SOLID STATE FUEL-AIR EXPLOSIVES WITH ENHANCED POWER AND
Stefan Kolev, Tsvetomir Tsonev
SURT Technologies LTD, Sofia, Bulgaria, e-mail: email@example.com
Phone (Stefan Kolev): +359 878 633801
Solid state fuel-air (enhanced blast or thermobaric) explosives have very promising features.
They can combine superior air blast impulse with metal fragmentation and metal acceleration
effects, thus enabling to create ordnance with improved effectiveness and combined modes of
action on the targets. Despite the efforts for practical application, however, most of the current
compositions are still based on obsolete types of polymers, oxidizers and production
technologies, which limit their performance and keep their production cost high. Here we
present the results of our practical solutions to these problems in two types of solid state
thermobaric explosives. They have air blast TNT equivalent of about 2.5 times and metal
fragmentation capabilities similar to that of TNT. Both types are thermally stable, cheap and
technologically suitable for mass production.
Solid state explosives that utilize atmospheric oxygen in order to create enhanced blast can be
grouped into two major categories . First group are homogenous mixtures of binder, brisant
explosive, optionally an oxidizer, and reducing agent, usually a metal powder. In some cases
the brisant explosive may play the role of binder. The second group are created using the so
called “annular design”. In this case the reducing agent, with optionally added oxidizer, is
placed around a core consisting of brisant explosive. Binder is used in order to cast or press
the outer layer around the high explosive core. Regardless of their high potential, both groups
suffer drawbacks that hinder their practical use. First group, the homogenous mixtures suffer
from incomplete burning of the metal particles in the atmosphere and for this reason, the
potential energy stored in the explosive cannot be converted to blast impulse with high
enough yield [2,3]. For this reason additional oxidizer, usually ammonium perchlorate, is
added to the mixture to support the combustion of the reducing agent. Ammonium perchlorate
decomposes slowly, it can not react in the detonation front. Therefore such explosives are
only effective in very high quantities as they depend on post detonation mixing and reaction
of oxidizer with the products of detonation. The annular design also suffers from poor
combustion of the reducing agent if prepared using non-active binder like HTPB. The high
price, low stability, and low mechanical properties of the active polymers (containing
fluorine, NO2) hinder their practical use. For example, active oxidizing polymers like teflon
and viton, although participating in the reaction and improving the yield of the blast, suffer
from low mechanical properties and high sensitivity. Moreover, it is very difficult to
incorporate such polymers in actual devices as the prepared explosives become brittle and
difficult to press around the explosive core. Thus, production of such ordnance, especially in
big calibers, becomes highly impractical .
In order to solve the problems associated with the practical use of solid state fuel air
explosives we used the same approaches for both homogenous mixture (denoted as H-TBX)
and annular design (denoted as A-TBX), Fig. 1. First an oxidizer with much faster kinetics
than ammonium perchlorate was chosen, it reacts very closely to the detonation front and
thus, our mixtures do not depend on the post detonation mixing of products. In the performed
tests the annular design was effective even in small diameter charges, 30 mm. We chose an
active polymer binder that has no negative influence on the oxygen balance of the systems.
The binder is thermally stable and as a result of this the mixtures are stable and operational
from -60 to 120o C for H-TBX and -60 to 250 o C for A-TBX. Casting techniques were used
and hardness of the final products was 40 Shore A. Mathematical model of the dynamics of
metal particles burning in the atmosphere was developed in order to insure that most of the
fuel will have time to heat, ignite and burn during the positive phase of the pressure. Metal
fuel particles type was chosen according to the calculations.
Fig. 1. Design of both types of solid state fuel-air explosives.
Series of tests were performed in order to evaluate the newly developed solid state fuel air
explosives. First, the air blast TNT equivalent was measured. For this test, 2.5 kg H-TBX
charges were cast in aluminum warheads and set off with 150 grams A-IX-1 booster (95%
RDX). Piezo sensors were used to record pressure changes, Fig. 2. Sensors were placed in
distances from 2 to 10 meters. Tests were performed in an open field, but the test site, with
about 20 meters radius, was dug 1 meter below the ground level, to guard from flying metal
TNT equivalent in impulse (Pa.s) was measured - about 2.5 times (the averaged value was
2.75 for H-TBX), Fig 3. Very similar results (averaged about 2.5 times TNT equivalent) were
obtained for A-TBX, tested analogously with 2.5 kg charges. Farther testing of 2.5 kg charges
of A-TBX, however, revealed its better air blast performance in the open field, related to the
faster aerobic energy release. Light emission, shot with the high speed camera, was also
higher for A-TBX than H-TBX.
Fig 2. Piezo sensors and the 2.5 kg H-TBX warhead. High speed footage (3 ms after
initiation) of the actual detonation is also shown. Diameter of the fireball is 7 meters.
Fig 3. TNT equivalent in impulse for H-TBX, measured at distances 2-10 meters and the
In order to study the fireball evolution after initiation, 5kg charges of A-TBX were prepared.
First, maximum diameter, volume and area of the fireball (simulated as a spheroid) were
studied and compared to the fireball produced from 5 kg “classical” thermobaric mixture
(Isopropyl nitrate/RDX/Aluminum ), Fig 4 and Table 1.
Fig 4. Comparison between the fireballs produced by A-TBX and RDX/IPN/Al.
Fig. 5. High speed comparison of SURT Tech. annular design with isopropyl nitrate
thermobaric composition and 95% RDX 5% wax (marked as RDX). All charges are 5 kg.
Table 1. Comparison between the fireballs produced by A-TBX and RDX/IPN/Al. All
charges are 5 kg.
The diameter of the RDX/IPN/Al fireball reaches its maximum value (6 m) about 2.3 ms after
charge initiation. At this point the volume is 47 m3 and its area is 50 m3. The diameter of A-
TBX fireball is much higher (10 m), reached 12 ms after charge initiation. Volume of A-TBX
fireball is 2.8 times higher than that of RDX/IPN/Al fireball and its area is 2.2 times higher.
The evolution of RDX, RDX/IPN/Al and A-TBX fireballs for 5 kg charges is shown in Fig. 5.
A-TBX generates the highest light output, which is another evidence for the very effective
Charges of H-TBX were additionally tested on wooden boxes piles with dimensions 1.7 x 2.5
x 3.5 m, Fig. 6. The charges were inserted in the center of the pile. A charge of 700 grams
95% RDX was also tested for comparison. As it can be seen, the thermobaric charge, which is
more energetic, induces much more damage on the empty boxes. Boxes are fragmented, and
pieces of them can be seen flying in the air, as with the RDX, the boxes remain mostly in one
piece. The longer time of aerobic burning that comes with the partially enclosed space and
lack of oxygen, created by the empty boxes, should also be noted. See the snapshot taken
from 200 fs, where the TBX still burns. In an open space, the aerobic reaction is completely
over in about 50-100 ms. About 90% of the mixture burns in the first 10-15 ms (5 kg
charges). Aerobic reaction is completed for much shorter times for smaller charges.
Scattering of the boxes was also studied, Fig. 7 and Table 2. 700 g RDX caused the boxes to
scatter in the area of 200 m2, while for 700 g H-TBX this area was 330 m2. The area of
scattering for 1000 g H-TBX was about 1470 m2. The last charge was too powerful and
disintegrated the boxes, smaller pieces of them flew higher distances.
Metal fragmentation effect of H-TBX was tested as 130 mm shell for M-46 howitzer was
filled with it and the obtained fragments studied. The weight of the shells was 33.4 kg and
they were fully loaded with 3.4 kg TNT and 4.0 kg H-TBX. Only fragments in the most
productive, medium size range (1-5 grams), are shown and analyzed, Fig. 8 and 9, Table 3.
Fig. 6. High speed comparison of SURT Tech. H-TBX with 95% RDX 5% wax. Test is done
on empty wooden boxes. Both charges are 0.7 kg. Snapshot is taken at 200 ms from initiation.
Fig. 7. Profile and picture of the wooden boxes scattering.
Table 2. Area of scattering for the wooden boxes by the tested charges.
Area of scattering, m2
1 kg H-TBX
0.7 kg H-TBX
0.7 kg RDX
Fig 8. Fragmentation of 130 mm shell for M-46 howitzer. Photos of 1-5 g fragments produced
by TNT and H-TBX.
Fig 9. Fragmentation of 130 mm shell for M-46 howitzer. Comparison of TNT and H-TBX in
the 1-5 g range. Numbers of the recovered fragments in the 1-5 g range are shown.
Table 3. Fragmentation of 130 mm shell for M-46 howitzer. Numbers of the recovered
fragments in the 1-5 g range are shown.
Very similar results for the fragmentation of the shells were obtained. In the range 1-5 g, the
total number of recovered fragments was 949 for TNT and 1115 for H-TBX. The total
number of recovered fragments for all ranges was 3382 for TNT and 2633 for H-TBX. Due to
the nature of the experiments, detonation in sand, we managed to recover only 84% of the
shell mass for TNT and 82% for H-TBX, so no farther statistical data was obtained.
Nevertheless, the H-TBX proved its multipurpose capabilities, both air blast and
fragmentation. This enables us to construct increasingly effective warheads with it, especially
penetration rounds for the missiles, artillery and tank guns, which will deliver solid state fuel-
air volume detonating explosive inside structures before initiation. Such rounds will also be
effective in the open field with their fragmentation capabilities.
Low and high temperature stability of H-TBX and A-TBX (outer layer material) was also
tested using 20 grams pieces of the explosives, Fig. 9 and Table 4. For H-TBX, tests were
conducted from -60oC to 100oC. No physical changes were observed and no measurable mass
change (<0.1 g/kg) was detected. Another experiment for one hour at 120oC was conducted
with H-TBX, again without changes. A-TBX was tested from -60oC to 220oC. Again no
physical change was observed and no measurable mass change (<0.1 g/kg) was detected.
A-TBX proved to be extremely insensitive to high temperature. In farther testing, it was
heated to 250oC for 30 minutes without measurable decomposition.
Both H-TBX and A-TBX have consistency of modeling clay (similar to HTPB propellants
and explosives) in unpolymerized state and Shore A hardness = 40 in hardened state. They
were easy to cast by hand (reaching about 95% TMD) and could also be vacuum cast in any
munitions. Theoretical maximum density (TMD) is 1.88 g/cm3 for H-TBX and 2.18 g/cm3 for
A-TBX (outer layer material). The production prices for both the homogenous mixture or
annular design are also low, about 20 USD/kg.
Fig 9. Testing the resistance of A-TBX to high temperature (1 hour at +150o C).
Table 4. Resistance of H-TBX and A-TBX to low and high temperature.
Table 5. Comparison of modern single event fuel-air explosives (thermobaric explosives).
~25 GPa b
a Only in enclosed space
b At the ends of the cylindrical charge
The properties of some modern single event fuel-air explosives (thermobaric explosives), that
have already found use in military ordnance are compared in Table 5. H-TBX and A-TBX,
unlike others, combine high air-blast impulses, metal fragmentation and metal acceleration
effects, high stability and low prices. Moreover, H-TBX and A-TBX can operate equally well
in enclosed spaces and open field and can be easily loaded in wide variety of ordnance from
40 mm underbarrel grenades to aviation bombs and cruise missiles.
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