膨胀石墨

本文介绍了膨胀石墨制备的几种方法,着重探讨在硫酸溶液中用化学氧化法和阳极电解氧化法制备石墨的硫酸层间化合物的基本原理和过程,进一步介绍了石墨的氧化物和石墨酸的生成原理及过程,并且简介了气体氧化法制备石墨层间化合物和在有机溶液中制备碱金属-石墨-有机物这类、层间化合物的方法。另外,对石墨层间化合物受热彭胀的机理、加热源的种类减少胀胀石墨制件中含(?)量的处理办法,以及减少清流石墨氧化中间产物的用水量等问题进行了文献综述。     

第二十届国际炭会议扩展摘要题录(续3)

11 D 层间化合物采用电化法在液氨中制备金属—氨石墨层间化合物 E. Stumpp, H. Alheid, M. Schwarz 690 石墨及涡轮层炭在液相锂插层中的不同表现 H. P. Boehm, P. Schoderbock 692 石墨化度对炭纤维溴化的影响 D. D. L. Chung 694 新颖化学气相沉积石墨纤维及其溴层间化合物的性能 J. R. Gaier, M. L. Lake, A. Moinuddin, M. Marabito 696 碘作为主要层间插入物的石墨层间化合物 C-C. Hung, D. Kucera 69     

石墨层间化合物成阶过程分析

主要从插层剂插入石墨、插层剂的扩散和阶结构的转变3个方面对石墨层间化合物成阶相关的过程进行讨论。从表面扩散、成核和电子转移3个方面介绍了插层剂进入石墨层间的过程;利用单相的方法分析了层内插层剂的扩散;从有无阶数变化两个方面讨论了阶结构的转化机制。     

石墨层间化合物成阶过程分析

主要从插层剂插入石墨、插层剂的扩散和阶结构的转变3个方面对石墨层间化合物成阶相关的过程进行讨论。从表面扩散、成核和电子转移3个方面介绍了插层剂进入石墨层间的过程;利用单相的方法分析了层内插层剂的扩散;从有无阶数变化两个方面讨论了阶结构的转化机制。     

新型钆石墨层间化合物复合材料的制备及表征

通过Hummers法制备氧化石墨,并以化学吸附法将氯化钆（GdCl3）饱和溶液中的钆离子引入氧化石墨（GO）,合成新型水合碳酸氧钆-氧化石墨层间化合物复合材料。采用XRD、FT-IR和TG-DTA对产物进行分析表征。表明,制备水合碳酸氧钆-氧化石墨层间化合物的最佳质量配比为m（Gd2O3）∶m（EG）=5∶1。通过TG-DTA分析确认,水合碳酸氧钆-氧化石墨层间化合物的还原温度为480℃。     

微波膨化钾-四氢呋喃-石墨层间化合物制备膨胀石墨

为了开发一种在无硫酸介入下制备膨胀石墨的新工艺,达到无有害硫残余的目的,以钾-四氢呋喃-萘的有机络合物溶液为介质,用电化学法合成了钾-四氢呋喃-石墨层间化合物,并对其进行微波膨化。对膨化石墨表面形貌和结构进行了表征分析,探讨了钾-四氢呋喃-石墨层间化合物的电解插层机理。结果表明:钾同四氢呋喃的有机溶剂共嵌入石墨层间,且石墨层间化合物膨化后,钾与四氢呋喃在微波作用下迅速从石墨层间膨胀出来得到石墨微薄片,这些石墨薄片彼此叠合形成片层状外观,构成膨胀石墨良好的孔隙结构。     

南墅鳞片石墨氯化铁层间化合物的溶剂法合成

由南墅鳞片石墨用溶剂法合成了三阶的氯化铁石墨层间化合物，合成中不用过分地隔离水。合成中石墨鳞片大小，溶液浓度，合成时间等对石墨层间化合物的阶数影响不大，但却使层间化的量发生很大变化。南墅小鳞片石墨很容易进行插入反应得到层间化合物。     

石墨层间化合物的制取及其应用

石墨层间化合物是一种新型的纳米材料,具有广泛的应用背景。本文介绍了石墨层间化合物的原理以及种类,几种制备方法：双室法、化学氧化法、电化学法、溶剂法、混合法、加压法等,并比较了他们各自的优缺点及应用现状。     

石墨层间化合物在插层过程中阶的转变模式

应用原位ＸＲＤ（Ｘ射线衍射）法，研究了石墨层间化合物（ＣＩＣ）在插层过程中阶次的转变模式。结果表明：不同的插层体系和插层条件产生不同的成核和扩散情况，从而导致在插层过程中试样的不同阶次转变模式。     

膨胀石墨与纳米分离技术

天然石墨鳞片经化学法进行插层后,形成一种层间化合物,在高温下,层间化合物会因热分解而使石墨层间沿着垂直方向膨胀数百倍,而形成一发泡碳材料,这种材料称为膨胀性石墨.膨胀性石墨是由纳米石墨薄片组成.纳米石墨薄片是以高度规律之石墨层堆叠而成,厚度约20～50 nm.再进一步使用纳米分离技术将纳米石墨薄片分离,并分散在树脂之中形成特殊的纳米石墨薄片复合材料.同时,探讨了几种物理法的纳米分散技术,以及用于分离纳米石墨薄片之原理.     

Graphite intercalation compounds as PEMFC electrocatalyst supports

Intercalation of metal chlorides into fine natural graphite flakes of 2 × 10⁻⁶ m in diameter was attempted. CuCl₂ was satisfactorily intercalated from the vapour phase. NiCl₂ and PdCl₂ were also intercalated from the liquid phase using chloroform solvent. The reduction products of the obtained graphite intercalation compounds were used as carbon supports of the platinum electrocatalyst for a proton exchange membrane fuel cell. Oxygen reduction activity was evaluated and it can be seen that natural graphite flakes treated using the intercalation technique provide different levels of activity from that of pristine natural graphite flakes. In particular, the catalytic activity was enormously improved when CuCl₂ was used as the intercalate.     

Scanning transmission electron microscopy of multiphases in graphite-alkali metal intercalation compounds

Structural and micro-analytical evidence is presented for the presence of multiphase regions in graphite-Rb intercalation compounds for stages n ? 2. The intercalate layers are composed of islands of alkali metal, ordered incommensurately with respect to the adjacent graphite layers and embedded in a background of disordered rubidium in the intercalate layer. The results confirm the non-integral stoichiometry of graphite alkali metal intercalation compounds for stages n ? 2.     

The electrochemical preparation and properties of ionic alkali metal-and NR4-graphite intercalation compounds in organic electrolytes

The preparation of graphite-alkali metal-solvent or graphite-NR₄-Solvent ternary intercalation compounds by electrochemical reduction of graphite is described. The reduction occurs stagewise and the complete formation of a defined stage can be recognized by a striking change in the potential of the graphite electrode. Under certain conditions the stoichiometry of intercalation compounds (e.g. C₄₈K(DMSO), C₂₄K(DMSO), C₁₈Li(DME) can be calculated from the coulombs consumed by a weighed graphite electrode until a step in potential occurs. The electrochemical intercalation of alkali metals into graphite is reversible. It may be reversed with a coulombic efficiency up to practically 100%, e.g. for C_nK(DMSO). A considerable co-intercalation of alkali metal salts from the electrolyte was not observed. From a preparative point of view, a great advantage over the direct chemical reduction of graphite is that a desired degree of intercalation can be specifically prepared. A coulometric determination of the intercalated cations is possible by way of an electrochemical reoxidation. Potential measurements of electrochemically prepared intercalation compounds with a well-defined degree of intercalation represent a simple method for investigating the thermodynamics of these reactions. Furthermore, by means of dynamic electrochemical methods, such as cyclic voltammetry, information about the kinetics of intercalation reactions is obtainable.     

Versatile behavior upon intercalation by chemical vapor transport of lanthanide trichlorides into graphite

Lanthanide trichlorides which hardly react with graphite have been moved into the latter by chemical vapor transport (CVT) thanks to a gaseous complex LnAl₃Cl₁₂ resulting from the reaction between LnCl₃ and AlCl₃. This complex molecule also allows the intercalation of LnCl₃ into graphite, AlCl₃ playing the role of a gaseous medium and/or co-intercalated species, depending on the structure of the pristine chloride. Well-defined stage-2 to 4 graphite intercalation compounds (GICs) have been synthesized by this CVT method, but efforts to get richer stage-1 compounds are still in progress. The 0 0 l structural study of stage-2 GICs performed by XRD reveals that interplanar distances of LnCl₃-GICs are higher than those classically observed for intercalated transition metal chlorides. The composition of all the stage-2 compounds studied has been established and ternary C-LnCl₃–AlCl₃ compounds with a significant excess of chlorine have been observed. The 2D structures of the different LnCl₃-GICs have been characterized by X-ray or electron diffraction and show that structural differences are noted between pristine and intercalated LnCl₃.     

Zur wirkung von zusatzstoffen bei der bildung von geordneten graphit-FeCl3-einlagerungsverbindungen

Intercalation compounds with strong disturbances in the stacking sequences of the layers are normally formed in the reaction of ferric chloride vapour with graphite [6]. Fully periodic sequences can be prepared, however, by addition of either chlorine, oxygen or water vapour [5]. The effect of these added substances has been investigated. Oxygen and water vapour do not act directly but liberate chlorine from ferric chloride in a preliminary reaction. The produced chlorine was detected quantitatively by spectrophotometry. If no additional time is allowed for the preliminary reaction, the ordering effect of oxygen (Table 2) and of water vapour is less than that of chlorine. The stacking order has been determined by X-ray diffraction [6]. It is quantitatively represented by the “degree of order” (“Bildungsgrad”) of a stage, with a value between zero (completely random sequence) and one (strictly periodical sequence).If chlorine is added only in the initial phase of the intercalation, then the ordering effect will be lost with progressive reaction. Thus the effect of chlorine does not result in any permanent change of the graphite. The rate of intercalation is reduced a little by the addition of chlorine (Fig. 2), probably as the result of the diffusioncontrolled kinetics. Thus the chlorine does not act like a catalyst causing an acceleration of an otherwise slow reaction step. The ordered compounds cannot be interpreted as secondary products of the disordered ones. therefore, and also not as alternative products which are kinetically promoted by addition of chlorine.X-Ray diffractometer recordings (Fig. 1) show that the effect of chlorine is much stronger in the final phase than in the initial phase. Following up quantitatively the degree of order, it became evident that with additional chlorine in the final phase a supplementary increase in order is possible. This works as long as the graphite takes up ferric chloride. A subsequent annealing with additional chlorine does not affect the order any more.For the model conception of the effect of chlorine the following conclusions can be drawn: a close connection exists between the motion of ferric chloride in the interior of the crystal and the eventual formation of periodic arrangements. We assume that the chemisorbed chlorine at the surface of graphite weakens the bond of ferric chloride to graphite by charge transfer. Thereby the mobility of ferric chloride between the graphite layers increases. In each small region (domain) periodical arrangements then can be formed more easily.     

界面涂层对碳纤维增强锂铝硅玻璃陶瓷复合材料力学性能影响的研究

采用溶胶凝胶法在碳纤维表面制备了Li2O/SiO2涂层,采用XRD技术对其层间结构进行了表征.结果表明在所得碳纤维的表面层形成了二阶的插层结构的石墨层间化合物,聚丙烯腈基碳纤维作宿主,锂离子作插层剂的,该插层化合物的生成提高了碳纤维增强锂铝硅玻璃陶瓷复合材料的抗弯强度.     

混酸插层制备膨胀石墨研究

对采用H2SO4-HNO3-KMnO4-H2O2混酸氧化插层体系制备膨胀石墨进行了研究,采用扫描电镜（SEM）、X射线衍射（XRD）、红外光谱（IR）和热重一差热法（TG-DTA）分析产物,并提出了氧化插层过程和机理。分析表明：插入剂的插入破坏了原有鳞片石墨层的紧密结构,使碳层间距增大,高温膨胀后,膨胀石墨呈蠕虫状或手风琴状蓬松结构,一个石墨蠕虫由许多微胞连接在一起组成,微胞之间呈现较大的狭缝裂开。氧化插层破坏了鳞片石墨原有的晶体结构,但是未破坏石墨的C—C键,20=29．5。处的特征峰是由石墨插层物结晶区引起的。可膨胀石墨片层。间存在SO4^2-、NO2阴离子插层物。可膨胀石墨在500℃之前的热失重和267℃附近较小的放热峰,均是由石墨插层物的气化、分解所致。     

A theory for the kinetics of intercalation of graphite

A theory, which takes into account the evaporation, transport and condensation of the intercalate outside the graphite and the diffusion and staging inside the graphite, is presented for the kinetics of intercalation of graphite. The theory has been applied to a number of intercalates (including Br₂, ICl, K, Rb, Cs, FeCl₃, NiCl₂, CuCl₂, PdCl₂, HNO₃, AsF₅, and SbF₅) at various temperatures. Ratecontrolling reaction steps have been identified for different types of intercalation compounds.     

Gold nano-sheets intercalated between graphene planes

The lamellar structure of graphite is known for allowing intercalation of numerous chemical species between its graphene planes. Considering the intercalation of the electron donors, some pure metals, several metallic alloys and even electronegative elements associated with electropositive metal lead to binary or ternary graphite intercalation compounds. In all cases, the presence of an alkali metal is essential in order to open the van der Waals’s intervals, what is performed in this study dealing with the graphite–potassium–gold original system. Gold is very particular since it is a true metal but strongly electronegative too. Associated with potassium, it becomes able to intercalate easily into graphite, leading to a first stage graphite–potassium–gold compound. This study displays the best synthesis conditions to prepare this pure ternary compound. The study of its 00l reflections leads to determine the repeat distance (1311 pm) with a five-layered stacking sequence of the intercalated sheet along the c-axis. Two potassium mono-layers surround a three-layered gold nanosheet, so that the c-axis expansion reaches 237%. A chemical formula K_1.30Au_1.50C₄, namely 0.7 metallic atom for one carbon atom, has been determined for this compound. A discussion concerning the charge transfer between graphene planes, potassium and gold atoms is also proposed.