Pyrotechnic Mixtures Research Articles

The influences of combinative effect of temperature and humidity on the thermal stability of pyrotechnic mixtures containing strontium nitrate as oxidizer

The influences of combinative effect of temperature and humidity on the thermal stabilities of three pyrotechnic compositions are investigated in the study. The thermal behavior for each pyrotechnic is analyzed by SETARAM thermal analyzer. Activation energy is determined by Kissinger method and critical temperature of thermal explosion (Tb) of pyrotechnic compositions is also calculated. The results of thermal analysis revealed that relative humidity could decrease the thermal stability of pyrotechnic mixtures. The critical temperature of thermal explosion (Tb) of each pyrotechnics decreased as the relative humidity increasing. Based on the value of Tb, the thermal stabilities of the pyrotechnic mixtures are in the order of Sr(NO3)2/Mg4Al3/PVC/PF > Sr(NO3)2/SrCO3/KClO4/Mg4Al3/PVC/PF > Sr(NO3)2/KClO4/Mg4Al3/PVC/PF. The thermal stability of Sr(NO3)2/Mg4Al3/PVC/PF show the best thermal stability than other two mixtures whether it is in the condition of humidity or not.

Water induced thermal decomposition of pyrotechnic mixtures – Thermo kinetics and explosion pathway

Pyrotechnic mixtures are susceptible to explosive decompositions. The aim of this paper is to generate thermal decomposition data for flowerpot tip, which is a mixture used in the tip of flowerpot fireworks for easy ignition. Several accidents were reported by using this mixture. The mixture is prepared by mixing barium nitrate, potassium nitrate, aluminum (666) and dextrin in a slurry manner with water. In the manufacturing process 40% water wt/wt is added to the mixture. The thermal characteristics of pure sample and water added sample were studied. Differential Scanning Calorimeter is used for screening tests and Accelerating Rate Calorimeter is used for detailed studies in adiabatic and isothermal mode. The self heat rate data obtained showed onset temperature for pure sample at 170.62 °C and the sample with water showed a much earlier onset at 95.71 °C in adiabatic mode. Also it gets decomposes even at 40 °C and starts exothermic characteristics with a substantial rise in system pressure of 32 bar in isothermal mode. The heats of exothermic decomposition and Arrhenius kinetics were computed.

Improving Strontium Nitrate-Based Extinguishing Aerosol by Magnesium Powder

Pyrotechnic mixtures can produce aerosol fire extinguishing agent by combustion and serve as an efficient and economic alternative to the halons. In this work, magnesium powder was used as an additive to improve the combustion performance of the strontium nitrate-based pyrotechnic aerosol fire extinguishing agent. Optimization was carried out regarding extinguishing time, residue mass, combustion temperature, corrosiveness, combustion product and mass burning rate. Even though magnesium powder is a high energy combustion agent, the results showed that the flame temperature could be controlled within a reasonable range of 700°C to 900°C by proper formulation, and the performance of the strontium nitrate-based aerosol fire extinguishing agent can be improved efficiently.

Preparation of Energetic Poly(azolyl)borates as New Environmentally Benign Green‐Light‐Emitting Species for Pyrotechnics

AbstractThree different energetic poly(azolyl)borates, potassium dihydridobis(4‐nitroimidazolyl)borate, sodium dihydridobis(4, 5‐dinitroimidazolyl)borate, and sodium dihydridobis(3, 4,5‐trinitropyrazolyl)borate, were synthesized as starting materials for metal‐free environmentally benign green‐light‐emitting substitutes for barium salts in pyrotechnical mixtures. The compounds were analyzed by NMR and Raman spectroscopy and high mass resolution spectrometry. Moreover, the energetic properties regarding physical and thermal stability were determined. The 11B NMR chemical shifts were calculated and compared to the experimental values and intense investigations on the formation of poly(4‐nitroimidazolyl)borates were performed. Furthermore, the solvolytic stability towards alcohol and water was tested.

Calculation of Explosion Performance of Pyrotechnic Mixtures by Minimum Free Energy Principle

Pyrotechnic mixtures commonly present fast combustible and even detonable reaction. The process of the reaction produces huge heat and gases, featuring the origin of explosion. Therefore, in the practical situations, some catastrophic disasters usually occur in the storage houses and production factories related to those materials. For the safety consideration, the assessment on the explosive performance of pyrotechnic mixtures becomes necessary. In the paper, the pressure, temperature, and amount of gases from reaction of pyrotechnic compositions are obtained by establishing an analytic procedure based on the minimum Gibbs free energy principle. The results provide an initial condition for the hydrodynamic computation on the blast effects coming from explosion of some specific accidents.

Spectroscopic Characterization of B/KNO3 Diode-Laser Induced Combustion

The combustion of a B/KNO3 pyrotechnic mixture was characterized by its chemiluminescence for the first time. The reaction was initiated by a continuous wave (cw) diode laser inside a novel multipurpose reaction cell, whose design and construction are described. As in the case of the extensively studied oxidation of boron by O2, the most intense luminescence, recorded in the 400-600 nm range, is assigned to BO2. Its appearance delay time (10(-2) to 10(-1) s) equals that measured for the pressure increase and is shortened as the laser power is increased. A band observed at 355 nm appears at longer delay times than the BO2 bands. The band, and some weaker ones, may be assigned to BO, although some bands expected for BO (based on reaction between B atoms and O2) are absent from the spectra. This observation is discussed in the text, and possible emission from BN is discussed. If the band is assigned to BO, the absence of known bands may be due to specific E-V resonance energy transfer. Possible oxidation mechanisms consistent with the different delay ignition times are discussed.

Dynamical and statistical behavior of discrete combustion waves: A theoretical and numerical study

We present a detailed theoretical and numerical study of combustion waves in a discrete one-dimensional disordered system. The distances between neighboring reaction cells were modeled with a gamma distribution. The results show that the random structure of the microheterogeneous system plays a crucial role in the dynamical and statistical behavior of the system. This is a consequence of the nonlinear interaction of the random structure of the system with the thermal wave. An analysis of the experimental data on the combustion of a gasless system (Ti + xSi) and a wide range of thermite systems was performed in view of the developed model. We have shown that the burning rate of the powder system sensitively depends on its internal structure. The present model allows for reproducing theoretically the experimental data for a wide range of pyrotechnic mixtures. We show that Arrhenius' macrokinetics at combustion of disperse systems can take place even in the absence of Arrhenius' microkinetics; it can have a purely thermal nature and be related to their heterogeneity and to the existence of threshold temperature. It is also observed that the combustion of disperse systems always occurs in the microheterogeneous mode according to the relay-race mechanism.

A Selection of Alkali and Alkaline Earth Metal Salts of 5,5′‐Bis(1‐hydroxytetrazole) in Pyrotechnic Compositions

AbstractThe dilithium (1), disodium (2), dipotassium (3) and dicesium (4) salt as well as the calcium (5), strontium (6) and barium (7) salt of 5,5′‐bis(1‐hydroxytetrazole) were prepared and characterized including NMR‐, IR‐ and Raman spectroscopy, mass spectrometry, elemental analysis and differential scanning calorimetry. The crystal structures of 1, 2 and 4–6 were additionally determined by single‐crystal X‐ray diffraction. The sensitivities of the salts towards impact, friction and electrostatic discharge were determined by means of BAM (Bundesanstalt für Materialforschung‐ und prüfung) methods. The potential use of 1, 6 and 7 as coloring agents in pyrotechnical mixtures as well as the utilization of 3 and 4 as additives in near infrared (NIR) emitting pyrotechnical formulations was examined.

Thermal Behavior and Non-Isothermal Kinetic Studies on Titanium Hydride–Fueled Binary Pyrotechnic Compositions

This study describes thermochemical properties and ignition characteristics of pyrotechnic compositions consisting of TiH2 + KClO3, TiH2 + KClO4, and TiH2 + Ba(NO3)2, where titanium hydride is used as fuel and KClO3, KClO4, and Ba(NO3)2 act as oxidants. Differential thermal analysis (DTA) and thermogravimetry (TG) techniques have been employed to elucidate the reaction process of these pyrotechnic systems. TG/DTA analysis of pure titanium hydride indicates that this compound decomposes at 535 °C. By replacing KClO3 with KClO4 as oxidizer in a titanium hydride–fueled mixture, the sensitivity of the mixture decreases. A TiH2 + KClO3 pyrotechnic mixture has a fusion temperature around 358 °C and ignition temperature around 472 °C. A TiH2 + KClO4 pyrotechnic system decomposes at 541.5 °C. However, replacing KClO4 with Ba(NO3)2 in this mixture, increases the ignition temperature of the mixture by at least 30 °C to ∼ 570 °C, which is a safe temperature for preventing activation of the mixture by accidental factors such as static electricity. The apparent activation energy (E), ΔG#, ΔH#, and ΔS# of the combustion processes were obtained from the DSC experiments. Thermokinetic data shows that the relative reactivity of these mixtures decrease in the following order: TiH2 + KClO3 > TiH2 + KClO4 > TiH2 + Ba(NO3)2.

2,4,6-Trinitrotoluene: A Surprisingly Insensitive Energetic Fuel and Binder in Melt-Cast Decoy Flare Compositions

Deceiving with TNT: Melt-cast pyrotechnic mixtures based on 2,4,6-trinitrotoluene (TNT)/KClO4 (see picture for flame) spectrally matched infrared decoy flares and show superior performance and greatly reduced sensitivity in comparison to common pyrotechnic or double-base material currently in use for IR countermeasure flares.

Kinetic Parameters of Binary Iron/Oxidant Pyrolants

The thermal properties of pyrotechnic mixtures containing iron powder as fuel and KNO3, KClO3, and KClO4 as oxidants are reported. The thermogravimetry–differential thermal analysis results for pure components and corresponding pyrotechnic mixtures revealed that the melting point, decomposition temperature, and rate of oxygen releasing of the oxidants have dominant effects on ignition reaction of the pyrotechnic mixtures. The apparent activation energy and activation parameters for the combustion processes were evaluated from the differential scanning calorimetry experiments. Based on the ignition temperatures obtained and the resulting kinetic data, the thermal reactivity of the pyrotechnic mixtures was found to decrease as in the order Fe + KClO3 > Fe + KNO3 > Fe + KClO4.

Emission spectra of pyrotechnic mixtures of heat flux simulators

Comprehensive optical spectroscopic studies of the combustion process of solid-state pyrotechnic mixtures based on Mg and Sr(NO3)2 have been carried out. Emission spectra of the mixtures in the ultraviolet, visible, and infrared wavelength regions have been studied under various atmospheric conditions taking into account radiation transfer in air along an optical path of observation up to 5 km long.

Thermoanalytical Investigation on Pyrotechnic Mixtures Containing Mg-Al Alloy Powder and Barium Nitrate

Abstract The thermal kinetics properties of pyrotechnic compositions consist of Ba(NO3)2+MgAl, Ba(NO3)2+MgAl+S, Ba(NO3)2+MgAl+KClO4 mixtures were investigated in this paper. Differential scanning calorimeter (DSC) had been employed to illustrate the reaction process of these pyrotechnic compositions. The apparent activation energy ( E ), frequency factor ( A ) and the critical ignition temperature of thermalexplosion were calculated by Kissinger approach, Ozawa approach and Satava-Setsak approach. The results show that adding of S and KClO4 both increase the value of E and A slightly. The critical ignition temperature of thermal explosion rises by adding of S or some KClO4. But with the increasing of KClO4 content, the critical ignition temperature of thermal explosion drops. Besides, the mixture consist of Ba(NO3)2+MgAl+S is considered unlikely to propagate detonation or deflagration, and the possibility of detonation or deflagration propagation is reduced to a certain degree when adding of KClO4 in Ba (NO3)2+MgAl mixture.

Studies on ignition and afterburning processes of KClO4/Mg pyrotechnics heated in air

Thermal behavior of KClO4/Mg pyrotechnic mixtures heated in air was investigated by thermal analysis. Effects of oxygen balance and heating rates on the TG–DSC curves of mixtures were examined. Results showed that DSC curves of the mixtures had two exothermic processes when heated from room temperature to 700 °C, and TG curve exhibited a slight mass gain followed by a two-stage mass fall and then a significant mass increase. The exothermic peak at lower temperature and higher temperature corresponded to the ignition process and afterburning process, respectively. Under the heating rate of 10 °C min−1, the peak temperatures for ignition and afterburning process of stoichiometric KClO4/Mg (58.8/41.2) was 543 and 615 °C, respectively. When Mg content increased to 50%, the peak ignition temperature decreased to 530 °C, but the second exothermic peak changed little. Reaction kinetics of the two exothermic processes for the stoichiometric mixture was calculated using Kissinger method. Apparent activation energies for ignition and afterburning process were 153.6 and 289.5 kJ mol−1, respectively. A five-step reaction pathway was proposed for the ignition process in air, and activation energies for each step were also calculated. These results should provide reference for formula design and safety storage of KClO4/Mg-containing pyrotechnics.

New Energetic Complexes of Copper(II) and the Acetone Carbohydrazide Schiff Base as Potential Flame Colorants for Pyrotechnic Mixtures

AbstractThe drive to find viable alternatives to common explosives has resulted in increased interest in the development of new transition‐metal organometallic energetic materials. To this end we report on the synthesis and characterization of the new energetic compounds, [CuX2(C7H14N4O)2·H2O] (X = ClO4–; NO3–), in addition to a new pathway to synthesizing copper hydrazinium chloride (CuCl3– N2H5+) in a clean facile way. All three complexes were characterized by low temperature single‐crystal X‐ray diffraction, while the two new compounds were also characterized by elemental analysis, thermogravimetric analysis, and differential scanning calorimetry. Because of the energetic nature of the new compounds, drop hammer and spark ignition tests were performed; Cu(NO3)2(C7H14N4O)2 was insensitive to both and Cu(ClO4)2(C7H14N4O)2 proved to be shock sensitive at high impact forces. It is expected that both of the compounds could be utilized in pyrotechnics as generators of green and blue colors, respectively.

Adiabatic thermokinetics and process safety of pyrotechnic mixtures

Pyrotechnic mixtures are susceptible to explosive decompositions. The aim of this paper is to generate thermal decomposition data under adiabatic conditions for fireworks mixtures containing potassium nitrate, barium nitrate, sulfur, and aluminum which are manufactured on a commercial scale. Differential scanning calorimeter is used for screening tests and accelerating rate calorimeter is used for other studies. The self heat rate data obtained showed onset temperature in the range of 275–295 °C for the fireworks atom bomb, Chinese cracker and palm leaf cracker. Of the three mixtures studied, atom bomb mixture had an early onset at 275 °C. The mixtures in general showed vigor exothermic decompositions. Palm leaf mixture exhibits multiple exotherm and reached a final temperature of 414 °C. The thermal decomposition contributes to substantial rise in system pressure. The heats of exothermic decomposition and Arrhenius kinetics were computed. The kinetic data are validated by comparing the predicted self heat rates with the experimental data.

Investigation on the Reaction of Powdered Tin as a Metallic Fuel with Some Pyrotechnic Oxidizers

AbstractThermogravimetry (TG), differential thermal analysis (DTA), and differential scanning calorimetry (DSC) have been used to examine the thermal behavior of Sn+KClO3, Sn+KNO3, and Sn+KClO4 pyrotechnic systems and the results were compared with thermal characteristics of individual constituents. TG curves for tin powder, heated alone in air, showed a relatively slow oxidation above 570 °C. From thermal results the decomposition temperatures of KClO3, KClO4, and KNO3, in nitrogen atmosphere, were measured at 472, 592 and 700 °C, respectively. For the Sn+KNO3 pyrotechnic system, the tin oxidation was completed within the range of 480 to 500 °C. Replacing KNO3 with KClO4 led to an increase of thermal stability of the pyrotechnic mixture. Among above‐mentioned pyrotechnic mixtures, Sn+KClO3 has the lowest ignition temperature at about 390 °C. The apparent activation energy (E), ΔG#, ΔH# and ΔS# of the combustion processes were obtained from the DSC experiments. Based on these kinetic data and ignition temperatures, the relative reactivity of these mixtures was found to obey in the following order: Sn+KClO3>Sn+KNO3>Sn+KClO4.

An Investigation on Decomposition Kinetics and Thermal Properties of Copper-Fueled Pyrotechnic Compositions

Thermal properties of pyrotechnic mixtures containing copper powder as fuel and NH4ClO4, KClO3, and KClO4 as oxidants are reported. The thermogravimetry (TG) differential thermal analysis (DTA) results for pure components and corresponding pyrotechnic mixtures showed that melting point, decomposition temperature, and rate of oxygen releasing of the oxidants have dominant effects on decomposition reaction of the pyrotechnic mixtures. Although NH4ClO4, KClO3, and KClO4 as pure oxidants are found to decompose at 321, 472, and 592°C, respectively, the pure fine copper powder oxidized at 271.5°C. On the other hand, the pyrotechnic systems Cu+NH4ClO4, Cu+KClO3, and Cu+KClO4 possessed decomposition temperatures of 283, 400, and 510°C, respectively. Based on the decomposition temperatures obtained and the resulted kinetic data (E, ΔG#, ΔH#, and ΔS#), obtained from differential scanning calorimetry (DSC), the thermal reactivity of the pyrotechnic mixtures found to decrease in the order Cu+NH4ClO4 >Cu+KClO3 >Cu+KClO4.

Effect of different additives on the thermal properties and combustion characteristics of pyrotechnic mixtures containing the KClO 4/Mg–Al alloy

The thermal properties and combustion characteristics of KClO 4/Mg–50%Al, KClO 4/Mg–50%Al with additives such as nitrocellulose (NC), urotropine and guanidine nitrate (GN) were studied experimentally using differential thermal analysis (DTA) and thermogravimetry (TG) and closed bomb experiments. The results of DTA–TG analysis revealed that additives could affect thermal stability and the decomposition temperature of KClO 4/Mg–50%Al alloy. The order of the ignition temperatures of mixtures ( T i) is KP/Mg–50%Al/urotropine (2#, 557.7 °C) > KP/Mg–50%Al/GN(3#, 553.6 °C) > KP/Mg–50%Al (1#, 538.8 °C) > KP/Mg–50%Al/NC (4#, 536.5 °C). On the other hand, the results of the closed bomb experiments confirm that the combustion pressures were all increased with the addition of additives. The ignition delay times of these mixtures are in the order KClO 4/Mg–50%Al (1#) > KClO 4/Mg–50%Al/GN (3#) > KClO 4/Mg 50%Al/NC (4#) > KClO 4/Mg–50%Al/urotropine (2#).

Improving safety performance of lactose-fueled binary pyrotechnic systems of smoke dyes

The lactose/KClO3 is a widely used pyrotechnic mixture to vaporize organic materials, such as smoke dyes. However, because of low ignition temperature of this mixture, serious precaution should be taken into account to prevent its accidental self-ignition. In order to find a safe and efficient alternative of this conventional mixture, KClO3 has been replaced by common oxidizing agents including KMnO4, KNO3, KClO4, Ba(NO3)2, PbO2 and NH4ClO4. TG and DTA analysis have been used to obtain thermal characteristic of the mixtures. Based on ignition temperature of the pyrotechnic mixtures we can divide them into four categories as follows: (1) the mixture igniting at low temperature, i.e., at about 200 °C. (2) Moderate temperature igniting mixture, in which ignition occurs at 300–400 °C. (3) High temperature igniting mixture with ignition temperature higher than 400 °C .(4) Not igniting mixtures. Also, the apparent activation energy (E), ΔG #, ΔH #, ΔS # and critical ignition temperature (T b ) of the ignition processes of low and moderate temperature igniting mixtures were obtained from the DSC experiments. Finally, among the investigated mixtures, lactose/KNO3 can be considered as a safe and efficient pyrotechnic composition for vaporization of organic materials, such as smoke dyes, due to its moderate safe ignition temperature.