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.     

Evaluation of 4‐(Dimethylsilyl) Butyl Ferrocene Grafted HTPB as a Burning Rate Modifier in Composite Propellant Formulation using Bicurative System

High burning rate composite propellants are achieved by incorporation of fine particles of oxidizer, transition metal oxides, and liquid ballistic modifiers. However, they pose processing problems, inertness to the composition and migration related issues. To overcome such problems, an attempt was made to incorporate ferrocenyl grafted HTPB as a burning rate modifier by partly replacing HTPB from 10 % to 50 % using TDI/ IPDI bicurative system and to study their processability in terms of viscosity, mechanical, thermal, sensitivity, and ballistic properties. The data on viscosity reveal that there is a marginal enhancement in end of mix viscosity as percentage of ferrocenyl grafted HTPB increases. The mechanical data reveal that tensile strength and elastic modulus increases, whereas percentage elongation decreases compared to base composition. The results on thermal properties infer that, as the percentage of ferrocenyl grafted HTPB increases, onset decomposition temperature decreases. The impact and friction sensitivity data also envisage that sensitivity increases in comparison to base composition. The data on ballistic properties revealed that there is ca. 53 % increase in burning rate, while decrease in “n” value from 0.39 to 0.2 was obtained compared to base composition.     

纳米氧化铅为燃烧催化剂的应用研究

运用红外光谱法研究纳米氧化铅对 HMX固相热分解的影响 ,通过静态靶线法燃速测试仪考察纳米氧化铅在推进剂中的实际应用效果。红外谱峰的变化表明 :氧化铅对 HMX的固相热分解直接起催化作用。通过纳米氧化铅在 NEPE推进剂中的实际应用效果表明 :纳米氧化铅可有效的降低 NEPE推进剂的燃速压力指数。     

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.     

Evaluation of Nano‐Co3O4 in HTPB‐Based Composite Propellant Formulations

Different propellant compositions were prepared by incorporating nano‐sized cobalt oxide from 0.25 % to 1 % in HTPB/AP/Al‐based composite propellant formulations with 86 % solid loading. The effects on viscosity build‐up, thermal, mechanical and ballistic properties were studied. The findings revealed that by increasing the percentage of nano‐Co₃O₄ in the composition, the end of mix viscosity, the modulus and the tensile strength increased, whereas the elongation decreased accordingly. The thermal property data envisaged a reduction in the decomposition temperature of ammonium perchlorate (AP) as well as formulations based on AP. The ballistic property data revealed an enhanced burning rate from 6.11 mm s⁻¹ (reference composition) to 8.99 mm s⁻¹ at 6.86 MPa and a marginal increase in pressure exponent from 0.35 (reference composition) to 0.42 with 1 % nano‐cobalt oxide.     

硝胺改性双基推进剂燃速压力指数的数值模拟

提出了硝胺改性双基推进剂燃速压力指数的化学数学模型,给出了燃速压力指数公式。利用此公式,可由推进剂的组成直接计算不同压力下的燃速压力指数,其结果不但反映出压力指数的变化趋势,而且在数值上与实测值也十分一致。同时,从基本模型出发,讨论了影响推进剂燃速压力指数的化学结构因素。     

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.     

含高氮化合物的高燃速CMDB推进剂的能量特性

利用能量计算程序计算了含高氮化合物3,6–双(1–氢–1,2,3,4–四唑–5–氨基)–1,2,4,5–四嗪(BTATz)的复合改性双基(CMDB)推进剂的能量特性,并研究了用3种含能添加剂高氯酸铵(AP)、六硝基六氮杂异伍兹烷(HNIW)、黑索今(RDX)和2种增塑剂1,5–二叠氮基–3–硝基–3–氮杂戊烷(DIANP)及二缩三乙二醇二硝酸酯(TEGDN)分别部分取代BTATz和硝化甘油(NG)后,对含BTATz的CMDB推进剂能量特性的影响规律。结果表明:无论推进剂中是否含铝粉,用BTATz取代CMDB推进剂中的硝化棉(NC)和NG后,将不同程度地降低原推进剂的各能量特性参数;用AP和HNIW部分取代BTATz后,可使BTATz–CMDB推进剂的理论比冲明显提高;用DIANP或TEGDN部分取代推进剂中的NG,各能量特性参数均随其含量增加而减小。     

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.     

Combustion Effects of Nitrofulleropyrrolidine on RDX‐CMDB Propellants

The effect of N‐methyl‐2‐(3‐nitrophenyl)pyrrolidino[3′,4′:1,2]fullerene (mNPF) on the decomposition characteristics of hexogen (RDX) was investigated using differential scanning calorimetry (DSC). The results show that mNPF can accelerate the decomposition of RDX, the peak temperature (T_p) of the exothermal decomposition is reduced by 6.4 K, and the corresponding apparent activation energy (E_a) is decreased by 8.7 kJ mol⁻¹. N‐methyl‐2‐(3‐nitrophenyl)pyrrolidino[3′,4′:1,2]fullerene (mNPF), carbon black (CB), and C₆₀ were used as combustion catalysts to improve the combustion performance of a composite modified double‐base propellant containing RDX (RDX‐CMDB). The burning rate experimental results show that mNPF has a stronger catalytic effect than C₆₀ and CB. The magnitude of the effect of the three carbon substances on the enhancement of the burning rate is as follows: mNPF>C₆₀>CB. The catalytic effects of different contents of mNPF on the burning rates of RDX‐CMDB propellants were also studied, and the results show that the burning rates of RDX‐CMDB propellants are improved with increasing mNPF content. The plateau burning rate of a RDX‐CMDB propellant can be increased to 19.6 mm s⁻¹ when 1.0 % mNPF is added, and the corresponding plateau combustion region occurs at 8–22 MPa.     

Effects of Different Metal Fuels on the Characteristics for HTPB‐based Fuel Rich Solid Propellants

The microstructures and granularity distribution of different metal particles were investigated and the energy, sensitivity, and combustion properties of fuel rich solid propellants with different metal particles were studied in detail. It was found that the magnesium particles are more uniform than other metal powders, the mean diameter of the magnesium particles d₅₀=67.6 μm is much higher than those of the other ones, which are in the range of 7.1 μm<d₅₀<20.5 μm. Additionally, the preparation process of the Mg‐based propellant is easier than those of the other ones. The experimental results showed that the propellant containing magnesium powder was less sensitive to friction and impact (165.1 NM and 21.9 NM, respectively), whereas, the burning rates of propellants with Zr and ZrH₂ particles increased, and the pressure exponents decreased.     

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 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.     

Comparative Studies of Pressure Sensitization of Zirconium Carbide and Zirconium Silicate on Burning Rates in a RDX‐AP based Composite Propellant

In a systematic study to compare the effects of the values of burning rate and pressure exponent in RDX‐AP based composite propellant, various compositions with varying percentages of zirconium carbide (ZrC) and zirconium silicate (ZrSiO₄) were formulated to select a suitable candidate. Various rocket parameters of each formulation were theoretically predicted by the NASA CEC‐71 program and the burning rate was evaluated in pressure range of 3–11 MPa. In addition, density, sensitivity, and thermal properties of compositions having maximum effects on pressure exponent’s values were also evaluated. It was concluded that ZrSiO₄ enhances the pressure exponent “n” value substantially, whereas ZrC doesn’t have significant effects on it as compared to base composition and also provides higher density values of composite propellant formulated.     

Burning Characteristics of Ammonium Nitrate‐Based Composite Propellants Supplemented with Fe2O3

Ammonium nitrate (AN)‐based composite propellants have attracted a considerable amount of attention because of the clean burning nature of AN as an oxidizer. However, such propellants have several disadvantages such as poor ignition and a low burning rate. In this study, the burning characteristics of AN‐based propellants supplemented with Fe₂O₃ as a burning catalyst were investigated. The addition of Fe₂O₃ is known to improve the ignitability at low pressure. Fe₂O₃ addition also increases the burning rate, while the pressure exponent generally decreases. The increasing ratio (R) of the burning rate of the AN/Fe₂O₃ propellant to that of the corresponding AN propellant vs. the amount of Fe₂O₃ added (ξ) depends on the burning pressure and AN content. R decreases at threshold value of ξ. The most effective value of ξ for increasing the burning rate was found to be 4 % for the propellant at 80 % AN, and the value generally decreased with decreasing AN content. According to thermal decomposition kinetics, Fe₂O₃ accelerates the reactions of AN and binder decomposition gases in the condensed‐ and/or gas‐phase reaction zones. The burning characteristics of the AN‐based propellant were improved by combining catalysts with differing catalytic mechanisms instead of supplementing the propellant with a single catalyst owing to the multiplicative effect of the former.     

Combustion Characteristics of a Novel Grain‐Binding High Burning Rate Propellant

The novel grain‐binding high burning rate propellant (NGHP) is prepared via a solventless extrusion process of binder and spherical propellant grains. Compared with the traditional grain‐binding porous propellants, NGHP is compact and has no interior micropores. During the combustion of NGHP, there appear honeycomb‐like burning layers, which increase the burning surface and the burning rate of the propellant. The combustion of NGHP is a limited convective combustion process and apt to achieve stable state. The larger the difference between the burning rate of the binder and that of the spherical granular propellants exists, the higher burning rate NGHP has. The smaller the mass ratio of the binder to the spherical granular propellants is, the higher the burning rate of NGHP is. It shows that the addition of 3 wt.‐% composite catalyst (the mixture of lead/copper complex and copper/chrome oxides at a mass ratio of 1 : 1) into NGHP can enhance the burning rate from 48.78 mm⋅s⁻¹ in the absence of catalyst to 56.66 mm⋅s⁻¹ at P=9.81 MPa and decrease the pressure exponent from 0.686 to 0.576 in the pressure range from 9.81 to 19.62 MPa.     

超高燃速推进剂燃速压力敏感性理论探讨

探讨了超高燃速推进剂(UHBPR)的燃速压力敏感性。通过理论分析，提出了一种降低LIHBRP燃速压力敏感性的方法。采取密度梯度的方法制造药柱，使药柱的密度从点火端到终了端呈现逐渐增加的趋势，可以极大地降低UHBRP燃速压力敏感性，在理论上燃速压力指数可以降低到零。     

The Effects of Porous Structure on the Burning Characteristics of Foamed NC‐Based Gun Propellants

The effects of porous structure on the burning characteristics of foamed NC‐based (nitrocellulose‐based) gun propellants were investigated by closed vessel and quenched combustion experiments. The foamed NC‐based TEGDN (triethylene glycol dinitrate) gun propellants with different porous structures were prepared by adjusting the process parameters in the foaming process. SEM (scanning electron microscopy) was used to observe the morphologies of foamed TEGDN propellants, and the densities of the foamed propellants were also measured to evaluate the porosities of foamed propellants. The experimental results showed that the burning characteristics of the novel foamed propellants are totally different from combustion characteristics of parallel‐layer. Further investigations revealed that the burning characteristics of the foamed NC‐based propellants largely depend on the porous structure, larger pores and higher porosity would lead to higher burning rate of the foamed TEGDN propellants.     

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.     

A Pressurized Vessel Test to Measure the Minimum Burning Pressure of Water‐Based Explosives

It is well known that water‐based commercial explosives locally ignited in closed vessels do not undergo self‐sustained combustion when the pressure is lower than some threshold value. The latter is usually referred to as the Minimum Burning Pressure (MBP) of the explosive and is now being used by some manufacturers as a basis of safety for many associated manufacture, transport, and handling processes. In the present work, both an apparatus based on hot‐wire ignition and an associated methodology were developed to measure the MBP of water‐based explosives. Typical results for various emulsion and water‐gel explosives are also reported and discussed. It is also shown that the technique could be used to characterize very insensitive explosive substances normally used as explosive precursors.