【作者】 王毅；

【导师】 李凤生；

【作者基本信息】 南京理工大学 ， 材料学， 2009， 博士

【摘要】 反应性材料（“Reactive Materials”）通常是指由两种或多种非炸药类固体物质所组成的亚稳态材料,其特点是密度较大、活性较高、感度很低,且在强机械冲击力的作用下才可被引发剧烈的化学反应而释放出以热能为主的巨大能量,多被应用于制造反应性破片（“Reactive Fragments”）、装填高速射弹、制造含能药型罩或爆炸成型弹丸等研究,以大幅提高武器战斗部毁伤目标的威力。目前,国外已明确将反应性材料作为先进含能材料立项研究,而国内对这种材料的研究尚处于起步阶段。就已有的研究结果而言,有望作为反应性材料的物质很多,其中铝热剂由于具有能量高、密度大、感度低、配方灵活等优点被国内外同行广泛认可。然而,传统铝热剂一般是由大粒度Al粉和微米金属氧化物组成的简单混合体系,其主要缺点是Al粉氧化反应活性低且氧化剂与还原剂的结合程度不高,常导致药剂反应速度慢、实际放热量低、反应过程不集中,特别是反应的起始温度通常很高（＞900℃）,这直接影响到了它们的点火和燃烧性能,使其很难成为真正意义上的反应性材料而进入实际应用。本研究旨在利用纳米及纳米复合技术,通过改善Al粉氧化反应活性和改善Al与氧化剂结合方式两种途径来提高铝热剂的反应性能,开发由纳米及纳米复合材料组成的铝热剂,通过考察这些特殊铝热剂的常规反应特性、冲击引发特性及反应过程机制,达到将此类物质初步应用为反应性材料的目的。首先,从改善传统Al粉的氧化反应活性方面入手,以表面包覆的方式来提高微米Al粉的反应效率,达到提高铝热剂反应性能的目的。采用原位置换法,通过对表面活性剂用量、反应温度、金属盐初始浓度及NH₄F浓度的调节,在近中性水溶液中实现了Ni、Co、Fe或Cu纳米粒子对微米Al粉的包覆,制备出了具有核壳结构的（Ni、Co、Fe或Cu）/Al四种纳米复合粉体。然后,将这四种复合粉体分别与WO₃、SnO₂、PbO、CuO和Fe₂O₃组成铝热剂,以反应的起始和放热峰温度、放热量、最大热流量及活化能作为主要性能参数,分别在Ar气和空气气氛中利用热分析研究了它们的铝热反应特性。结果表明,被上述过渡金属纳米粒子包覆处理后,Al粉的反应活性明显提高,其中纳米Ni粒子对铝热反应的促进效果最佳。另外,对原料Al粉和复合粉体的氧化过程机制进行研究后发现,传统微米Al粉的氧化反应受到了其表面氧化层的严重制约,常导致其反应速度慢、反应不完全;而复合粒子特殊的核壳结构则在很大程度上避免或缓解了这种制约,其表面的过渡金属纳米粒子能够代替大部分氧化层并起到“桥梁”的作用使外界氧迅速、便捷地到达到活性Al核的表面,显著提高了Al的氧化反应活性。其次,从改善Al与氧化剂结合方式入手,以将两者相互复合的方式来提高它们之间的接触面积,达到提高铝热剂反应性能的目的。采用溶胶.凝胶法,以Fe（NO₃）₃·9H₂O为前驱体盐,1,2-环氧丙烷为该盐的水解加速剂,分别实现了纳米Al粉、亚微米Al粉、微米Al粉或粗Al粉与纳米Fe₂O₃的复合,成功地制备出了四种Fe₂O₃/Al纳米复合铝热剂,其中Al颗粒被无定形纳米Fe₂O₃粒子致密包覆。研究发现,设定反应初始温度=19℃、Fe（NO₃）₃·9H₂O初始浓度=0.37mol·L^-1、1,2-环氧丙烷用量=2.005 mL·g_硝酸铁^-1为制备的最佳工艺条件。热分析结果表明,Al与Fe₂O₃结合方式以及Al粉粒度等显著影响了铝热剂的反应性能。复合药剂比简单混合的药剂具有更低的反应起始温度和放热峰温度（降低50℃～70℃）,这十分有利于提高药剂的点火性能;随着Al粉粒度的减小,铝热反应放热峰温度降低、放热量升高,最大热流量增加,其中纳米Fe₂O₃包裹纳米Al粉所组成的复合药剂在660℃前就基本反应完。过程机制研究结果表明,若药剂中有效Al含量较低则铝热反应进行不完全,残渣中会有大量FeAl₂O₄、Fe₃O₄或FeO等中间产物存在,此时体系表现为较低的反应性能。第三,尝试以改变材料晶体结构的方式来提高传统微米Al粉的氧化反应活性,达到提高铝热剂反应性能的目的。通过正反双向对转球磨法制备了Mg含量分别为10wt.%、20wt.%和30wt.%的Mg-Al合金粉,并研究了三种Mg-Al合金与Fe₂O₃的热反应特性。表征结果表明,微米Al粉和Mg粉经合金化处理后其晶粒度由＞100nm降低至25nm左右;热分析结果表明,Mg的引入及晶粒度的细化显著提高了微米Al的铝热反应性能,合金粉与Fe₂O₃在Al（Mg）熔化前就能发生剧烈的固.固相反应,并且随着Mg含量的增加,铝热反应的DSC放热峰提前、最大热流量增加。最后,为验证上述常规反应性能很高的特殊铝热剂是否也具有反应性材料所必备的冲击引发特性,将传统铝热剂和由纳米及纳米复合材料组成的铝热剂分别添加适量辅助成分后压制成Φ10mm×10mm的药柱并装入钢质弹丸中。采用实弹射击的形式,以装满柴油的钢质密封罐为靶,以击燃靶罐中的柴油为目的,考察了这类材料的冲击引发特性。试验结果表明,尽管传统铝热剂药柱在发射时足够钝感且击中靶罐后可以被侵彻靶罐时所产生的冲击力引发,但其引发后所放出的热量和产生的温度还不足以将难挥发的柴油引燃,燃烧火焰反而最终被油浇灭;而由纳米过渡金属/Al复合材料、Fe₂O₃/Al纳米复合药剂和具有纳米级晶粒度Mg-Al合金粉组成的铝热剂所压制的药柱击中靶罐后不但具有良好的点火性能,点火后还能发生较强烈的爆燃,其放出的热量和产生的火焰引燃了部分飞溅出来柴油。这说明,由纳米及纳米复合材料组成的铝热剂具有较好的冲击引发特性,有望作为冲击引发的反应性材料应用于武器战斗部中。更多还原

【Abstract】 The term of "reactive materials" denotes a class of energetic materials that generally combine two or more non-explosive solids.This kind of mixtures/composites always have high density,high reactivity and of low sensitivity and can be ignited to release a mass of chemical energy when they undergo a strong impact action.At present,in order to enhance the power of warhead,there is also interest in and initial work underway to examine the application of reactive materials in fabricating reactive fragments,charging in high-speed projectile and replacing standard metal liners in shaped charges or explosively formed penetrators.Some studies indicated that many kinds of metastable materials may be used as reactive materials,in which thermites are most promising because of their large exothermic heat,high density,reliable safety,and desired thermal properties that can be readily tailored by varying ratios of oxidizer to fuel.However,traditional thermites are usually composed of coarse Al particles and micron metal oxide.This kind of thermites usully exhibit the poor reactivity,such as lower burnning rate,deficient heat release,and hard ignition(T_ign.＞900℃), which can not be used as reactive materials and find no application further.This study intends to improve the reactive property of thermites via promoting the reactivity of Al powder or enhancing the combination between the fuel and oxidizer.Concretely,the paper aims at exploring the thermites made up of nanocomposites and investigating the thermites with high reactivity and potential application in reactive materials.Firstly,to promote the thermal reactivity of micron Al powder,a kind of core-shell metal/Al nanocomposite has been prepared by a facile displacement method in the near neutral aqueous solution via controlling the dosage of surfactant,temperature,initial concentration of metallic salts and NH₄F,in which the micron Al cores were tightly coated in nanometer Ni,Co,Fe and Cu particles.After preparation,these metal/Al nanocomposites were blended with metal oxides that included WO₃,SnO₂,PbO,CuO and Fe₂O₃ powders. Using the onset and peak temperature,heat release,maximal heat flow and active energy as the parameters to evaluate the performance of thermite reaction,the reactivity of the above mixtures has been investigate via thermal analysis.The results indicated that metal/Al particles have great higher thermal reactivity than raw Al powders,among which Ni/Al is the best one.In addition,the possible oxidation mechanisms of raw Al and metal/Al were discussed.It is found that the progress of oxidation process for raw Al was severely limited by the Al₂O₃ layers wrapped on the surface of active Al core,but the metallic nanoparticles within metal/Al nanocomposites improved the oxidation mechanism of Al by reducing the deleterious influences of the Al₂O₃ layer and bridging the gap between fuel and oxidizer.So, the oxidizer can react with active Al easliye,which is confirmed by great improvement in the thermal reactivity of micron Al powder.Next,in order to enhance the combination and contacting area between fuel and oxidizer, a kind of Fe₂O₃/Al nanocomposite has been prepared by sol-gel method under a mild and low-toxicity condition via introducing of 1,2-epoxypropane as the agent for speeding up the hydrolyzation of Fe（Ⅲ） ions,in which nanometer,submicron,micron and coarse four kinds of Al particles were combined tightly with nanometer ferric oxide,respectively.The optimal technical parameters were located at initial temperature of 19℃,Fe（NO₃）₃·9H₂O initial concentration of 0.37mol·L^-1 and 1,2-epoxypropane dosage of 2.005 mL·g_硝酸铁^-1.Results of thermal analysis revealed that the composing between Al and Fe₂O₃ and the particle size of Al obviously affected the reactivity of thermites.If nanometer Fe₂O₃ particles compactly coated on the surface of Al,the peak temperature of the thermite reaction is lower than that of mixed sample by 50℃～70℃.Moreover,as the particle size of Al decreases,the values of peak temperature decrease and the heat release and of max heat flow increases linearly.The study of reactive mechanisms reveals that if the fraction of active Al in thermite system is low,the residue will present many intermediate products such as FeAl₂O₄,Fe₃O₄ or FeO etc.,which is attributed to an incomplete reaction process and results in a low reactivity.Thirdly,we tried to promote the reactivity of micron Al particles via changing their crystal structure.Accordingly,three kinds of Mg-Al alloys have been prepared by bidirectional-rotation milling,in which the content of Mg is 10wt.%,20wt.%and 30wt.%, respectively.Sample characterization showed that the crystallite size of micron Al had been decreased from＞100nm to about 25nm after alloying with Mg.Thermal analysis illustrated that the reactivity of Al has been enhanced obviously due to the introducing of Mg and decreasing of Al crystallite.The thermite reaction of Al with Fe₂O₃ was initiated even before the melting point of Al（Mg）,which is a solid-solid reaction.Moreover,as the fraction of Mg increased in Mg-Al alloy,the peak temperature in DSC traces decreased and the maximum heat flow increased.Finally,to confirm that whether the thermite with high reactivity also can be impact initiated,the traditional thermite and the thermites made up of nanocomposites were pressed into pillars with the size ofΦ10mm×10mm after adding some accessorial ingredients.The pillars were charged into steel projectiles,and then were shot to impact against the sealed steel-pot that filled up with diesel oil.This test aims at igniting the diesel oil by the energy released from the thermite reaction.The experimental results showed that although the pillars pressed by traditional thermite can be ignited by impact action in the course of penetration, but the reaction heat and flame are not mighty enough to light up the diesel oil with low volatility.As a result,the combustion flame was stamped out by the diesel oil.Successfully, the pillars fabricated by nanocomposites thermites can not only be ignited after impacting the target,but also exhibit a blazing deflagration with igniting the part of the diesel oil. Undoubtedly,the thermites made up of nanocomposites can become a kind of impact initiated energetic materials,and will find promising applation in as reactive materials in the warhead.更多还原