182 Propellants, Explosives, Pyrotechnics 23, 182ą187 (1998)
Burning Behavior of Composite Propellant Containing Fine Porous
Ammonium Perchlorate
Makoto Kohga and Yutaka Hagihara
Department of Chemistry, The National Defense Academy, Hashirimizu 1ą10ą20, Yokosuka, Kanagawa, 239-8686 (Japan)
Abbrandverhalten von Komposit-Treibstoffen mit Gehalt an fein Mode de combustion de propergols composites contenant un per-
�
porosem Ammoniumperchlorat chlorate d'ammonium microporeux
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Fein poroses Ammoniumperchlorat (FPAP) wurde hergestellt durch Du perchlorate d'ammonium microporeux (FPAP) a ete synthetise
Spruhtrocknung. Das Abbrandverhalten eines Treibstoffs mit FPAP par sechage par pulverisation. Le mode de combustion d'un propergol
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wurde untersucht und verglichen mit einem Treibstoff mit feinem a base de FPAP a ete etudie et compare a un propergol contenant du
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nichtporosem Ammoniumperchlorat (PAP), bei welchem die mittlere perchlorate d'ammonium �n sans porosite (FAP), dont la granulo-
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Korngro�e fast dieselbe war wie bei FPAP. Die Ergebnisse sind wie metric moyenne etait a peu pres la meme que celle du FPAP. Les
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folgt: (1) Die Abbrandgeschwindigkeit des Treibstoffs mit FPAP resultats sont les suivants: (1) La vitesse de combustion du propergol a
nimmt zu bei zunehmendem FPAP-Gehalt. (2) Wenn die Treibstoffe base de FPAP augmente avec la teneur de FPAP. (2) Lorsque les
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mit FPAP oder PAP dieselbe Zusammensetzung haben, ist die propergols a base de FPAP ou de FAP possedent la meme composi-
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Abbrandgeschwindigkeit des Treibstoffs mit FPAP gro�er als dieje- tion, la vitesse de combustion du propergol a base de FPAP est
nige des Treibstoffs mit PAP bei unterschiedlichen Drucken. (3) Die superieure a celle du propergol a base de FAP pour des pressions
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Temperaturemp�ndlichkeit des Treibstoffs mit FPAP nimmt ab mit differentes. (3) La sensibilite a la temperature du propergol a base de
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zunehmendem Druck. (4) Es wurde gefunden, da� die Unterschiede im FAP est relativement constante sous des pressions differentes, mais a
Abbrandverhalten des Treibstoffs mit FPAP und des Treibstoffs mit base de FPAP elle diminue lorsque la pression augmente. (4) On a
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PAP ihre Ursache haben in der Porositat von FPAP. montre que les differences de modes de combustion du propergol a
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base de FPAP et du propergol a base de FAP eteient dues a la porosite
du FPAP.
Summary prepared by heating in temperature range of 500 Ką560 K
and decomposing a part of AP particles.
A �ne porous ammonium perchlorate (FPAP) was prepared by the
It is reported that �ne porous AP (FPAP) can be prepared
spray-drying method. The burning behavior of a propellant containing
by the spray-drying method(5), in which the droplets of an
FPAP was investigated and compared with that of a propellant con-
AP solution atomized by pneumatic atomizer are dried by
taining a �ne ammonium perchlorate without porosity (FAP), of which
the mean diameter was almost the same as that of FPAP. The results the air stream of high temperature. The mean diameter and
are as follows: (1) The burning rate of the propellant containing FPAP
the speci�c surface area of FPAP prepared by the spray-
increases with increasing FPAP content. (2) When the propellants
drying method are about 3.5 mm and 2.16103 m2=kg,
containing FPAP or FAP have the same composition, the burning rate
respectively. Since FPAP has the particle characteristics
of the propellant containing FPAP is larger than that of the propellant
containing FAP at various pressures. (3) The temperature sensitivity of which combines that of a �ne AP and that of a porous AP,
a propellant containing FAP is relatively constant at various pressures.
the burning behavior of the propellant containing FPAP is
However the temperature sensitivity of the propellant containing FPAP
particularly interesting.
decreases with increasing pressure. (4) It was found that the differ-
The purpose of the present study is to study the burning
ences in the burning behavior of the propellant containing FPAP and
the propellant containing FAP are caused by the porosity of FPAP.
behavior of composite propellants containing FPAP as
oxidizer. When the propellant is prepared with only FPAP,
the maximum FPAP content in the propellant is 73 wt%.
Therefore, the propellant containing 80 wt% AP is prepared
by mixing FPAP and a ground commercial AP (GrAP). The
1. Introduction
effect of FPAP content in the propellant on the burning rate
based on a bimodal oxdizer, which is different in the rela-
Ammonium perchlorate (AP) is the most widely used
tive amounts of FPAP and GrAP in the propellant con-
oxidizer in composite propellants. The burning rate of AP
taining 80 wt% AP, is examined. And the measurements of
composite propellants can be controlled by the physical
the combustion wave structures at different initial pro-
properties of the combustion wave structure such as dif-
pellant temperatures are done in order to determine the
ferent sizes of AP particles. For example, it is generally
mode of the temperature sensitivity of burning rate of the
known that the burning rate of propellants increases with
propellant containing FPAP.
decreasing the mean diameter of AP particles. And the
burning rate of propellants containing porous AP (PAP) has
been studied in some references(1ą3), where the positive
effect of PAP on the burning rate of propellants is proved. 2. Experimental
PAP used in the earlier papers(1,2,4) was prepared by the
thermal decomposition of large AP particles, of which the In this study, three kinds of AP are used as oxidizer:
mean diameter was larger than 177 mm. Because PAP was FPAP, �ne AP(FAP), and GrAP. As mentioned above,
# WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998 0721-3115/98/0408ą0182 $17.50�:50=0
Propellants, Explosives, Pyrotechnics 23, 182ą187 (1998) Burning Behavior of Composite Propellant 183
Table 1. Propellant Compositions Tested in this Study
Ingredients Propellant Composition (wt %)
A B C D E F G H
GrAP 80 72 56 40 32 32 0 0
FPAP 0 8 24 40 48 0 73 0
FAP 0 48 0 73
HTPB 20 27
FPAP is prepared by the spray-drying method and the mean
particle diameter is about 3.5 mm. The mean particle dia-
meter of FAP is about 3 mm, which is almost the same as
that of FPAP. GrAP is prepared by grinding a commercial
Figure 1. Burning rate of Propellants AąE measured at 288 K.
AP for 5 minutes in a vibration ball mill, and the mean
particle diameter of GrAP is about 105 mm. HTPB
(hydroxy-terminated polybutadiene) is used as a binder. The Table 2. Burning Behavior of Experimental Propellants
compositions of propellants tested in this study are shown in
Prop. Burning rate (mm=s) Pressure
Table 1. The propellant mixtures are then cured for 4 days
exponent
at 333 K. HTPB is cured with isophorone diisocyanate. 0.7 MPa 1 MPa 3 MPa 5 MPa 7 MPa ( )
The size of each strand is 10 mm610 mm in cross sec-
A 3.58 4.05 5.92 7.06 7.93 0.35
tion and 40 mm in length. The side of each strand is
B 3.96 4.21 6.27 7.55 8.52 0.36
inhibited by silicon resin. The burning rate is measured in a C 4.00 4.57 7.09 8.69 9.94 0.40
D 5.32 6.22 10.09 12.64 14.66 0.44
chimney-type strand burner which is pressurized with
E 5.70 6.74 11.34 14.44 16.93 0.47
nitrogen. The strand burner is set in a temperature condi-
F 4.81 5.61 9.03 11.26 13.03 0.44
tioner which is operated at a temperature of 288 1.5 K or
333 2 K. The temperature of the nitrogen is also condi-
tioned by a heat exchanger set in a temperature conditioner.
Propellant E is almost the same as that of Propellant F. The
The ignition of each strand is conducted by an electrically
difference in the composition between Propellant E and
heated nichrome wire attached on the top of each strand.
Propellant F depends on whether AP mixed in the pro-
The burning rate is measured in a pressure range of 0.7 MPa
pellants was FPAP or FAP. It indicates that the positive
to 7 MPa, and is calculated with the cutoff period of two
effect of FPAP on the burning rate is attributed to the
fuses which penetrate the strand at 25 mm distance.
porosity of FPAP, since the mean diameter of FPAP is
almost the same as that of FAP. In order to reveal the
combustion process of the propellant containing FPAP, the
following qualitative analysis was done. The Żame of AP
3. Results and Discussion
composite propellant is a so-called diffusion Żame, and the
model of Multiple Flames(6) is generally accepted as a
3.1 Burning Rate Characteristics
The burning rates of Propellants AąE measured at 288 K
are shown in Figure 1. Their burning rates increase linearly
in a plot of log r versus log P in the pressure range of
0.5 MPaą8 MPa. The measured burning rates and pressure
exponents are given in Table 2. In order to make more clear
the effect of FPAP content on the burning rate at various
pressures, the relationship between FPAP content and the
burning rate at various pressures is shown in Figure 2. It is
seen that the burning rate increases with increasing FPAP
content at various pressures, and especially the increments
of burning rate at high pressures are larger than those at low
pressures.
The burning rate of Propellant F measured at 288 K is
shown in Figure 3. The measured burning rates and pressure
exponent are also given in Table 2. It is seen that the
burning rate of Propellant E is larger than that of Propellant
Figure 2. The effect of FPAP content on the burning rate.
F in the pressure range tested, and the pressure exponent of
184 M. Kohga and Y. Hagihara Propellants, Explosives, Pyrotechnics 23, 182ą187 (1998)
a lower pressure the AP particles protruded above the
exposed surface of the binder to a greater height and at a
higher pressure they recessed. In other words, at a low
pressure the regression rate of the AP particles is less than
that of the binder and vice versa at higher pressures(7,8). As
mentioned above, the AP monopropellant Żame is formed
on AP particles exposed to the burning surface. It seems that
when the regression rate of the AP particles is larger than
that of the binder, the location of each Żame is brought
closer to the burning surface. This indicates that (dT=dx)s�
increases with increasing difference between the regression
rate of the AP particle and that of the binder. Consequently
the location of each Żame is dependent on the diffusion
distance to react with the oxidizer and binder decomposition
products and the difference between the regression rate of
the AP particle and that of the binder.
As given in Table 2, the burning rate of Propellant E is
Figure 3. Burning rates of Propellants E and F.
larger than that of Propellant F. The reason is considered as
follows. The decomposition area of FPAP particles is wider
model of the Żame structure. According to the model of
than that of FAP particle, because FPAP particles are por-
Multiple Flames, the Żame structure of AP composite pro-
ous. At a constant pressure, namely when the diffusion
pellant consists of the AP monopropellant Żame, the pri-
distance to react with the oxidizer and binder decomposition
mary Żame, and the �nal diffusion Żame. The AP
products is constant, the regression rate of FPAP particles is
monopropellant Żame, which is composed of AP decom-
larger than that of FAP particles. And it suggests that the
position products, is not considered to occur at the pro-
location of each Żame of Propellant E is brought closer to
pellant surface, but to extend from the surface. The primary
the burning surface, and (dT=dx)s� of Propellant E is larger
Żame is a premixed Żame with the oxdizer and binder
than that of Propellant F. In order to con�rm this, the
decomposition products mixing completely before reaction
burning surface of Propellants G and H extinguished was
occurs. And the �nal diffusion Żame follows the primary
observed under a scanning electron microscope (SEM). The
Żame. On the other hand, the burning rate is given by the
SEM photographs of the burning surface of both propellants
heat balance equation at the burning surface as follows:
extinguished at atmospheric pressure are shown in Figure 4.
lgdT=dxąs�
In Figure 4, holes exist at the burning surface of Propellant
r � 1ą
G, and AP remains in the hole on the burning surface of
cprpTs To Qs=cpą
Propellant H. It is found that the regression rate of FPAP
where r is burning rate, l is thermal conductivity, (dT=dx) is particles is larger than that of FAP particles, even at a low
temperature gradient in the vicinity of the burning surface, c pressure. As mentioned above, at a lower pressure the AP
is speci�c heat, r is density, Ts is temperature at the burning particles protruded above the exposed surface of the binder
surface, To is initial temperature of propellant, and Qs is to greater height and at a higher pressure they recessed.
heat per unit mass generated at the burning surface. Sub- Therefore, the burning surface of Propellant G extinguished
scripts g, p, and s � mean gas phase, propellant, and gas at atmospheric pressure was similar to the burning surface
phase at the burning surface, respectively. When the com- of the propellant extinguished at a high pressure. The result
positions of propellant are constant, it can be assumed that supports the above consideration.
lg, cp, rp, and Ts of the propellants are almost the same
values, respectively, at the same pressure. When To is
constant, Eq. (1) indicates that the burning rate increases
with increasing (dT=dx)s�. Consequently (dT=dx)s� is a
dominant factor on the burning rate. It can be considered
that (dT=dx)s� is dependent on the location of each Żame;
and when the location of each Żame is brought close to the
burning surface, (dT=dx)s� increases. In general, the burn-
ing rate increases with increasing pressure. This can be
explained as follows. The diffusion distance to react with
the oxidizer and binder decomposition products decreases
with increasing pressure, and the location of each Żame is
brought closer to the burning surface. This implies that
(dT=dx)s� increases with increasing pressure. On the other
hand, when the burning surface of a propellant extinguished
Figure 4. SEM micrographs of the burning surface of Propellants G
and H extinguished.
by rapid depressurization was observed, it was found that at