【作者】 赵军；

【导师】 徐复铭；

【作者基本信息】 南京理工大学 ， 材料学， 2007， 博士

【摘要】 碳包裹纳米金属粒子是一种新型的纳米复合材料，其性质相对稳定的碳层可以保护金属粒子不发生物理、化学变化，防止金属纳米粒子长大和团聚，甚至可以将碳层的性能赋予被包裹的粒子，使其在电子、磁记录、电波屏蔽／吸收、催化剂、抗菌剂、生物医学等方面有广泛的应用前景，因此这一材料在上个世纪九十年代一出现便成为研究的热点。本文采用一种新的制备方法，即以阳离子交换树脂（D113）为碳源，金属离子为金属源，首次采用离子交换的方法将金属离子引入到聚合物中，得到含金属的聚合物前驱体，然后在400-700℃热解制备碳包裹纳米金属及合金粒子，本文的制备方法具有工艺简单、纳米金属粒度可控、容易操作、成本低等特点。深入研究了制备工艺条件对碳包裹纳米金属粒子形态的影响，并结合X射线衍射仪、元素分析仪、红外光谱、电子显微镜等现代分析手段对材料的结构、性能进行详细分析；初步分析了其形成机理；并研究了其催化性能、磁性能和吸波性能。400-700℃热解载镍和载钴的前驱体（Ni／D113，Co／D113）可获得碳包裹面心立方结构（fcc）的纳米镍、钴粒子，未发现镍、钴的氧化物和碳化物，镍、钴粒子的晶粒尺寸随着热解温度的升高不断增大。而在同样的条件下热解载铁树脂（Fe／D113），热解产物中铁的晶体结构与热解温度有关，400℃热解产物为铁的氧化物；500℃热解产物为体心立方结构（bcc）的单质铁；600-700℃的热解产物为bcc单质铁和铁的碳化物（Fe₃C）。400-700℃热解载铁、镍D113前驱体（Fe-Ni／D113）和载铁、钴D113前驱体（Fe-Co／D113）分别获得了碳包裹fcc结构铁镍合金和bcc结构铁钴合金纳米粒子。颗粒的点阵常数随合金颗粒中铁含量的增加而增大；纳米合金的晶粒随热解温度的升高而增大。包裹纳米粒子的壳层碳结构因热解温度的不同而不同，400-500℃时，壳层碳为无定型碳；600-700℃时，400-500℃热解形成的无定型碳壳层石墨化，同时被包裹金属粒子明显长大。通过对形成机理进行分析认为，600-700℃热解过程中，核金属对壳层的无定型碳具有催化石墨化作用；而被包裹粒子的长大是由于被包裹金属对外层的无定型碳产生催化石墨作用时，导致核金属的裸露，相互融并引起的。采用热分析法考察了碳包裹纳米金属及合金粒子对高氯酸铵（AP）热分解的催化作用。结果表明，碳包裹纳米金属及合金粒子使AP的高温分解温度大幅下降，高温分解的表观活化能降低，热分解反应的速率加快，分解放热量提高。同时探讨了对AP催化热分解的机理。碳包裹纳米金属及合金粒子的磁性与被包裹纳米金属和合金粒子的尺寸有关。矫顽力H_c大于相应的块体材料，先随试样中粒子尺寸的减小而增大，在达到单畴尺寸D_s附近的极值后，随试样中粒子尺寸的减小而减小；比饱和磁化强度M_s小于相应的块体材料，随试样中粒子尺寸的增大而单调增大，并逐渐接近块体材料的值；碳包裹纳米合金粒子的磁性还与粒子的合金成分有关。500℃制得的碳包裹纳米铁、镍、铁钴合金和铁镍合金粒子为吸收剂（质量分数为50％）；石蜡为粘结剂，采用弓形法电磁波反射吸收测试结果表明，涂层厚为2mm时，碳包裹纳米铁粒子的吸波性能最好，在11.7GHz频率时吸收峰值R_min为-10 dB，频宽△dB可达6.0 GHz；当涂层厚为1.0 mm左右时，R_min向高频方向移动，频宽下降。更多还原

【Abstract】 Carbon-encapsulated nano metal particle is a new type ofnano-composite material.The role of the carbon coating in this material is to isolate the particles from eachother, thus avoiding the drawbacks caused by interactions between closely compactedunits, such as the oxidation of the bare nano metal particles. Moreover, the carboncoating can endow these particles with other properties, and then to be able to bewidely used as electronic, magnetic recording, electromagnetic shield/absorbing materials,catalysts, antibacterial materials and biomedicine etc. Since the first finding ofCarbon-encapsulated nano metal particle, it has attracted a great deal of researchinterest. In this thesis, a novel method for the preparation of carbon-encapsulated nanometal particle was proposed, in which D113 resin, a kind of cation exchange resin, wasused as carbon source and metal salt as metal source in order to preparecarbon-encapsulated nano metal （Ni, Co, Fe） and alloy （Fe-Ni, Fe-Co） particles viapyrolysis in the range of 400-700℃. Simplicity, low cost, and controllability ofparticle size are the favorable features of this preparation method.The structural morphologies of the carbon-encapsulated nano metal and alloyparticles are investigated by XRD, IR, SEM, TEM, HRTEM etc and the effects ofpreparation conditions on morphologies of Carbon-encapsulated nano metal and alloyparticle are studied. The formation mechanism is also discussed. Catalytic, magnetic andelectromagnetic absorbing properties are studied as well.Carbon-encapsulated Ni and Co nano-particles are prepared by pyrolysis of Ni/D113and Co/D113 precursors from 400℃to 700℃. It reveales that the nickel and cobaltparticles existe mainly in the form of fcc Ni and Co phase, and no evidence of Ni and Cooxides or carbides are observed, and it is found that the particles sizes of Ni and Coincrease with the increasing of pyrolytic temperature. But when Fe/D113 precursor ispyrolysed in the range of 400-700℃, the crystal structure of the iron particle is different.The products are mainly iron oxides andα-Fe as Fe/D113 precursor pyrolysed at 400℃and 500℃respectively, and as the pyrolytic temperature increases to the range of600-700℃,α-Fe and Fe₃C are observed. Carbon-encapsulated fcc iron-nickel and bcciron-cobalt alloy nano-particles are prepared by pyrolysis of Fe-Ni/D113 and Fe-Co/D113precursors from 400℃to 700℃. The lattice constant of the nano alloy particle increaseswhen increasing the Content of Fe in the nano alloy particles, and the nano alloy particle sizes increase when increasing the pyrolytic temperature.It is found that the structure of the carbon coating is amorphous carbon in thecarbon-encapsulated nano metal and alloy particle when pyrolytic temperature is in therange of 400-500℃, and the amorphous carbon coating changes to graphite whenpyrolytic temperature is in the range of 600-700℃. And the size of encapsulatednanoparticle increases as well. A mechanism reflecting these changes is proposed.The catalysis of these carbon-encapsulated nano metal and alloy particles on thethermal decomposition of NH₄ClO₄ （AP） is investigated by thermal analysis. Resultsindicate that the carbon-encapsulated metal nano and alloy particles lower the higher peaktemperature of AP thermal decomposition. Thermal decomposition dynamics test showsthat the carbon-encapsulated nano metal and alloy particles can lower the activation energyof AP higher temperature decomposition effectively, and increase reaction rate constant ofAP decomposition as well. In addition, the catalytic mechanism of AP thermaldecomposition is discussed.The experimental results show that magnetism of carbon-encapsulated nano metaland alloy particles depends on the nano metal and alloy particle size, which is largelyinfluenced by pyrolysis temperatures. The coercivities H_c of the samples at roomtemperature are much higher than those of the corresponding bulk material, and H_cincreases with the decrease of the particle size firstly, and H_c reaches maximum valuewhen the particle size is about single-domain size （D_s）. As the particle size is less than D_s,H_c decreases with the decrease of the particle size. The saturation magnetization M_s ofcarbon-encapsulated nano metal and alloy particles increase with pyrolytic temperatureincreasing, and are less than those of bulk materials. Moreover magnetism ofcarbon-encapsulated nano alloy particles is influenced by the constituent of alloy particles.Electromagnetic absorbing property tests of carbon-encapsulated iron, nickel, FeNiand FeCo alloy nano particles pyrolysed at 500℃indicate that carbon-encapsulatediron nano-particles has more strongly electromagnetic absorbing efficiency than theothers. For 50% mass fraction in wax and 2 mm-thickness of carbon-encapsulated ironnano-particles, at f=11.7 GHz, R_min=-10dB and△dB=6.0 GHz.更多还原