Effect of nanostructures on the exothermic reaction and ignition of Al/CuOx based energetic materials

Al/CuOx based micro- and nanoenergetic materials (EMs) have been made by the thermal oxidation of Cu thin films deposited onto silicon substrates followed by Al integration through thermal evaporation. The micro- and nano-EMs are then characterized by scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, differential thermal analysis, and differential scanning calorimetry. By comparing the thermite reactions and ignition properties of Al with micro-CuOx and Al with nano-CuOx, we show experimentally that one-dimensional nanostructures (CuO nanowires) and nano-Al affect greatly the exothermic behaviors and ignition properties of the Al/CuOx based EMs. The higher surface energy associated with the CuO nanowires and the deposited nano-Al is believed to be a possible factor contributing to the enhanced exothermic reactions that occur below the melting point of Al and the smaller ignition delay and lower ignition energy.     

纳米钴酸铜的制备以及对高氯酸铵的催化性能

采用盐助溶液燃烧法,以硝酸铜和硝酸钴为原料,尿素为燃烧剂,KCl为反应惰性盐制备尖晶石型纳米钴酸铜。采用XRD、FT-IR、Raman和TEM等测试手段对产物进行了表征。结果表明,制得的纳米粒子具有较完美的晶体结构,分散性较好,粒径约为50nm。利用热分析法考察了纳米钴酸铜对高氯酸铵热分解的催化作用。结果显示纳米钴酸铜具有较高的催化活性,添加2%的纳米钴酸铜热分解温度降低136℃,催化效果优于单一组分的纳米金属氧化物。     

Gas-phase and heat-exchange effects on the ignition of high- and low-exothermicity porous solids subject to constant heating

This article investigates the ignition of low-exothermicity reactive porous solids exposed to a maintained source of heat (hotspot), without oxygen limitation. The gas flow within the solid, particularly in response to pressure gradients (Darcy’s law), is accounted for. Numerical experiments related to the ignition of low-exothermicity porous materials are presented. Gas and solid products of reaction are included. The first stage of the paper examines the (pseudo-homogeneous) assumption of a single temperature for both phases, amounting to an infinite rate of heat exchange between the two. Isolating the effect of gas production and flow in this manner, the effect of each on the ignition time is studied. In such cases, ignition is conveniently defined by the birth of a self-sustained combustion wave. It is found that gas production decreases the ignition time, compared to equivalent systems in which the gas-dynamic problem is effectively neglected. The reason for this is quite simple; the smaller heat capacity of the gas allows the overall temperature to attain a higher value in a similar time, and so speeds up the ignition process. Next, numerical results using a two-temperature (heterogeneous) model, allowing for local heat exchange between the phases, are presented. The pseudo-homogeneous results are recovered in the limit of infinite heat exchange. For a finite value of heat exchange, the ignition time is lower when compared to the single-temperature limit, decreasing as the rate of heat exchange decreases. However, the decrease is only mild, of the order of a few percent, indicating that the pseudo-homogeneous model is in fact a rather good approximation, at least for a constant heat-exchange rate. The relationships between the ignition time and a number of physico-chemical parameters of the system are also investigated.     

热塑性装饰材料点燃性能研究

利用锥形量热仪研究了典型热塑性装饰材料的点燃性能,并利用数值模拟结合线性回归方法导出了适合热中型材料的点燃模型。利用此模型对实验得到的点燃时间进行了分析,得到了材料的临界热辐射通量、点燃温度与热物性参数,结果表明研究得到的材料热辐射通量与点燃温度、点燃时间和文献中给出的值比较吻合,导出的模型具有较好的适用性。     

Theoretical prediction of piloted ignition of polymeric fuels in microgravity at low velocity flows

A numerical model developed for the prediction of the piloted ignition delay of solid polymeric materials exposed to an external radiant heat flux is used to predict the ignition delay and critical heat flux for ignition of solid fuels in microgravity at low velocity flows. The model considers the coupled thermochemical processes that take place in the condensed phase, including oxidative and thermal pyrolysis, phase change, radiation absorption, and heat and mass transfer in a multi-phase and multi-composition medium. Ignition is considered to occur when a critical pyrolysate mass flow rate is reached at the sample surface. Microgravity experimental surface temperature and ignition delay data previously obtained in a KC-135 aircraft are used to infer, in conjunction with the theoretical analysis, the critical mass flow rate for ignition. This value is then used to predict the ignition delay as a function of the external radiant heat flux, and the critical heat flux for ignition. Calculations are made for Polymethylmethacrylate (PMMA) and a Polypropylene/Fiberglass composite at airflows of 0.09 and 0.15 m/s under microgravity conditions and at 1.0, 1.75 and 2.5 m/s under normal gravity. The experiments and theoretical predictions show that the ignition delay and critical heat flux for ignition decrease as the forced airflow velocity decreases. It is predicted that at the tested lower velocities, the critical heat flux for ignition is close to half the value measured in normal gravity. The results have important implications since they indicate that materials could ignite easier under the conditions expected in spacecraft, and consequently stricter design specifications may be needed for fire safety.     

神经网络模型在预测Ni-Al系热爆点火时间中的应用

基于人工神经网络的原理,对热爆法制备Ni-Al系金属间化合物中的控制参数进行了研究,选取了加热速率、颗粒尺寸、压坯密度三个参数,通过对此参数的调控可以影响热爆反应的点火时间及反应过程.本文采用BP算法来训练网络,对热爆反应中的过程参数与热爆点火时间的映射关系进行了函数逼近,建立了热爆点火时间的神经网络模型.根据该模型可以预测热爆的点火时间,为控制热爆反应加压过程提供了可靠的依据.     

乳化炸药热点火的实验研究

本文就乳化炸药基质和乳化粉状炸药的热点火实验进行了研究。通过爆发点实验和热板实验得到了这两种物料的５ｓ爆发点温度和热板临界着火温度，并与理论研究进行了比较。     

Effects of carbon nanotubes additions on flash ignition characteristics of Fe and Al nanoparticles

The influences of carbon nanotubes (CNTs) additions on the flash ignition characteristics of Iron (Fe) and aluminum (Al) nanoparticles (NPs) were presented. CNTs can be used as the additive to these metal nanoparticles for improving the flash ignition and burning processes. Different mass fractions of CNTs additions were considered. The mixture of Al and CNTs could combust in air with obvious giant flame, whereas the mixture of Fe and CNTs combusted under a relative stable condition with slight red light. The temperature distributions were measured using non-contact optical method and showed that Al NPs mixed with CNTs were burning at a higher temperature level than Fe NPs. Although different mass fractions of CNTs cannot significantly change the overall flash ignition phenomenon, CNTs additions influenced the minimum ignition energy (MIE) of mixtures. The appropriate content of CNTs addition can decrease the Fe NPs MIE significantly. However, the Al NPs MIE decreased all along with the increase of CNTs content. The micro- and nano- structures of Fe and Al NPs with CNTs additions before and after ignitions were examined by scanning electron microscope and high-resolution transmission electron microscopy. It was found that the special thermal conductive characteristics of CNTs and the cross-connected features for metal particles with CNTs caused the enhancement of flash ignition.     

乳化炸药热点火的实验研究

本文就乳化炸药基质和乳化粉状炸药的热点火实验进行了研究。通过爆发点实验和热板实验得到了这两种物料的５ｓ爆发点温度和热板临界着火温度，并与理论研究进行了比较。     

The energy required to ignite micropyretic synthesis. Part II: unstable Ti + 2B reaction

In the previous study, the influences of micropyretic parameters on the ignition energy for lower exothermic heat and lower activation energy of stable Ni–Al reaction have been studied. In this study, we studied the effect of ignition energy on the unstable Ti + 2B micropyretic reaction, which has higher exothermic heat and higher activation energy. Three-dimensional maps are generated to illustrate the influences of micropyretic synthesis parameters on the required ignition energy. In addition, the comparisons in the ignition energy for the micropyretic reactions with Ni + Al and Ti + 2B are studied. The numerical calculation indicates that the changes in the ignition energy caused by the thermal conductivity for the micropyretic reaction with Ti + 2B is smaller as compared with for the micropyretic reaction with Ni + Al. However, the required ignition power is found to significantly change with the thermal conductivity for the NiAl micropyretic reaction when a higher pre-exponential factor is taken in the calculation. In addition, the difference in the required ignition energy caused by the thermal conductivity is noted to be larger for the Ni–Al micropyretic reaction with a lower pre-exponential factor.     

氧化铜用做补偿点火药的实验研究

在利用导火索作为延期体的电秒延期雷管和导爆管秒延期雷管过程中,为了提高一次点火的可靠性,通常要在导火索延期体的点火一端,涂敷少量的点火补偿药.曾用作补偿药的组成有KClO3-C-DDNP系列和Pb3O4-Si或Pb3O4-Si-Fe系列,而试验和检验过程中,经常出现雷管瞎火、干燥过程中自燃,使用过程出现瞎火、丢炮等现象,给生产和应用带来很大的不便.探讨了利用氧化铜作为点火补偿药的主要成分,作为导火索延期体的点火补偿药的可行性.     

Impact ignition of nano and micron composite energetic materials

Nanoscale reactive materials demonstrate three orders of magnitude reduced laser ignition sensitivity compared to their micron scale counterparts. Reduced ignition delay times have been reported for a variety of nano composites including aluminum combined with another metal (e.g., Ni), metallic oxides (e.g., MoO₃, Fe₂O₃, CuO, WO₃), or polymer binders such as polytetrafloroethylene (Teflon™). A new reported melt dispersion mechanism associated with nano-aluminum particle ignition explains the enhanced thermal ignition sensitivity associated with nano-aluminum composites. As a comparison to laser thermal ignition behaviors, this study focuses on impact induced ignition of nano- and micron-aluminum particle composites that also include Ni, MoO₃, or Teflon. A modified type-12 impact tester is used to measure ignition of the energetic composites to drop weight impact. Ignition is determined using high-speed thermal imaging. To assess the influence of the alumina passivation shell on the ignition dynamics, oxide-free nano-aluminum passivated with a perfluoroalkyl carboxylate self-assembled monolayer has also been investigated. Results show that the difference in ignition sensitivity between nano and micron composites is significantly greater with laser than with mechanical ignition and the melt dispersion mechanism does not describe impact ignition.     

Stagnation-point spray flame ignition by an isothermal surface

We present a theory of stagnation-point spray flame ignition by an isothermal hot surface. A mixture of fuel droplets and air flowing against an isothermal hot surface (such as a hot ignition probe) is considered. The spray of droplets is modelled using the sectional approach, and a mono-sectional case is adopted for simplicity. A single global chemical reaction is assumed for the case when ignition occurs. The mathematical analysis makes use of a small parameter that is exploited for an asymptotic approach. The analysis produces a criterion for ignition that includes effects of the flow field, the reactants and the fuel spray-related parameters. Numerical computations reveal the way in which the spray impacts on whether ignition will occur or not.     

空间材料二次电子发射特性测试

空间材料的二次电子发射系数是表征航天器表面充电状态的重要参数 ,对于卫星表面带电的预测及卫星防带电设计选材具有重要的作用。为了测量空间材料二次电子发射特性 ,研制了专门的测试装置。介绍了该实验装置的主要结构、性能及技术指标等 ,通过应用计算机数据采集系统 ,并研制专门的数据处理软件 ,提高了装置的自动测量能力。实验说明 ,该装置用于空间材料的二次电子发射特性测试中测量方便、准确     

一种苦味酸钾/高氯酸钾/硫化锑电引火药头的研制

研制一种由苦味酸钾、高氯酸钾、硫化锑与聚乙烯醇混制的无起爆药电引火药头,对该药头试样的耐热和吸湿性、感度、相容性、点火可靠性、电学特性等参数进行了测试。试验结果表明,该药头各项性能指标明显优于KClO3/C/DDNP系电引火药头,由该药头组装的无起爆药延期电雷管具有延期精度高、发火可靠性好、安全环保等优点,是一种理想的电引火药头。     

类石墨桥膜的发火可靠性研究

以相同工艺制作类石墨桥膜点火桥,对其进行蘸药等处理，形成点火头结构;升降法试验得到不同激发条件下50%发火时的电流或电压，并验证其发火可靠性；测试点火头的响应状态，得到裸桥状态下类石墨桥膜对不同能量输入的响应。以相同方式制作桥丝式点火头，得到发火参数与电压、电流特性。涂覆有150目下叠氮肼镍(NHA)的类石墨桥膜，99%恒流发火电流为325.65 mA；99%恒压发火电压为2.43 V；在电容47 μF条件下99%脉冲发火电压为10.45 V。同样蘸药的桥丝式点火头，99%恒流发火电流为89.61 mA；在电容47 μF条件下99%脉冲发火电压为4.72 V。对比发现，类石墨桥膜点火头在使用钝感药剂时可满足0.99（0.90置信度下）可靠度要求。     

冷阴极气体放电电子枪的研制

为了促进冷阴极电子束加工技术在国内的发展,在深入研究冷阴极电子发射机理基础之上,设计制造了一种自主知识产权的冷阴极气体放电电子枪,对该电子枪的结构、阴极功能及其参数、阳极功能及其参数、CST仿真软件确定聚焦线圈参数的方法进行了介绍.通过实验发现:每一种放电气体的最小“点火”电压与放电气体种类、气流量大小有关;氦、氩等纯...     

铜芯脚线储能焊接工艺方法改进

论文根据实际需要研究了铜芯脚线—镍鉻合金丝储能焊接的工艺方法,从铜芯材料、焊接工具材质及焊接工艺参数等方面进行了改进,并对用该种工艺方法制作的引火元件的电阻、静拉力、电性能参数、发火时间、储存性能等指标进行了实验对比。结果表明,用该工艺制作的引火元件能够满足产品技术指标的要求,研究结果具有实际应用价值。     

An analysis of evolution of grain size-lattice parameters dependence in nanocrystalline TiO2 anatase

Due to the specific properties of nanocrystalline materials in comparison with crystalline materials, it is essential to investigate their structural parameters like lattice parameters and grain sizes. We used the Rietveld method and refined electron powder data (recorded with selected area electron diffraction—SAED) on nanocrystalline (nc) TiO₂-anatase prepared by sol–gel route. We correlated refined lattice parameters with average grain size obtained from transmission electron microscopy (TEM) images. We give preliminary results on relative changes of lattice parameters a and c vs. the mean grain size in nc TiO₂-anatase.     

PTFE/Al/MoO3复合材料的力学和反应性能

使用模压烧结法制备不同PTFE体积分数的PTFE/Al/MoO3复合材料,借助扫描电子显微镜(SEM)和X射线衍射仪(XRD)对材料进行表征,并研究该复合材料的准静态压缩性能和动态冲击性能。结果表明:PTFE/Al/MoO3复合材料的强度随着PTFE的增加先增加后降低,当PTFE体积分数为70%时达到最大的80MPa,且该试样能够在准静态压缩条件下发火,发出巨大的爆炸声和明亮的火光,而其他试件在同等条件下未见发火现象。动态冲击条件下,PTFE/Al/MoO3复合材料均能发生爆炸反应,但随着PTFE的增加,剧烈程度逐渐降低,反应产物为AlF3,Al2O3,Mo,C,表明Al与PTFE和MoO3都发生了氧化还原反应。在材料强度和组分的双重影响下,PTFE/Al/MoO3复合材料发火所需能量随着PTFE的增加,呈现先降后升的趋势。