Burning Rate Characterization of GAP/HMX Energetic Composite Materials

The burning rate of the energetic materials composed of glycidyl azide polymer (GAP) and HMX particles was characterized in order to elucidate the heat release process during burning. Since GAP is an energetic polymer and burns by itself, the addition of HMX increases the flame temperature and alters the burning rate characteristics. Experimental observations indicate that the gas phase structure consists of a two‐staged gas phase reaction: the burning rate is controlled by the first‐stage reaction zone and the final flame is formed at the second‐stage reaction zone. The heat flux transferred back from the first‐stage reaction zone to the burning surface increases as pressure increases and the heat released at the burning surface remains unchanged when pressure is increased.     

Combustion of GAP Based Energetic Pyrolants

Glycidyl azide polymer (GAP) is a high energy material used as a fuel component and binder of propellants and gas generators. High temperature products are formed by the scission of the chemical bond N₃ when GAP is decomposed. The major decomposition products are N₂, CO, and C. Though GAP contains no oxidizer fragments in its products, an addition of metal particles increases the energy of GAP. A mixture of GAP and metal particles forms a high energy metal based GAP pyrolant, i.e. GAP/metal pyrolant. The metals examined are Al, Mg, B, Ti, and Zr. The results indicate that the thermal decomposition and burning rate are dependent on the type of metals mixed.     

含能聚合物/硝基胍复合含能材料的制备及表征

以含能聚合物(EP)和硝基胍(NQ)为原料,采用溶剂/非溶剂法制备了EP/NQ复合含能材料,采用扫描电镜(SEM)、比表面积测试法(BET)和X射线衍射(XRD)对其形貌和结构进行了表征,用热重-差示扫描量热法(TGDSC)对比分析了EP/NQ复合含能材料及其物理共混物的热性能。结果表明,EP/NQ复合含能材料具有三维纳米网络结构,NQ沉积在EP上面,其平均粒径为49~62nm,NQ的长针状结晶消除;与EP相比,EP/NQ复合含能材料的比表面积降低,且随着NQ质量分数由40%增至60%,EP/NQ复合含能材料的比表面积由54.599m2/g降至25.02m2/g;EP/NQ复合含能材料具有单一的热分解峰特性,热分解峰温比NQ提前55~59℃,且随着NQ质量分数由40%增至60%,EP/NQ复合含能材料的热分解峰温由200.1℃升至203.7℃;EP/NQ复合含能材料的分解热显著高于EP/NQ物理共混物。     

Preparation and Properties of HMX Coated with a Composite of TNT/Energetic Material

To improve the safety of HMX without sacrificing energy properties, the composites of TNT and an energetic material (HP‐1) were used to coat HMX particles by a method of integrating solvent–nonsolvent with aqueous suspension‐melting. SEM (scanning electron microscopy) and XPS (X‐ray photoelectron spectrometry) were employed to characterize the samples. The effect of the processing parameters, such as mass ratio of HP‐1 to TNT (MRHT), stirring speed, and cooling rate, on the quality of coated samples were investigated and discussed. The mechanical sensitivity, thermal sensitivity, thermal decomposition characteristic, and heat of detonation of raw and coated HMX samples were also measured and contrasted. Results show that when MRHT, stirring speed in the second stage and cooling rate are 1 : 5, 1000 r⋅min⁻¹ and 5 °C⋅min⁻¹ respectively, the optimal coating effect is achieved. Compared with that of raw HMX, both impact and friction sensitivity of HMX coated with 2.5 wt.‐% TNT and 0.5 wt.‐% HP‐1 decrease obviously, whereas there is a slight change in their thermal sensitivity and thermal decomposition characteristics. Meanwhile, such surface coating does not result in the decrease of its energy properties.     

Mechanism of Catalytic Effects on AMMO/HMX Composite Propellants Combustion Rates

Thermal decomposition and the burning properties of AMMO/HMX propellants have been investigated. The heat generated by the AMMO decomposition initiated and accelerated the thermal decomposition of HMX, and the reaction between decomposed AMMO and HMX depended upon the heating rate. The rate determining step of the reaction path was different in higher and lower heating rate conditions. 2,2-bis(ethylferrocenyl)propane (CFe) and copper chromite (CuC) significantly altered the mechanisms of the thermal decomposition and the burning properties. CFe showed an increase in burning rate with a slight increase in burning rate exponent. However, CuC yielded high values for the burning rate exponent. The combined additive yielded the highest burning rate with the lowest burning rate exponent. The influence of CuC on the burning rate exponent disappeared by the combination with CFe. Though CFe and the combination additive improved the ignitability of the propellants, the propellant with CuC was difficult to ignite because of the relatively small quantity of heat feedback and/or heat released by the decomposition.     

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.     

Thermal Decomposition of Energetic Materials 81. Flash Pyrolysis of GAP/RDX/BTTN Propellant Combinations

The pyrolysis of a 50/50 mixture of RDX/GAP‐diol cured with the isocyanate compound N‐100, and a 70/21/9 mixture of RDX/BTTN/ GAP‐polyol cured with HMDI were studied by the T‐jump/FTIR spectroscopy technique. To understand the behaviors better, pyrolysis was also conducted on pure N‐100, pure BTTN, GAP‐diol cured with N‐100, and 70/30 BTTN/GAP‐polyol cured with HMDI. Pure N‐100 and the cured propellants liberate a large quantity of HMDI upon pyrolysis. This result reveals that the urethane bonds break early in the reaction sequence and the curing agent begins to vaporize from the matrix. The 50/50 RDX/GAP mixture decomposed with relatively little smoke or residue, which sharply contrasts with its reported behavior upon combustion. The difference can be attributed to the mismatch between the heating rates of flash pyrolysis and combustion. During pyrolysis the RDX and GAP are able to remain in contact longer such that fuel‐oxidizer reactions occur between them. During combustion the two compounds may segregate due to evaporation of most of the RDX. Hence the GAP decomposes in the condensed phase giving smoke and residue without the benefit of oxidation by NO₂ from the RDX. This discrepancy does not exist with the more fuel‐oxidizer balanced 70/21/9 mixture of RDX/BTTN/GAP, where the interaction of the fuel and oxidizer species is strong.     

An Advanced GAP/AN/TAGN Propellant. Part II: Stability and Storage Life

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) and including non‐lead ballistic modifiers, was formulated. The propellant was designed so as to produce non‐acidic and non‐toxic exhaust products while still providing reasonably good burning rate and impulse. This propellant was characterized with respect to thermal and chemical stability and storage life by a variety of test methods. The data indicate that the propellant exhibits good stability and is suitably safe for prolonged storage. Characterization data for this propellant with regard to processing parameters, tensile properties, and ballistic performance are presented in a companion paper.     

Optical Properties of Energetic Materials: RDX,HMX, AP,NC/NG,and HTPB

Optical properties of RDX, HMX, AP, HTPB/IPDI and a catalyzed NC/NG propellant (N5) were obtained from 2.5 μm to 18 μm using FTIR transmission spectrometry. Scattering-corrected KBr pellet methodology was used for the crystalline materials. Absorption index (k) was measured directly and refractive index (n) was deduced using dispersion theory. At 10.600 μm the absorption coefficients were AP, 190 cm⁻¹ (240 cm⁻¹ at 10.6036 μm); HTPB/IPDI, 360 cm⁻¹; N5, 510 cm⁻¹; RDX, 2800 cm⁻¹; and HMX, 5670 cm⁻¹.     

Combustion mechanism of HMX

The combustion wave structure and thermal decomposition process of HMX were examined in order to elucidate the burning rate characteristics of HMX. The combustion wave can be divided into three zones: nonreactive solid-phase, surface reaction, and gas-phase reaction zones. Measurements with micro-thermocouples revealed that the heat flux produced in the surface reaction zone is approximately equal to the heat flux transferred back from the gas phase to the burning surface. Accordingly, the reaction process in the suface reaction and the gas phase zones plays a dominant role in the burning rate of HMX. The gas phase reaction zone consists of a two-stage reaction process: the first stage is the exothermic rapid reaction process between NO₂ and aldchydes, and the second stage is the exothermic slow reaction process between NO and N₂O and remaining fuel species. The luminous flame zone which is determined to be the second stage reaction process approaches rapidly the burning surface as pressure increases. However, the luminous flame reaction appears to be little responsible for the burning rate of HMX. Examinations of the quenched burning surface of HMX samples revealed that the burning surface melts and forms a noncrystallized intermediate material. The surface structure appears to be different from the structure of thermally degraded HMX samples which were obtained by a thermogravnmetric analysis.     

含能聚氨酯热塑性黏合剂GAP/PBAMO的性能

以聚双叠氮甲基氧杂环丁烷(PBAMO)为硬段,聚缩水甘油醚(GAP)为软段,采用一锅法扩链合成了含能聚氨酯黏合剂(GAP/PBAMO).实验中合成了不同硬段含量的黏合剂,并采用FT-IR、NMR、GPC、XRD、DSC和SEM等对其结构和性能进行了表征.结果表明,硬段质量分数为66.7%时,该热塑性黏合剂具有较好的耐热...     

CL-20/开口多壁碳纳米管复合含能材料的制备与性能

以开口多壁碳纳米管(SMWNTs)为原料,六硝基六氮杂异伍兹烷(CL-20)为填料,采用超声吸入法制备CL-20/SMWNTs纳米复合含能材料;利用TEM、DSC-TG、XRD对样品进行表征,并对其进行激光点火试验。结果表明,CL-20晶粒填充到SMWNTs内部,填充部位在SMWNTs的端口,呈颗粒状排列。与纯CL-20相比,CL-20/SMWNTs纳米复合含能材料的起始分解温度由原来的239.6℃降至229.6℃,分解峰温也由原来的221.4℃降至173.6℃。CL-20/SMWNTs纳米复合含能材料光敏感性强,激光能量50W时可将其点燃。     

纳米多孔硅基复合含能材料的研究进展

综述了纳米多孔硅和纳米多孔硅基复合含能材料的国内外研究现状,通过分析认为该类复合含能材料具有反应活性高、能量可控、性能可调以及燃烧产物污染小等优点,具有很好的应用前景,但从目前的研究现状来看,还存在感度高、安全性能差、易氧化等缺点,且其爆炸反应机理也不明确,还需进一步进行制备工艺和爆炸反应机理方面的研究。     

Heats of Combustion and Formation of New Energetic Thermoplastic Elastomers Based on GAP,PolyNIMMO and PolyGLYN

Heats of combustion and formation of various energetic thermoplastic elastomers (ETPE), corresponding to linear copolyurethanes based on an energetic prepolymer and a diisocyanate, were measured by a calorimetric method. These ETPEs were synthesized from three different molecular weights of glycidyl azide polymer, from poly(3‐nitratomethyl‐3‐methyloxetane) and from poly glycidyl nitrate. The prepolymers were also analyzed for comparison with the corresponding ETPEs. A significant difference of the heats of formation was observed between the prepolymers and their ETPEs, while the heats of combustion were similar.     

含能材料燃烧过程中热分解化学的研究进展

从模拟燃烧条件、组分相互作用、组分物理状态、分析测试技术等几方面介绍了含能材料燃烧过程中热分解化学研究近几年来的最新进展。着重介绍燃烧热分解中的基元反应对建立推进剂燃烧新型模型的重要性、氧化剂和黏合剂及催化剂之间的相互作用、氧化剂的黏度和相态变化对燃烧和热分解过程的影响。     

Gas Generator Materials Consisting of TAGN and Polymeric Binders

This study introduces a new type of gs generator on the basis of triaminoguanidine nitrate with polymeric binders in the form of polyurethane polymers, cellulose acetate and the azidopolymer GAP with nitroplasticizer. TAGN propellants demonstrate low burning temperatures, high yields of gaseous products adn adjustable medium to high burning velocities. Together with high chemical and thermal stabilities, good mechanical properties to high and low temperatures, no exhaust of corrosive gases and very low sensitivity, the gas-generator propellants exhibit outstanding properties.     

Composite Energetic Materials Containing Nitrotriazalone Formed by Molecular Inclusion

The explosive properties of inclusion compounds containing the monoanion of the energetic compound 3‐nitro‐1,2,4‐triazol‐5‐one (NTO⁻) non‐covalently bound to either of two larger, energetic, receptor complexes, namely 1‐(2,4‐dinitrophenyl)‐1,4,7,10‐tetraazacyclododecanezinc(II) or 1‐(2,4‐dinitrophenyl)‐1,4,7,10‐tetraazacyclododecanecopper(II), both as their monoperchlorate salts, are reported. The sensitivity of the receptor host–guest complexes to electrostatic discharge or friction was not found to differ from that displayed by the separate components. However, for thermal sensitivity it was found that whereas NTO⁻ desensitized the Zn(II) receptor complex it sensitized the Cu(II) receptor complex. For sensitivity to impact, measured using the Rotter impact test, it was found that NTO⁻ sensitized the Zn(II) receptor complex, but desensitized the Cu(II) receptor complex.     

Combustion of Energetic Materials in an Acoustic Field (Review)

The review summarizes the long-term experience in theoretical research of combustion of gasifying condensed systems with periodically varied pressure. Most results are obtained within the framework of the Zel'dovich-Novozhilov theory. The main properties of the linear function of the burning rate response to harmonically varied pressure are discussed. The concept of nonlinear response functions is introduced, which is illustrated by the explicit form of a number of second-order response functions. A new phenomenon is described: bifurcations of response functions with a varied amplitude or frequency of pressure oscillations. For the simplest gunpowder model containing three parameters only, the sequence of bifurcations of doubling of the burning rate oscillation period is studied, which finally leads to a random combustion regime. An analytical relation between the linear response functions to harmonically varied pressure and to an oscillating radiant heat flux is noted. An example of calculating the response function with allowance for thermal inertia of the gas phase is presented. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 6, pp. 116–136, November–December, 2005.     

Fabrication and Properties of Insensitive CNT/HMX Energetic Nanocomposites as Ignition Ingredients

Cyclotetramethylene tetranitramine (HMX)‐coated carbon nanotube (CNT) nanocomposites with uniform structures were prepared using the recrystallization method. Characterization (SEM, TEM, XRD, BET, etc.) was performed to determine the micromorphology, crystal structure, and specific surface area. The energetic particles were homogeneously distributed on the surfaces of the CNTs, and the maximum thickness of the coating layer was approximately 120 nm, whereas the average crystal size was less than 50 nm. The test results of the thermal behavior showed that the thermal decomposition temperature decreased as the CNT content increased, and the maximum thermal conductivity was approximately 27.3 times higher than that of pure HMX. The sensitivities of the CNT/HMX nanocomposites to impact, friction, and shock were maximally reduced by 73 %, 29 %, and 74 % compared with those of pure HMX, respectively, which demonstrated a significant safety improvement. In the CNT/HMX nanocomposites, aluminum and ferric oxide were used to fabricate a new type of ignition composition. Based on comparative studies, the results showed that the ignition composition was porous and that its particles were more evenly distributed compared with the conventional counterparts. The thermal conductivity was improved by 21 %. The impact and friction sensitivities were also maximally reduced by 21 % and 27 %, respectively. The combustion heat was also increased by 9 % compared with that of a mixture of the same components.     

Convective Regime of Filtration Combustion of Energetic Materials in a Cocurrent Flow of Their Combustion Products

The convective regime of filtration combustion of energetic materials in a cocurrent flow of their combustion products is studied using a model with extremely simplified kinetics and heat transfer, which shows instability of the process. It is shown that the more accurate twotemperature model describes a steadystate regime. In this regime, the gas temperature on the hot boundary of the heating zone is well below the combustion temperature, and the solidphase temperature is well below the temperature proposed in recent studies on this topic. It is pointed out that the twotemperature approach is unjustified and intragranular nonisothermicity must be taken into account for convective regimes. It is shown that the threetemperature model, which takes into account this effect, does not give a stable steadystate solution.