Thermal behavior of ammonium perchlorate and metal powders of different grades

Article abstract of DOI:10.1007/s10973-005-7035-7

The effects of aluminum (Al) and nickel (Ni) powders of various grain sizes on the thermal decomposition of ammonium perchlorate (AP) were investigated by TG and DSC in a dynamic nitrogen atmosphere. The TG results show that Al powders have no effect on the thermal decomposition of AP at conventional grain size, while the nanometer-sized Ni powders (n-Ni) have a great influence on the thermal decomposition of AP with conventional and superfine grain size. The results obtained by DSC and an in situ FTIR analysis of the solid residues confirmed the promoting effects of n-Ni. The effects of n-Ni have been ascribed to its enhancement on the gas phase reactions during the second step decomposition of conventional grain size AP.

Full text of DOI:10.1007/s10973-005-7035-7

Journal of Thermal Analysis and Calorimetry, Vol. 85 (2006) 2, 315–320
THERMAL BEHAVIOR OF AMMONIUM PERCHLORATE AND METAL
POWDERS OF DIFFERENT GRADES
1
1
1*
2
2
2
J. Zhi , W. Tian-Fang , L. Shu-Fen , Z. Feng-Qi , L. Zi-Ru , Y. Cui-Mei , L. Yang ,
2
2
L. Shang-Wen and Z. Gang-Zhui
3
1
Department of Chemistry Physics, University of Science and Technology of China, Hefei 230026, P.R. China
Xian Modern Chemistry Research Institute, Xian 710065, P.R. China
Shanxi Institute of Power Machinery, Xian 710025, P.R. China
2
3
The effects of aluminum (Al) and nickel (Ni) powders of various grain sizes on the thermal decomposition of ammonium perchlor-
ate (AP) were investigated by TG and DSC in a dynamic nitrogen atmosphere. The TG results show that Al powders have no effect
on the thermal decomposition of AP at conventional grain size, while the nanometer-sized Ni powders (n-Ni) have a great influence
on the thermal decomposition of AP with conventional and superfine grain size. The results obtained by DSC and an in situ FTIR
analysis of the solid residues confirmed the promoting effects of n-Ni. The effects of n-Ni have been ascribed to its enhancement on
the gas phase reactions during the second step decomposition of conventional grain size AP.
Keywords: aluminum, ammonium perchlorate, FTIR, nano metal powder, nickel
Introduction
most of the researches carried out on investigating the
thermal behavior of AP were only based on TG and
DTA [7–14]. Such studies may lead to a rather specula-
tive mechanism with no further supporting evidence.
Further studies should be carried out based on the ther-
mal analysis together with some other techniques. FTIR
techniques have been widely used today to characterize
materials [21, 22]. In particular, in situ FTIR analysis,
which can follow sample residue’s FTIR properties over
a long period of time at a specified temperature, is a
technique which provides data for a comprehensive un-
derstanding decomposition processes.
In the present work, the effects of Al and Ni pow-
ders of different grain sizes on the thermal decomposi-
tion characteristics of g-AP have been studied by TG.
As the TG results show that n-Ni have a great influence
on the thermal decomposition of g-AP. The studies are
specifically extended to investigate the decomposition
of g-AP and the g-AP and n-Ni mixture by DSC and
in-situ FTIR. The thermal decomposition of s-AP and
the s-AP/n-Ni and s-AP/s-Ni mixture have also been
studied by TG. Such studies may offer useful clues for
the application of nano metal powders in propellants in
order to obtain a better control of their combustion.
Great interest has been generated by the development of
nano materials. Nano materials are represented by parti-
cles with average grain diameters in the range of 1 to
100 nm [1–2]. One interesting characteristic of nano
powders is that the number of atoms at the surface of the
particle is comparable with the number of atoms in the
bulk of the particle. Nano materials also contain lattices
with high concentrations of dislocations and large sur-
face areas. Thus, nano materials exhibit high chemical
reactivity, which allows a number of nanometer-sized
metals to undergo reactions that were previously consid-
ered impossible. New types of propellant containing
nano metal powder have been developed [3–6].
AP is one of the main oxidizing agents used in var-
ious propellants. The burning behavior of propellants is
sensitive to the thermal decomposition of oxidizing
agents like AP. Understanding of the complex
physicochemical processes that underlying the thermal
decomposition of such materials can provide a link be-
tween the thermal decomposition and the burning pro-
cess of the propellant. Many investigators have studied
the thermal decomposition of AP as a neat compound or
as mixtures in the presence of certain inorganic materi-
als, such as metals, metal oxides and other salts [7–20].
However, the AP investigated were only of coarse grain
size (g-AP) [7–14, 16–18, 20]. Little research has been
extended on AP of fine grain size. Because AP of differ-
ent grain size will have different thermal behavior, stud-
ies extended on superfine AP (s-AP) or nanometer-sized
AP will lead to interesting results [19]. Furthermore,
Experimental
Samples
The powdered sample of AP (technical pure) was sieved
to two grain diameters (g-AP, 80 mm; s-AP 1.1 mm).
*
Author for correspondence: lsf@ustc.edu.cn
1
388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©
2006 Akadémiai Kiadó, Budapest

ZHI et al.
Mixtures of metal powders and g-AP were prepared by
corded with a Nicolet MAGNA-IR 750 spectrometer
using KBr pellets in the temperature range of 20–420°C
with an interval of 10°C and a heating rate of 2°C min
in air atmospheres. The FTIR analysis was performed
on the solid residue of the sample during the thermal de-
composition.
carefully mixing of the two components in a polished
porcelain container with acetone as the dispersant. The
g-AP and metal powders mixtures with mass ratio of
–1
4:1, 8:1 and 16:1 are prepared. Mixtures of metal pow-
ders and s-AP were prepared by mechanical mixing
only in the absence of the dispersant. The s-AP and
n-Ni mixtures with mass ratio of 4:1 are prepared. The
metal powders used in this study were: g-Al (10 mm,
supplied by Xian Modern Chemistry Research Inst.),
nano aluminum (n-Al, 83 nm, produced by the elec-
tro-explosion process, oxygen content <1.8mass%,
supplied by Sheng Tai nano Ltd.), superfine nickel
powders (s-Ni, 3 mm, supplied by Xian Modern Chem-
istry Research Inst.) and n-Ni (16 nm, prepared by
g-ray radiation synthesis method in our laboratory).
The procedures of the preparation of n-Ni are de-
scribed in the next section. The grain size of the sam-
ples is specified by the manufacturer.
Results and discussion
TG and DSC for the mixtures of AP and metal powders
The TG/DTG data for g-AP and the mixtures of g-AP
and metal powders (with mass ratio of 4:1) are sum-
marized in Table 1. The TG/DTG curves for g-AP in
nitrogen show two mass loss steps (Fig. 1). The first
step is accompanied by about 25% mass loss in the
temperature range of 280 to 329°C (i.e., the low-tem-
perature decomposition step). The second step is ac-
companied by about 72% mass loss in the temperature
range of 329 to 370°C (i.e., the high-temperature de-
composition step). Addition of Al powders (n-Al and
g-Al) only slightly lowers the peak temperature of the
high-temperature decomposition of g-AP and has al-
most no effect on the low-temperature decomposition
of g-AP (Table 1). While for the mixture of g-AP and
n-Ni, the second step of the decomposition of g-AP
was notably enhanced by the addition of n-Ni pow-
The solutions for g-ray radiation were prepared
by dissolving analytically neat NiSO
tilled water. NH ·H O was added as a complexing
·6H O in dis-
4 2
3
2
2
agent for Ni ions and NH H O/NH buffer pair to
+
+
3
2
4
adjust the pH of the solution. Sodium dodecyl sul-
phate was used as a surfactant, and isopropanol was
used as a scavenger for hydroxyl radicals in our ex-
periments. The solutions were de-aerated by bubbling
with neat nitrogen, and then irradiated in the field of a
1
5
60
2
.59·10 Bq Co g-ray source. After irradiation, the
Table 1 TG/DTG data for AP and mixture of AP/metal
powders
metal particles were separated from solutions, washed
with distilled water several times, and then dried to
powders in vacuum. All reagents used in the radiation
experiment above were analytically pure grade. The
Ni powders were then collected in hexane (commer-
cial quality) to prevent the oxidation of n-Ni powders
in air [23]. The grain size of n-Ni was determined us-
p
T /°C
Sample
LTD
HTD
g-AP
307
312
309
308
311
353
327
330
348
350
g-AP/n-Ni
g-AP/s-Ni
g-AP/n-Al
g-AP/g-Al
ing a D/Max-rA X-ray diffractometer (CuK radia-
a
tion), Rigaku. The calculated results show that the av-
erage grain size of the n-Ni is 16 nm.
Instrumental
The thermal decomposition analysis was performed by
using a differential scanning calorimeter, (TA Instru-
ments, DSC Model 910), and a thermogravimetric ana-
lyzer (TA Instruments, TA Model 2950). A constant
sample mass of 2.0±0.1 mg was used in all experiments.
TG and DSC were performed in a dynamic atmosphere
–1
of nitrogen with flow rates of 100 and 40 mL min , re-
spectively. The TG and DSC experiments were per-
formed using open platinum sample pans and sealed Al
sample pans, respectively. In this paper, the enthalpy
values for the g-AP and n-Ni mixture are based on per
gram of g-AP, but not the mixture. The in-situ FTIR
spectra of g-AP and the g-AP/n-Ni mixture were re-
Fig. 1 TG/DTG curves for g-AP, g-AP/s-Ni(4:1) and
g-AP/n-Ni (4:1) in nitrogen (0.1 MPa; 10°C min )
–1
316
J. Therm. Anal. Cal., 85, 2006

THERMAL BEHAVIOR OF AMMONIUM PERCHLORATE AND METAL POWDERS OF DIFFERENT GRADES
ders, since the g-AP/n-Ni mixture displayed a large
DTG peak at 327°C and was completed at 336°C
lead to the third exothermic peak for neat AP ob-
served from 370°C to above 450°C. With the addition
of n-Ni, the weak endotherm of g-AP phase transition
remains around 244°C, the first and third exothermic
peak is absent. And the thermal decomposition of the
g-AP/n-Ni mixture shows only one overlapping
exotherm peaked at 322°C and ended at 350°C. The
third exothermic peak for neat g-AP above 370°C is
not observed for the g-AP/n-Ni mixture. The over-
lapped exotherm is consistent with the TG/DTG data
illustrated in Fig. 1.
The TG/DTG curves for the mixtures of g-AP
and n-Ni with mass ratios of 4:1, 8:1 and 16:1 are
shown in Fig. 3. The TG/DTG data are summarized in
Table 3. The DTG peak temperature for the mixtures
increases gradually with a decrease of n-Ni content.
When the mass ratio of g-AP to n-Ni is changed from
(
Fig. 1). The advance of the second step causes more
overlapping between the two steps of decomposition
of g-AP into nearly one step. Compared to s-Ni, the
presence of n-Ni shifted the end temperature and the
DTG peak for the second step of g-AP decomposition
to a lower temperature. The results suggest that n-Ni
is more effective than s-Ni on promoting the decom-
position of g-AP.
The DSC curve for g-AP is shown in Fig. 2. The
DSC data for g-AP and the g-AP and metal powders
mixture (with mass ratio of 4:1) are summarized in
Table 2.
4
:1 to 16:1, the first-step peak temperature of g-AP
changes from 312 to 308°C. In the second step, the
peak temperature decreases 18.0 from 353°C for neat
g-AP to 335°C for the g-AP/n-Ni (16:1) mixture. It is
interesting that the peak temperature in the low-tem-
perature decomposition step of g-AP is higher when
metals are added (Figs 1 and 2). With the decrease of
the content of n-Ni, the peak temperatures for the
low-temperature decomposition step of g-AP will de-
crease simultaneously (Fig. 3). The previous DSC
studies (Table 2) also showed that the total heat re-
leased during the decomposition step of neat g-AP is
–
1
Fig. 2 DSC curve for g-AP in nitrogen (0.1 MPa; 10°C min )
–
1
The weak endothermic with peak temperature
44°C on the DSC curves for g-AP is due to the crys-
tal transformation of AP from orthorhombic to cubic.
Two main exothermic peaks remain around 318 and
lower from 2177 to 1330 J g when n-Ni powders are
added. The decrease in the heat released together with
increasing peak temperature for the low-temperature
2
3
47°C, respectively. They correspond to the two mass
loss steps on the TG/DTG curves for g-AP (Fig. 1).
As shown in Fig. 1, the decomposition of g-AP is
clearly a two-step process. However, three exother-
mic peaks are observed in the DSC (Fig. 2). The third
exothermic peak for neat AP is observed from 370°C
to above 450°C (Fig. 2). As the TG/DTG curves for
g-AP (Fig. 1) has shown that 2.6% residues will re-
main when the whole decomposition has completed at
3
70°C. An inconspicuous mass loss process will exist
above 370°C. And because the TG experiments were
performed using open pans, while the DSC with
closed containers. Secondary reactions take place be-
tween the gases trapped in the closed pan will notably
enhance the reactions above 370°C. All these will
Fig. 3 TG/DTG curves for g-AP with various n-Ni contents in
–1
nitrogen (0.1 MPa; 10°C min )
Table 2 DSC data of g-AP and mixture of g-AP/n-Ni metal powders
LTD
HTD
Third stage
Sample
s
T /°C
–1
–1
–1
T
p
/°C
DH/J g
T
p
/°C
T
e
/°C
DH/J g
T
p
/°C
DH/J g
g-AP
245
244
318
180
347
322
370
450
1619
1330
426
378
g-AP/n-Ni
J. Therm. Anal. Cal., 85, 2006
317

ZHI et al.
decomposition step of g-AP when 20 mass% of n-Ni
is added may be due that the metal is inert in the first
step and acts as a heat sink.
The decomposition of g-AP is clearly a two-step
process. For s-AP, there is only one DTG peak at
The addition of n-Ni lowers the peak tempera-
ture of s-AP by 40°C, which is similar to the promot-
ing effects of n-Ni on the high temperature decompo-
sition step of g-AP. The addition of s-Ni to s-AP also
lowers the DTG peak temperature of s-AP by 32°C.
Thus, compared to s-Ni, n-Ni is more effective in pro-
moting the decomposition of s-AP.
3
57°C corresponding to the high-temperature step de-
composition as shown in Fig. 4. The TG/DTG data
for s-AP and the s-AP and n-Ni mixture (with mass
ratio of 4:1) are summarized in Table 3.
In-situ FTIR analysis for g-AP and the mixtures of
g-AP and n-Ni
The FTIR results presented in this paper are some ex-
amples of our first effort to study the thermal decom-
position of AP. In-situ FTIR was used to compare the
solid residues obtained from the thermal decomposi-
tion of neat g-AP and the g-AP/n-Ni mixture.
The FTIR spectra at 20°C for g-AP and the
g-AP/n-Ni mixture are shown in Fig. 5. The peaks at
–1
–1
300–3000 and 1409 cm (1571–1245 cm ) can be as-
3
signed to the stretching and bending vibrations of the
+
N–H bond in the NH ion, and the peaks at around
4
–1
–
088 and 627 cm can be assigned to the ClO anion
1
4
Fig. 4 TG/DTG curves for s-AP, s-AP/n-Ni (4:1) and
s-AP/s-Ni (4:1) in nitrogen (0.1 MPa; 10°C min )
–1
Table 3 TG/DTG data for g-AP and mixture of g-AP and
n-Ni with different content
p
T /°C
Sample
LTD
HTD
g-AP/n-Ni (4:1)
g-AP/n-Ni (8:1)
g-AP/n-Ni (16:1)
312
311
308
327
330
335
Fig. 5 FTIR spectra for g-AP and g-AP/n-Ni at 20°C in air
It is considered that the thermal decomposition
of solid AP occurs at some partial surface sites of its
crystal. For large crystal grain size (i.e. g-AP), the re-
action site (nucleus formation) forms easily on the
crystal surface and the reaction rate increases [13].
That makes the large crystal cracks and forms smaller
[
24].
The FTIR spectra for g-AP at the low-temperature
range (200, 280 and 310°C) and high-temperature
range (360 and 400°C) are compared to that for 20°C
in Fig. 6. The intensities of the peaks at 3300–3000 and
crystals. If NH (gas) released during the decomposi-
3
–1
1
409 cm (N–H) decrease as the temperature in-
tion of AP overspread the whole active center, the de-
composition of AP begins the slow process. When
temperature rise continuously, the potential reaction
centers will be activated again by the desorption of
creases. The spectra obtained for 400°C show that the
intensities are about 10 and 5% of those for 20°C. And
they remained as weak peaks when the temperature
was raised to 400°C. The intensity of the peaks at
NH . For s-AP, the internal stress formed by decom-
3
–1
around 1088 and 627 cm decreased slowly between
200 and 400°C. When the temperature reached 400°C,
the peak area around 1088 and 627 cm has decreased
position products is not intensive enough to crack the
AP crystal into smaller grains. So, there is none exist
of distinctly low temperature decomposition step be-
–1
nearly to half of that value at 20°C.
The relatively slower disappearance of ClO in
cause NH formed in the initial steps overspread the
3
–
4
crystal surface of s-AP. Thus the thermal decomposi-
tion of s-AP provided an opportunity to evaluate the
high-temperature step decomposition of g-AP.
the lattice may be due to the electron-transfer during
the thermal decomposition of AP. Electron-transfer in
the AP crystal will lead to the conversion of NH ClO
4
4
318
J. Therm. Anal. Cal., 85, 2006

THERMAL BEHAVIOR OF AMMONIUM PERCHLORATE AND METAL POWDERS OF DIFFERENT GRADES
into NH +ClO , followed by the dissociation of NH
4
quickly between 200 and 400°C as compared with the
slower process relating to the decomposition of neat
g-AP shown in Fig. 6. When the temperature reached
400°C, the peaks for g-AP/n-Ni at around 1088 and
4
4
4
to NH +H, and the transfer of charge between ClO
3
–
and ClO within the lattice until a free ClO reaches
4
4
the surface of the particle [8, 12–14]. At the surface of
the particle, it undergoes decomposition to gaseous
–1
627 cm showed a weak peak.
–
products. This means that the disappearance of ClO4
All these confirm the promoting effects of n-Ni
on the second step decomposition of g-AP. It is
known that the decomposition of neat AP is con-
trolled by two processes. One occurs at lower temper-
ature (240 to 270°C) and produces mainly H O, O ,
+
will lag behind the disappearance of NH in the crys-
4
tal lattice, which corresponds with the FTIR results
shown in Fig. 6.
The FTIR spectra for g-AP/n-Ni at the tempera-
tures 20, 200, 280 and 310°C shown in Fig. 7 are sim-
ilar to that of g-AP shown in Fig. 6. That is, in the
temperature range of 200–310°C, the n-Ni powders
have no promoting effect in the low temperature de-
composition step of g-AP. These provide direct evi-
dence to support the conclusion drawn from the ther-
mal analysis experiment, i.e., the metal is inert in the
first step and acts as a heat sink.
2
2
Cl , N O, NH and HCl, and is shown to occur in the
3
2
2
solid phase within the AP crystal. The second process
is dissociative sublimation of AP to NH +HClO fol-
3
4
lowed by reactions between these two products in the
gas phase [7, 15]. Thus the promoting effects of n-Ni
on the second step may be ascribed to promote the gas
phase reactions during the decomposition of g-AP.
As previous studies have revealed, in the pres-
ence of the transition metal or transition metal oxides,
The difference for g-AP/n-Ni and g-AP lies in the
FTIR spectra under heating conditions 360 and 400°C,
as shown in Fig. 7. The addition of n-Ni to g-AP leads
to a rapid decrease of the intensity of peaks related to
the gaseous oxygen-rich products, such as HClO (g),
4
may migrate to the surface of the transition metal or
transition metal oxides by surface diffusion and de-
compose heterogeneously [12, 16]. n-Ni will be able
to greatly promote the redox reactions between the
–1
the vibration of N–H at 3300–3000 and 1409 cm .
They had nearly completely disappeared when the
temperature reached 400°C. While the intensities of
given gaseous products, especially those released
–
from ClO , which are oxidative rich. The quick de-
–1
the peaks at around 1088 and 627 cm decreased
4
–
crease of the intensity of the peak related to ClO in
4
g-AP with the existence of n-Ni (Fig. 7) has provide
evidence to support such inference. During the step of
high temperature decomposition of AP, the gas-phase
reactions will then be influenced. It will lead to a
change in the distribution of the gaseous products.
The decomposition of g-AP is then promoted.
Conclusions
The effects of aluminum and nickel powders of vari-
ous grain sizes on the thermal decomposition of AP
were investigated by TG and DSC in a dynamic nitro-
gen atmosphere. The thermal decomposition of g-AP
showed two separate mass-loss steps. The TG results
show that aluminum powders have no effect on the
thermal decomposition of AP, while the n-Ni powders
have a great influence on the thermal decomposition
of g-AP and s-AP. The results show that n-Ni mainly
promote the second step decomposition of g-AP,
while it is inert in the first step and acts as a heat sink.
The results of the in-situ FTIR for the decomposition
residue of g-AP confirmed the promoting effects of
n-Ni. The dominant effects of n-Ni may be ascribed to
promotion of the gas phase reactions during the sec-
ond step of the decomposition of g-AP. That is to pro-
mote the redox reaction rate between the gaseous
products during the thermal decomposition of AP.
The FTIR results also suggest that the disappearance
Fig. 6 FTIR spectra for g-AP in air
Fig. 7 FTIR spectra for g-AP/n-Ni in air
J. Therm. Anal. Cal., 85, 2006
319

ZHI et al.
–
of ClO will lag behind the disappearance of NH in
+
4 Z. Jiang, S. F Li and F. Q. Zhao, J. Energ. Mater.,
0 (2002) 165.
4
4
2
D. A. Yagodnikov and A. V. Voronetskii,
the crystal lattice during the heating conditions,
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speculative electron-transfer mechanism.
5
6
7
Combust. Expl. Shock, 33 (1997) 49.
M. M. Mench, K. K. Kuo, C. L.Yeh and Y. C. Lu,
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Acknowledgements
8
9
We greatly appreciate the financial support provided by the Na-
tional Natural Science Foundation of China (No. 50476025).
2
75 (1996) 83.
0 S. A. Halawy and S. S. Al-Shihry, J. Therm. Anal. Cal.,
5 (1999) 833.
1
5
Nomenclature
11 S. A. Halawy and M.A. Mohamed,
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12 L. L. Liu, F. S. Li, L. H. Tan, Propellants, Explos.,
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Al
aluminum
AP
ammonium perchlorate
1
1
3 P. W. M. Jacobs, Combus. Flame, 13 (1969) 419.
4 T. Ganga Devi, M. P. Kannan and B. Hema,
Thermochim. Acta, 285 (1996) 269.
DSC differential scanning calorimeter
DTA differential thermal analysis
DTG derivative thermogravimetry
1
1
1
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6 R. Behrens and L.Minier, Sand-97-8422C.
7 K. Kishore and M. R. Sunitha, AIAA Journal,
FTIR Fourier transform infrared spectroscopy
g-Al micron-sized Al powder (10 µm)
g-AP conventional AP powder (80 µm)
HTD step of high temperature decomposition
LTD step of low temperature decomposition
n-Al nanometer-sized Al powder (83 nm)
1
7 (1979) 1118.
8 M. Rajic and M. Suceska, J. Therm. Anal. Cal.,
3 (2001) 375.
1
6
st
19 A. Pivkina, Yu. Frolov, S. Zavyalov, 31 International Py-
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Ni
nickel
n-Ni nanometer-sized Ni powder (16 nm)
s-AP superfine AP (1.1 mm)
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s-Ni superfine nickel powders (3 mm)
2
1 M. F. Silva, C. A. da Silva and F. C. Fogo,
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TG
thermogravimetry
T
T
p
s
peak temperature of DTG and DSC
crystal transformation temperature of AP from
orthorhombic to cubic
22 F. Barontini, K. Marsanich and V. Cozzani,
J. Therm. Anal. Cal., 78 (2004) 599.
2
2
3 Y. Champion and J. Bigot, Nanostr. Mat., 10 (1998) 1097.
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e
end temperature of decomposition
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