Thermal Decomposition of RDX Composite Propellants

The thermal decomposition characteristics of RDX, binders, and RDX composite propellants were studied using thermal analytical techniques. Three kinds of binders were tested to elucidate the role of binder on the burning rate of the propellants. There were no apparent correlations between the thermal decomposition rates of binders and the burning rates of propellants, whereas there was a correlation between the decomposition temperature and the burning rate of the propellants. It is found that the major factor which controls the burning rate is the initial thermal-decomposition stage of the binders. Thus, the burning rate of nitramine composite propellants appeared to be largely dependent on the physical and chemical properties of binder.     

Burning Rate Augmentation of BAMO Based Propellants

Thermal decomposition and the burning properties of BAMO based propellants with HMX or AN/HMX have been investigated. The heat generated by the azide binder decomposition initiated and accelerated the thermal decomposition of HMX and AN. Ammonium perchlorate (AP) and lead stearate with carbon black significantly altered the mechanisms of the thermal decomposition and the burning properties of the HMX based propellants. AP showed an increase in burning rate with a slight decrease in burning rate pressure exponent. The lead catalyst yielded high value of the burning rate with the lowest pressure exponent. The ammonium dichromate also influenced the mechanisms of the thermal decomposition and the burning properties of the AN/HMX samples. The combination of ammonium dichromate and copper chromite was the most effective on the burning rate augmentation of AN/HMX based propellants. AN sublimed and evaporated from the condensed phase and mainly reacted exothermically in the gas phase HMX and AN/HMX based propellants showed smokeless burning characteristics in the small rocket motor combustion tests.     

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.     

含黑索今酮的火药热分解及燃烧性能研究

用ＤＳＣ技术考察了７种含黑索今酮（Ｋｅｔｏ－ＲＤＸ）火药的热分解特性,并对其中３种进行了密闭爆发器测试。将ＤＳＣ数据对动力学方程进行拟合以求得动力学参数。从密闭爆发器测试结果转换得到了该３种火药的燃速－压力曲线,并对其进行了转折性分析。结果表明,向火药中加入Ｋｅｔｏ－ＲＤＸ可提高火药燃速并降低其热分解表观活化能。含Ｋｅｔｏ－ＲＤＸ的火药其燃速压力指数在低压区较在高压区为高。在火药中同时存在有Ｋｅｔｏ－ＲＤＸ和ＲＤＸ对火药热分解和燃烧的稳定性是不利的。仅由Ｋｅｔｏ－ＲＤＸ与双基粘结剂组成的火药,其燃速压力指数较由ＲＤＸ与双基粘结剂组成的火药为低。     

Storage stability of solid rocket fuels. 2. Effect of oxidizer loadings

Ageing behaviour, leading to ballistic changes, has been studied as a function of oxidizer loading in polystyrene/ammonium perchlorate solid-propellants. The ageing studies were carried out at 100 °C in air. Change in burning rate decreased as the oxidizer loading increased from 75 to 80%. The change in thermal decomposition rates both at 230 and 260 °C also decreased as the oxidizer loading in the propellants increased. The shapes of the plots of the changes in burning rate and thermal decomposition rate (230 and 260 °C) at different storage times for different oxidizer-loaded propellants seem to be exactly similar. These results lead to the conclusion that the thermal decomposition of the propellant may be responsible for bringing about the ballistic changes during the ageing process. Infrared studies of the binder portion of the aged propellant indicate that peroxide formation takes place during the course of ageing and that peroxide formation for a particular storage time and temperature increases as the loading decreases.     

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.     

CL-20含量及其粒度级配对NEPE推进剂燃烧性能的影响

采用静态与水下声发射法测试了CL-20含量及其粒度级配对NEPE推进剂燃速与压强指数的影响;采用DSC与TG-IR联用研究了CL-20对NEPE推进剂热分解行为的影响。结果表明,随着CL-20质量分数由42%增至50%,推进剂燃速与压强指数上升,燃烧效率提高,表明CL-20氧化能力高于GAP/硝酸酯含能黏合剂体系;随着CL-20/HMX、CL-20/Al质量比增高,推进剂燃速上升,燃烧效率上升;CL-20对推进剂燃速和压强指数的贡献高于HMX;随着CL-20/AP质量比增高,CL-20/AP混合体系分解产物氧化能力降低,燃烧反应速率降低,燃速降低;CL-20粒度级配对NEPE推进剂燃烧行为影响显著,当CL-20的粒径(d50)在5~50μm时,随着细粒度CL-20含量增高,推进剂燃速与燃速压强指数下降;当体系中存在超细粒度CL-20(d50=500nm)时,推进剂燃速与燃速压强指数随着超细粒度CL-20含量的增加而有所增加,4种粒度CL-20对NEPE推进剂燃速的贡献顺序为:粗粒度>中粒度>超细粒度>细粒度。     

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。     

基于动力学过程的固体推进剂降速机理

根据朗缪尔单分子吸附原理和AP分解的质子转移机理,分别在AP晶体界面和气相混合区中确立物质守恒关系,分析了AP在不同分解速率下气相混合区中NH_3和HClO_4的气相分子浓度关系;将其与AP晶体气固交界面的反应强度进行关联,建立了一种能够分析压强变化状态对推进剂燃速影响的动力学机理,并推导了相应的物理过程,通过实验将AP/降速剂(CaCO_3或NH_4C_2O_4)的TG-DSC分析结果与药条燃速结果进行了对比。结果表明,该降速机理能够解释降速剂对推进剂燃速和压强指数的多种作用,CaCO_3能够使AP的热失重分解温度出现一定程度的前移,因此对控制推进剂的高压压强指数有利,而NH_4C_2O_4不具备这种效果。     

含1,3,3-三硝基氮杂环丁烷CMDB和NEPE推进剂的燃烧性能和热行为

利用燃速和火焰结构测试、TG-DTG和高压DSC实验分别研究了含1．3，3-三硝基氮杂环丁烷(TNAZ)的两类(TZ-CMDB和TZ-NEPE)推进剂的燃烧性能和热行为，发现了TNAZ对推进剂燃速、压力指数和火焰结构的影响及高压下TNAZ对上述两类推进剂中其它含能组分分解的影响，并得出常压下TZ-CMDB和TZ-NEPE推进剂受热时，TNAZ挥发和分解的温度范围为58～190℃。     

高能单元推进剂化学结构和热分解特征与燃速的相关性

利用以准一维气相反应流为基础的固体推进剂稳态燃烧模型,研究了高能单元推进剂AP、HM X、RDX、CL-20和NQ的化学结构、热分解特征与燃烧性能的相关性。改进了高能单元推进剂燃速预估模型,使其可由高能单元推进剂的化学结构和基本热分解特性出发,预估单元推进剂的燃烧性能。通过与实测燃速的比较,验证了模型假设的合理性。     

火药热分解特性与燃烧稳定性间相关性的分析

火药热分解过程的复杂性与其燃烧稳定性之间,存在有某种统计性的增函数关系。火药热分解特性对其燃烧特性的影响,是通过燃烧过程中亚表面热分解表观活化能的变化来实现的,当环境温度和压力较低时,亚表面的热分解特性,与常规条件下该火药的热分析结果相近。对于热分解过程较为复杂的火药,随着环境压力和温度的升高,其亚表面的分期机理和表观分解活化能将发生改变,亚表面分解速率随压力的变化规律也要发生变化,这就导致了燃烧过程的不稳定性,而对于那些热分解过程较为简单的火药,则不会出现这种情况,此外,本文还提出,火药中某些组分的爆燃是导致一些火药燃速压力指数较高的原因。     

还原型锡酸铅粒度对Al/HMX/CMDB推进剂燃烧性能及安定性的影响

为研究还原型锡酸铅粒度对Al/HMX/CMDB推进剂燃烧性能及安定性的影响,采用干筛法筛选6种不同粒度的还原型锡酸铅,制备了含不同粒度还原型锡酸铅体系的推进剂;通过燃速靶线试验、甲基紫试验与热加速老化试验得到推进剂的燃速、压强指数、甲基紫变色时间和贮存寿命。结果表明,随还原型锡酸铅粒径由7.0μm减至2.5μm,Pb²⁺及SnO₂的催化活性逐渐增大,活化中心愈多,该体系推进剂在15~20MPa范围内的燃速逐渐增加,压强指数由0.30减至0.17;同时还原型锡酸铅粒度的减小加速了该体系推进剂的自催化作用,造成其安定性下降,当还原型锡酸铅的粒径为2.5~3.5μm时,推进剂的安定性显著降低。     

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.     

RDX改性双基球形小粒药的燃烧特性

讨论了改性双基球形小粒药中RDX颗粒的分布和RDX热分解的特点,提出了RDX改性双基球形小粒药的燃烧机理。通过密闭爆发器实验测定了RDX改性双基小粒药的燃烧特性,并对实验结果进行了理论分析。结果表明,改性双基球形小粒药中RDX与双基火药基体的分解是各自独立进行的;随着压力的升高,改性双基小粒药的燃速将大于改型双基小粒药的燃速。     

Thermal Decomposition Behaviors and Burning Characteristics of Ammonium Nitrate/Polytetrahydrofuran/Glycerin–based Composite Propellants Supplemented with MnO2 and Fe2O3

Although a polytetrahydrofuran (PTHF) blend with added glycerin as a crosslinking modifier is an effective binder for improving the performance of a propellant, a burning catalyst is required for the combustion of the ammonium nitrate (AN)/PTHF/glycerin propellant. MnO₂ and Fe₂O₃ are useful burning catalysts for AN‐based propellants. The thermal decomposition behaviors of the AN/PTHF/glycerin propellant supplemented with MnO₂ and Fe₂O₃ catalysts, and the catalytic effect of these catalysts on the burning characteristics was investigated in this study. The thermal decomposition behaviors of these propellants depended on the kind of catalyst used. The propellants containing MnO₂ burned above 4 MPa, while those containing Fe₂O₃ burned above 0.5 MPa. The burning rate increased in the order, (AN/PTHF/Fe₂O₃)<(AN/PTHF/MnO₂)<(AN/PTHF/MnO₂/Fe₂O₃). The improvement in the ignitability and burning rate was dependent on the kind of catalyst used. The burning characteristics of the AN/PTHF/glycerin propellants were improved by the combined effect of multiple catalysts with differing catalytic mechanisms, as compared to the propellant supplemented with any single catalyst.     

Determination of the Decomposition Behavior of Double-Base Propellants at Low Temperatures

Thermal and mechanical stability are very important characteristics of energetic materials used as ingredients of propellants compositions. For the determination of the thermal decomposition behavior of solid double base propellants, usually gravimetric, calorimetric, and chemical methods are being employed. At ICT, the decreasing rates of stabilizers determined by high-performance chromatography at different temperatures are successfully used as a mean to forecast the chemical life time of propellants containing nitric esters. On the other hand, the mechanical properties are evaluated by measuring the tensile strength with a more or less accuracy. In the last years, the increasing performance of the gel-permeation chromatography enabled the determination of the molecular weight and the molecular weight distribution of nitrocellulose in different propellants. In this connection a linear relationship between temperature and depolymerization rate was obtained. This relationship corresponds fairly well with the stabilizer depletion rate and the drop in the mechanical properties.     

Characterization studies on aging properties of acetyl ferrocene containing HTPB‐based elastomers

In composite solid propellants, low‐molecular‐weight species such as burning rate catalysts, plasticizer, etc. which migrate into liner and thermal insulation layers during curing and storage invariably result in poor mechanical and ballistic properties of the propellants. In the present study, the migration of the burning rate catalyst, acetyl ferrocene, was investigated spectrophotometrically (UV–visible) by evaluating the extent of hindrance to such migration after applying a barrier (liner) of various crosslink densities between the additive (HTPB‐TDI‐plasticizer–acetyl ferrocene) and nonadditive (HTPB‐TDI) gumstocks replicating the propellant and insulating layer, respectively. Enhancing the crosslink densities of liner via a trifunctional aziridine crosslinking agent inhibited migration. The aging of additive gumstock was done at 60°C and its mechanical properties and extent of acetyl ferrocene migration were also evaluated and analyzed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2538–2545, 2006     

Iron Nanoparticle Additives as Burning Rate Enhancers in AP/HTPB Composite Propellants

Burning rate measurements were carried out for ammonium perchlorate/hydroxyl‐terminated polybutadiene (AP/HTPB) composite propellants with iron (Fe) nanoparticles as additives. Experiments were performed in a strand burner at pressures from 0.2 to 10 MPa for propellants containing approximately 80 % AP and Fe nanoparticles (60–80 nm) at concentration from 0 to 3 % by weight. It was found that the addition of 1 % Fe nanoparticles increased burning rate by factors of 1.2–1.6. Because Fe nanoparticles are oxidized on the surface and have high surface‐to‐volume ratio, they provide a large surface area of Fe₂O₃ for AP thermal decomposition catalysis at the burning propellant surface, while also providing added energy release due to the oxidation of nanoparticle sub‐shell Fe. The increase in burning rate due to Fe nanoparticle content is similar to the increase in burning rate caused by the addition of iron oxide (Fe₂O₃) particles observed in prior literature.     

Research on the Combustion Properties of Propellants with Low Content of Nano Metal Powders

A comparison of various experimental results for combustionrelated properties evaluation, including burning rates, deflagration heat, flame structures and thermal decomposition properties, of AP/RDX/Al/HTPB composite propellants containing nano metal powders is presented. The thermal behavior of n‐Al (nano grain size aluminum) and g‐Al (general grain size aluminum i.e., 10 μm) heated in air was also investigated by thermogravimetry. The burning rates results indicate that the usage of bimodal aluminum distribution with the ratio around 4 : 1 of n‐Al to g‐Al or the addition of 2% nano nickel powders (n‐Ni) will improve the burning behavior of the propellant, while the usage of grading aluminum powders with the ratio 1 : 1 of n‐Al to g‐Al will impair the combustion of the propellant. Results show that n‐Al and n‐Ni both have a lower heating capacity, lower ignition threshold and shorter combustion time than g‐Al. In addition n‐Al is inclined to burn in single particle form. And the thermal analysis results show that n‐Ni can catalyze the thermal decomposition of AP in the propellant. The results also confirm the high reactivity of n‐Al, which will lead to a lower reaction temperature and rather higher degree of reaction ratio as compared with g‐Al in air. All these factors will influence the combustion of propellants.