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

 Nghiên cứu khoa học công nghệ 
Tạp chí Khoa học và Công nghệ nhiệt đới, Số 21, 12-2020 55
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 
1 Potassium perchlorate KClO4 Purity ≥ 99,5% 
Aladin Company 
(China) 
2 Magnesium Mg Purity ≥ 99 % Xilong Company (China) 
3 Strontium carbonate SrCO3 Purity ≥ 98,5% 
Xilong Company 
(China) 
4 Polyvinyl chloride (C2H3Cl)n SG-3 grade 
Shanxi Company 
(China) 
 Nghiên cứu khoa học công nghệ 
Tạp chí Khoa học và Công nghệ nhiệt đới, Số 21, 12-2020 56
No Names Formulas Requirements Sources 
5 Novolac resin C13H12O2 
Softening temperature > 
90oC; 
Phenol content: 0,1-3,0% 
Anti-aircraft and 
airforce Technical 
Institute (Vietnam) 
6 Ethanol C2H6O Ethanol > 96% 
Xilong Company 
(China) 
2.2. Preparation of pyrotechnic mixture samples 
- Preparation of components: KClO4, SrCO3 were dried at (7080)oC in 4 
hours, Mg, PVC, novolac resin were dried at (4050)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 
(810) 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: 
𝑉 = ଴.ଶ଻ଷ .∆௉ .௏್
೎்.௠
 (1)
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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Tạp chí Khoa học và Công nghệ nhiệt đới, Số 21, 12-2020 57
𝑝 = ா(଴.଺ଶ÷଴.଻଺ µ௠).ଵ଴଴
ா(଴.ସ÷଴.଻଺ µ௠)
 (2) 
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 
Samples 
Weight contents, % Kb, 
% 
Qv(cal.), 
cal/g 
Qv(exp.), 
cal/g 
V(cal.), 
mL/g 
V(exp.), 
mL/g KClO4 Mg 
M1 17 30 -37.8 1095 977 135 166 
M2 21 26 -33.3 1015 944 168 190 
M3 25 22 -28.8 840 841 237 250 
M4 29 18 -24,3 665 722 308 243 
M5 33 14 -19,8 490 669 375 234 
* Note: cal. - calculation results; exp. - experimental data. 
 Nghiên cứu khoa học công nghệ 
Tạp chí Khoa học và Công nghệ nhiệt đới, Số 21, 12-2020 58
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. 
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. 
Fig. 2. Spectrum of the flame of M3 sample 
10,4 
9,5 
8,1 
6,3 6,2 
0
2
4
6
8
10
12
10 15 20 25 30 35
Bu
rn
in
g 
ra
te
, m
m
/s
Mg content, % 
0
0,1
0,2
0,3
400 500 600 700 800
In
te
ns
ity
Wave length, nm 
 Nghiên cứu khoa học công nghệ 
Tạp chí Khoa học và Công nghệ nhiệt đới, Số 21, 12-2020 59
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 
 Nghiên cứu khoa học công nghệ 
Tạp chí Khoa học và Công nghệ nhiệt đới, Số 21, 12-2020 60
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. Мельников В.Э., Современная пиротехника, Наука, Москва, 2014, tr.376-377. 
3. Инженерные боеприпасы. Руководство по материальной части и 
применению, Книга первая. Военное издательство МО СССР, Москва, 
1976, tr.185-186. 
4. Шидловкий А.А., Основы пиротехники, Машиностроение, Москва, 1973, tr.98. 
5. 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. Шидловкий А. А., Основы пиротехники, Машиностроение, Москва, 1973, 
tr.198. 
8. 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. 
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Tạp chí Khoa học và Công nghệ nhiệt đới, Số 21, 12-2020 61
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. 
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