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

Thermogravimetry (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.     

Thermal decomposition of pyrotechnic mixtures containing either aluminum or magnesium powder as fuel

Thermal behavior of energetic materials is critical to safe production, storage, handling or even demilitarization. In this work, the thermal behavior of Al, Mg, CuO, KMnO₄ and also three mixtures containing Al + CuO, Mg + CuO and Mg + KMnO₄ were studied experimentally using differential scanning calorimetry and thermogravimetry. These mixtures are sometimes used as pyrotechnic mixtures in military industries. Also, the influence of different heating rates (5, 10, 15 and 20 °C/min) on the DSC behavior of the mixtures was verified. The results showed that as the heating rate was increased, melting points and ignition temperatures of the mixtures were increased. On the other hand, TG-DSC analysis for Mg + KMnO₄ mixture indicates that this mixture melts at 283.0 °C and decomposed at 292.1 °C. By replacing KMnO₄ with CuO as the oxidizer of the magnesium, these temperatures enhanced to 368.7 °C and 408.3 °C, respectively. However, replacing Mg with Al in the Mg/CuO mixture decreases the melting and ignition temperatures of the mixture to 231.4 °C and 271.9 °C, respectively. The activation energy for each pyrotechnic mixture was computed. Also, the values of ΔS^#, ΔH^# and ΔG^# of their reaction were calculated.     

Laser Ignition of Various Pyrotechnic Mixtures – an Experimental Study

Ignition of several pyrotechnic mixtures by diode‐laser was studied experimentally using a novel combustion chamber. The ignition delay times dependence on laser intensity could be fit by the expression t_ign=aI⁻ⁿ for all compositions, with I being the laser intensity at target and n=1.4–2.1. This is roughly in accordance with thermal ignition theories assuming a semi‐inert solid. Differences in ignition delay times did not depend on fuel alone or oxidizer alone. The temperature of oxidizer decomposition does not correlate with ignition delay time. Furthermore, the steady state combustion temperature, deduced from emission spectra of the composition products are not correlated with ignition delay time. It is proposed that chemical reactions, taking place in the gas‐phase or in the solid‐phase, play a significant role, but are not solely responsible for ignition delay time. The seemingly uncorrelated ignition delay results between pyrotechnics containing either the same fuel or oxidizer hamper the construction of a “unified theory” for laser ignition of pyrotechnic mixtures.     

Kinetics and mechanism of reaction between acrylic acid or methacrylic acid and some oxiranes in the presence of N,N-dimethylaniline catalyst

The reactions of acrylic and methacrylic acids in ethylene oxide, propylene oxide, or glycerin epichlorohydrin were carried out in DMF in the presence of N, N-dimethylaniline catalyst. The kinetic equations describing these equations have been devised and activation parameters ΔH^#, ΔS^#, and ΔG^# calculated. The mechanism of the reaction has been proposed and verified by using kinetic and instrumental methods © 1998 SCI     

Non‐Isothermal Kinetic Study of the Thermal Decomposition of Melamine 3‐Nitro‐1,2,4‐triazol‐5‐one Salt

Study on thermal behavior of 3‐nitro‐1,2,4‐triazol‐5‐one (NTO) salts was required to obtain important data for application purposes. These compounds have been shown to be useful intermediates for gun propellant ingredients, high energetic ballistic modifiers for solid propellants and other potential applications. In this paper, thermal decomposition and non‐isothermal kinetics of melamine 3‐nitro‐1,2,4‐triazol‐5‐one salt (MNTO) were studied under non‐isothermal conditions by DSC and TG methods. The kinetic parameters were obtained from analysis of the DSC and TG curves by Kissinger and Ozawa methods. The critical temperature of thermal explosion (T_b) was 574 K. The results show that MNTO is thermally more stable than NTO when compared in terms of the critical temperature of thermal explosion. Finally, the values of ΔS^#, ΔH^#, and ΔG^# of its decomposition reaction were calculated.     

Fuel—Oxidant Particle Contact in Binary Pyrotechnic Reactions

The number of points of contact between particles of fuel and particles of oxidant in various pyrotechnic mixtures have been calculated on the assumption that the fuel and oxidant powders consist of uniform spherical particles of different sizes. The calculated numbers of contact points are compared with the experimental burning rates of these mixtures. In spite of the severe approximations made, there is a qualitative connection between the calculated numbers of contact points, N_R, and the measured burning rates, v, of those pyrotechnic compositions which are presumed to burn mainly via solid-solid reactions.     

Thermoanalytical investigation on some boron–fuelled binary pyrotechnic systems

This paper describes the thermochemical properties and ignition characteristics of pyrolants consist of B + KNO₃, B + PbO₂ and B + Ba(NO₃)₂ mixtures, where boron is known as fuel and KNO₃, PbO₂ and Ba(NO₃)₂ act as oxidant. Differential thermal analysis (DTA) and thermogravimetry (TG) techniques have been employed to elucidate the reaction process of these pyrolants. The results of the experiments suggest that boron particles react exothermally with the gaseous decomposition products of KNO₃ at 540 °C. Also, boron particles react exothermally with PbO₂ and Ba(NO₃)₂ at 436 °C and 551 °C, respectively. Furthermore, the effect of heating rate on the thermal decomposition of pyrolants was investigated by DSC. The apparent activation energy (E), ΔG^# and ΔS^# of the decomposition 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 following order:B/PbO₂ > B/KNO₃ > B/Ba(NO₃)₂     

Ignition and combustion of pyrotechnic compositions based on microsized and ultra-nanosized aluminum particles in a moist medium in a two-zone gas generator

This paper presents the results of an experimental study of the ignition and combustion of pyrotechnic compositions based on microsized and ultra-nanosized aluminum particles in a model two-zone gas generator using water as oxidizer. The flow of combustion products from the gas generator was video recorded, and the condensed products sampled behind the nozzle exit were studied by chemical and particle-size analyses. It was found that the replacement of microsized aluminum particles by ultra-nanosized particles in the samples led to a ≈17% decrease in the active aluminum content in the condensed phase, a 10–15% increase in the efficiency of the process in the gas generator (completeness of conversion of the pyrotechnic composition to combustion products), and a factor of about three decrease in the ignition delay.     

Properties of a Gas‐Generating Composition Related to the Particle Size of the Oxidizer

In general gas generators are defined as devices which produce force or power in the form of gas. In the present work we will focus on cold gas generators actuated by pyrotechnics. These gas generators are often applied for pressurizing or inflating systems in which high temperatures are not acceptable. Typical applications are: airbags, seat‐belt tensioners, fire extinguishers. Depending on the application, gas‐generating materials have to fulfil a series of requirements, such as good performance reproducibility, easy and reliable ignition, low explosion temperature, high yield of gas, low yield of condensed products, specific gas composition, and adequate burning rate and vivacity. In previous work a whole range of possibly suitable single compounds, such as sodium azide, double base propellant, azodicarbonamide, guanidine derivatives and azole derivatives were studied. These compounds – whether or not stoichiometrically mixed with an oxidizer (e.g. KNO₃, KClO₄ or NH₄NO₃) – were theoretically and experimentally examined in order to evaluate their combustion properties. The objective of this work is to experimentally investigate the influence of the particle size of an oxidizer on the combustion behavior of a gas‐generating pyrotechnic mixture. As an example a series of nitroguanidine (NQ) / potassium nitrate (KNO₃)‐mixtures with well‐defined KNO₃‐particle size fractions are selected. Raman spectroscopy is used to examine the constituent distribution within the bulk and thus the mixing efficiency. Closed vessel tests are used to experimentally compare ignition delay, burning rate, dynamic vivacity, and yield of gas. The composition of the combustion gases is examined through gas analysis. The experiments show that a decrease of the particle size of the KNO₃‐particles has a positive influence on the mixing efficiency and on the investigated combustion properties of a NQ/KNO₃‐composition. The combustion process of this mixture becomes better controllable when a small KNO₃‐particle size fraction is selected, but its combustion behavior is comparable to that of a NQ/KNO₃‐mixture containing a broad KNO₃‐particle size distribution.     

Thermal and spectroscopic studies of poly(N‐vinyl pyrrolidone)/poly(vinyl alcohol) blend films

Poly(N‐vinyl pyrrolidone) (PVP) and poly (vinyl alcohol) (PVA) homopolymers and their blended samples with different compositions were prepared using cast technique and subjected to X‐ray diffraction (XRD) measurements, infrared (IR) spectroscopy, ultraviolet/visible spectroscopy, and thermogravimetric analysis (TGA). XRD patterns of homopolymers and their blended samples indicated that blending amorphous materials, such as PVP, with semicrystalline polymer, such as PVA, gives rise to an amorphous structure with two halo peaks at positions identical to those found in pure PVP. Identification of structure and assignments of the most evident IR ‐ absorption bands of PVP and PVA as well as their blends in the range 400–2000 cm^?1 were studied. UV–vis spectra were used to study absorption spectra and estimate the values of absorption edge, E_g, and band tail, E_e, for all samples. Making use of Coats‐Redfern relation, thermogravimetric (TG) data allowed the calculation of the values of some thermodynamic parameters, such as activation energy E, entropy ΔS^#, enthalpy ΔH, and free energy of activation ΔG^# for different decomposition steps in the samples under investigation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Ignition and combustion of pyrotechnic compositions based on micro- and nanoparticles of aluminum diboride in air flow in a two-zone combustion chamber

This paper presents the experimental study of ignition and combustion of micro- and nanoparticles of aluminum diboride as part of pyrotechnic energy-saturated compositions in a gas generator with an air afterburner chamber and the thermodynamic calculations of combustion of pyrotechnic compositions based on aluminum diboride in air. The discharge of the combustion products from the afterburner chamber is recorded on video. It is shown that replacing micron aluminum diboride by powdered diboride with a mass-average diameter of particles equal to ≈270 nm in the pyrotechnic composition and increasing the pressure in the afterburner chamber cause the combustion efficiency in air to increase by 5–20%.     

Evaluating diethanolammonium chloride as liquid solvent for gas separation from experiments and theoretical calculations

This study explored diethanolammonium chloride ([DEA]Cl) as a potential ionic liquid from low-cost and commercial ones for gas separation. There are three kinds of functional sites in [DEA]Cl: acidic  NH₂⁺, hydrogen-bond  OH, and nucleophilic Cl⁻. The separation of NH₃/N₂/H₂, SO₂/CO₂/N₂, and H₂S/CO₂/CH₄ was considered, because the three mixtures are extensively involved in many industrial processes. The experimental results demonstrated that [DEA]Cl exhibited excellent ability to separate the mixture of NH₃/N₂/H₂. The [DEA]Cl also exhibited the proper capacity to separate SO₂/CO₂/N₂, but the capacity of [DEA]Cl for the separation of H₂S/CO₂/CH₄ was inferior. The theoretical calculations revealed that  NH₂⁺ and  OH worked synergistically to contribute to the ability of [DEA]Cl for excellent separation of NH₃ from NH₃/N₂/H₂, with Cl⁻ contributing to the proper separation of SO₂ from SO₂/CO₂/N₂. This study provides experimental and theoretical basis for the industrial application of [DEA]Cl in the area of gas separation.     

Equilibrium of benzidine inclusion adsorption on cyclodextrin copolymer

Insoluble β‐cyclodextrin (β‐CD) copolymer was prepared by reacting β‐CD with hexamethylene diisocyanate, and its inclusion adsorption behavior was investigated. The physical and chemical properties of CD copolymer were characterized by SEM, FTIR, DSC, TGA, XRD, and BET N₂ adsorption. The effects that shaking time and temperature exerted on the inclusion adsorption of benzidine on CD copolymer have been studied at relative low initial benzidine concentration. The procedure of the inclusion adsorption could be described by the Freundlich equation, and the thermodynamic constants ΔH^θ, ΔS^θ and ΔG^θ were obtained simultaneously. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Experimental Study of Ozone Generation by Negative Corona Discharge in Mixtures of N2 and O2

Ozone generation by negative DC corona discharge in N₂-O₂ mixtures has been experimentally investigated using a coaxial wire-cylinder corona reactor operating at room temperature and atmospheric pressure. The experiments have been carried out under different gas flows (15 cm³ min^?1 to 200 cm³ min^?1) and gas compositions (5% to 90% of O₂), and the effect of these parameters on the corona current, the ozone density and the efficiency of the ozone generator have been analyzed. The global rate coefficients for ozone formation and destruction have also been evaluated, and their values compared with those reported by other authors. The maximum efficiency for ozone production was found in gas mixtures with oxygen content about 70–80%.     

Nanoenergetic Gas‐Generators: Design and Performance

Nanoenergetic gas‐generator (NGG) mixtures may have various potential military applications from aircraft fuels to rocket propellants, explosives, and primers. To find reactions generating the highest pressure peak, we studied eight nanoenergetic reactions. The Al/Bi₂O₃ reaction generated the highest pressure pulse among the eight thermite reactions. We developed a highly efficient, one step process for synthesis of Bi₂O₃ nanostructured particles. Its use generated about a three times higher peak pressure (∼10 MPa) than when using commercial bismuth oxide nanoparticles (3 MPa). The pressure in the vessel rose very rapidly to a peak value for a duration of ∼0.02 ms and ΔP/Δt of up to 500 GPa s⁻¹. Increasing the crystallinity of the bismuth oxide nanoparticles increased the peak gas pressure by 25%. The maximum pressure×volume (PV) value obtained at m=0.1 g with our synthesized Bi₂O₃ was 707 Pa m³ much higher than that reported in the literature (33 Pa m³) for the same sample mass. Addition of carbon to the reactant mixtures did not increase the peak pressure. Addition of up to 3 wt.‐% of boron to the thermite systems increased the peak pressure by ∼50%.     

Selective synthesis of TiO2 nanopowders

Nanosized anatase, rutile, brookite, and mixtures of these materials taken in different ratios are synthesized using the detonation method with variations in the densities and ratios of explosives composed of the TiO₂ precursor, NH₄NO₃, and C₃H₆N₃(NO₂)₃. It is shown that the phase composition, the phase content, and the average particle size of TiO₂ nanopowders depend on the composition of the explosive mixtures and their densities. When the weight ratio between the C₃H₆N₃(NO₂)₃ compound and the TiO₂ precursor lies in the range 0.695–1.270, the average size of rutile particles is larger than that of anatase particles by a factor of approximately two.     

Effect of the polysilane structure on its solution fluorescence quenching

We studied the solution fluorescence quenching of poly(methylphenethylsilane) (1^#), poly(dimethylsilane‐co‐methylphenethylsilane) (2^#), poly(n‐hexylmethylsilane) (3^#), and poly(dimethylsilane‐co‐n‐hexylmethylsilane) (4^#) by such quenchers as CCl₄, CHCl₃, Cl₂CHCHCl₂, and methyl benzoate. We treated the fluorescence quenching data using the equations F₀/F = 1 +K_SV[Q],F₀/F exp(−NV[Q]) = 1 +K_SV[Q], and ln(F₀/F) =NV[Q], where F and F₀ are the fluorescence intensity with and without the addition of a quencher, respectively; K_SV, the Stern–Volmer constant; [Q], the quencher concentration; N, Avogadro's constant; and V, the volume of the active sphere. For the systems with both static quenching and dynamic quenching, we calculated their contributions and the critical quencher concentration [Q]_C and determined the nature of the fluorescence quenching in different quencher concentration ranges. We observed that, under the condition of the same quencher, the fluorescence quenching of the polysilane homopolymer is smaller than that of its corresponding polysilane copolymer, that is, 1^# < 2^# and 3^# < 4^#, and that for the fluorescence quenching of the same polysilane by different chlorohydrocarbons the fluorescence quenching ability of CCl₄ is larger than that of CHCl₃ and Cl₂CHCHCl₂. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 133–139, 2000     

Reactions of trithiocyanuric acid with oxiranes. II. Kinetics and mechanism of reactions

The study of the kinetics of the addition of trithiocyanuric acid to oxiranes (i.e., ethylene oxide and propylene oxide) in DMSO solution in the presence of triethylamine as a catalyst is described. The effects of the acid group concentration, the concentration of oxirane, and the catalyst on the course of the reaction was studied. The rate equation describing the addition was derived. The reaction order with respect to the oxirane, catalyst, and reactive groups of the acid were 0.5, 0.5, and 1.5, respectively. The mechanism of addition was proposed. The influence of temperature on the course of the reaction was also studied. The activation parameters (ΔH^#, ΔS^#, ΔG^#) were calculated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2081–2088, 2000     

Interpolymer‐specific interactions and miscibility in poly(styrene‐co‐acrylic acid)/poly(styrene‐co‐N,N‐dimethylacrylamide) blends

The miscibility or complexation of poly(styrene‐co‐acrylic acid) containing 27 mol % of acrylic acid (SAA‐27) and poly(styrene‐co‐N,N‐dimethylacrylamide) containing 17 or 32 mol % of N,N‐dimethylacrylamide (SAD‐17, SAD‐32) or poly(N,N‐dimethylacrylamide) (PDMA) were investigated by different techniques. The differential scanning calorimetry (DSC) analysis showed that a single glass‐transition temperature was observed for all the mixtures prepared from tetrahydrofuran (THF) or butan‐2‐one. This is an evidence of their miscibility or complexation over the entire composition range. As the content of the basic constituent increases as within SAA‐27/SAD‐32 and SAA‐27/PDMA, higher number of specific interpolymer interactins occurred and led to the formation of interpolymer complexes in butan‐2‐one. The qualitative Fourier transform infrared (FTIR) spectroscopy study carried out for SAA‐27/SAD‐17 blends revealed that hydrogen bonding occurred between the hydroxyl groups of SAA‐27 and the carbonyl amide of SAD‐17. Quantitative analysis carried out in the 160–210°C temperature range for the SAA‐27 copolymer and its blends of different ratios using the Painter–Coleman association model led to the estimation of the equilibrium constants K₂, K_A and the enthalpies of hydrogen bond formation. These blends are miscible even at 180°C as confirmed from the negative values of the total free energy of mixing ΔG_M over the entire blend composition. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1011–1024, 2007     

Preparation,Characterisation and Performance of Microencapsulated Red Phosphorus

Microencapsuled red phosphorus (MRP), with a phenolic resin coating layer, was successfully prepared. It was characterized by Fourier‐transform infrared spectroscopy (FTIR) and Scanning electron microscope (SEM). Meanwhile its water absorption, thermostability, thermodynamic properties and critical ignition temperature (T _b) have been studied. The results show that the MRP which is coated with phenolic resin can decrease the water absorption, increase thermostability and critical ignition temperature (T _b) significantly, compared with red phosphorus (RP). The thermodynamic properties which include apparent activation energy (E ), pre‐exponential factor (A ), activation entropy (ΔS ^#), activation enthalpy (ΔH ^#) and Gibbs free energy (ΔG ^#) of RP and MRP are obtained. Moreover, the MRP can reduce the water absorption and friction sensitivity of red phosphorus smoke agent significantly with the best content of phenolic resin is 0.5 % or 1 %.