Thermal behavior of aluminum powder and potassium perchlorate mixtures by DTA and TG

Article abstract of DOI:10.1016/j.tca.2005.11.045

In this work the thermal decomposition characteristics of micron sized aluminum powder + potassium perchlorate pyrotechnic systems were studied with thermal analytical techniques. The results show that the reactivity of aluminum powder in air increases as the particle size decreases. Pure aluminum with 5 μm particle size has a fusion temperature about 647°C, but this temperature for 18 μm powder is 660°C. Pure potassium perchlorate has an endothermic peak at 300°C corresponding to a rhombic-cubic transition, a fusion temperature around 590°C and decomposes at 592°C. DTA curves for Al₅/KClO₄ (30:70) mixture show a maximum peak temperature for thermal decomposition at 400°C. Increasing the particle size of aluminum powder increases the ignition temperature of the mixture. The oxidation temperature increased by enhance in the aluminum content of the mixture.

Full text of DOI:10.1016/j.tca.2005.11.045

Thermochimica Acta 443 (2006) 129–131
Short communication
Thermal behavior of aluminum powder and potassium
perchlorate mixtures by DTA and TG
∗
S.M. Pourmortazavi , M. Fathollahi,
S.S. Hajimirsadeghi, S.G. Hosseini
Faculty of Material and Manufacturing Technologies, Malek Ashtar University of Technology,
P.O. Box 16765-3454, Tehran, Iran
Received 24 November 2005; accepted 25 November 2005
Available online 19 January 2006
Abstract
In this work the thermal decomposition characteristics of micron sized aluminum powder + potassium perchlorate pyrotechnic systems were
studied with thermal analytical techniques. The results show that the reactivity of aluminum powder in air increases as the particle size decreases.
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Pure aluminum with 5 ␮m particle size has a fusion temperature about 647 C, but this temperature for 18 ␮m powder is 660 C. Pure potassium
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perchlorate has an endothermic peak at 300 C corresponding to a rhombic–cubic transition, a fusion temperature around 590 C and decomposes at
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5
92 C. DTA curves for Al /KClO (30:70) mixture show a maximum peak temperature for thermal decomposition at 400 C. Increasing the particle
5 4
size of aluminum powder increases the ignition temperature of the mixture. The oxidation temperature increased by enhance in the aluminum
content of the mixture.
©
2005 Elsevier B.V. All rights reserved.
Keywords: Potassium perchlorate; Aluminum powder; Thermal behaviour; Ignition temperature; Particle size effect; Pyrotechnic
1
. Introduction
2. Experimental
Potassium chlorate and potassium perchlorate are the main
2.1. Materials
oxidizer in many compositions of propellants and pyrotechnics
1–5].
This paper presents the results of a study on potas-
[
Potassium perchlorate (mesh 300) was purchased from
Merck (Tehran, Iran). Highly pure aluminum powders (5
and 18 ␮m particles size) were prepared by metals labo-
ratory of Malek Ashtar University of Technology (Tehran,
Iran).
sium perchlorate/aluminum powder mixtures by simultane-
ous thermogravimetry–differential thermal analysis (TG/DTA).
The aim of this study was investigation of the effect of alu-
minum content and particle size on the thermal behavior of
different compositions of aluminum + potassium perchlorate
mixtures. Thermal behaviour of pure micro-sized aluminum
and its composition with explosives has been reported previ-
ously [6,7], but to the best our knowledge nothing has been
published on the thermal behaviour of aluminum + potassium
perchlorate.
2.2. Procedure
A thermobalance (Stanton, model TR-01, sensitivity 0.1 mg)
with a differential thermal analysis attachment (STA 1500)
was used for DTA/TG studies. In this study, the heat-
◦
ing rate was 10 C/min in air at 1 bar and the sample
mass was 4.0 mg. Four mixtures (30/70 and 50/50 mass
%
Al/KClO4) as well as pure potassium perchlorate and two
samples of pure aluminum powders with different particle
sizes (5 and 18 ␮m) were examined. Before testing, all sam-
ples were stored in a vacuum oven at 65 C for at least
◦
∗
Corresponding author. Tel.: +98 21 22952285; fax: +98 21 22936578.
E-mail address: pourmortazavi@yahoo.com (S.M. Pourmortazavi).
3 h.
0
040-6031/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2005.11.045

1
30
S.M. Pourmortazavi et al. / Thermochimica Acta 443 (2006) 129–131
3
3
3
. Results
.1. Thermal behaviour of the individual components
.1.1. Aluminum powders
Aluminum powders (with 5 and 18 ␮m particle size) were
examined in air to assess oxidation characteristics (Fig. 1). The
powders exhibit an exothermic peak below the melting point of
◦
Al (∼660 C). The first mass gain for the 18 ␮m sized Al was
◦
observed at 490–610 C, and for aluminum with 5 ␮m particle
size at 484–603 C. The 5 ␮m particle size aluminum has a lower
melting point (647 C) than 18 ␮m aluminum (660 C).
◦
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Fig. 2. TG and DTA curves for potassium perchlorate (sample mass, 4.0 mg;
heating rate, 10 C/min; air atmosphere and potassium perchlorate with 50 ␮m
particle size).
3
.1.2. Potassium perchlorate
DTA and TG curves of pure potassium perchlorate are shown
◦
◦
in Fig. 2. An endothermic peak at 300 C corresponds to a
rhombic–cubic transition. The melting point is at 590 C with
decomposition [8,9], oxygen and potassium chloride (KCl) are
produced [10–12].
◦
◦
an endothermic peak at about 587 C, which corresponded with
the temperature of fusion of potassium perchlorate. A sharp
◦
exotherm occurs near 600 C with a mild reduction (about 4.9%)
in the mass of sample that corresponds to the reaction of alu-
minum powder with potassium perchlorate according to:
3
3
.2. Binary mixtures
.2.1. Aluminum (5 µm particle size)/potassium
8Al + 3KClO4 → 4Al2O3 + 3KCl
perchlorate mixture
The TG and DTA curves for Al /KClO4 mixture (30:70)
are shown in Fig. 3a. An endothermic peak at 300 C corre-
sponds to the rhombic–cubic transition. The DTA curve shows
Fig. 3b show the TG–DTA results for Al5/KClO4 with mass ratio
5
◦
◦
of 50:50. After the endothermic peak at 300 C corresponding
◦
to the rhombic–cubic transition, an endotherm occurs at 596 C
Fig. 3. TG and DTA curves for mixture of aluminum powder with 5 ␮m particle
Fig. 1. TG and DTA curves for pure aluminum powder: (a) 5 ␮m particle size
and (b) 18 ␮m particle size (sample mass, 4.0 mg; heating rate, 10 C/min; air
size and potassium perchlorate with mass ratio (a) 30:70 and (b) 50:50 (sample
mass, 4.0 mg; heating rate, 10 C/min; air atmosphere and potassium perchlorate
◦
◦
atmosphere).
with 50 ␮m particle size).

S.M. Pourmortazavi et al. / Thermochimica Acta 443 (2006) 129–131
131
3.2.2. Aluminum (18 µm particle size)/potassium
perchlorate mixture
TG–DTA data for Al18/KClO4 mixtures are presented in
Fig. 4. As can be seen in Fig. 4a, there are three thermal transi-
tions, two are endothermic and another is exothermic. The first
◦
endotherm at 300 C is the rhombic–cubic transition of KClO4.
◦
Anotherendothermat605 Ccorrespondstofusionofpotassium
perchlorate. The exothermic peak at 608 C, where the mass
◦
decreases is related to the reaction between aluminum powder
and potassium perchlorate. Fig. 4b shows TG and DTA curves
for Al18/KClO4 (50:50) mixture. These results show the igni-
tion temperature of the mixtures also increased when a higher
content of aluminum powder was used.
References
[
1] M. Fathollahi, S.M. Pourmotazavi, S.G. Hosseini, Combust. Flame 138
2004) 304–306.
(
[
[
[
2] D.M. Griffiths, J.A. Oliver, Combust. Flame 24 (1975) 21–25.
3] F.S. Scanes, Combust. Flame 23 (1974) 363–371.
4] S.G. Hosseini, S.M. Pourmortazavi, S.S. Hajimirsadeghi, Combust.
Flame 141 (2005) 322–326.
[
[
[
5] S.G. Singh, P. Felix, D.K. Pandey, Thermochim. Acta 411 (2004) 61–
71.
6] D.E. Jones, P. Brousseau, R.C. Fouchard, A.M. Turcotte, Q.S.M. Kwok,
J. Therm. Anal. Calorim. 61 (2000) 805–817.
7] C.E. Aumann, G.L. Skofronick, J.A. Martin, Vac. Sci. Technol. 13 (3)
(1995) 1178.
Fig. 4. TG and DTA curves for mixture of aluminum powder with 18 ␮m particle
size and potassium perchlorate with mass ratio (a) 30:70 and (b) 50:50 (sample
[8] M.M. Mench, C.L. Yeh, K.K. Kuo, Proceedings of the 29th Interna-
tional ICP Conference, Karlsruhe, Germany, June 30–July 3, 1998, pp.
30/1–30/15.
◦
mass, 4.0 mg; heating rate, 10 C/min; air atmosphere and potassium perchlorate
with 50 ␮m particle size).
[
9] E.S. Freeman, D. Edelman, Anal. Chem. 31 (1959) 624.
[
[
[
10] V.N. Simonenko, V.E. Zarko, Proceedings of the 30th International
ICP Conference, Karlsruhe, Germany, June 29–July 2, 1999, pp. 21/1–
due to the fusion of potassium perchlorate. An exotherm with a
limited decrease in the mass (about 3.4%) occurs at 615 C,
which corresponds with the reaction between aluminum and
potassium perchlorate. The results show ignition temperature
depends on aluminum content. A higher content of aluminum
powder increases the decomposition temperature.
◦
21/14.
11] P.F. Pokhil, A.F. Belyaev, Y.V. Frolov, V.S. Logachev, A.I. Korotkov,
Combustion of Powdered Metals in Active Media, Nauka, Moscow,
1972.
12] J.H. Mclain, Pyrotechnic from the Viewpoint of Solid State Chemistry,
The Frankline Institute Press, 1980, p. 156.