Double-base Propellants Research Articles

Numerical Simulation of Three Dimensional Flow Fields for Extrusion Process of GR-35 Double-base Propellant

Due to the instability of materials and the screw's rotation friction, it will be dangerous in the screw extrusion process of solid propellant. Because there were so much nitroglycerin and solid part in GR-35 double-base propellant, it was more difficult in spiral extrusion for this important propellant than others. In order to solve this problem, the Polyflow software was used to simulate the spiral extrusion process of GR-35 in this paper. Then four parameters (the temperature, the pressure, the shearing rate and the velocity) were analyzed at the axial direction (Z=0.02 m and Z=0.08 m). Then, these parameters of Z direction were analyzed by a line near the arris. According to the results, no matter the value of temperature, pressure, shearing rate or velocity, was larger in screw arris position. In addition, the values of temperature and pressure will increase as the extrusion processes while the velocity and the shearing rate will decrease. The simulated results can be used to optimize the technological in the process of screw extrusion of solid propellant and decrease the risks in process.

Formulation and Characterization of a New Nitroglycerin‐Free Double Base Propellant

AbstractDouble base propellants composed of nitrocellulose (NC) and nitroglycerine (NG) are widely used. However, the inclusion of liquid NG presents both stability and performance problems: the NG may migrate from the propellant in storage, and it softens the propellant at high inclusion levels. In this work, the novel nitrate ester 1,4‐dinitrato‐2,3‐dinitro‐2,3bis(nitratomethylene) butane (SMX) is considered as a replacement for NG in a double base propellant. Thermochemical calculations indicate improved performance when compared with the common double base propellant JA2 at SMX loadings above 40 wt‐%. Also, since SMX is a room temperature solid, migration may be mitigated. Both unplasticized and plasticized propellants were formulated to enable the study of the interaction of SMX with nitrocellulose. Thermal analysis of unplasticized propellant showed a distinct melt‐recrystallization curve, which indicates that a solid phase solution is being formed between SMX and NC, and that SMX would not act as plasticizer. Analysis of propellant prepared with diethyleneglycol dinitrate (DEGDN) plasticizer indicates that the SMX is likely dissolved in the DEGDN. The plasticized material also showed similar hardness and modulus to JA2. Safety characterization showed that sensitivity is similar to JA2. In short, replacing NG with SMX results in a new family of propellants with acceptable safety characteristics and which may also offer improved theoretical performance.

A theoretical prediction of the molecular and electronic structures, thermodynamic properties, and stability of 1,3-diazido-2-methyl-2-nitropropane (DAMNP)

1,3-Diazido-2-methyl-2-nitropropane (DAMNP) is a newly synthesized azido compound and may be a potential candidate of the plasticizer of propellants. For better understanding its properties, the molecular conformations, electronic structure, IR spectrum, thermodynamic properties, pyrolysis mechanism, and specific impulse (IS) were studied using the B3LYP/6-31++G** method of density functional theory (DFT). The electronic structure of DAMNP was analyzed by the natural atomic charges, bond orders, donor–acceptor interactions, and molecular electrostatic potential (MEP). Results show that the main contributions to the highest occupied molecular orbital and the lowest unoccupied molecular orbital are from –N3 and –NO2, respectively. The most negative area on the MEP locates at the O atoms of –NO2, which agrees with the atomic charges distributions. The pyrolysis mechanism was investigated by considering three possible bond dissociations (C–N3, C–NO2, and N–N2). Results show that the pyrolysis of DAMNP starts from the rupture of N–N2 finished cooperatively via the H-transfer process to eliminate N2. The lowest energy needed for pyrolysis is 165.13 kJ mol−1. To verify the reliability of the method, the organic azido compound CH3N3 was also considered. DAMNP has a slightly higher thermal stability than CH3N3. However, using DAMNP to replace the plasticizer nitroglycerin of the nitramine modified double-base propellant leads to a decrease in IS. Therefore, whether DAMNP can be really used as a plasticizer or not is worth further considerations.

Synthesis, thermal behavior, and application of 4-amino-3,5-dinitropyrazole lead salt

Lead salt of 4-amino-3,5-dinitropyrazole (PDNAP) was synthesized from 4-amino-3,5-dinitropyrazole by the process of metathesis reaction, and its structure was characterized by IR, element analysis, TG, and DSC. The thermal decomposition kinetics and mechanism were studied by means of different heating rate differential scanning calorimetry (DSC) and thermolysis in situ rapid-scan FTIR simultaneous. The effects of PDNAP as an energetic combustion catalyst on the combustion performance of the solid propellant were studied. The results show that the peak temperature is 319.2 °C on DSC curve. The kinetic equation of major exothermic decomposition reaction is $$ \frac{{\text{d}}\alpha}{{\text{d}}T} = \frac{{10^{15.45} }}{\beta }4(1 - \alpha )[ - \ln \left( {1 - \alpha } \right)]^{{{3 \mathord{\left/ {\vphantom {3 4}} \right. \kern-0pt} 4}}} \exp ({{ - 1.972 \times 10^{5} } \mathord{\left/ {\vphantom {{ - 1.972 \times 10^{5} } {RT}}} \right. \kern-0pt} {RT}}). $$ The PDNAP is shown by IR spectroscopy to convert to PbO during the decomposition process. Combustion experiments show PDNAP can reduce the burning rate pressure exponent of the double-base or composite-modified double-base propellant.

Direct Real-Time Detection of Vapors from Explosive Compounds

The real-time detection of vapors from low volatility explosives including PETN, tetryl, RDX, and nitroglycerine along with various compositions containing these substances was demonstrated. This was accomplished with an atmospheric flow tube (AFT) using a nonradioactive ionization source coupled to a mass spectrometer. Direct vapor detection was accomplished in less than 5 s at ambient temperature without sample preconcentration. The several seconds of residence time of analytes in the AFT provided a significant opportunity for reactant ions to interact with analyte vapors to achieve ionization. This extended reaction time, combined with the selective ionization using the nitrate reactant ions (NO3(-) and NO3(-)·HNO3), enabled highly sensitive explosives detection from explosive vapors present in ambient laboratory air. Observed signals from diluted explosive vapors indicated detection limits below 10 ppqv using selected ion monitoring (SIM) of the explosive-nitrate adduct at m/z 349, 378, 284, and 289 for tetryl, PETN, RDX, and NG, respectively. Also provided is a demonstration of the vapor detection from 10 different energetic formulations sampled in ambient laboratory air, including double base propellants, plastic explosives, and commercial blasting explosives using SIM for the NG, PETN, and RDX product ions.

Preparation and characterization of energetic materials coated superfine aluminum particles

This work is devoted to protect the activity of aluminum in solid rocket propellants by means of solvent/non-solvent method in which nitrocellulose (NC) and Double-11 (shortened form of double-base gun propellant, model 11) have been used as coating materials. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize the morphology of coated Al particles. Other characterization data of coated and uncoated Al particles, such as infrared absorption spectrum, laser particle size analysis and the active aluminum content were also studied. The thermal behavior of pure and coated aluminum samples have also been studied by simultaneous thermogravimetry–differential thermal analysis (TG–DTA) and differential scanning calorimetry (DSC). The results indicated that: superfine aluminum particles could be effectively coated with nitrocellulose and Double-11 through a solvent/non-solvent method. The energetic composite particles have core-shell structures and the thickness of the coating film is about 20–50nm. The active aluminum content of different coated samples was measured by means of oxidation–reduction titration method. The results showed that after being stored in room temperature and under 50% humidity condition for about 4months the active aluminum content of coated Al particles decreased from 99.8 to 95.8% (NC coating) and 99.2% (Double-11 coating) respectively. Double-11 coating layer had a much better protective effect. The TG–DTA and DSC results showed that the energy amount and energy release rate of NC coated and Double-11 coated Al particles were larger than those of the raw Al particles. Double-11 coated Al particles have more significant catalytic effect on the thermal decomposition characters of AP than that of NC coated Al particles. These features accorded with the energy release characteristics of solid propellant.

Chemical Desensitization of Explosives. Part 1. Effect of Ethyl Centralite on the Properties of an RDX-Based PBX

The effects of the addition of ethyl centralite, a commonly used stabilizer in double-base propellants, on a cyclotrimethylenetrinitramine (RDX)-based polymer-bonded explosive (PBX) were investigated. A reduction in sensitivity to impact was observed with increasing ethyl centralite content along with a reduction in explosiveness. Small-scale gap tests also show a reduction in sensitivity to shock initiation. High-performance liquid chromatography (HPLC) analysis of impact-stressed samples showed traces of 4-nitro- and 2-nitro-ethyl centralite and N-ethyl-N-nitrosoaniline; these results indicate the possibility that the mechanism of desensitization may, at least partially, be chemical in nature.

Mechanism study of stabilization of double-base propellants by using zeolite stabilizers (nano- and micro-clinoptilolite)

The mechanism of stabilization of double-base rocket propellants (DBPs) using inorganic stabilizer (nano- and micro-clinoptilolite) was investigated. The surface structures of the stabilizers, the double-base propellants containing the new stabilizers and the effect of the stabilizers on the surface behavior of propellants and vice versa were checked using XRD and Electron Microscope (AFM and TEM techniques). The results obtained from XRD suggested that the crystalline structure of the new inorganic stabilizers was completely changed when it was introduced into the propellants which may be attributed to the pressing processes of DBPs with stabilizers under very high pressure during their mixture preparation. The results obtained from Atomic Force Electron Microscope (AFM) and TEM indicated that nano-clinoptilolite particles become more regularly arranged on the propellant surface than micro-clinoptilolite which gives the stabilizer a higher ability to absorb more nitrogen oxide. The work aimed chiefly to use zeolite stabilizers for DBPs instead of classically used organic compounds; in order to avoid the harmful and carcinogenic organic products coming from the reaction of NOx gases with these organic stabilizers. This is achieved by studying the thermal behavior of these zeolites via investigation of their surface interaction with NOx gases obtained during stabilization process and suggesting possible interaction mechanism.

Study on the Notch Strength and Notch Sensitivity of Composite Modified Double-Base Propellants

To obtain the notch strength of the composite modified double base (CMDB) propellant, three-point bending tests on the single-edge U-notched thin plate specimens and uniaxial tensile tests on standard tensile specimens were carried out at 20°C. Experimental data include three parts in different range of the stress concentration factor Kt of specimens. The stress concentration factor Kt of the specimens have a distinct effect on the notch strength in a specific range. When Kt is less than the notch sensitivity factor KbN which is approximately equal to 1.35, the notch strength of CMDB propellant is approximately equal to its fracture strength and independent of the stress concentration factor of test specimens. When Kt is upper than 2.41, the notch strength change to be steady to a proper value which associate with the fracture toughness of the propellant . This shows that the CMDB propellant is insensitive to notch. The tensile test data is used to predict the value of the notch strength and notch sensitivity factor,and the prediction fit well with the test results of the notched specimens in a specific range.

Stable Isotopes of Nitrate Reflect Natural Attenuation of Propellant Residues on Military Training Ranges

Nitroglycerin (NG) and nitrocellulose (NC) are constituents of double-base propellants used notably for firing antitank ammunitions. Nitroglycerin was detected in soil and water samples from the unsaturated zone (pore water) at an active antitank firing position, where the presence of high nitrate (NO3(-)) concentrations suggests that natural attenuation of NG is occurring. However, concentrations alone cannot assess if NG is the source of NO3(-), nor can they determine which degradation processes are involved. To address this issue, isotopic ratios (δ(15)N, δ(18)O) were measured for NO3(-) produced from NG and NC through various controlled degradation processes and compared with ratios measured in field pore water samples. Results indicate that propellant combustion and degradation mediated by soil organic carbon produced the observed NO3(-) in pore water at this site. Moreover, isotopic results are presented for NO3(-) produced through photolysis of propellant constituents, which could be a dominant process at other sites. The isotopic data presented here constitute novel information regarding a source of NO3(-) that was practically not documented before and a basis to study the contamination by energetic materials in different contexts.

Thermal decomposition properties of double-base propellant and ammonium perchlorate

The thermal decomposition properties and the heat of combustion (ΔH) of samples with different ammonium perchlorate (AP)/double base propellant (DB) mass ratios under argon atmosphere were studied by the thermogravimetry–differential scanning calorimetry–mass spectrometry–Fourier transform infrared spectroscopy (TG–DSC–MS–FTIR) and automatic calorimeter method. The results show that decomposition process of AP/DB samples in negative and zero oxygen balance (OB) is different from that in positive OB. With the increasing of AP in the AP/DB samples, the decomposition of the samples becomes more and more severe. When the OB of the samples is positive, the phenomenon of deflagration or explosion could be observed in the decomposition process. The sample with OB = 0 has the greatest heat of combustion.

Experimental investigation of the factors affecting the burning rate of solid rocket propellants

The burning rate of the solid rocket propellants is one of the most important factors that determine the performance of the rocket. The burning rate of rocket motors running with solid propellant is called flame regression, which occurs with the ignition in the fuel grain perpendicular to the burning surface. This study investigates the effects of the addition of metal-based high-energy matter (Aluminum) into the content of the propellant produced within the scope of development project. The study starts with the manufacture of propellant samples. For the data input in the burning rate measurement device, the determination process of energy levels of the manufactured propellant samples with a calorimeter is performed. Then, the other data related to the propellants to be measured for the burning rate, such as energy level of the propellant, the propellant density, the maximum combustion temperature, and the physical sizes of the propellants, were inputted to the computer of the burning rate measurement device. The 22g of the sample propellant to be measured for burning rate was placed in a part of the burning rate measurement device, “closed bomb” which has a capacity of 200cm3. Burning rate measurements were performed at the same time in a constant-volume environment under different pressures. The burning rate of the double base propellant without aluminum (DB-1) was compared with other double base fuels in which aluminum was added by 2% (DB-2) and 4% (DB-3). It was found that the burning rates and burning heat of new fuels manufactured by adding aluminum to the content of the standard double base fuel (DB-1) increased.

Infrared radiation signature of exhaust plume from solid propellants with different energy characteristics

The infrared radiation signature of the plume from solid propellants with different energy characteristics is not the same. Three kinds of double-base propellants of different energy characteristics are chosen to measure the infrared spectral radiance from 1000cm−1 to 4500cm−1 of their plumes. The radiative spectrum is obtained in the tests. The experimental results indicate that the infrared radiation of the plume is determined by the energy characteristics of the propellant. The radiative transfer calculation models of the exhaust plume for the solid propellants are established. By including the chemical reaction source term and the radiation source term into the energy equation, the plume field and the radiative transfer are solved in a coupled way. The calculated results are consistent with the experimental data, so the reliability of the models is confirmed. The temperature distribution and the extent of the afterburning of the plume are distinct for the propellants of different energy characteristics, therefore the plume radiation varies for different propellants. The temperature of the fluid cell in the plume will increase or decrease to some extent by the influence of the radiation term.

Experimental Study and Modeling of the Combustion Wave of Metalized Solid Rocket Propellants

The combustion waves of double-base propellants containing reactive metals such as aluminum (Al), magnesium (Mg), boron (B), nickel (Ni) and Mg-Al mechanical alloy (Mg/Al=3/4) has been experimentally investigated by means of thermal couple method. The heat effect of metals in the condensed phase which might control the burning characteristics of the double-base propellant was systematically investigated and descriptions of the detailed combustion physical model of the metals from solid phase to liquid phase or to gas phase are also included. Moreover, a numerical calculation method for analyzing combustion wave structure of metallized propellants has been designed and the fitting functions for thetemperature profiles were obtained by Origin 7.5 software. It is believed that in gas phase there would be multi-stage reaction mechanism and that the reaction mechanism would be identical in condensed phase for different metallized propellants, only the heat release value was different.

Combustion of double-base propellants of various compositions containing ammonium nitrate

The combustion of various propellants containing ammonium nitrate (AN) is studied. It is shown that the effect of AN on the burning rate depends on the heat of combustion of the starting propellant, the amount of AN, and the pressure at which combustion occurs. Thus, AN slightly increases the burning rate of low-calorific value propellants and significantly reduces that of high calorific value formulations. It is shown that combined catalysts can considerably increase (by a factor of up to ≈6 at a pressure of 2–4 MPa) the burning rate of propellants containing 50–70% of AN, and reduce the pressure dependence of the burning rate.

Effect of Initial Temperature on the Interior Ballistics of a 120-mm Mortar System

In this study, the effect of the initial temperature of a 120-mm mortar system on its interior ballistics was investigated using four different experiments: temperature-conditioned closed bomb firings for determining the temperature sensitivity of the ignition cartridge's M48 double-base propellant and instrumented firings of temperature-conditioned flash tubes, ignition cartridges, and an instrumented mortar simulator (IMS). The results of these experiments reveal that, for initial temperatures of –12 °C and greater, the mortar system and its subcomponents exhibited regular initial-temperature-dependent behavior, with increasing initial temperature causing monotonically increasing propellant burning rates and monotonically decreasing ignition delays, which produce monotonically increasing system pressures and pressure differentials in the flashtube, ignition cartridge, and IMS. However, some anomalous behavior was discovered for temperatures around –46 °C. At this initial temperature, the closed bomb firings indicated that brittle fracture of the M48 propellant granules used in the ignition cartridge occurs. This phenomenon explains the occurrence in the IMS firings of dramatically increased variation in pressure-time behavior and projectile muzzle velocity for charge 4 firings as compared to higher temperatures, as well as the occurrence of maximum tube pressures for –46 °C firings, being greater than those for 21 °C firings for charge 0. However, one of the –47 °C closed bomb firings does not exhibit evidence of grain fracture and yet produces a higher propellant burning rate than the –12 °C firings, suggesting that a fundamental change in reaction kinetics or flame structure is occurring at extremely low temperatures. This supposition is bolstered by evidence of a liquid layer existing on the surface of M48 propellant granules ejected from the ignition cartridge during the –46 °C firings—a phenomenon that does not occur at the higher initial temperatures and is not theorized to occur in double-base solid propellant combustion. Based on the flash tube experiments alone, the flash tube was determined to have a weak effect on the initial-temperature-dependent behavior of the mortar system; however, IMS testing with two different flash tube configurations revealed significant differences in longitudinal pressure wave amplitude and projectile muzzle velocity in charge 4 firings between the two configurations at –46 °C, suggesting that the uniformity of combustion product discharge from the flash tube could significantly affect the performance of the mortar at low temperatures.

Definition of a JA-2 Equivalent Propellant to be Produced by Continuous Solventless Extrusion

In order to eliminate residual solvents in ammunition and to reduce the emissions of volatile organic compounds to the atmosphere, the U.S. Army ARDEC has teamed with TNO in developing a new process for the production of solventless propellant for tank ammunition. To reduce the costs of solventless propellants production, shear roll mill and continuous extrusion processing was investigated. As described in this paper JA-2 a double base propellant cannot be processed without solvent by the extrusion process. An alternative JA-2 equivalent propellant was defined. The aim of this work is to demonstrate the manufacturing of this propellant by solventless continuous twin screw extrusion processing while maintaining gun performance characteristics of conventional JA-2 propellant. This is elucidated by explicitly researching the relationship between interior ballistic properties of the gun propellant and utilizing a continuous manufacturing process. Processing conditions were established, and the propellant was manufactured accordingly. The extruded propellant has the desired properties, which resulted in a comparable gun performance as the conventional JA-2 propellant.

A Study of Experimental Method for Mechanical Properties of Solid Propellant under Hydrostatic Compressive Loading

Mechanical behavior of solid propellant material under multi-axial loads has attracted much attention in engineering application. According to the properties of solid propellant material, a kind of triaxial compressive device for solid propellant material was designed by utilizing the operating principle of the soil triaxial compressive device. The structural features and operating principle were expounded, and some notes should be paid attention during tests, and mechanical properties of a kind of double-base propellant material under hydrostatic loading were investigated, and some very meaningful data and conclusions were obtained. The results show that the yield strength and compressive strength of double-base propellant material under hydrostatic loading have obtained more remarkable enhancement than those without the hydrostatic pressure effect. The experimental device and the test results may lay the foundation for further research into a viscoelastic-plastic constitutive model of solid propellant material.

Research on Expansion Technique of Lateral Supporting Structure in Explosive Neutralization System Based on Mechanical Mechanics

This paper is focused on the lateral supporting structure of the explosive neutralization system, using the massive gas produced by double base propellant burning in an instance as the expanding power of the lateral supporting structure, which drive the structure to expand smoothly due to the prescribed requirements. In order to accomplish such a complicated physical and chemical process, we choose proper double base propellant and analyses the theory of the burning of double base propellant, build the model instant burning; then calculate parameters such as the force of push, expansion time, make a prototype based on theoretical calculation and make a plan of the experiment. The results of the experiment indicate that the reliability and security of the double base propellant, which is the expanding power of the structure, and that the expanding time of the structure basically tally with the theoretical calculation results.

Effects of Lead Complex-Based BTATz on Thermal Behaviors, Non-Isothermal Reaction Kinetics and Combustion Properties of DB/RDX-CMDB Propellants

The composite double base(DB)/hexogen(RDX)-modified double base(CMDB) propellants(Nos.DB001 and CMDB100) were prepared with the lead complex of 3,6- bis(1H-1,2,3,4- tetrazol- 5- ylamino)-1,2,4,5-tetrazine(LCBTATz),with and without the ballistic modifier.Their thermal behaviors and nonisothermal decomposition reaction kinetics were investigated by thermogravimetry,derivative thermogravimetry(TG- DTG),and differential scanning calorimetry(DSC).For the LCBTATz-DB propellant,there was one mass loss stage in the TG curve and one exothermic peak in the DSC curve over the temperature range350-540 K.For LCBTATz-CMDB,there were two continuous exothermic stages in the TG curve,and only one corresponding exothermic peak in the DSC curve over the range 390-540 K.The exothermal decomposition reaction mechanisms of LCBTATz-DB and LCBTATz-CMDB follow the functions f(α)=α-1/2and f(α)=2(1-α)3/2,respectively(α:conversion degree).The self-accelerating decomposition temperatures(TSADT),thermal ignition temperatures(TTITT),critical temperatures of thermal explosion(Tb),adiabatic timesto-explosion(tTlad),and thermodynamic parameters of activation reaction were calculated,and the thermal safety was evaluated.For DB001,TSADT=444.50 K,TTITT=453.96 K,Tb=471.84 K,and tTlad=39.36 s.For CMDB100,TSADT=442.38 K,TTITT=452.89 K,Tb=464.13 K,and tTlad=21.3 s.As a high-efficiency combustion catalyst,LCBTATz in double-base propellants increases the propulsion rate and reduces the pressure index for larger scale pressures.This makes the DB propellant appear to have a significant super burning effect at 2- 8 MPa and a"mesa effect"at 8-12 MPa.Meanwhile,the pressure exponent of the CMDB propellant decreased to 0.18.