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The preparation and characterization of the red flame pyrotechnic used in signal mines

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THE PREPARATION AND CHARACTERIZATION OF THE RED  
FLAME PYROTECHNIC USED IN SIGNAL MINES  
ĐÀM QUANG SANG (1), NGUYỄN VĂN BỘ (2), PHAN VĂN TRƯỜNG (2),  
NGUYỄN VĂN THÀNH (2), ĐỖ MINH HIẾU (2)  
1. INTRODUCTION  
Signal flame pyrotechnic is a type of pyrotechnic mixtures, which can burn and  
form a characteristically color flame. They are used to send signals when military  
operations occur on lands or at seas. Currently, the signal color system used is mainly  
red, yellow, and green. The flame color is generated by the radiation of molecules,  
atoms, and ions in the combustion product. For example, the red color is due to the  
radiation of the SrCl molecule, the yellow color - the Na atom, etc. Signal flame  
pyrotechnics often include oxidizers (strontium nitrate, barium nitrate, potassium  
nitrate, potassium perchlorate), fuels (magnesium, PAM-3), colorants (polyvinyl  
chloride-PVC, sodium oxalate, copper oxide), binders (novolac resin, colophony) [1].  
In the military, signal flame pyrotechnics are loaded into signal missiles,  
signal bullets, and signal mines, etc. [2]. Signal mines are used to detect enemy  
intrusion into a military zone or to simulate the operation of anti-personnel mines in  
military training [3]. When the signal mines are activated, colored flame stars are  
sequentially ignited and launched to a height from 5 to 15 m. Among the colored  
flame pyrotechnics, red flame mixtures are widely used by the characteristically  
colored flame is easily recognizable at long distances. The red flame pyrotechnic  
often contains salts of strontium, chlorinated compounds to form SrCl by the  
following reaction:  
2SrO + Cl2 ⇄ SrCl + O2  
The studies on the preparation and characterization of colored flame  
pyrotechnics, in general, and red flame mixtures, in particular, are less published.  
This paper presents some research results on the preparation and determination  
properties of the red flame pyrotechnic used in signal mines.  
2. EXPERIMENTAL  
2.1. Materials  
Chemicals used to prepare pyrotechnic mixtures are presented on Tab. 1.  
Tab. 1. Chemicals used to prepare red flame pyrotechnic mixtures  
No  
Names  
Formulas  
Requirements  
Sources  
Aladin Company  
(China)  
1
Potassium perchlorate  
KClO4  
Purity ≥ 99,5%  
Xilong Company  
(China)  
Xilong Company  
(China)  
Shanxi Company  
(China)  
2
3
4
Magnesium  
Mg  
Purity ≥ 99 %  
Purity ≥ 98,5%  
SG-3 grade  
Strontium carbonate  
Polyvinyl chloride  
SrCO3  
(C2H3Cl)n  
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No  
Names  
Formulas  
Requirements  
Sources  
Softening temperature >  
Anti-aircraft and  
airforce Technical  
5
Novolac resin  
C13H12O2  
90oC;  
Phenol content: 0,1-3,0% Institute (Vietnam)  
Xilong Company  
6
Ethanol  
C2H6O  
Ethanol > 96%  
(China)  
2.2. Preparation of pyrotechnic mixture samples  
- Preparation of components: KClO4, SrCO3 were dried at (7080)oC in 4  
hours, Mg, PVC, novolac resin were dried at (4050)oC in 4 hours. KClO4,  
Sr(CO3)2, Mg, and PVC specificated by the 38 #/cm sieves (particle size is smaller  
than 0.153 mm). The novolac solution with 40% of weight concentration was  
prepared by dissolving novolac resin in ethanol 96%.  
- Mixing: The required quantities of different ingredients (KClO4, Mg,  
Sr(CO3)2, and PVC) were weighed and mixed by brushing them from 3 to 4 times  
through 15 #/cm sieves. The achieved mixture was blended thoroughly in the  
novolac solution in such a way that the content of novolac resin in the pyrotechnic  
samples is 8%. The wet pyrotechnic mixtures were preliminarily dried in the air in  
(810) min and then passed through the 9 #/cm sieves. Finally, the red flame  
pyrotechnic samples were dried at a temperature range of 55÷60oC in 4 hours.  
2.3. Characterization  
The heat of combustion is determined on the PARR 6200 apparatus (USA)  
with 2 grams of sample weight. The volume of gaseous products is measured on the  
Lutron 9017 manometer and calculated by the formula:  
ꢀ.ꢁꢂꢃ .∆ꢄ .ꢅ  
ꢆ
푉 =  
(1)  
ꢇ .ꢉ  
ꢈ
Where V is the volume of gaseous products, mL/g; ∆P is the difference between  
values of pressure in the combustion chamber before and after measurement, mbar; Tc  
is the temperature of the combustion chamber, which equals the room ambient  
temperature, K; Vb is the volume of the combustion chamber equals to 334 mL; m -  
sample weight equals to 2 grams.  
The burning rate is obtained as a ratio between the distance traveled of the  
combustion front and the corresponding time interval determined by using a digital  
camera [4]. To measure burning rate, the red flame pyrotechnic was loaded into a  
steel tube with 4.2 mm in diameter. The distance between the starting and ending  
points on steel tube is 19.3 mm. Each measuring was carried out in three times then  
calculating the average value.  
The color purity of flame is calculated as the ratio between the area of the red  
light spectrum (= 620-760 nm) and the area of the visible light spectrum (= 400-  
760 nm) [5]:  
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(
)
ꢊ ꢀ.ꢋꢁ÷ꢀ.ꢂꢋ µꢉ .ꢌꢀꢀ  
푝 =  
(2)  
ꢊ(ꢀ.ꢍ÷ꢀ.ꢂꢋ µꢉ)  
The decomposition temperature is determined by thermogravimetric analysis  
(TGA) performed on a Netzsch STA 409 PC using the dynamic method with about  
15 mg of powder samples. The temperature was scanned from 50 to 550oC at a rate  
of 10oC/min. The friction sensitivity was carried out by a BAM Friction Tester  
according to STANAG 4487.  
3. RESULTS AND DISCUSSION  
3.1. Effect of KClO4/Mg ration on the characteristics of the pyrotechnic  
mixture  
In the pyrotechnic mixtures, KClO4 is the oxidizer and Mg is the fuel. The  
KClO4/Mg ratio determines energy characteristics and pyrotechnic effects. The  
concentrations of SrCO3, PVC and novolac resin are fixed and equal to 40%, 5%,  
and 8%, respectively. In this study, the ratio of KClO4/Mg was changed from 17/30  
to 33/14. Results of the theoretical calculation (by COMBUS software [6]) and  
experiment data of oxygen balance Kb, combustion heat Qv, specific volume of  
gaseous products V are presented in Tab. 2.  
From the results in Tab. 2, when the KClO4/Mg ratio increases from 17/30 to  
33/14 (corresponding to decreasing Mg content), the oxygen balance increases and  
the combustion heat decreases. This is explained by the fact that the combustion of  
Mg is a strongly exothermic reaction. M4, M5 samples do not meet the requirements  
for colored flame pyrotechnic due to the combustion heat less than 800 cal/g [7].  
In addition, Tab. 2 also shows that the calculated results are consistent with the  
experimental data. This indicates that the combustion in the calorimeter bomb is as  
equilibrium and adiabatic as the calculation assumed and it is possible to use the  
COMBUS software to predict the thermodynamic properties of the pyrotechnic  
mixtures forming a lot of the combustion products in solid-state.  
Tab. 2. Effect of KClO4/Mg ratio on energetic characteristics of the red flame  
pyrotechnic samples  
Weight contents, %  
Kb,  
%
Qv(cal.)  
cal/g  
,
Qv(exp.)  
cal/g  
,
V(cal.)  
,
V(exp.),  
Samples  
mL/g  
135  
168  
237  
308  
375  
mL/g  
166  
190  
250  
243  
234  
KClO4  
17  
Mg  
30  
26  
22  
18  
14  
-37.8  
-33.3  
-28.8  
-24,3  
-19,8  
1095  
1015  
840  
977  
944  
841  
722  
669  
M1  
M2  
M3  
M4  
M5  
21  
25  
29  
665  
33  
490  
* Note: cal. - calculation results; exp. - experimental data.  
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Besides the thermodynamic characteristics, the burning rate is also a particularly  
important parameter affecting the burning time of stars. The burning rate of samples  
was measured at a pressed density of 1.56 g/cm3. The change of the burning rate  
according to the Mg content (KClO4/ Mg ratio respectively) is shown in Fig. 1. It is  
clear that, when increasing the Mg content, the burning rate increases. This is due to  
the increase in the combustion heat and thermal conductivity of pyrotechnic samples.  
12  
10,4  
9,5  
10  
8
8,1  
6,3  
6,2  
6
4
2
0
10  
15  
20  
25  
30  
35  
Mg content, %  
Fig. 1. Affect of Mg content on burning rate  
M1, M2 samples with the high burning rate (> 9 mm/s) are not suitable for  
manufacture signal stars due to short burning time. Therefore, the appropriate  
ingredient for red flame pyrotechnic is as follows: 25% KClO4, 22% Mg, 40%  
SrCO3, 5% PVC, and 8% iditol (M3 sample).  
Other important technical characteristics of the M3 sample were determined  
such as spectroscopy, color purity of flame, thermal behavior, and friction sensitivity.  
3.2. Technical characteristics of the M3 sample  
a) Spectrum and color purity of flame  
The spectrum of flame of the M3 sample are shown in Fig. 2. The red color of  
the flame is generated by the radiation of SrCl and SrOH molecules [8]. Spectral  
lines of SrCl, SrOH are in the wavelength range 636 - 688 nm. Strong spectral lines  
of potassium are at 766.5 and 769.9 nm of wavelengths.  
0,3  
0,2  
0,1  
0
400  
500  
600  
700  
800  
Wave length, nm  
Fig. 2. Spectrum of the flame of M3 sample  
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The color purity of flame is calculated by formula (2) equal to 91% (the  
technical requirements for color purity of flame is greater than 70 - 75% [1]). Thus,  
the flame has a characteristically red color, meeting the technical requirements.  
b) The thermal behavior  
Fig. 3 shows the TGA diagram of the M3 sample. In a range of temperatures  
from 100oC to 300oC, polyvinyl chloride and a part of novolac resin are  
decomposed. At the temperature closing to 525oC, the reaction between potassium  
perchlorate and magnesium occurs. It can be confirmed that the ignition process of  
this pyrotechnic mixture occurs at the decomposition temperature of potassium  
perchlorate.  
c) The friction sensitivity  
The recorded value of friction sensitivity of the red flame pyrotechnic was  
32.4 kg according to STANAG 4487 (one explosion among six tests). In the  
meantime friction sensitivity of other explosives such as RDX - one explosion  
among ten tests at 12.4 kg of weight; HMX - one explosion among 10 tests at 11.6  
kg of weight; PETN - one explosion among 10 tests at 6.4 kg of weight; LX-11-0 -  
one explosion among 10 tests at 32.4 kg of weight. Thus the red flame pyrotechnic is  
relative safety to friction action in manufacturing, storage, transport, and using.  
Fig. 3. TGA diagram of the M3 sample with KClO4/Mg ratio of 25/22  
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d) Preparation of stars for signal mines  
To load the signal mines, the red flame pyrotechnic is compressed into a  
cylinder with an outer diameter of 23.5 mm, an inner diameter of 0.5 mm, a height  
of 11.0 mm, and a density of 1.6 g/cm3 (Stars-Fig. 4). The tests of signal mines show  
that the stars ensure mechanical durability and stable burning.  
Fig. 4. Stars of red flame pyrotechnic mixture  
4. CONCLUSIONS  
Thus, the KClO4/Mg ratio strongly affects on the combustion heat, the specific  
volume of the gaseous product, and the burning rate of the red flame pyrotechnic  
mixture. Exist a reasonable KClO4/Mg ratio to meet the technical requirements to  
prepare stars for signal mines. The pyrotechnic mixture has technical characteristics  
such as the high color purity of the flame. In addition, its small frictional and heat  
sensitivities indicate that it is relative safe in production conditions export, transport,  
storage and use.  
REFERENCES  
1.  
Мадякин Ф.П., Пиротехнические составы цветных огней, Казанский  
химико-технологический институт им. С. М. Кирова, Казань, 1978, tr.14-30.  
2.  
3.  
Мельников В.Э., Современная пиротехника, Наука, Москва, 2014, tr.376-377.  
Инженерные боеприпасы. Руководство по материальной части и  
применению, Книга первая. Военное издательство МО СССР, Москва,  
1976, tr.185-186.  
4.  
5.  
Шидловкий А.А., Основы пиротехники, Машиностроение, Москва, 1973, tr.98.  
Шидловкий А.А., Основы пиротехники, Машиностроение, Москва, 1973,  
tr.197.  
6.  
Dam Quang Sang, Nguyen Van Tuan, The prediction of Composition of  
Combustion Products and Energetic-Ballistic Characteristic of Gun  
Propellants, Journal of Science and Technique, 2017, 82:156-163.  
7.  
8.  
Шидловкий А. А., Основы пиротехники, Машиностроение, Москва, 1973,  
tr.198.  
Dominykas Juknelevicius Lina Mikoliunaite Simas Sakirzanovas Rytis  
Kubilius Arunas Ramanavicius, A Spectrophotometric Study of Red  
Pyrotechnic Flame Properties Using Three Classical Oxidizers: Ammonium  
Perchlorate, Potassium Perchlorate, Potassium Chlorate. Z. Anorg. Allg.  
Chem. Journal. 2014, 640(12):2560-2565.  
60  
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SUMMARY  
This paper presents the influence of oxidizer/fuel ratios on several energetic  
characteristics (combustion heat, gaseous volume, burning rate) of the red flame  
pyrotechnic containing potassium perchlorate, magnesium, strontium carbonate,  
polyvinyl chloride, and novolac resin. Based on the received experimental data and  
theoretical results, the reasonable potassium perchlorate/magnesium ratio of 25/22 is  
determined. The pyrotechnic mixture has the combustion heat of 841 cal/g, the  
gaseous volume of 250 ml/g, the burning rate of 8,1 mm/s at a pressed density of 1.56  
g/cm3, the color purity of 91%, the decomposition temperature of 525oC, and small  
friction sensitivity. The pyrotechnic mixture can be used for red stars in signal mines.  
Keywords: Pyrotechnic; potassium perchlorate, magnesium, strontium  
carbonate.  
Nhận bài ngày 13 tháng 10 năm 2020  
Phản biện xong ngày 04 tháng 11 năm 2020  
Hoàn thiện ngày 11 tháng 11 năm 2020  
(1) Học viện Kỹ thuật Quân sự  
(2) Viện Độ bền Nhiệt đới, Trung tâm Nhiệt đới Việt - Nga  
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