Nitramine Propellants Research Articles

Thermal decomposition kinetics and storage life prediction of nitramine propellants with different energetic plasticizers based on model-fitting method

The research on the thermal decomposition of propellant is critical to determining its safe storage life. The thermogravimetry (TG) testing of nitramine propellants plasticized by nitroglycerin (NG), glycidyl azide polymer (GAP), 2,2-dinitropropanol hexanoate (DNPH), and N-butyl-2-nitratoethylnitramine (BuNENA) was performed under non-isothermal circumstances. The thermal decomposition mechanism of propellant was then analyzed using the model-fitting method, and the storage life was predicted based on the mechanism. The results show that when heated to the same mass loss, the temperature of GAP-NC-RDX, BuNENA-NC-RDX, and DNPH-NC-RDX is higher than that of NG-NC-RDX. GAP-NC-RDX, BuNENA-NC-RDX, and DNPH-NC-RDX propellants have superior thermal stability to that of NG-NC-RDX. The kinetic mechanism functions and equations of the propellants were calculated, and multi-step reaction models of the thermal decomposition were built. The major thermal decomposition mechanism of nitramine propellants was discovered to be composite autocatalytic decomposition (Kamal-Sourour equation), which means that the reaction of reactants and the reaction catalyzed by products occur in tandem. The decomposition depth of propellants increases as the temperature rises during the same storage time. The storage lifetimes of GAP-NC-RDX, BuNENA-NC-RDX, DNPH-NC-RDX, and NG-NC-RDX propellants at 288 K are 28.71 years, 24.49 years, 18.34 years, and 16.33 years, respectively. The inclusion of GAP, DNPH, and BuNENA in the formulation improves the storage life of propellant more than NG. This study offers an attractive strategy for analyzing the decomposition mechanism of propellant with a multi-step decomposition reaction and forecasting its storage life.

Nusselt Number Distribution Due to Supersonic Flow Impingement and Confinement

When a missile is launched from a canister, the impingement of the exhaust Bases on the plenum chamber creates a complex, viscous/shock interaction flow field. In order to study the rocket plume heat transfer effects on the closed and open plenum chambers, static rocket motor firings are carried out. Static tests are conducted in a small-scale rocket motor loaded with a typical nitramine propellant to produce a nozzle exit Mach number of 3. This supersonic jet is made to interact with the plenum chamber having closed and open sides. The distance between the nozzle exit and the plenum chamber back plate is varied from 6.3 to 9.6 times the nozzle exit diameter for the closed plenum chamber and 5.9 to 9.4 times the nozzle exit diameter for the open plenum chamber. In the plenum chamber, the heat flux has been measured using slug type heat flux gauges mounted at different locations. The temperature - time data are analyzed to obtain an insight into the flow field in the plenum chamber. Thirteen static tests are carried out to obtain the effect of axial distance between the nozzle exit and the plenum chamber back plate, and stagnation pressure in the rocket motor on the local heat transfer, characterized by Nusselt number in the closed and open plenum chambers.

Constant-volume combustion performance of mixed charge of foamed propellant with nitramine propellant

Foamed propellants based on polymer bonded nitramine explosives show high burning rates due to their porous structure and showed great potential for combustible cartridge case. Thus, the in-depth study of the co-combustion behavior of the foamed propellant and matching propellant is necessary. In this paper, closed bomb tests were used to study the co-combustion performance of nitramine propellant (RGD7) and surface coated nitramine propellant (SC-RGD7) mixed with foamed propellant. The influence of foamed propellant’s proportion in mixed charges on the combustion behavior was studied and analysed. It was found that the maximum dynamic vivacity and the value of B at maximum dynamic vivacity of mixed charge increased with the increase of added foamed propellant, resulting in better combustion progressivity. Meanwhile, the ignition delay of foamed propellant influenced the first stage of combustion, and the penetration combustion of foamed propellant influence the middle stage.

Studies on conversion of waste nitramine and fuel-rich-based propellants into liquid fertilizer

ABSTRACTThe current demilitarization processes employ open burning/open detonation which is not permitted by the environmental protection agency. Therefore, a systematic study has been carried out to convert waste/rejected nitramine propellant (NP) and fuel-rich-based propellant (FRP) into liquid fertilizer by digesting in dilute nitric acid followed by neutralization with potassium hydroxide and phosphoric acid. The obtained liquid fertilizers were fully characterized for nitrate, phosphate and ammonium ions along with potassium. Further, the effect of liquid fertilizers of NP and FRP on cluster bean plants was studied by taking different concentrations from 25 to 150 mL, and their effects on germination pattern, shoot growth, thickness of stem, size and number of leaves, number of pods and length over a full-grown period of plants were investigated. The results reveal that the germination index increases as the content of liquid fertilizer increases and the same trend was observed with respect to root and shoot growth. Also, broadness and the number of leaves showed an encouraging effect as concentration increases. Further, the final product, i.e. the number of pods of cluster bean and length in each pod was found to be more for liquid fertilizer of NP compared to FRP-based liquid fertilizer.

Identification of initial decomposition reactions in liquid-phase HMX using quantum mechanics calculations

Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, (HMX), also known as octogen, is a commonly used ingredient in solid propellants and explosives. As a result, many experimental and theoretical studies have investigated HMX to elucidate its liquid-phase and gas-phase decomposition behavior. In various experimental efforts, including both fast and slow thermolysis, the results indicate that ring opening occurs very early due to the presence of carbon-containing species, such as HCN, H2CO, HNCO, CO and CO2. After a lengthy search using quantum mechanics, ring-opening and subsequent reactions have been identified which may occur in both liquid and gas phases. Two existing pathways – 1) HONO elimination and 2) NNO2 homolysis – are re-examined for liquid-phase decomposition, and early ring-opening reactions have been identified. Three additional pathways – 1) reaction with NO and formation of ONTNTA, 2) prompt oxidation via HONO and ONNO2 addition, and 3) hydrogen abstraction via NO2– are also identified along with early ring-opening reactions in each pathway. The proposed pathways for decomposition of HMX are similar to that of RDX presented earlier [37]. The quantum mechanics calculations are performed using density functional theory (DFT) at the B3LYP/6-311 + + G(d,p) level. Conductor-like Polarizable Continuum Model (CPCM) is used to account for solvation effects with water as solvent within the Gaussian program package. Intrinsic reaction coordinate calculations have also been performed to verify that the reactants are indeed connected to the expected products. Similar to RDX, HONO elimination appears to be the initiation reaction followed by early ring-opening reactions. Results also indicate simultaneous formation of formaldehyde and N2O from early ring-opening reactions. Competing bimolecular reactions with NO2, HONO and ONNO2 are also investigated in the liquid phase, which explain the experimentally observed autocatalytic behavior. These reactions can assist in the development of a detailed liquid-phase chemical kinetics mechanism of nitramine propellants containing RDX and HMX.

Study on the effect of RDX content on the properties of nitramine propellant

Abstract Four kinds of nitroamine propellants with different RDX contents (10%, 20%, 30% and 40%) were prepared to study the effect of RDX content on the mechanical properties and combustion properties of nitroamine propellant. The mechanical properties and combustion properties of nitroamine propellant at the normal temperature (20 °C) and low temperature (−40 °C) were test by using impact testing machine, drop hammer impact test machine and closed bomb vessel. The test results show that the impact strength of 30% RDX-contained nitramine propellant is maximum, but 40% RDX-contained nitramine propellant has the minimum impact strength. And the crushing height of propellant with 20% RDX-contained was the highest, but the crushing height of propellant with 40% RDX-contained the lowest. With the increase in RDX content in nitramine propellant, the energy of nitramine propellant increases and its burning rate reduces, but 40% RDX-contained nitramine propellant did not meet this trend at the low temperature because of its poor mechanical properties.

Effect of varied proportion of GAP-ETPE/NC as binder on thermal decomposition behaviors, stability and mechanical properties of nitramine propellants

To improve the thermal performance and mechanical properties of nitramine propellant, varied proportions of GAP-ETPE/NC were applied as binders. The thermal behavior of propellants was investigated by using differential scanning calorimetry (DSC), the thermal stability of the propellants was studied by methyl violet experiment and vacuum stability test, and the mechanical properties were also examined. It was found that the DSC curve of GAP-ETPE shows a single exothermic peak at around 250 °C, and TG-DTG curves of GAP-ETPE exhibit two major steps of mass loss. GAP-ETPE has a good compatibility with nitrocellulose, and there is no interaction between GAP-ETPE and RDX in solid phrase. When increasing the proportion of GAP-ETPE content in the binder system, the decomposition peak of nitrocellulose disappears gradually and the peak temperature of main decomposition increases. Meanwhile, activation energy and frequency factor calculated by Kissinger and FWO methods using non-isothermal thermoanalytical data all increase slightly. And the thermal stability of propellant gets improved greatly when GAP-ETPE is introduced into the binder system. When the proportion of GAP-ETPE/NC is 1:1 and 1:2 in the binder system, the mechanical properties of nitramine propellant are relatively excellent.

Quantum mechanics investigation of initial reaction pathways and early ring-opening reactions in thermal decomposition of liquid-phase RDX

Cyclotrimethylene trinitramine (RDX) is a commonly used ingredient in solid propellants and explosives. As a result, RDX has been the subject of many experimental and theoretical investigations to elucidate its liquid-phase and gas-phase decomposition. In our experimental effort involving Fourier Transform Infrared (FTIR) spectroscopy and time-of-flight mass spectrometry (ToFMS) of fast thermolysis of RDX, the results indicate that ring-opening occurs very early due to the presence of carbon-containing species among the detected gas-phase species, such as HCN, H2CO, CO and CO2. Two existing pathways – 1) HONO elimination and 2) NNO2 homolysis – are re-examined for liquid-phase decomposition and early ring-opening reactions have been identified after a lengthy search using quantum mechanics. Three additional pathways – 1) reaction with NO and formation of ONDNTA, 2) prompt oxidation via HONO and ONNO2 addition, and 3) hydrogen abstraction via NO2– are also identified along with early ring-opening reactions in each pathway. The quantum mechanics investigation is based on using density functional theory (DFT) at the B3LYP/6-311++G(d,p) level. The liquid-phase studies use the Conductor-like Polarizable Continuum Model (CPCM) for solvation with water as solvent within the Gaussian program package. Intrinsic reaction coordinate calculations have also been performed to verify that the reactants indeed are connected to the expected products. Results explain the mechanistic details of the formation of early carbon containing species, simultaneous formation of formaldehyde and N2O, as well as the formation of minor species such as HNCO and HOCN. Proposed reactions can account for the experimentally observed autocatalytic behavior and can assist in the development of a detailed chemical kinetics mechanism of nitramine propellants containing RDX and possibly HMX.

Theoretical Study of the Turbulent Combustion of Nitramine Propellant

ABSTRACTOur analysis of the burning of nitramine propellant in a turbulent shear flow involves several preparatory considerations, their development, and subsequent implementation. Involved are the thermochemistry and chemical kinetics of nitramine combustion, a flow model, and a turbulence model. Li and Williams (1996) provide a reduced mechanism for nitramine combustion, one appropriate for incorporation in a turbulent flow analysis. Our fluid mechanical model consists of simple shear flow with a specified thickness and a specified velocity and turbulent intensity in its external stream. The chemical composition of this external stream consists of the complete first stageof the combustion of nitramine. Given the overall complexity of the system, we adopt the model of turbulence rather than a more complete Reynolds stress model. A key parameter in the equations resulting from these considerations is a Reynolds number based on conditions in the external stream and on the shear layer thickness. We exploit the large magnitude of this number in flows of applied interest and carry out an asymptotic analysis. As in related analyses the shear layer is found to involve a two-layer structure: a thin layer which is adjacent to the nitramine surface and in which molecular and turbulent transport exchange dominance, and a thick outer layer involving only turbulent transport. A significant finding from the asymptotic analysis is that combustion of the products of the devolitization of nitramine is confined to the thin inner layer. There are several important consequences of this finding. A parameter relating the characteristic flow and chemical times is determined by the solution for the inner layer. The outer layer involves no combustion and constant density. Since mass transfer is involved, the asymptotic analysis exposes the significant effect of mass transfer on the usual log-law behavior of the mean velocity at the outer edge of the wall layer. Solutions are given for the inner layer for four pairs of values for the two parameters determining the rate of nitramine consumption and the turbulent intensity in the external flow. The outer layer is then described through a representative solution of the corresponding equations. Moreover, an elegant solution for the combustion in the case of laminar flow is presented.

Comparison of simplified models for nitramine propellant combustion

Although 1,3,5-Trinitroperhydro-1,3,5-triazine (RDX) and Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) are very similar molecularly and their burning rates as a function of pressure are nearly identical, it is well known that they differ significantly in temperature sensitivity, especially at low pressures. To understand these differences better, three simple models were applied to HMX and RDX combustion. Both the Denison–Baum–Williams and Li–Williams–Margolis models have previously been calibrated for use with RDX. However, the RDX calibration of the Ward–Son–Brewster model was developed in the present work. All three models were compared with relevant measured data including: burning rate, flame stand-off/thickness, combustion stability, and temperature sensitivity. It was shown that all models are capable of accurately determining the burning rate of HMX and RDX as a function of pressure at the baseline initial temperature, but only two of the models are capable of capturing the variation in temperature sensitivity for both HMX and RDX, and only one model can replicate all the other measured characteristics within experimental uncertainty. Analysis using this model suggests that the surface reaction of RDX is much less exothermic than HMX and that there is a shifting between the gas phase and surface reaction dominance with pressure for HMX. This explains why the temperature sensitivity for RDX is nearly flat for low pressures while the temperature sensitivity for HMX increases significantly as the pressure decreases. Importantly, these trends are achieved without adding significant model complexity or having parameters change with pressure or initial temperature.

Study on the Burning of Grain-molded Propellant

The investigation of the burning of grain-molded propellant comprises progressive burning, ignition and internal ballistic property. The grain-molded propellant is extruded by high energy nitramine propellant in the professional mould. The grain-molded propellant was studied by closed-bomb test, ignition simulation equipment test and 30 mm simulation gun test. The characteristics of p-t and L-B curves were analyzed for different density of grain-molded propellant. The influence law of density on the burning property of the grain-molded propellant was obtained. The results show that the bigger the density of the grain-molded propellant is, the better its progressivity is. And the progressivity of sample3 is the best, whose density is 1.25 g•cm-3. The muzzle velocity of sample3 increases 5.3% than that of high energy nitramine propellant.

Ballistic Modification of Nitramine Propellants with Special Reference to NG-PE-PCP-Based High Energy Propellants

The burning rate pressure relationship is one of the important criteria in the selection of the propellant for particular applications. The pressure exponent (η) plays a significant role in the internal ballistics of rocket motors. Nitramines are known to produce lower burning rates and higher pressure exponent (η) values. Studies on the burning rate and combustion behavior of advanced high-energy NG/PE-PCP/AP/Al- and NG/PE-PCP/HMX/AP/Al-based solid rocket propellants processed by a conventional slurry cast route were carried out. The objective of present study was to understand the effectiveness of various ballistic modifiers viz. iron oxide, copper chromite, lead/copper oxides, and lead salts in combination with carbon black as a catalyst on the burning rate and pressure exponent of these high-energy propellants. A 7–9 % increase in the burning rates and almost no effect in pressure exponent values of propellant compositions without nitramine were observed. However, in case of nitramine-based propellants as compared to propellant compositions without nitramines, slight increases of the burning rates were observed. By incorporation of ballistic modifiers, the pressure exponents can be lowered. The changes in the calorimetric values of the formulations by addition of the catalysts were also studied.

Theoretical Analysis of Plasma Enhancement of Propellant Burning Rate

AbstractA theoretical model of the combustion of a nitramine solid propellant in the presence of a plasma jet is proposed. Unlike standard double‐base compositions, nitramine propellants exhibit experimental evidence that plasma induces a burning rate enhancement. The model is based on heat transfer considerations and proposes a closed‐form solution of the enhancement of the propellant burning rate as a function of the thermophysical parameters of the system. The model provides a good qualitative agreement with experimental results.

Fracture toughness of nitramine and composite solid propellants

Test results of compact tension (CT) specimens, are presented for fracture toughness evaluation of nitramine (in extruded and slurry cast conditions) and composite solid propellants. For notched strength evaluation of cracked configurations, failure assessment diagram is generated utilizing the inherent flaw model. Testing of solid propellant CT specimens need specialized facilities as the spring force of the clip-on type crack opening displacement (COD) gauge, generally used for metallic materials, is high enough to open-up the crack even before commencement of actual test. Therefore, a non-contacting type video extensometer was employed. Fracture toughness of the extruded nitramine propellant is found to be higher, compared to those of slurry cast nitramine and composite propellants.

Comparison of fracture models to assess the notched strength of composite/solid propellant tensile specimens

Modifications are made in the well-known inherent flaw model as well as in the stress fracture models for accurate prediction of notched tensile strength of composite laminates containing holes or slits. To examine the adequacy of these modifications, fracture data on different composite materials reported in the literature are considered. The notched strength estimates from the present fracture models are found to be close to the existing test results. An attempt is made to correlate the fracture data of center crack tension specimens made of nitramine and HTPB-based propellant materials. The present analysis results from the above simple models are found to be in good agreement with test results. This study confirms the applicability of the above three fracture models to solid propellant materials having relatively low stiffness and strength. Since the notched strength estimates of composite/solid propellant tensile specimens are close to the test results, any one of them can be utilized while evaluating the notched tensile strength of specimens.

Modeling Laser-Induced Ignition of Nitramine Propellants With Condensed and Gas-Phase Absorption

A numerical analysis has been developed to study the laser-induced ignition of nitramine propellants with both condensed-phase and gas-phase absorption. The analysis is based on the time-dependent conservation equations of mass, energy, and species concentration in both the gas and condensed phases. A comprehensive chemical kinetics scheme involving 45 species and 232 steps is used to study the detailed heat-release mechanism in the gas phase. The analysis has been applied to investigate the ignition delay and key chemical processes involved in the laser-induced ignition of HMX monopropellant. Results show gas-phase absorption of laser energy enhances the ignition process, but reduces the dependency of ignition delay on the laser intensity. The process consists of inert heating, thermal decomposition, primary-flame occurrence, secondary-flame preparation and formation, and, finally, establishment of steady-state combustion.

Condensed-phase processes during combustion of solid gun propellants. II. nitramine composite propellants

Burning samples of nitramine composite solid gun propellants were quenched, and the burned surfaces examined microscopically and by chemical analysis. Studies were carried out on XM39 and M43 propellants, on an HMX-polyester composition (HMX2) and on pure RDX, at pressures ranging from atmospheric (0.1 MPa to 2.0 MPa). Scanning electron microscopy examination of quenched samples burned at these low pressures indicates that a liquefied layer 100 to 300 μ thick forms during combustion of these nitramine compositions. Bubbles are present, especially at the lower pressures. Gas chromatography mass spectrometry analysis suggests that in the case of XM39, ethyl centralite stabilizer is depleted in the surface layers relative to the plasticizer acetyl triethyl citrate. High-performance liquid chromatography studies indicate that for XM39 (and presumably for M43), HMX2, and RDX, the surface layers exhibit formation of the mechanistically significant nitrosoamines MRDX (also known as ONDNTA) and DRDX. Examination of the burned surfaces of XM39 and of HMX2 by photoacoustic Fourier-transform infrared spectroscopy and by microreflectance Fourier-transform infrared spectroscopy indicates the presence of increased amounts of binder and its decomposition products. Examination of the burned surface of RDX by photoacoustic Fourier-transform infrared indicates the presence of RDX decomposition products. These observations suggest the occurrence of a significant amount of condensed-phase decomposition. Depth profiling, by surface-abrasion and by cross-section examination, indicates that in the nitramine propellants the molten oxidizer layer is overlain by a layer (∼20 μ thick) of binder and its decomposition products. The roles of vaporization and of thermal decomposition in the liquid layers of the nitramine propellants are also discussed; it appears that both play significant roles.

Influence of pressure-driven gas permeation on the quasi-steady burning of porous energetic materials

A theoretical two-phase-flow analysis is developed to describe the quasi-steady propagation, across a pressure jump, of a multi-phase deflagration in confined porous energetic materials. The difference, or overpressure, between the upstream (unburned) and downstream (burned) gas pressure leads to a more complex structure than that which is obtained for an unconfined deflagration in which the pressure across the multi-phase flame region is approximately constant. In particular, the structure of such a wave is shown by asymptotic methods to consist of a thin boundary layer characterized by gas permeation into the unburned solid, followed by a liquid/gas flame region, common to both types of problems, in which the melted material is preheated further and ultimately converted to gaseous products. The effect of gas flow relative to the condensed material is shown to be significant, both in the porous unburned solid as well as in the exothermic liquid/gas melt layer, and is, in turn, strongly affected by the overpressure. Indeed, all quantities of interest, including the burned temperature, gas velocity and the propagation speed, depend on this pressure difference, leading to a significant enhancement of the burning rate with increasing overpressure. In the limit that the overpressure becomes small, the pressure gradient is insufficient to drive gas produced in the reaction zone in the upstream direction, and all gas flow relative to the condensed material is directed in the downstream direction, as in the case of an unconfined deflagration. The present analysis is particularly applicable to those types of porous energetic solids, such as degraded nitramine propellants, that can experience significant gas flow in the solid preheat region and which are characterized by the presence of exothermic reactions in a bubbling melt layer at their surfaces. 7 refs., 6 figs.

Radiation Emitted from Rocket Plumes

AbstractThe signature of rocket plumes can be used for detection, identification and guidance of rockets. The objective was to investigate the signature of various types of solid rocket propellants by application of spectroscopic methods. The emission and transmission characteristics of plumes were studied experimentally, the results were analyzed based on molecular bands and continuum radiation. The model formulations include a nitramine propellant, a double‐base propellant and a composite propellant. Applied were rapid‐scanning filter wheel spectrometers for the wavelength region from 1.2 μm to 14 μm with a time resolution of 50 spectra/s and a wavelengths resolution of 1% of actual wavelength. The UV/VIS wavelengths region was recorded by an OMA system with wavelength resolution of 0.1 nm and 1 nm and time resolution of 10 spectra/s. Molecular bands of water and carbon dioxide dominate in the near infrared and infrared. Depending on composition, continuous radiation indicates particles in the rocket exhaust. A code was developed to calculate molecular bands and continuous radiation using temperature and species distributions found by thermodynamic estimation to obtain the radiance of the plume. Comparison with experimental data delivered plume temperatures.

Influence of energetic materials on the energy‐output of gun propellants

AbstractFor the formulation and preparation of gun propellants containing high energetic compounds, methods have been described how to improve the performance. In addition thermodynamic data such as flame temperature, mole number, mean molecular weight, heat of explosion and specific energy were discussed, which are of main influence for the energy‐output of energetic materials. In connection with the improvement of performance, a list of components was established, which could be used to increase the energy without increasing the sensitivity of the propellants. At first, the aim was to replace conventional plasticizers by several energetic plasticizers. Taking into account different propellant formulations, the thermodynamic parameters have been calculated which are of interest for improvement of the specific energy. On the other hand, nitramine propellants manufactured at our Institute using different binder systems such as polybutadiene (PB), glycidylazide polymer (GAP) and cellulose acetate butyrate (CAB) have been investigated in a closed bomb in order to evaluate the energy‐output and in addition the reaction products by gas analysis. The performance of these LOVA‐propellants was discussed in connection with heat of formation, oxygen balance and the kind of polymeric binder system. Finally, energetic compounds such as NTO, CL‐20, TNAZ, ANTA and ammonium dinitramide (ADN) have been calculated using the ICT‐Thermodynamic Code, in order to assess the energy‐output and to be able to discuss a possible improvement of the performance.