see Figure 6-4~. The violence of the
reaction is then compared with a baseline such as JA2 (a nitrocellulose gun propellant
5 Joseph A. Lannon, RDC/Picatinny. 2001. Presentation to the committee. July31.
6 N. Eldredge, Picatinny Arsenal. 2001. Presentation to the committee. December 13.
31
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32
ADVANCED ENERGETIC MATERIALS
developed in Germany). According to recent results reported to the committee, a high-energy
layered propellant can be similar in reaction violence to the baseline JA2 if the geometry of
the layered propellant is chosen properly.7 The sensitivity of the test result to geometry was
large, and more work would have to be done in this area.
~—~
[Shaped Charge I
~ :~:~:~:~:~:~
~ ..
Wow_ __! _~ ~
~ Conditioning Armory ~
_ _ . ... _
_ - _
.~
Pendulum Face
FIGURE 6-4 Typical test setup for a pendulum test used to evaluate advanced layered
propellant.
Chemical propulsion research in the Army is not all internal. A significant amount of
research is solicited from academia, national laboratories, and industry. Eleven universities
are addressing topics including the theory of energetic reactions, heat and shock pulses on
energetic materials, high-temperature energetic kinetics, and seven others. Research in the
physics and chemistry of propulsion will further validate molecular and macroscopic
modeling.
In a parallel and complementary effort, the Army's Electrothermal Chemical (ETC) gun
program has been a prolonged technological effort to produce a gun in which electrical
energy is used to augment and control the release of the chemical energy of the propellant.
The muzzle energy comes entirely from the chemical energy, rather than from the electrical
energy. Significant performance enhancements using ETC technology with existing or
advanced propellants have been demonstrated. The ETC effort should continue to work on
the development of high-energy propellants possessing acceptable vulnerability
characteristics. The present program is focusing on the identification of gun propellants with
the desired properties and on the extension of ETC technology to medium-caliber guns.
Reduction to a fielded system remains many years away.
Navy Research Activities
As with the Army, the Navy has some very strong points, as well as some shortcomings
in its propellant programs. Research in Navy propellant design has suggested areas in which
the Navy proposes to continue work. For example, a layered gun propellant approach came
out of Navy research in ETC propulsion design. In collaboration with the Army, the Navy is
7 P.C. Braithwaite. 2002. Update on Advanced Gun Propellant Efforts, presentation to the committee
during its visit to ATK Thiokol Propulsion, Brigham City, Utah, May 22.
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AD VANCED G UN PROPELLANTS
33
looking at low-CO-content propellants with high-nitrogen compounds such as 1,5-diazido-3-
nitraza pentane (DANPE). The theoretical advantage of using materials such as DANPE is
illustrated in Table 6-2. These numbers are especially impressive when compared with those
for current propellants such as JA2, which has similar flame temperatures and an impetus of
1151 J/g.
TABLE 6-2 Theoretical Benefits of Systems Using DANPE
Ingredients Impetus (J/g) Tv (K) Gas MW
TNAZ + DANPE (40/60) 1439 3490 20.16
RDX + DANPE (55/45) 1425 3497 20.40
CL-20 + DANPE (40/60) 1419 3527 20.67
NOTE: The acronyms are spelled out in Appendix C.
SOURCE: R.L. Simmons. 1996. Guidelines to Higher Energy Gun Propellants. Paper 22 in
Proceedings of the 27th International Conference of Institute of Chemical Technology, KarlsruLe,
Germany. June 25-28.
The Navy is also evaluating new energetic ingredients such as Field Operating Activity
(FOA) Organic Explosive 7 (FOX-7y, FOA Organic Explosive 12 (FOX-12), dihydrazinotetrazine
(HzTz), triaminoguanidinium azobitetrazolate, and bis-aminotetrazolyl-tetrazine (BTATz) as
new ways of tailoring propellant burning rates to meet the demands of layered propellants.s 9
As with the Army propellants, the first layer provides a relatively cool burn, while the second
layer releases much higher energy. This approach maintains a stable gun pressure that
increases muzzle energy, as described above, but at the same time it is predicted not to
increase tube wear significantly. More research is needed to see what happens at the
boundary layer of these two materials, especially when they are made of dissimilar
compounds.
The Navy has also had success in using energetic thermoplastic binders to develop
green propellants.~° These binders are costly, so the Navy is looking at twin screw
continuous extrusion processes to compensate for the higher material costs by reducing
manufacturing costs. Using this technology, Navy researchers at NSWC-IH have successfully
processed sufficient TPE-based propellants through a twin screw extruder to support a series
of 5-in. gun firings.
Figure 6-5 shows the extrusion of a slab material through a twin screw extruder (TSE).
In this case a single material is being extruded. Research is currently being pursued at
NSWC-IH to explore the possibility of using two separate TSEs to extrude layered propellant in
a single operation. ~ It should be noted that this technology has been successfully used in
the food processing industry for several years. Whether it will be possible to manufacture
layered gun propellants effectively and efficiently using this technology remains to be
demonstrated.
R.J. Cramer. 1998. Advanced Gun Propellants. Presentation at 35th JAN NAF Combustion Meeting,
Tucson, Ariz., December 7-11.
9 C. Walsh.2001. Advanced Gun Propellant Formulations. Presentation at Energetics for Naval Gun
Ammunition Technical Exchange Workshop, Waldorf, Md., October 23.
~°J.M.Goldwasser,ONR. 2001. Presentationto the committee. July31.
it C. Walsh and C. Knott. 2002. Advanced Gun Propellant Formulations. Presentation at the 2002
National Defense Industrial Association Guns and Ammunition Symposium, Panama City, Fla., April
15-16.
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34
FIGURE 6-5 Slab extrusion using a twin screw extruder.
FINDINGS AND RECOMMENDATIONS
ADVANCED ENERGETIC MATERIALS
New technologies offer promise in advancing the state of the art in propellants.
However, it is the opinion of the committee that reduced, unstable funding has significantly
affected these efforts. Limited 6.2 funding in this area reduces the ability to exploit
advances in basic research, and most 6.3 funding is being used to better package old
technologies. As a result of this lack of funding and focus, the workforce and the facilities for
gun propellants continue to age. If this trend persists, technological innovations will be
severely hampered and the recruitment of the brighter minds in the field will be difficult.
Specific technical recommendations of the committee are as follows:
.
· The development of high-energy layered propellants with a focus on vulnerability and
producibility should be continued.
· The exploration of high-nitrogen compounds as novel gun propellant ingredients in a
variety of configurations should be pursued, with a requirement for an early
demonstration.
System-level efforts should be continued at a modest level for barrel wear, chamber
design, and modeling.
i2 The Army and the Navy have numerous codes that model these systems. However, the committee
is not able to specify a particular modeling technique. The perception of the committee is that with
the improvements in modeling turbulent flow and erosion phenomena, the continuation of modeling
efforts is warranted.
Representative terms from entire chapter:
energetic materials
