Combustion Mechanism of Azide Polymer

The combustion wave structure and thermal decomposition process of azide polymer were studied to determine the parameters which control the burning rate. The azide polymer studied was glycidyl azide polymer (GAP) which contains energetic – N₃ groups. GAP was cured with hexamethylene diisocyanate (HMDI) and crosslinked with trimethylolpropane (TMP) to formulate GAP propellant. From the experiments, it was found that the burning rate of GAP propellant is significantly high even though the adiabatic flame temperature of GAP propellant is lower than that of conventional solid propellants. The energy released at the burning surface of GAP propellant is caused by the scission of N N₂ bond which produces gaseous N₂. The heat flux transferred back from the gas phase to the burning surface is very small compared with the heat generated at the burning surface. The activation energy of the decomposition of the burning surface of GAP propellant, E_s, is determined to be 87 kJ/mol. The burning rate is represented by r = 9.16 × 10³ exp(–E_s/RT_s) where r (m/s) is burning rate, T_s (K) is the burning surface temperature, and R is the universal gas constant. The observed high temperature sensitivity of burning rate is correlated to the relationship of (∂T_s/∂T₀)_p = 0.481 at 5 MPa, where T₀ is the initial propellant temperature.     

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.     

Thermal Decomposition of AMMO/AP Composite Propellants

Thermal decomposition of AMMO/AP composite propellants was studied by DTA, TGA and DSC in helium atmosphere. The effects of accelerated aging at 347 K for 370 days on decomposition kinetics were also measured. AMMO/AP propellant showed two different decomposition steps, which were mainly the AMMO binder decomposed region and the reaction of AP dominated region. These regions were separated at around 20 % weight loss point at the condition used in this study. AMMO binder decomposition and AP decomposition were strongly related each other. The heat generated by the AMMO binder decomposition initiated and accelerated the thermal decomposition of AP. Although both Fe₂O₃ and CFe activated the thermal decomposition of AMMO/AP propellants, CFe mainly accelerated the decomposition of AMMO binder and Fe₂O₃ catalyzed the AP reactions which consisted of the AP decomposition and the reaction between decomposed AP and decomposed AMMO binder. AMMO/AP composite propellants were thermally stable even after aging at 347 K for 370 days.     

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.     

Thermal Decomposition of BAMO Copolymers

The effects of copolymerization of THF, as an inert component, AMMO, as an energetic one and NMMO, as a nitrate ester, with BAMO on their thermal decomposition are reported here. Although the thermal decomposition of the BAMO and NMMO units in B/N(7/3) carry out independently and the heat generated by the NMMO unit decomposition accelerates the BAMO unit decomposition, the THF and AMMO units do not affect that of the BAMO unit in B/T(7/3) and B/A(7/3). One exothermic peak in DSC is shown for B/A(7/3) and B/T(7/3) except for B/N(7/3) which shows two peaks. One peak at lower temperature is from the NMMO unit decomposition and the other is from the BAMO unit. The rate of decomposition of B/A(7/3) is the same as that of poly(BAMO), which indicates that the reactivity of the AMMO unit is equal to that of the BAMO unit. In propellant, containing 75% HMX and 25% copolymer binder, burning rate of B/A(7/3)/HMX is faster than that of B/N(7/3)/HMX. Although the heat of decomposition for B/A(7/3) in DSC is smaller than that for B/N(7/3), that of B/A(7/3)/HMX is larger than that of B/N(7/3)/HMX. The reaction occurred in the condensed phase of the propellant, therefore, may play an important role in the combustion.     

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.     

Influence of carbon on combustion characteristics of Magnesium-Sodium Nitrate Propellant

Effect of addition of carbon in the form of graphite and carbolac on the combustion characteristics of Magnesium-Sodium nitrate propellant has been studied. Results indicated that the burning rate of the propellant increased significantly by the addition of graphite upto 2%. Thermal decomposition studies revealed that the graphite particles in addition to its absorption of thermal energy being an inert material react with the decomposed products of the sodium nitrate just above the burning surface of the propellant for the exothermic heat release. This heat release which is high at low concentration of graphite is seen causing high burning rate. Any further increase in graphite concentration beyound 2% reduces the burning rate as the thermal energy absorption exceeds the heat release at the burning surface. When carbon in the form of carbolac was used in the composition reactive species diffuse out prior to the sample ignition without participating in the combustion thus reduces the burning rate. The heat of reaction data supported the suggested mechanism.     

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.     

Thermal characteristics of energetic polymers based on tetrahydrofuran and oxetane derivatives

Thermal characteristics and decomposition behaviors of energetic polymers based on oxetane derivatives, 3,3'-bis(azidomethyl)oxetane (BAMO), 3-azidomethyl-3'-methyloxetane (AMMO), 3-nitratomethyl-3'-methyloxetane (NMMO), and 3,3'-bis(ethoxymethyl)oxetane (BEMO), were studied by means of differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA). These polymers were found to exhibit low glass transition and large decomposition onthalpies which were brought about by the attached azide (? N₃) and nitrato (? ONO₂) groups. The decomposition enthalpies depended on the types and contents of the energetic substituents. The NMMO-based polymers exhibited relatively higher decomposition enthalpies and less thermal stability than the others. Furthermore, the thermal stability of the polymers was further improved by partial curing treatment. These results reveal that these polymers are potentially useful for application in energetic propellant binders. © 1995 John Wiley & Sons, Inc.     

Thermal Decomposition of BAMO/HMX Propellants

Thermal decomposition of BAMO [bis(azidomethyl)oxetane/tetrahydrofuran copolymer]/HMX composite propellants was studied by isothermal TGA (thermogravimetric analysis) and DSC (differential scanning calorimetry) in helium atmosphere, which was showing overall two steps first-order kinetics. The effects of cross-link ratio on the accelerated aging of the BAMO/HMX propellants were also measured with infrared spectroscopy and gas chromatography. The accelerated aging was conducted at 347 K for several weeks. BAMO/HMX propellants for a very low cross-link ratio made the cavity between HMX and BAMO binder by N₂, CO₂, and H₂O evolutions during accelerated aging. An exotherm, generated by the decomposition of azide binder, initiated and accelerated the thermal decomposition of HMX. The burning rate of BAMO/HMX propellant was larger than those of BAMO binder and HMX, respectively. However, the propellant could not maintain the combustion at low pressure, at which its burning rate was equal to that of BAMO binder.     

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。     

铅盐催化剂对GAP少烟推进剂燃烧性能的影响

采用DSC研究了不同形貌的铅盐催化剂CH-Ⅰ和CH-Ⅱ对AP热分解行为的影响,获得了其热分解反应的动力学参数,并考察了催化剂对GAP少烟推进剂燃烧性能的影响。结果表明,铅盐催化剂能够降低AP的低温分解反应活化能,提高高温分解反应速率。在GAP少烟推进剂中,加入铅盐催化剂CH-Ⅰ和CH-Ⅱ,能够显著提高其高压下的燃速,15~25MPa内的压强指数分别由不加催化剂时的0.46降至0.35和0.34。AP的热分解行为与GAP少烟推进剂燃烧紧密相关。AP热分解反应的加快是推进剂燃速提升的主要原因,催化剂的催化活性与其形貌和粒度有关。催化剂CH-Ⅱ的催化效果优于催化剂CH-Ⅰ。     

Effect of Binders on the Burning Rate of AP Composite Propellants

The burning rate characteristics of ammonium perchlorate (AP) based composite propellants is studied as a function of the chemical nature of the polymers used as binders. The following five types of polymers are used:(1) hydroxy‐terminated polybutadiene (HTPB)(2) polypropyleneglycol (PPG)(3) polysulfide (PS)(4) polyesterpolyol (PO)(5) azidomethylmethyloxetane (AMMO) Experiments are conducted using differential thermal analysis (DTA), thermogravimetric analysis (TG), and burning rate analysis. The AP/PS propellant shows the highest burning rate and the AP/PO propellant shows the lowest burning rate within the propellants tested. Though the burning rate appears to be very dependent on the type of binder used, the characteristics of burning rate versus pressure cannot be correlated with the thermochemical data obtained by DTA and TG. The results of the photographic observation of the burning surface indicate that the formation of a melting layer of the binder reduces the burning rate due to the reduced reaction rate between the binder and the AP particles.     

Effects of Copolymerization Ratio of BAMO/NMMO and catalyst on sensitivity and burning rate of HMX propellant

Three different copolymerization ratios of BAMO/NMMO copolymers were studied for the requirement of not only a high specific impulse but also an insensitive munition characteristics for HMX composite propellant. These molar ratios of BAMO/NMMO were 8/2, 7/3, 6/4. Although the heat of DSC measured was relatively largest in B/N(7/3) propellant, there was no difference in the thermal decomposition characteristics. The exothermic reactions of azide binder and of HMX occurred in the same temperature region. The faster burning rate was obtained by the more BAMO ratio in the binder. The shock sensitivity was the lowest in B/N(7/3) HMX composite propellant. This unexpected stability might be caused by the physical effect of the molecular structure of B/N(7/3) which might contribute to the sudden dumping of the impact shock. Although the detonation velocity, because faster as BAMO ratio, increased like as the burning rate, the detonation pressure was the lowest in B/N(7/3) propellant. The mixture of catocene and copper chromite augmented the burning rate 1.6 times with decreasing temperature sensitivity.     

纳米ZnO立方体催化AP热分解及其在HTPE推进剂中的应用

为改善高氯酸铵(AP)的性能,从而改善复合固体推进剂的燃烧性能,采用AP辅助的金属有机骨架结构(MOF)热分解法合成纳米ZnO立方体催化剂(n-ZnO/cube);采用XRD、FESEM、TEM等对其形貌进行了表征,分析了其比表面积和孔径分布;采用TG-DTA分析了其对AP热分解的影响;将其加入到HTPE推进剂中,测试了其对推进剂工艺性能、安全性能、力学性能及燃烧性能的影响。结果表明,n-ZnO/cube催化剂具有大的比表面积(70.5m2/g)和大量的孔道结构,将AP热分解的高温分解峰从413℃降至279℃,放热量从584J/g增至1520J/g,分解活化能从151.1kJ/mol降至65.3kJ/mol;将质量分数2%的n-ZnO/cube加入到HTPE推进剂中,推进剂的燃速(20℃,6.86MPa)从12.01mm/s提高到16.16mm/s,工艺性能、安全性能、力学性能、燃速压强指数(0.42,20℃,3~16MPa)、燃速温度敏感系数(2.02×10^-3℃^-1,-55~70℃,6.86MPa)均未受到明显影响,表明纳米ZnO立方体结构对AP热分解表现出良好的催化性能,是HTPE推进剂的一种具有潜力的燃烧调节剂。     

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.     

B12H12［N(C2H5)4］2对NEPE推进剂燃烧性能的影响

研究了硼氢化合物 B1 2 H1 2 [N(C2 H5 ) 4] 2 对 NEPE推进剂燃烧性能的影响 ,采用 DSC分析了 B1 2 H1 2 [N(C2 H5 ) 4] 2 与 NEPE推进剂主要组分硝酸酯的相容性以及对推进剂固化反应的催化作用和对高氯酸铵、硝胺常压热分解的催化作用 ,并利用恒压静态燃速仪测试了推进剂在 4～ 1 1 MPa的燃烧速度和燃速压力指数     

A Study of Solid Propellant Containing Titanium Hydride

The burning rate characteristics of the propellant containing TiH₂ have been examined in order to understand the effect of TiH₂ addition on the combustion wave structure. The burning rate increases and the pressure exponent of burning rate decreases as the addition of TiH₂ increases. Using very fine thermocouples which were embedded within the propellant samples, the heat transfer process in the combustion wave was determined. The results indicate that the heat flux feedback from the gas phase to the burning surface increases when TiH₂ is mixed within the propellants.     

ETPE发射药的热分解特性与燃烧机理

通过DSC、PDSC分析了点火延迟时间长及难点火ETPE发射药燃烧过程中的热分解特性。用中止燃烧实验装置、SEM电镜观察研究了ETPE发射药燃烧表面的形貌变化及燃烧规律。结果表明,ETPE发射药热分解过程主要由其配方中含能添加剂RDX的热分解过程决定,RDX组分与含能黏结剂BAMO/AMMO聚合物体系之间的燃烧不同步性是造成ETPE发射药点火燃烧性能不佳的主要原因。根据ETPE发射药燃烧过程的特点,归纳出该类发射药的燃烧机理。