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.     

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.     

RDX-CMDB推进剂燃速温度敏感系数的实验研究

为了揭示RDX-CMDB推进剂中各常见组分对其燃速温度敏感系数的影响规律,制备了一系列含RDX、铝粉及燃烧催化剂的CMDB推进剂样品。采用氮气靶线法测得其在2~14MPa下的燃速温度敏感系数(σp)。讨论了RDX含量、铝粉、燃烧催化剂对RDX-CMDB推进剂燃速温度敏感系数的影响。结果表明,提高工作压强、增加RDX含量、添加燃烧催化剂均有助于降低RDX-CMDB推进剂在一定初始条件下的燃速温度敏感系数。配方中引入铝粉后可降低中低压下RDX-CMDB推进剂的燃速温度敏感系数,且燃速温度敏感系数几乎不随压强变化而变化。选用含邻苯二甲酸铅和没食子酸铋锆作燃烧催化剂,均可在2~10MPa下降低RDX-CMDB推进剂的燃速压强指数,同时降低燃速温度敏感系数。     

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.     

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.     

Effect of ZrC content on the properties of biomorphic C–ZrC–SiC composites prepared using hybrid precursors of novel organometallic zirconium polymer and polycarbosilane

A novel organometallic zirconium polymer was synthesized through the copolycondensation using n-butyllithium, 1,4-diethynylbenzene, phenylacetylene and zirconium tetrachloride as raw materials. Then biomorphic C–ZrC–SiC composites were fabricated from corn stover templates by precursor infiltration and pyrolysis process using hybrid polymeric precursors containing the organometallic zirconium polymer and polycarbosilane. The microstructure, mechanical properties and oxidation resistance of the composites were investigated. With ZrC content increasing, the mechanical properties of the composites were enhanced due to dispersion strengthening and grain fining of the homogeneously dispersed ZrC nanoparticles. The oxidation behavior of C–SiC–ZrC indicated that the oxidation resistance of the composite was reduced at 1000 °C but improved at 1500 °C with the increase of ZrC content. The improved oxidation resistance was mainly attributed to a proper ZrC content, the formation of ZrSiO₄ layer on the surface of the composite, and its matrix microstructure characterized by a nano-sized dispersion of ZrC–SiC phases.     

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.     

复合催化剂对Al/HMX/CMDB推进剂安定性的影响

含有复合催化剂的Al/HMX/CMDB推进剂样品,在放置3~4周后,爆热、燃速下降,压强指数升高。为找到具体原因,对推进剂试样进行了燃烧性能、真空安定性及DSC热分解实验,并对实验结果进行了系统分析。结果表明:复合催化剂中超细的SnO2具有较强的催化活性,催化推进剂在常温下进行热分解,最终导致推进剂安定性、爆热、燃速下降,压强指数升高。推进剂性能的恶化,严重影响其正常使用。     

Plateau Burning Characteristics of AP Based Azide Composite Propellants

The site and mechanism by which iron oxide catalyst acted to enhance burning rate and produced plateau burning behavior at high pressure was studied. The condensed phase chemistry study was conducted by isothermal thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and rapid-scan FTIR spectroscopic technique. Uncatalyzed ammonium perchlorate (AP) based azide composite propellant showed unstable combustion at relatively lower pressure region. The heat balance at the buring surface would be unstable at these pressures. However, iron oxide altered the burning property of the propellant and enhanced the burning rate with the plateau-mesa burning characteristics. Such pressure insensitiveness of the burning rate indicated that the condensed phase chemistry played important role in the catalytic mechanism of action. According to the microrocket motor tests, physical effect, melted fuel binder covered the AP particles and prevented the further decomposition of AP, had not affected the plateau burning. Fe₂O₃ was more effective on the burning rate augmentation than Fe₃O₄. However, the pressure exponent of the burning rate point of view Fe₃O₄ was favored catalyst to the propellant used here.     

新型高能高强度JMZ发射药的燃烧特性

为探索混合硝酸酯增塑的聚醚聚氨酯黏合剂体系的新型发射药的燃烧性能,通过密闭爆发器常规实验和高压实验．研究分析了JMZ发射药在不同压力范围的燃烧特性。结果表明,JMZ发射药在低压下的燃速压力指数较大,具有高含量RDX硝胺发射药的共同特征,但在高压下的燃速压力指数逐渐变小,与制式发射药相当,在燃速压力指数的变化过程中不存在明显的转折现象。另外,JMZ发射药在起始阶段表现出了良好的燃烧渐增性,对身管武器的应用是十分有利的。     

An Advanced GAP/AN/TAGN Propellant. Part I: Ballistic Properties

A solid rocket propellant based on glycidyl azide polymer (GAP) binder plasticized with nitrate esters and oxidized with a mixture of ammonium nitrate (AN) and triaminoguanidine nitrate (TAGN) was formulated and characterized. Non‐lead ballistic modifiers were also included in order to obtain a propellant with non‐acidic and non‐toxic exhaust. This propellant was found to exhibit a burning rate approximately twice that of standard GAP/AN propellants. The exponent of the propellant is high compared to commonly used composite propellants but is still in the useable range at pressures below 13.8 MPa. This propellant may present a good compromise for applications requiring intermediate burn rate and impulse combined with low‐smoke and non‐toxic exhaust.     

Composite Propellant Based on a New Nitrate Ester

Composite propellants based on the solid nitrate ester 2,3‐hydroxymethyl‐2,3‐dinitro‐1,4‐butanediol tetranitrate (SMX) were theoretically and experimentally examined and compared to formulations based on ammonium perchlorate (AP). Thermochemical equilibrium calculations show that aluminized SMX‐based formulations can achieve theoretical sea level specific impulse values upwards of 260 s. Both ignition sensitivity (tested via drop weight impact, electrostatic discharge, and BAM friction) and physical properties (hardness and thermal properties) are comparable to those of the AP‐based formulations. However, the SMX‐based formulation could be detonated using a high explosive donor charge in contact with the propellant. Differential scanning calorimetry of the SMX‐based propellant indicated an exotherm onset of 140 °C, which corresponds to the known decomposition temperature of SMX. The propellant has a high burning rate of 1.57 cm s⁻¹ at 6.89 MPa, with a pressure exponent of 0.85. This high pressure sensitivity might be addressed using various energetic and/or stabilizing additives. With good performance and high density, SMX‐based composite propellants may offer a promising perchlorate‐free alternative to existing AP‐based formulations.     

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.     

Effect of Zirconium on the Densification of Reactively Hot‐Pressed Zirconium Carbide

Densification mechanisms involved during reactive hot pressing (RHP) of zirconium carbide (ZrC) have been studied. RHP has been carried out using zirconium (Zr) and graphite (C) powders in the molar ratios 1:0.5, 1:0.67, 1:0.8, and 1:1 at 40 MPa, 800°C–1200°C for different durations. The volume fractions of phases formed, including porosity, are determined from the measured density and from Rietveld analysis. Increased densification with an increasing nonstoichiometry in carbon has been observed. Microstructural and X‐ray diffraction observations coupled with the predictions of a model based on the constitutive laws governing plastic flow of zirconium suggest that the better densification of nonstoichiometric compositions arise from the higher amount of starting Zr and also the longer duration of its availability for plastic flow during RHP. Volume shrinkage due to reaction between Zr and C and the gradual elimination of the soft metal phase limit the final density achievable. Based on these observations, a two‐step RHP carried out at 800°C and 1200°C leads to a better densification than a single RHP at 1200°C.     

含硼富燃推进剂压强指数的影响因素

为获得含硼推进剂压强指数的主要影响因素,采用捏合机混合物料,真空浇注、恒温固化的方法制备推进剂试样,靶线法测试推进剂(0.5～1.5MPa)燃速,用u=apn方程求得推进剂的压强指数.实验结果表明,HTPB含量、AP含量及粒度级配、催化剂含量对推进剂的压强指数均有不同程度的影响.HTPB含量减少、AP含量增加、AP重均直径减小、催化剂含量增加,均可提高推进剂的压强指数.     

Pot Life Problem and its measure with a reduced smoke propellant production

Typical reduced smoke type composite propellants mainly composed of hydroxyl-terminated polybutadiene (HTPB) and ammonium perchlorate (AP) have a drawback that these propellant grains have a high response function of the burning rate to cause acoustic pressure oscillation. The addition of a small fraction (0.5% ∼ 1.2wt%) of zirconium (Zr) or zirconium oxide powders to propellant compositions has been known to be effective for suppressing such a combustion instability. It is also notified, however, Zr powder would incur the acceleration of urethance forming reaction so as to make the pot life of the HTPB/AP propellant dough shorter. This paper reports that tetracycline (TC) is available to offset such a trouble in curing process brought about by Zr powder addition.     

纳米镍粉对Al-CMDB和CL-20-CMDB推进剂燃烧性能的影响

为了研究粒径为50nm的纳米镍粉(nano-Ni)对含Al改性双基(Al-CMDB)推进剂、含六硝基六氮杂异伍兹烷(CL-20)改性双基(CL-20-CMDB)推进剂燃烧性能的影响,通过吸收-压延的方法制备了推进剂样品,用靶线法测试了推进剂的燃速,并计算了压强指数。通过电镜扫描、火焰照片、燃烧波、熄火表面形貌及元素分析和DSC分析了纳米镍粉对Al-CMDB推进剂燃烧性能影响的原因。结果表明,在Al-CMDB推进剂中加入nano-Ni可大幅度提高推进剂燃速,降低推进剂的压强指数;当加入质量分数0.7%的nano-Ni时推进剂10MPa的燃速达到35.59mm/s,8~20MPa压强指数从0.43降低至0.17,15~20MPa出现麦撒效应。在CL-20-CMDB推进剂中加入质量分数0.5%的nano-Ni能明显提高推进剂的中低压(4~10MPa)燃速,8~20MPa压强指数约为0.01,15~20MPa出现麦撒效应。     

Studies on n‐Butyl Nitroxyethylnitramine (n‐BuNENA): Synthesis,Characterization and Propellant Evaluations

The laboratory synthesis of the energetic plasticizer n‐buNENA was scaled up to one kg batch size and the compound was fully characterized by spectral data and elemental analysis. N‐buNENA was formulated with CMDB and EDB propellant compositions. The results showed an improvement in mechanical properties and burning rate over a wide range of pressure along with acceptable limits of hazard and thermal stability as compared to DEP based propellant systems.     

Thermal and structural characterization of quasi‐nanometer zirconium carbon/polyurethane composites prepared under roller pressure

In this study, we use quasi‐nanometer zirconium carbon (ZrC) to compose with polyurethane (PU) resin under roller pressure to study the interaction between the ZrC particle and PU molecules in the composite films, and find that the values of tensile strength, modulus, energy at break, T_m of soft‐segment, and T_g of soft‐segment, and weight percentage of char yield are increased, and elongation and char yield temperature are decreased with the increase of ZrC composed in PU, as this composed amounts are lower than 2.5%. The infrared spectroscopic spectra and wide angle X‐ray diffraction patterns reveal that the ether and ester groups of PU polymer can interact with ZrC to lower the interlayer distance of the crystal of PU polymer in composites. We assure that the interaction between the particles of ZrC and PU under roller pressure is in preparation process and account that the interaction between the particle and PU molecule will be an important factor to evaluate whether the particle in the composite is even and perfect. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 191–197, 2006     

Correlation of parameters in the burning rate law and its influence on intraballistic characteristics of a rocket motor

Experimental data demonstrating the correlation of parameters in the power-law dependence of the burning rate of composite solid propellants on pressure are reported. The reasons for changes in the burning rate due to changes in propellant mixing conditions are discussed. The deviation of the pressure in the combustor of a solid-propellant rocket motor is analyzed with due allowance for the correlation of parameters in the burning rate law. It is shown that the relative deviation of the burning rate depends on pressure at which propellant combustion occurs. Moreover, for each propellant, there exists a pressure level at which the burning rate deviation is theoretically equal to zero, regardless of the differences in propellant compositions and properties.