超级铝热剂Al/CuO前驱体的制备、表征、热分解机理及非等温分解反应动力学

以硝酸铜、无水乙醇、1,2-环氧丙烷和纳米铝粉为原料, 在超声振荡条件下, 采用溶胶-凝胶法制备了纳米复合含能材料——超级铝热剂Al/CuO的前驱体. 利用热重-差示扫描量热-傅里叶变换红外-质谱(TG- DSC-FTIR-MS)联用技术, 研究了纳米Al/CuO溶胶-凝胶前驱体的热行为和分解过程及机理. 利用不同升温速率下的TG-DTG分析, 研究了纳米超级铝热剂Al/CuO的溶胶-凝胶前驱体的热分解反应机理, 采用了6种动力学分析方法进行动力学参数计算, 得到前驱体分解反应的表观活化能、反应级数、频率因子等动力学参数, 纳米Al/CuO前驱体分解反应的动力学方程为: dα/dt=10^14.0×4α^3/4exp(-2.0×10⁴/T).     

铝热剂反应性冲击热点分析

 采用激光粒度扫描仪测量了二元混合物铝热剂（Al+Fe₂O₃）原料的粒径分布,在电子显微镜下观察了铝颗粒、氧化铁颗粒的颗粒形状及两者按照化学配比混合后的颗粒接触状态。综合粒径分布和反应体系的化学配比关系,得到两种反应物的特征粒径和混合物的颗粒布局。根据特征粒径和颗粒布局,建立了该反应体系的等效细观模型,该细观模型能够保证得到与实际颗粒体系相一致的具有统计意义的孔穴结构。采用无网格粒子方法,数值模拟了铝热剂体系在不同冲击速度作用下,基本氧化铁颗粒排列形成的热点特征。研究表明,氧化铁三颗粒紧密排列的模式为形成单独热点的最基本排列,在平面冲击作用下,二元不同粒径的含能材料混合物形成热点的尺寸由初始孔穴尺寸确定,而热点温度受冲击速度影响较大。采用轻气炮对不同密度和配比的铝热剂进行了冲击点火实验,并将测量和数值计算结果进行了对比分析,结果表明,两者的定性结论吻合较好。     

Dependence of size and size distribution on reactivity of aluminum nanoparticles in reactions with oxygen and MoO3

The oxidation reaction of aluminum nanoparticles with oxygen gas and the thermal behavior of a metastable intermolecular composite (MIC) composed of the aluminum nanoparticles and molybdenum trioxide are studied with differential scanning calorimetry (DSC) as a function of the size and size distribution of the aluminum particles. Both broad and narrow size distributions have been investigated with aluminum particle sizes ranging from 30 to 160 nm; comparisons are also made to the behavior of micrometer-size particles. Several parameters have been used to characterize the reactivity of aluminum nanoparticles, including the fraction of aluminum that reacts prior to aluminum melting, heat of reaction, onset and peak temperatures, and maximum reaction rates. The results indicate that the reactivity of aluminum nanoparticles is significantly higher than that of the micrometer-size samples, but depending on the measure of reactivity, it may also depend strongly on the size distribution. The isoconversional method was used to calculate the apparent activation energy, and the values obtained for both the Al/O₂ and Al/MoO₃ reaction are in the range of 200-300 kJ/mol.     

A multi-step reaction model for ignition of fully-dense Al-CuO nanocomposite powders

A multi-step reaction model is developed to describe heterogeneous processes occurring upon heating of an Al-CuO nanocomposite material prepared by arrested reactive milling. The reaction model couples a previously derived Cabrera-Mott oxidation mechanism describing initial, low temperature processes and an aluminium oxidation model including formation of different alumina polymorphs at increased film thicknesses and higher temperatures. The reaction model is tuned using traces measured by differential scanning calorimetry. Ignition is studied for thin powder layers and individual particles using respectively the heated filament (heating rates of 10³–10⁴ K s^?1) and laser ignition (heating rate ～10⁶ K s^?1) experiments. The developed heterogeneous reaction model predicts a sharp temperature increase, which can be associated with ignition when the laser power approaches the experimental ignition threshold. In experiments, particles ignited by the laser beam are observed to explode, indicating a substantial gas release accompanying ignition. For the heated filament experiments, the model predicts exothermic reactions at the temperatures, at which ignition is observed experimentally; however, strong thermal contact between the metal filament and powder prevents the model from predicting the thermal runaway. It is suggested that oxygen gas release from decomposing CuO, as observed from particles exploding upon ignition in the laser beam, disrupts the thermal contact of the powder and filament; this phenomenon must be included in the filament ignition model to enable prediction of the temperature runaway.     

Detonation models of fast combustion waves in nanoscale Al-MoO3 bulk powder media

The combustion of nanometric aluminum (Al) powder with an oxidiser such as molybdenum trioxide (MoO₃) is studied analytically. This study focuses on detonation wave models and a Chapman-Jouget detonation model provides reasonable agreement with experimentally-observed wave speeds provided that multiphase equilibrium sound speeds are applied at the downstream edge of the detonation wave. The results indicate that equilibrium sound speeds of multiphase mixtures can play a critical role in determining speeds of fast combustion waves in nanoscale Al-MoO₃ powder mixtures.     

Al与α-Fe2O3纳米界面铝热反应的从头计算分子动力学研究

在正则系综统下,温度为2000 K时,利用基于密度泛函理论的第一性原理分子动力学计算方法对Al与赤铁矿α-Fe₂O₃的铝热反应进行了研究. 模拟得出Fe–O键的数量随着时间的增加而减小,Al–O键和Fe–Fe键的数量随时间的增加而增大;同时Fe离子总的电荷量随时间的增加而减小,而Al离子总的电荷量随时间的增加而增大. 模拟结果表明,在Al/Fe₂O₃铝热反应中发生了氧化还原反应,Al被氧化,Fe离子被还原;在界面处生成Al–O键,Fe–O键发生断裂;氧化还原反应完成需约3 ps. 关键词： 铝热反应 密度泛函理论 分子动力学 正则系综     

氧化锰纳米管及其超级铝热剂:制备及对环三亚甲基三硝胺热分解的影响

采用水热法制备了MnO2纳米管,以其与纳米铝粉为原料,采用超声分散复合的方法,制备了超级铝热剂Al/MnO2。利用粉末X射线衍射(XRD)、扫描电子显微镜(SEM)及能量散射光谱仪(EDS)对产物的物相、组成、形貌和结构进行分析表征,并运用差示扫描量热法(DSC)研究了MnO2纳米管及其超级铝热剂对环三亚甲基三硝胺热分解特性的影响。结果表明,水热法制备的纳米MnO2呈管状均匀分布,球形纳米Al与管状纳米MnO2相互依附,分散较均匀;MnO2纳米管及其超级铝热剂的加入均改变了环三亚甲基三硝胺的热分解行为及分解历程,使原有占主导的液相分解变为二次的气相反应加剧,使环三亚甲基三硝胺主分解峰形发生了明显的改变。     

有镁热反应吗——由一道高考化学题引起的思考

通过近似计算2Al＋Fe2O3=2Fe＋Al2O3,3Mg＋B2O3=2B＋3MgO,Na＋KCl=K↑＋NaCl等金属热还原反应在298 K时的标准摩尔吉布斯自由能变ΔrGøm、标准摩尔反应热ΔrHøm及标准摩尔熵变ΔrSøm,判断这些反应能否进行及焓变、熵变对反应的贡献。     

Effect of carbon nanotube addition on the thermite reaction in the Al/CuO energetic nanocomposite

Abstract

In this work, the Al/CNT/CuO nano-thermite samples are prepared by ultrasonic mixing with variable CNT content. The morphology of nano-thermites analysed by electron microscopy revealed that the CNTs are dispersed and there are intimate contacts between fuels (Al and CNT) and oxidiser (CuO) constituents of the nano-thermite. Raman spectroscopy technique is used to analyse the structural integrity of the CNTs in the nano-thermite. The thermite reaction characteristics are evaluated by simultaneous thermogravimetric analysis/differential scanning calorimetry technique. The exothermic enthalpy of the Al/CNT/CuO nano-thermite samples increased with increasing CNT content. The effect of Al particle size and Al/Cu molar ratio variation on the thermite reaction enthalpy is also analysed. The ignition temperature of the thermite reaction is also lowered by 71 °C than that of Al/CuO nano-thermite. The activation energy for thermite reaction of Al/CNT/CuO nano-thermite is also lowered by 23% to that of pure Al/CuO. The residues of the nano-thermites after the thermite reaction at 1010 °C are collected and analysed by the X-ray diffraction.