【作者】 杨丽；

【导师】 刘洪波；

【作者基本信息】 湖南大学 ， 材料科学与工程， 2012， 博士

【摘要】 石墨层间化合物（GICs）具有高导电、导热、密封、能量储存及转换等诸多优良特性，应用潜力巨大。但传统的制备方法，如双室法、液相插层法、电化学法等要么条件过于苛刻，要么结构难以控制，未能实现批量制备。熔盐法属于液相插层法之一，是制备三元及多元GICs的常用方法，设备及工艺简单，是最有可能实现GICs批量制备的方法之一。其工艺中需要抽真空并密封，因此反应器为玻璃管，便于熔封和加热。然而玻璃反应器的容积小、耐热温度低、耐压性能差，大大限制了新型GICs的合成及性能研究。本文以天然鳞片石墨为宿主，FeCl₃和NiCl₂为插入物，通过省掉抽真空环节的简化熔盐法制备了三元FeCl₃-NiCl₂-GICs，并对其工艺因素、插层过程及FeCl₃-NiCl₂-GICs还原前后的微波吸收性能进行了详细研究。具体结论如下：1、系统考察了省掉抽真空环节后的熔盐法制备过程中，各工艺因素对FeCl₃-NiCl₂-GICs阶结构的影响，设计并加工了大容量不锈钢反应器。结果表明，在玻璃反应器中存在定量空气（反应中空气的量无增减）的条件下，可以获得不同阶结构的GICs。产物阶结构随石墨粒度、石墨/氯化物比、NiCl₂/FeCl₃比、反应温度、反应时间及压力等工艺因素的变化规律与传统熔盐法一致；由未抽真空而引入的定量空气中的氧会与石墨反应，但主要分布在鳞片的表面及边缘，对FeCl₃-NiCl₂-GICs的整体结构未造成大的影响。以此为依据自行设计的不锈钢反应器的GICs单次制备量约为250g，实现了实验室GICs的小批量制备。熔盐法制备工艺的简化和反应器的改进为新型GICs制备、性能及应用研究创造了条件。2、根据三元GICs的结构特点，提出了四个有效表征三元FeCl₃-NiCl₂-GICs结构完善程度的评价指标：目标阶的体积分数V1、单个鳞片内Ni元素分布的均匀程度σ，产物中Ni与Fe元素的摩尔比S、产物与反应物中Ni和Fe元素的摩尔比之比S′。以上述四个参数为标准，对FeCl₃-NiCl₂-GICs的阶结构进行调控，确定了新反应器中合成纯阶FeCl₃-NiCl₂-GICs的最佳工艺条件。三元FeCl₃-NiCl₂-GICs结构评价指标的确立，避免了只用阶数作为多元GICs结构表征的片面性，突出了其结构特点，实现了GICs三元化程度的定量表征，对三元GICs微结构及工艺优化具有指导意义。采用XRD、SEM、EDS、Raman、HRTEM等分析手段对纯阶FeCl₃-NiCl₂-GICs的表面形貌、元素组成及分布、晶体结构等微观结构进行了表征。结果表明，FeCl₃、NiCl₂与天然鳞片石墨进行插层反应后，形成了石墨碳层与FeCl₃和NiCl₂交替排列，尺寸为5-10nm的GIC岛畴结构，其晶格条纹出现了弯曲，丧失了石墨中原有的连贯的特征；受插层反应剧烈程度的影响，一阶GICs的鳞片边缘遭到较大程度的腐蚀而呈锯齿状，随着GICs阶数的升高腐蚀程度逐渐减弱，逐渐接近原始石墨的形貌特征。3、详细研究了FeCl₃-NiCl₂-GICs在2-18GHz波段的微波吸收性能，及与之相关的导电性和磁性。微波吸收性能研究表明，FeCl₃-NiCl₂-GICs是一种吸收效果良好的轻质微波吸收剂，尤其在低频区；其微波损耗机制以介电损耗为主，因此其吸波性能受GICs导电率的影响；在考察范围内吸收剂与粘结剂石蜡的最佳质量比为1：1。粒度为100目的一阶FeCl₃-NiCl₂-GICs的微波损耗最大，吸波材料（MAM）厚度为5mm时最大理论反射损耗（TRL）为-11dB，匹配频率为3.2GHz。4、对三元FeCl₃-NiCl₂-GICs的插层过程及NiCl₂的扩散方式进行了详细研究。按三元FeCl₃-NiCl₂-GICs的插层反应特点可将其反应过程分五个阶段：FeCl₃、NiCl₂的选择性吸附和插层阶段、FeCl₃-GICs骨架形成阶段、FeCl₃、NiCl₂联合扩散的三元化初期阶段、NiCl₂单独嵌入三元化阶段、阶畴三元化阶段。其中的控制环节为第三元NiCl₂的扩散，在微区及阶畴内的均匀程度及插入量控制着GICs的三元化程度。对于FeCl₃、NiCl₂与石墨组成的混合体系，在500℃以下72h以内，第三元NiCl₂在石墨层间的扩散方式为单独嵌入和与FeCl₃联合插入，以单独嵌入式为主。FeCl₃-NiCl₂-GICs插层过程及机理的研究结论则为我们指明了改善三元GICs微结构的方法和途径。5、对FeCl₃-NiCl₂-GIC的还原工艺及还原产物的微波吸收性能进行了系统考察。实验确定了氢气、金属Na、水合肼及硼氢化钠等还原剂对FeCl₃-NiCl₂-GICs的还原效果。结果表明氢气对Cl元素的去除效果最好，且不会引入杂质。在此基础上，系统考察氢气为还原剂的还原过程中，还原温度、还原时间及石墨粒度等工艺参数对还原效果的影响。最佳还原条件下，二阶FeCl₃-NiCl₂-GICs还原产物中Cl元素的摩尔百分含量为31%。还原产物的物相构成为FeNi合金、石墨和FeCl₂，其中合金颗粒尺寸在20-200nm之间，均匀的分散在石墨烯层片间。造成FeCl₂不能被完全还原的主要原因是石墨的空间位阻效应。FeCl₃-NiCl₂-GIC还原产物的磁性为软磁性，其微波吸收性能较GICs有所增强，是一种较好的宽频、轻质微波吸收剂。MAM厚度为1mm时FeNi/C500损耗量大于-4dB的带宽为7GHz，覆盖了整个Ku（12.4-18GHz）波段；FeNi/C600在低频区具有较好的微波吸收效果，MAM厚度为2mm时，其最大反射损耗为-4.5dB，匹配频率为3.5GHz。6、以FeCl₃-NiCl₂-GIC的研究结果为指导，设计并制备了FeCl₃-CoCl₂-GICs及其还原产物，所得的FeCo/石墨纳米复合材料具有更好的微波吸收性能。三元过渡金属氯化物-GICs还原方法、工艺及性能的研究结果，为新型过渡金属/石墨纳米复合材料的设计及制备提供了实验依据，展示了一条设计和制备新型质轻、宽频的微波吸收材料的途径。更多还原

【Abstract】 With many excellent characteristic, Graphite intercalation compounds （GICs）have a great potential application on high electrical and thermal conductivities,sealing, energy storage and conversion performances, etc. Howerver, it is difficult instably controlling the material structure and improving the yield of the products byuse of the traditional preparation methods of GICs including the two-zone vaportransport technique, the liquid intercalation method, and the electrochemical method,etc. The molten salts method which has simple process and equipment belongs to theliquid intercalation method, and is usually used to prepare ternary ormulti-component GICs. It has the biggest possibility to produce GICs with a largescale, while the reactor needs to be vacuumized and airproofed, so glass tube is usedas the reactor, of which the volume is small and the heat-resistant temperature is low.In this dissertation, ternary FeCl₃-NiCl₂-GICs were synthesized by molten saltsmethod in air. The natural graphite powders were used as host material and themixture of NiCl₂and FeCl₃were used as intercalants. The technological factors,process and microwave absorption properties of FeCl₃-NiCl₂-GICs and its reductionproducts were investigated. The conclusions are summarized as follows:（1） Systematic investigations were carried out on the effects of technologicalfactors upon the stage index of FeCl₃-NiCl₂-GICs under the new technique, and thestainless steel reactor with big volume was designed and employed. The results showthat the ternary FeCl₃-NiCl₂-GICs with different stage structure can be obtained inthe glass tube with a little air. The influence of particle size of graphite, reactiontemperature, reaction time, pressure, NiCl₂/FeCl₃and C/transition metal chlorideson the stage index of FeCl₃-NiCl₂-GICs, were similar with that of theFeCl₃-NiCl₂-GICs prepared in vacuum. XPS results showed that the oxygen elementmainly distributed on the surface of graphite flakes and have little influence on otherparts of GICs when it reacted with graphite. The weight of the products prepared inthe stainless steel designed and manufactured by ourselves was ca.250g for eachreaction. The process simplification and the improvement in reactor of the moltensalts method pave the way for the preparation of new GICs, the performance andapplication research.（2） In order to evaluate the microstructure and the conditions of ternaryFeCl₃-NiCl₂-GICs, four parameters were put forward, i.e., the volume fraction of theobject stage GICs（V1）, the Ni standard deviation of the products（σ）, Ni/Fe ratio in the products （S）, and the ration of Ni/Fe ratio of the products and Ni/Fe ratio in rawmaterials（S′）. According to these parameters, the optimized preparation conditionsof the FeCl₃-NiCl₂-GICs with pure stage index in the new container were obtained.The four parameters have guiding significance for the microstructre and processoptimization of ternary GICs. And the quantitative characterization of the degree ofdiversification for ternary GICs is realized by them.The microstructure of the FeCl₃-NiCl₂-GICs such as surface morphology,composition, element distribution, crystal structure was investigated by XRD, SEM,EDS, Raman and HRTEM. The results show that the FeCl₃&NiCl₂and the layer ofgraphite are arranged alternately, and the stage domain size is about5-10nm. Due tothe intercalation reaction, the broken lattice fringes of graphite are no longer straight.The flake edge of the corroded zigzag stage1FeCl₃-NiCl₂-GICs was observed. Withthe increase of the stage index of GICs, the corroding degree is weakened and finallylooks like the original graphite.（3） The properties of microwave （2-18GHz）absorption of the GICs werestudied in details. It is found that FeCl₃-NiCl₂-GICs are good microwave absorbingmaterials（MAM） and have an optimum absorption efficiency lying in lowerfrequency region. The main microwave absorption mechanism of GICs is dielectricloss, and the absorbing capability of GICs is related to the electrical conductivity ofGICs. The optimal mass ratio of GICs and paraffin wax is1:1. The maximum TRL ofthe stage1FeCl₃-NiCl₂-GICs which size is100mush is-11dB when the thickness ofMAM is5mm, and the matching frequency is3.2GHz.（4）The intercalation process of FeCl₃-NiCl₂-GICs and the diffusion of NiCl₂were analyzed. The results show that the intercalation process is divided into fivestages. The first is the selective absorption involved the intercalation between FeCl₃and NiCl₂. The second stage is the formation stage of FeCl₃-GICs. The third is theNiCl₂distribution stage including NiCl₂and FeCl₃together. The forth is thedistribution stage of NiCl₂alone. And the last one is the NiCl₂intercalating with theGICs domain stage. The speed of the intercalation process is greatly depended on thediffusion of Ni. The intercalation ways of NiCl₂are either embedding or meltingtogether with FeCl₃to form NiFe2Cl8when the condition is under500℃and lessthan72h, and the method of embedding is predominant. These conclusions about theintercalation process and mechanism show the method and way to improve themicrostructure of ternary GICs to us.（5） The reduce conditions of FeCl₃-NiCl₂-GICs and the properties of microwaveabsorption of the reduction products were investigated in details. The reductioneffects of FeCl₃-NiCl₂-GICs by H2, Na, hydrazine hydrate and sodium borohydride were studied. The results show that the reduction effect by H2is the best, and noimpurity is introduced into reduction products in H2reduction environment. Thereduced conditions of FeCl₃-NiCl₂-GICs by H2, such as temperature, time and theparticle size of graphite, were investigated. The results indicate that the content ofthe Cl in the reduction product is decreased with increasing of reduction temperature,prolonging of reduction time and the minimizing the particle size ofFeCl₃-NiCl₂-GICs. The molar content of Cl in the reduction product, which wasprepared by reducing the stage2under the optimized conditions, is about31%. Thereduction products of FeCl₃-NiCl₂-GICs are composed of FeNi, graphite and FeCl₂.A lot of FeNi particles with size of20²00nm are located in the graphite layers. Thekey reason that the FeCl₃-NiCl₂-GICs cannot be reduced thoroughly is the sterichindrance effect of graphite.The reduction products of FeCl₃-NiCl₂-GICs, a kind of soft magnetic material,have good microwave absorption properties. The absorbed frequency bandwidth ofthe FeNi/C500reaches7GHz, covering the whole Ku band （12.4-18GHz）, when thethickness of MAM is1mm. The maximum TRL of FeNi/C600is-4.5dB at3.5GHzwhen the thickness of the MAM is2mm, which exhibits good absorption efficiencyat lower frequency region.6、According to these research conclusions, FeCl₃-CoCl₂-GICs and its reductionproducts were designed and manufactured, and the the properties of microwaveabsorption of them were investigated. These studies about the reduction method,process and performance of ternary transition metal chlorides-GICs provide theexperimental evidences for the design and preparation of the new transition metal/graphite nanocompositions, and set out a way to design and preparate the new MAMwith the low density and wide-frequency properties.更多还原