Research on Perfusion Explosives from SF‐3 Double‐Base Propellants Using Supercritical CO2

Perfusion explosives were prepared using porous SF‐3 propellants, which were synthesized by a supercritical fluid foaming process. Scanning electron microscopy (SEM) was used to characterize the porous SF‐3 propellants. Massive holes were generated after the foaming process. The density of perfusion explosives using foamed SF‐3 propellants exceeds 1.3 g cm⁻³, and the detonation velocities exceed 6000 m s⁻¹. Underwater energy tests and high‐speed photography were carried out to investigate the detonation performance of perfusion explosives. The results showed that perfusion explosives using unfoamed SF‐3 propellants could not be detonated. However, perfusion explosives using their foamed analogs could be detonated herein.     

Stability of Non‐isothermally Treated Double‐Base Propellants Containing Different Stabilizers in Comparison with Molecular Orbital Calculations

In this research work some malonanilide derivatives (M1‐M5) have been prepared and used as stabilizers for double‐base propellants (DBPs). Their stabilization effect has been compared with the effect of N,N‐diethyldiphenylurea (C1) as a classical stabilizer. Thermal analysis (TA) study under non‐isothermal conditions was carried out on propellant samples containing stabilizers. This study gave information about the thermal stability effect of different stabilizers on DBPs, thermal decomposition and some thermodynamic parameters. The non‐isothermal (TGA and DSC) results show that the o‐dinitromalonanilide (M3) has the highest thermal stability effect on the propellant samples. The molecular orbital calculations such as energy gap (ΔE), net charge, E_LUMO, E_HOMO, IP, and E_a were done and compared with TA experimental data. It was finally concluded that there is no single factor controlling the stabilizing effect of different stabilizers on thermal stability of DBPs. There is a group of factors that play important role in detecting the stabilizing effect of stabilizers on DBPs such as energy gap, charge density on the o‐position of the benzene ring and the net charge on the benzene ring itself.     

Investigation of the Burning Behavior of Cryogenic Solid Propellants

Cryogenic Solid Propellant (CSP)‐technology is a new approach to develop more powerful rocket motors. CSPs include the advantages of classical solid propellants to save weight as well as those of a high energy content and safety of modern liquid propellants. The charges consist of liquid and/or gaseous fuels and oxidizers, both frozen. Two main versions of CSP‐technology can be realised: 1. Mono‐CSPs show the burning behavior of solid propellants. Experiments with mono‐CSPs have been carried out under inert pressure conditions in a window bomb. Mono‐CSPs have a stable burning behavior with a constant regression rate which follows the Vieille's law under varying pressure conditions. 2. The advantage of high safety is obtained by assembling oxidizer and fuel in sandwich configurations. The grain geometry governs the burning behavior. Such systems can be externally controlled, e.g. by the heat from a gas generator or they can work self‐sustained. A Rod‐in‐Matrix burner shows self‐sustained combustion in an inert pressure atmosphere with overall burning rates in a similar range as solid rocket propellants which obey also a Vieille‐like pressure law. Disc stack burners have also been investigated, the combustion of which is strongly dependent on the disc thickness. For a short time Mach's nodes have been observed in the exhaust plume of a disc stack burner. Currently, the temperature ranges are limited to the boiling temperature of liquid nitrogen. Therefore, liquid oxidizers like H₂O₂ have been used. However, for the first time a propellant strand of polymer rods embedded in solid oxygen was prepared and burnt. The experiments with CSPs end in the combustion of a small rocket motor showing no serious technical obstacles. Simplified models based on the heat flow equation can simulate the burning characteristics of the frozen energetic materials including phase transitions.     

降低固体推进剂燃速研究进展

综述了复合推进剂、硝酸酯增塑聚醚(NEPE)推进剂和改性双基推进剂在降低燃速方面的研究进展,并指出未来降低固体推进剂燃速研究的重点为向推进剂中引入含能降速剂及采用热分解温度较高且能量较高的新型含能材料。     

用ACP提高固体推进剂的燃速

用快燃物ACP提高改性双基推进剂、AP／HTPB复合推进剂和N-15D推进剂的燃速,取得了非常显著的效果。在HMX和RDX改性双基推进剂配方中加入不同粒度不同含量的ACP,推进剂的燃速均能提高,压强指数基本无变化。在AP基复合推进剂配方中加入ACP,其燃速均有不同程度的提高,而且在7～15MPa的压强范围内,压强指数小于0．45。成功地进行Ф64mm发动机试验,并获得稳定的P-t曲线。N-15D推进剂配方的燃速较低,加入ACP后,燃速也有提高,压强指数稍有增大。结果表明,加入ACP后燃速提高效率分别是：HMX改性双基推进剂配方为40．62％,RDX改性双基推进剂配方为38．00％,复合推进剂配方为37．35％,N-15D推进剂配方为9．90％。     

A Desorption Electrospray Ionization Mass Spectrometry Study of Aging Products of Diphenylamine Stabilizer in Double‐Base Propellants

Double‐base propellants consisting of nitrocellulose, nitroglycerin and stabilizer undergo chemical and physical changes upon aging, leading to changes in ballistic power and presenting explosive hazards. During aging, PTFE seals of the glass ampoules used in the aging studies undergo a yellow discoloration. This report studies the discoloration of the liners using desorption electrospray ionization (DESI), a gentle surface analysis technique based on electrospray ionization. The color bodies in the PTFE liners were identified by DESI together with tandem mass spectrometry to be the nitrated derivatives of the diphenylamine stabilizer: dinitro‐, trinitro‐, and tetranitrodiphenylamine. While increased nitration decreases vapor pressure of the DPA species, an increase in solubility in the PTFE liners occurs. This may account for these species not previously being observed during early aging studies as they are preferentially absorbed into the liners, which were not extracted prior to high performance liquid‐ chromatography analysis.     

Burning Rate Evaluation of Composite Solid Propellants. A simplified approach

One of the principal parameters associated with a solid propellant is its linear burning rate. Many attempts have been made in the past to determine theoretically the burning rates of solid propellants by the use of appropriate combustion models. The object of the present paper is to propose a simplified theory of burning rate suitable for composite solid propellants. While the paper follows basically the scheme suggested for this purpose by Beckstead, Derr and Price using multiple flamelets, certain simplifying assumptions have been introduced with a view to make the model easier to operate. An attempt is also made in the paper to extend it to the case of aluminized solid propellants as well on the basis of a specific hypothesis regarding the role of aluminium. The relevant transcendental equations of combustion were solved on a digital computer. The burning rates and related characteristics were evaluated by this technique for two specific ammonium perchlorate-based solid propellants, one aluminized and the other non-aluminized, and the results obtained agree reasonably with the reported experimental trends.     

Burning Mechanism of Aluminized Solid Rocket Propellants Based on Energetic Binders

This paper reports results obtained from an experimental study of the combustion mechanism of aluminized propellants based on an energetic binder. The techniques used in this investigation include:     

固体推进剂的PDSC特征量与燃速的相关性

把双基、改性双基、交联改性双基和NEPE推进剂等32个配方的高压差示扫描量热(PDSC)特征量△Sd与燃速u用经验方程u=ku[p△Sd]1/2进行了关联,其中:p为压强,△Sd=△Hd/(Te-To),△Hd为分解热,To为放热起始温度,Te为放热结束温度.在迄今PDSC试验能达到的压力范围内得到了满意的结果.获得的燃速与PDSC特征量相关因子ku能用以考核燃速催化剂的作用和推进剂组分的影响.     

Effect of Particle Orientation on the Burning Rate of Ammonium-Perchlorate-Based Solid Propellants

Combustion, Explosion, and Shock Waves - This paper addresses the effect of oxidizer particle orientation on the burning rate of ammonium-perchlorate-based heterogeneous solid propellants....     

Research on Titanium‐Containing Micro‐Porous Propellants with Rapid Burning Rate

Micro‐porous propellants containing titanium powder were obtained by supercritical CO₂ (SC CO₂) foaming technique. The morphologies of the micro‐porous propellants were characterized by scanning electron microscopy (SEM) and energy‐dispersive X‐ray spectroscopy (EDS) measurement. The burning rate, the impetus, and the heat of explosion of the micro‐porous propellants were measured by the closed vessel test and the calorimetric bomb test. The results show that the porosity increased with increasing titanium powder content; compared with Benite, the burning rate was substantially improved, and the maximum values of the impetus and the isochoric heat of explosion increased by 51.4 % and 6.5 %, respectively. The Ti‐containing micro‐porous propellants with rapid burning rate and better energetic properties described in this paper may have the potential to replace Benite as igniter material in a flame igniter of a gun propellant charge.     

Measurement and Analysis of the Burning Rate of HAN‐Based Liquid Propellants

A new device for measuring the linear burning rate of liquid propellants at high pressures is reported. High‐pressure environments were generated by the combustion of solid propellants. The coated propellants, which burn progressively, were introduced to maintain the approximate constant‐pressure environments. By use of ion probe transducers, measurements were made of the spread velocity of the flame surface, i.e. the apparent linear burning rate of the HAN‐based liquid propellant LP1846 (HAN =hydroxylammonium nitrate) was measured quantitatively at pressures from 6 to 28 MPa. The results show that it follows the exponential burning rate law. The burning rate coefficient and exponent were fitted by least‐squares methods. Based on the experiment, a simplified model of the linear burning rate of HAN‐based liquid propellants at high pressures was developed. The numerical simulation is found to be in good agreement with the experimental data.     

Influence of an Electric Field on the Burning Behavior of Solid Fuels and Propellants

An experimental study on the effects of an applied external electric field on the combustion behavior of solid fuels and solid propellants has been conducted. In an opposed flow burning configuration, application of an electric field was shown to extinguish a paraffin fuel and gaseous oxygen flame over a broad range of operating conditions. When subjected to the electric field, burning paraffin fuel strands were found to extinguish at various axial locations relative to the exit of the oxidizer gas jet. Extinguishment location was found to be a function of field strength as well as electrode surface area, while changes in polarity did not significantly alter the results. In addition, the combustion behaviors of two composite solid rocket propellants were studied while subjected to an external electric field. Both propellants were based on HTPB/AP combinations, with one propellant containing aluminum and the other being non‐aluminized. Application of an electric field to the composite solid rocket propellant strands demonstrated decreases in propellant burning rate under all operating conditions for both propellants including changes in polarity. The flame structure of the aluminized propellant was examined closely as the luminosity, flame length, and flame width varied significantly with field strength and burning location of the strand relative to the electrodes.     

Development of Polyurethane‐Based Solid Propellants Using Nanocomposite Materials

Mechanically‐activated nanocomposites (MANCs) of nano‐aluminum (nAl)/X (X=Cu, Ni, Zn, Mg, and graphite) were used as replacements for reference nAl powder and as catalytic ingredients in polyurethane (PU) propellants. The effects of their use on combustion heat, burning rate, and thermal decomposition were investigated. It was found that MANCs have catalytic effects and the modified propellants have enhanced the released heat, burning rate, and thermal decomposition properties. MANCs‐based propellants have improved the processing and the mechanical properties with acceptable safety aspects. They can be used for catalytic applications in solid propellants to improve their energetic, burning rate, and thermal decomposition characteristics.     

Burning Rate – Pressure Relationship of NG‐PE‐PCP‐based High Energy Propellants

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/HMX/AP/Al based solid propellant processed by slurry cast route were carried out using varying percentages of HMX and AP. It was observed that propellant compositions containing only AP and Al loaded (total solids 75 %) in NG plasticized PE‐PCP binder produce comparatively lower pressure exponent (η) values similar to AP‐Al filled HTPB based composite propellants. However, energetic propellants containing high level of nitramine (40–60 %) produce high pressure exponent (0.8–0.9) values in the same pressure range. Incorporation of fine particle size AP (ca. 6 μm) and change in its concentration in the propellant composition reduces η value marginally and influences the burning rate. However, such compositions have higher friction sensitivity.     

Burning Characteristics of Ammonium Nitrate‐based Composite Propellants Supplemented with MnO2

Ammonium nitrate (AN)‐based composite propellants have several major problems, namely, a low burning rate, poor ignitability, low energy, and high hygroscopicity. The addition of a burning catalyst proved to be effective in improving the burning characteristics of AN‐based propellants. In this study, the burning characteristics of AN‐based propellants supplemented with MnO₂ as a burning catalyst were investigated. The addition of MnO₂ is known to improve the ignitability at low pressure. The most effective amount of MnO₂ added (ξ) for increasing the burning rate is found to be 4 %. The increasing ratio with ξ is virtually independent of the burning pressure and the AN content. However, the pressure exponent unfortunately increased by addition of MnO₂. The apparent activation energy of the thermal decomposition for AN and the propellant is decreased by addition of MnO₂. From thermal decomposition kinetics it was found that MnO₂ could accelerate the thermal decomposition reaction of AN in the condensed phase, and therefore, the burning characteristics of the AN‐based propellant are improved.     

Burning Characteristics of Ammonium Nitrate‐based Composite Propellants Supplemented with Ammonium Dichromate

Ammonium nitrate (AN)‐based composite propellants have attracted much attention, primarily because of the clean burning nature of AN as an oxidizer. However, such propellants have some disadvantages such as poor ignition and low burning rate. Ammonium dichromate (ADC) is used as a burning catalyst for AN‐based propellants; however, the effect of ADC on the burning characteristics has yet to be sufficiently delineated. The burning characteristics of AN/ADC propellants prepared with various contents of AN and ADC have been investigated in this study. The theoretical performance of an AN‐based propellant is improved by the addition of ADC. The increase in the burning rate is enhanced and the pressure deflagration limit (PDL) becomes lower with increasing amount of ADC added. The increasing ratio of the burning rate with respect to the amount of ADC is independent of the AN content and the combustion pressure. The optimal amount of ADC for improving the burning characteristics has been determined.     

Effects of Twin‐Screw Extrusion Processing on the Burning Rate of Composite Propellants

A new process for continuous manufacturing of composite propellants has been developed using Twin Screw Extrusion (TSE). The effects of TSE‐processing on the burning rates of an ammonium perchlorate (AP)‐based composite propellant have been characterized over a wide composition range (79 to 87 wt. % AP) and a wide range of screw speeds (45 to 85 RPM) using a quadratic model for an experimental Response Surface Analysis (RSA) based on the Kowalski, Cornell, and Vining (KCV) algorithm. Using Student‘s T‐test, it was determined that burning rates obtained from strand‐burning rate tests at 3.5 MPa, 7.0 MPa, and 10.5 MPa are affected only by the individual ingredients, the interaction between the coarse AP particles and the binder, and the screw speed. Measured burning rates were found to be 40% to 100% higher than Petite Ensemble Model (PEM) predictions, which was accounted for by modifying the PEM through a power law relationship with pressure that includes a rule‐of‐mixtures dependence of the exponent and coefficient on the weight fraction of coarse and fine AP particles. The resulting modified PEM reduced differences between the predictions and experimental data by 79% at 3.5 MPa, 83% at 7.0 MPa, and 78% at 10.5 MPa.     

Burning Behavior of Nitramine Gun Propellants under the Influence of Pressure Oscillations

By means of DNDA nitramine fractions in the formulation, it is hoped to produce gun propellants that have an almost temperature‐independent burning behavior. The reason for this behavior is not clear yet. In the last years, it has become known that pressure oscillations may occur in the hole channels of gun propellant grains that may lead to a modification of the burning. To analyze the impact of such oscillations on the burning behavior of DNDA powders, tests with two different DNDA powders were performed in a closed vessel. In both cases, it could be demonstrated that the oscillations have a determining influence on the temperature behavior.     

Determination of Chemical and Mechanical Properties of Double Base Propellants during Aging

Thermal and mechanical stability of rocket and gun propellants are very important properties with regard to safety during storage and handling and to the interior ballistics behavior during combustion. However, our knowledge of how these properties are connected is poor. In order to better understand the aging behavior of double base propellants, the following properties were measured between 60 °C and 90 °C: the depletion of the stabilizers, the degradation of the molecular weights of nitrocellulose and the decrease of the mechanical properties (tensile strength and strain at break). The evaluation of the kinetic parameters of the different aging processes mentioned has shown that stabilizer depletion, molecular weight degradation of nitrocellulose and decrease of mechanical properties must be closely connected.