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1、Materials Science andEngineering of CarbonFundamentalsMaterials Science andEngineering of CarbonFundamentalsSecond EditionMichio InagakiFeiyu KangAMSTERDAM BOSTON HEIDELBERG LONDONNEW YORK OXFORD PARIS SAN DIEGOSAN FRANCISCO SINGAPORE SYDNEY TOKYOButterworth-Heinemann is an imprint of ElsevierButter

2、worth-Heinemann is an imprint of Elsevier225 Wyman Street,Waltham,MA 02451,USAThe Boulevard,Langford Lane,Kidlington,Oxford,OX5 1GB,UKFirst edition 2006Second edition 2014Copyright 2014 Tsinghua University Press Limited.Published by Elsevier Inc.All rights reserved.No part of this publication may be

3、 reproduced,stored in a retrieval system or transmittedin any form or by any means electronic,mechanical,photocopying,recording or otherwisewithout the prior written permission of the publisher.Permissions may be sought directly from Elseviers Science&Technology RightsDepartment in Oxford,UK:phone(1

4、44)(0)1865 843830;fax(144)(0)1865 853333;email:.Alternatively you can submit your request online byvisiting the Elsevier web site at http:/ selectingObtaining permission to use Elsevier material.NoticeNo responsibility is assumed by the publisher for any injury and/or damage to persons orproperty as

5、 a matter of products liability,negligence or otherwise,or from any use oroperation of any methods,products,instructions or ideas contained in the material herein.Because of rapid advances in the medical sciences,in particular,independent verificationof diagnoses and drug dosages should be made.Brit

6、ish Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British LibraryLibrary of Congress Cataloging-in-Publication DataA catalog record for this book is available from the Library of CongressISBN:978-0-12-800858-4For information on all Butterworth-Heineman

7、n publicationsvisit our website at http:/Printed and bound in the US14 15 16 17 1810 9 8 7 6 5 4 3 2 1PrefaceOne of the authors(M.Inagaki)has been emphasizing the importance of nanotexture,as well as structure,to understand carbon materials.In 1985,he proposed the classifi-cation of nanotexture of c

8、arbon materials on the basis of preferred orientation schemaof anisotropic layers of carbon hexagons,planar,axial,point and random orientation.Nanotexture is formed during carbonization of organic precursor,as well asstructure,and governs the structure development during heat treatment at hightemper

9、atures,which has been understood as graphitizing and non-graphitizing.Nanotextures can explain the reason why fibrous carbon materials exist,such as car-bon fibers and tubes,and the spherical carbons,such as carbon blacks and fullerenes,from strongly anisotropic carbon layers consisting mainly of he

10、xagons.In order toconvince of the importance of nanotextures in carbon science and engineering,hepublished a book in Japanese entitled Materials Engineering of Carbons in 1985,and another book in Japanese entitled New Carbon Materials?Structure andFunctions with his friend,Y.Hishiyama in 1994.In 200

11、0,the book in English enti-tled New Carbons?Control of Structure and Functions from Elsevier added theconcept of carbon families,diamond,graphite,fullerene and carbyne,to follow therapid progress in science,engineering and applications of carbon materials.However,he strongly felt that,even though ma

12、ny young scientists and engineersare interested in and working on nanocarbons,such as carbon nanotubes and gra-phenes,fundamental knowledge on carbon materials is necessary for them.Mostbasics of carbon materials were already clarified before 1985.The books,whichgive such fundamental knowledge on ca

13、rbon materials,are rather few and also itmust be handy and easy to buy.Therefore,he discussed with Prof F.Kang anddecided to publish the book from Tsinghua University Press,China,entitledCarbonMaterialsScienceandEngineering?FromFundamentalstoApplications.The book aims to give comprehensive informati

14、on firstly on funda-mental science on preparation and characterization of various carbon materials,and secondly on engineering and applications of various carbon materials,on thebasis of the same basic concept as published before,i.e.,classifications based oncarbon families and nanotextures.Since so

15、 many copies have been sold mostly in China,the present authors(M.Inagaki and F.Kang)decided to write advanced science and engineering oncarbon materials under the corporation of two more authors(M.Toyoda andH.Konno)by taking in recent developments,and it was published in September,2013,with the tit

16、le Advanced Science and Engineering on Carbon by twopublishers,Tsinghua University Press and Elsevier.At the same time,the publish-ers asked the present authors to revise and up-date the previous book CarbonMaterials Science and Engineering?From Fundamentals to Applications.Here,the revised version

17、is presented.ixIn this revised version,the content is largely revised and up-dated,forexample,a chapter of nanocarbons is newly added,although fundamentals in car-bon science and engineering do not change and the basic concepts,carbon fami-lies and nanotextures,are still valid.The authors hope to pr

18、ovide fundamentalscience and engineering on carbon materials,associated with some applications,to young graduate students who are working on various carbon materials and alsoengineers whose works are more or less related to carbon materials.It will be agreat pleasure for the authors if they will alw

19、ays bring this book with them to dis-cuss their results and to read the scientific papers published.They may find outhow the data they got and/or those published either agree or disagree with thegeneral information explained in this book,and also what is missing from thisbook.xPrefaceAcknowledgments

20、The authors would like to express their sincere thanks to the people who kindlyprovided the data and figures for this book,the names and affiliations of contri-buted persons being mentioned in the caption of figures and tables.They alsothank all of the people who took care of this book in Tsinghua U

21、niversity Pressand also in Elsevier.xiCHAPTER1Introduction1.1 Carbon materialsCarbon C is one of the abundant elements on the Earth,because almost all organ-ics are composed from carbon networks,and it is very familiar in our daily lives,for example,ink for newspapers,lead for pencils,activated carb

22、ons in refrigera-tors,etc.Carbon materials,which consist mainly of carbon atoms,have been usedsince prehistoric era as charcoal.In Japan,a large amount of charcoal(about 800tons)was reported to be used for casting a great image of Buddha in Nara from747?750.Soft graphite has been used for a long tim

23、e as lead and carbon blacksas black inks.Diamond crystals are fascinating for all human beings not only asjewels but also the hardest materials were found to consist of carbon atoms,thesame atoms as lubricating soft graphite in 1799.Nowadays various carbon materi-als are used in our daily lives,thou

24、gh many of them are inconspicuous;activatedcarbon produced from coconut shells for a filter of tobacco,carbon fibers for rein-forcement of rackets and fishing rods,leads for automatic pencils,activatedcarbons for deodorization in refrigerators,membrane switches composed ofgraphite flakes for keyboar

25、ds of computers and various instruments,etc.Charcoalmay be the first carbon material used practically,as it has been used since thepre-historic age.Carbon materials started to be used as electrodes for batteriesaround 1800.Since 1878,large-sized carbon rods were used as electrodes for ironrefining,w

26、hich were industrially produced by heat treatment at high temperatures(as high as 3000?C)and called graphite electrodes because crystalline graphitestructure was well developed in most of them.Later on,various carbon materialshaving graphitic structure for various applications were developed,which w

27、erecalled graphite materials,even though the development of graphitic structure isnot complete.At the same time,carbon materials without noticeable graphitestructure,such as charcoal,were also developed and opened new applications.There was no clear definition and no clear-cut classification on what

28、 graphitematerials are and what carbon materials are.In the present book,however,wewill use the term carbon materials for materials composed predominantly ofcarbon element,irrespective of their structure,so including fullerenes and carbonnanotubes,and also the terms either carbon materials or carbon

29、s for the mate-rials without three-dimensional graphite structure.On the other hand,graphitematerials and sometimes graphites were used for the materials which havethree-dimensional graphite structure,even partly.In industry,the term graphiteMaterials Science and Engineering of Carbon:Fundamentals.D

30、OI:http:/dx.doi.org/10.1016/B978-0-12-800858-4.00001-2 2014 Elsevier Inc.All rights reserved.1and graphitized are often used,even though graphite structure is not developedappreciably;for example PAN-based carbon fibers heat-treated at a high tempera-ture used to be called graphite fibers,even thoug

31、h almost no graphite structurewas developed,as will be explained later in detail.Polycrystalline graphite materials have been used in various fields of indus-tries using their different properties.Their characteristics can be summarized asfollows;(1)high thermal resistance in non-oxidizing atmospher

32、e,(2)high chemi-cal stability,(3)high electrical and thermal conductivities,(4)small thermalexpansion coefficient and,as a consequence,high thermal shock resistance,(5)very light weight,(6)high mechanical strength at high temperatures,(7)high lubricity,(8)highly reductive at high temperatures and ea

33、sily dissolvedinto iron,(9)non-toxic,(10)radiation resistance,and(11)low absorptioncross-section and high moderating efficiency for neutron.Since all polycrystalline graphite materials consist of parallel stacking of car-bon hexagonal layers,like graphite,which are called crystallites,their properti

34、esof a bulk material are strongly governed by different factors,such as how largethe crystallites are,how these anisotropic crystallites orient in the bulk,to whattemperature they were heat-treated,etc.The preferred orientation of crystallites inbulk graphitic materials depends strongly on the condi

35、tion of forming process andthe heat treatment temperature governs the size and perfection of the structure.Therefore,most of the properties of carbon materials distribute in a wide range.In Fig.1.1,electrical conductivity,bulk density,thermal expansion coefficient(expansivity),and tensile strength a

36、re compared for different carbon materials,including natural graphite,various fibrous carbon materials,and graphite interca-lation compounds(GICs).Polycrystalline graphite is a good electric conductor,but its electrical conduc-tivity of roughly 23105S/m is inferior to metals.By intercalation of diff

37、erentspecies into the interlayer spaces of graphite,however,electrical conductivity ismuch improved and becomes even higher than that of metallic copper.Thermalexpansion coefficient of graphite single crystal is very high along the c-axis(per-pendicular to the graphite layer plane),but negative(i.e.

38、,shrinkage)along thea-axis(parallel to the layer).In polycrystalline graphite materials,this anisotropyin thermal expansion is spaciously averaged,depending strongly on the size andarrangement of crystallites(i.e.,structure and texture).In fibrous carbons,it ismainly governed by expansion along the

39、layer planes and so rather small values.In most of physical properties,such as electrical and thermal characteristics,thehighest and the lowest values are realized in the directions perpendicular and par-allel,respectively,to graphite layers,as shown on the electrical conductivity andthermal expansi

40、on coefficient in Fig.1.1.Mechanical properties,such as tensilestrength,and bulk density are texture-sensitive characteristics and so they show awide range of values,in general.The practical values for various carbon materialsincluding polycrystalline graphite materials(high-density isotropic graphi

41、te andgraphite electrodes)are inferior to the theoretical values for graphite singlecrystal,because of their polycrystalline nature.2CHAPTER 1 Introduction108AsFs-Graphiteintercalation compounds(GIC)FeCb-GICGraphite(single crystal)Graphite(along c-axis)Graphite(single crystal)Graphite whiskerVapor-g

42、rown carbon fiber(3000C)Vapor-grown carbon fiberPAN-based carbon fiberHigh density isotropic graphiteHigh density isotropic graphiteGlassy carbonTensile strength/MPaThermal expansivity/106/CGraphite electrodePAN-based carbon fiber(1000C)PAN-based carbon fiber(3000C)Graphite(along a-axis)Pitch-based

43、carbon fiber(3000C)Pitch-based carbon fiberHigh densityGraphite electrodePitch-based carbon fiberGlassy carbonPorous glassy carbonPorous carbonisotropic graphiteK-Bi-GICNatural GraphiteHighly orientedGraphite whiskerVapor grownGraphite electrodeGlassy carbon(3000C)Glassy carbon(1000C)PAN-based carbo

44、n fiberPAN-based carbon fiber(3000C)PAN-based carbon fiber(3000C)PAN-based carbon fiber(1000C)Vapor grown carbon fiber(as-prepared)carbon fiber(3000C)pyrolytic graphite(HOPG)1071061051040.51.01.52.028.3105110310410501Density/g/cm3Electrical conductivity/S/mAgCuAuAuFIGURE 1.1Range of various properti

45、es of carbon materials.1.2 Short history of carbon materialsDevelopment of carbon materials was discussed by dividing into three periods,before 1960,between 1960 and 1985 and after 1985,as summarized in Table 1.1.The year 1960 may be said to be the beginning of the era of new carbons,becauseof the i

46、nventions of carbon fibers from poly(acrylonitrile),pyrolytic carbons byCVD process,and glass-like carbons from thermosetting resins,which werecompletely different from the carbon materials used before 1960.Up to 1960,four carbon materials were known and had practical applicationsin various fields o

47、f industries;artificial graphite blocks mainly used for steelrefining,carbon blacks for ink and reinforcement of rubbers,and activatedcarbons for water purification,in addition to natural diamond.These carbon mate-rials,except diamond because of its very different appearance and properties,were prop

48、osed to be called classic carbons.In 1960,three carbon materials,carbon fibers,glass-like carbons,and pyro-lytic carbons were developed,which were completely different from classiccarbons in their production processes and also properties.Following these threecarbon materials,different kinds of carbo

49、n materials had been developed underthe modifications in precursors,preparation conditions,etc.So,we called thesecarbon materials new carbons,in the contrast to classic carbons.After the findingof graphite intercalation compounds having a high electrical conductivity,higherTable 1.1Carbon PeriodsPer

50、iodYearsCarbon MaterialsDevelopedRemarksIPre-1960Artificial graphite blocksActivated carbonsCarbon blacksNatural diamondMass productionSale in either tons or kilogramsII1960?1985Various carbon fibersGlass-like carbonsPyrolytic carbonsHigh-density isotropicgraphitesIntercalation compoundsVarious comp

51、ositesSynthetic diamondDiamond-like carbonsIntroduction of various techniquesfor the production of carbonmaterials(e.g.,CVD,compositewith other materials,etc.).Development of new applicationsSale mostly in gramsIIIPost-1985FullerenesCarbon nanotubesGrapheneNano-sizedSale in milligrams4CHAPTER 1 Intr

52、oductionthan copper,a boom in research on intercalation compounds has arisen in aworld-wide scale,although it could not open the practical applications.The year 1985 was another epoch for carbon materials,where a carbon cage con-sisting of 60 carbon atoms was found,which was named buckminsterfullere

53、ne C60and followed by a series of carbon cages,such as C70,C86,etc.In 1991,multi-walledcarbon nanotubes were reported,which was followed by the finding of single-wallcarbon nanotubes.In 2004,a single hexagonal carbon layer was reported.Finding ofthese novel carbons,nanocarbons,attracted pronounced a

54、ttention to nano-scalescience and technology,and accelerated the development of the science related tonanotechnology.In the course of nanotechnology development,the word nanocar-bons came to be often used.Also,structure and texture of most carbon materialswere required to be controlled in nanometer

55、scale for all applications.1.3 Classic carbons,new carbons,and nanocarbons1.3.1 Classic carbonsThe fundamental science and technology on classic carbons,artificial graphiteblocks,carbon blacks,and activated carbons,were established before 1960,in theperiod I(Table 1.1).It has to be emphasized,howeve

56、r,that these carbon materialsare principal products and principal incomes for carbon industries world-widecurrently.In Fig.1.2,photographs of these carbon materials are shown.These three-carbon materials have a wide range of sizes;graphite electrodes representing arti-ficial graphite blocks are used

57、 in a size of about 700 mm in diameter and about3 m in length,carbon blacks are spherical particles with the diameter from 10 to afew hundred nanometers,activated carbons are porous materials with irregularFIGURE 1.2Classic carbons.(a)Graphite electrodes(b)Carbon blacks(c)Activated carbons.51.3Class

58、ic carbons,new carbons,and nanocarbonsshapes.Diamond is so rare in nature and expensive as to be measured by usingthe unit of carat,different from other carbon materials(gram).1.3.2 New carbonsThe important developments related to carbon materials since 1960,in the periodsof II and III,are listed in

59、 Table 1.2.The period II started with the developmentsof PAN-based carbon fiber,pyrolytic carbon,and glass-like carbon,all three ofthem being completely different from classic carbons.Carbon fibers 1,which were produced by carbonization of poly(acrylonitrile)fibers after oxidation(PAN-based carbon f

60、ibers;Fig.1.3),fascinated people bytheir high strength and flexibility and many demonstrative pictures,for example,hanging an automobile by a thin string of carbon fibers,were published in variousjournals.The developments of other kinds of carbon fiber followed in the 1970s,including pitch-based and

61、 vapor-grown carbon fibers.In contrast to carbon fibers,glass-like carbon was very hard and brittle,and its gas impermeability which hadnever been realized in classic carbons was amazing 2.It was named from itsconchoidal fracture surface,similar to soda-lime glass.Now different products ofglass-like

62、 carbon were industrially developed,as shown in Fig.1.4.PyrolyticTable 1.2Topics Related with Carbon MaterialsYearBasic ScienceMaterials DevelopmentTechnologyDevelopment1960PAN-based carbon fibersPyrolytic carbonsGlass-like carbonsElectrodes for electricdischarge machining1965Mesophasespheres in pit

63、chNeedle-like cokesMesophase-pitch-basedcarbon fibers1970Biocompatibility ofcarbon materialsVapor-grown carbon fibersCarbon prostheses1975High conductivityof GICsMesocarbon microbeads1980Diamond-likecarbon filmsIsotropic high-densitygraphitesCarbon-fiber-reinforcedconcreteCarbon electrode forfuel ce

64、ll1985Buckminsterfullerene C60,followed by variousfullerenesFirst wall for fusion reactor1990Superconductivityof K3C60Carbon nanotubes,single-wall and multi-walled1995Carbon anode for lithiumion rechargeable batteries6CHAPTER 1 Introductioncarbons were produced by a completely different technique fr

65、om conventionalones,chemical vapor deposition(CVD)3,though it is very common in materialproduction nowadays.Their strong anisotropy in various properties,such as elec-trical and thermal conductivities,gave a quite new aspect for the application ofFIGURE 1.3Carbon fibers.FIGURE 1.4Products of glass-l

66、ike carbon.71.3Classic carbons,new carbons,and nanocarbonscarbon materials.Pyrolytic carbons prepared in well-controlled conditions couldhave very high crystallinity,i.e.,well-developed and well-oriented basal planes ofgraphite,by treatment under high temperature and high pressure,which werecalled h

67、ighly oriented pyrolytic graphite(HOPG)and developed new applicationsas a monochrometer for X-rays and neutrons 4.This CVD process was success-fully applied for carbon coating of nuclear fuel particles 5.Formation of optically anisotropic spheres in pitches,mesophase spheres,andtheir coalescence,whi

68、ch was firstly reported in 1964 6,motivated many funda-mental studies,structure of the spheres,growth and coalescence mechanism ofspheres and formation of bulk mesophase,and created new carbon products,needle-like cokes which were the essential raw materials for high-power graphiteelectrodes,mesopha

69、se-pitch-based carbon fibers with high performance,andmesocarbon microbeads for different applications 7(Fig.1.5).Thin flakes of natural graphite were successfully used to produce the mem-brane switches,of which the construction was schematically shown in Fig.1.6.They contributed to promote the ligh

70、t weight and small size of modern electron-ics,by being used as keyboards for computers,switching boards for various elec-tric equipments,etc.Good biocompatibility of carbon materials,found around 1970,led to the devel-opment of various prostheses,such as heart valve,tooth root,etc.8.Around1980,indu

71、strial technology for producing isotropic high-density graphite blocks byusing so-called rubber-press was established and created various applications;reflectors for high-temperature gas-cooled reactors,various jigs for the synthesis ofsemiconductor crystals and also the electrodes for electric disc

72、harge machining.Around 1985,a small amount of mixing of carbon fibers to cement paste was foundto result in a pronounced reinforcement of concrete 9.Its first practical applica-tion was the construction of the Arshaheed monument in Iraq and then it wasapplied in different buildings(Fig.1.7).Today,no

73、t only carbon-fiber-reinforcedFIGURE 1.5Mesophase spheres formed in a pitch.8CHAPTER 1 Introductionconcrete but also carbon fibers themselves are used in the field of civil engineering,such as in buildings,bridges,and various constructions 10.Finding of high electrical conductivity of AsF5?graphite

74、intercalation com-pound,higher than metallic copper,gave a strong impact to scientists andengineers 11.The researchers did not give a practical application of these inter-calation compounds,mainly because of their poor stability in air.However,prac-tical use of carbon materials as anode for lithium

75、ion rechargeable batteries hasled to a great success(Fig.1.8)and contributed to the development in personalFIGURE 1.6Membrane switches and their construction.FIGURE 1.7Buildings that used carbon-fiber-reinforced concrete.(a)Arshaheed monument in Iraqand(b)Ark Hills Tower in Tokyo.91.3Classic carbons

76、,new carbons,and nanocarbonscomputers and portable telephones,which was based on intercalation and deinter-calation of lithium ions into the graphite gallery 12.As one of the energy stor-age devices,electrochemical capacitors are developed,they are based on physicaladsorption and desorption of ions

77、on porous carbon electrodes to form electricdouble layers.1.3.3 NanocarbonsIn 1985,a cage(cluster)composed of 60 carbon atoms C60(buckminsterfuller-ene)was firstly reported to be isolated from the soot obtained by laser irradiationon a graphite block 13,of which the structure consisted of 20 hexagon

78、s with 12pentagons of carbon atoms(Fig.1.9a).This carbon cluster C60was spherical,inother words,all chemical bonds are closed in the cage.These cages are crystal-lized to form the face-centered cubic crystal by cubic closest packing.It can bedissolved into some organic solvents,such as benzene,hexan

79、e,etc.,and behavesas a molecule.Later,cages with different sizes,such as C70,C76,C82,.andalso multi-walled cages were found and isolated.These are called fullerenes.Doping of alkali metals into all interstices of the fullerene crystals(tetrahedraland octahedral sites of cubic closest packing of cage

80、s)was found to give super-conductivity 14.Cages containing metal atoms,such as La,Sc,etc.,were syn-thesized 15.In 1996,The Nobel Prize in Chemistry was awarded jointly toR.F.Curl Jr.,Sir H.W.Kroto,and R.E.Smalley for their discovery of fullerenes.In 1991,carbon nanotubes were reported 16 and later s

81、ingle-wall carbonnanotubes were found 17,18.In 1960,fibrous carbons had been synthesized byarc discharging between carbon electrodes,which were called graphite whiskersbecause of their high crystallinity 19.In 1976,a single-wall carbon nanotubewas observed in the first step of the growth of vapor-gr

82、own carbon fibers byFIGURE 1.8Lithium-ion rechargeable batteries.(a)Principle of charge/discharge(b)An example ofconstruction.10CHAPTER 1 IntroductionCVD method using minute particles of catalyst iron 20(Fig.1.10).The namingof carbon nanotube 17 was very timely for the start of nanotechnology in var

83、i-ous fields.In 2004,the preparation of graphene,a single two-dimensional sheet of carbonatoms,was firstly reported,as shown in Fig.1.11 21,although the termgraphene was proposed in 1986 22.The Nobel Prize in Physics 2010 wasawarded jointly to A.Geim and K.Novoselov for groundbreaking experimentsreg

84、arding the two-dimensional material graphene.Nanocarbons were defined as not only their sizes of primary particles are innanometer scale,but also their structures and/or textures are controlled in nano-meter scale 23.Either nano-size or nano-structure of carbon materials hadto be consciously control

85、led to govern their properties and functions.They werediscussed in more detail by emphasizing some novel techniques to produceFIGURE 1.9Fullerene and carbon nanotube.FIGURE 1.10Single-wall carbon nanotube 18.111.3Classic carbons,new carbons,and nanocarbonsnanocarbons 24.Nanocarbons were classified m

86、ainly based on their preparationprocesses as follows.(I)Nano-sized carbonsCarbon materials of which sizes are in nanometers,for example,carbon nanotubes,carbon nanofibers,fullerenes and graphene,were classified into following three:(I-a)Carbons produced through vaporization of carbon clusters or fra

87、gments.(I-b)Carbons produced through catalytic effects of nano-sized metallicparticles.(I-c)Carbons produced through other processes,such as template,polymerblend,etc.(II)Nano-structured carbonsCarbon materials of which structure and textureare designed and controlled in nanometer scale were classif

88、ied into thefollowing four:(II-a)Carbons produced through controlling nano-size pores.(II-b)Carbons produced through designing molecular structure in precursors.(II-c)Carbons produced through controlling the carbonization process ofprecursors.(II-d)Carbons consisting of different component carbons a

89、nd producedthrough controlling their interfaces in nanometer scale.Fullerenes and carbon nanotubes were firstly synthesized through carbonvapors produced by arc discharging(I-a)and then expanded to new synthesismethod by CVD process using nano-sized metallic particles,such as Fe and Ni(I-b),mainly i

90、n order to increase the production efficiency of these nanocarbonmaterials.Unique processes for the production of nano-sized carbons,which maybe classified into(I-c),and also interesting results,have been reported on nano-structured carbons classified into category II 24.Some of the results areexpla

91、ined in Section 2.4.FIGURE 1.11Atomic force microscopic image of single hexagonal carbon layer,graphene 21.12CHAPTER 1 Introduction1.4 Construction and purposes of the present bookThe present authors published Carbon Materials Science and Engineering?From Fundamentals to Applications in 2006,and bri

92、efly revised and up-datedthe version in 2011.We are going to publish an advanced science of carbon mate-rials titled Advance Materials Science and Engineering of Carbon fromTsinghua University Press and Elsevier by focusing on specific items.Duringediting of the manuscript on advanced science,revisi

93、on and up-dating of the pre-vious book published from Tsinghua University Press was strongly recommendedby the publishers,and the authors also thought it necessary,because of the rapiddevelopment of science and engineering on carbon materials,not only in carbonnanotubes and graphenes but also in por

94、ous carbons.Therefore,the authorsdecided to publish the present book under the same title.The present book is aiming to give basic and thorough understanding of variouscarbon materials,and to be useful in understanding the advanced carbon science andengineering focuses on different carbon materials.

95、The present book is constructedfrom two parts,Fundamental Science of Carbon Materials and Engineering andApplications of Carbon Materials,in addition to this Introduction.In 1 Introduction,a brief review of carbon materials is presented before get-ting into the detailed discussion on science and eng

96、ineering of various carbonmaterials in the following chapters,by explaining how widely different carbonmaterials have been developed,which have been called classic carbons,new car-bons,and nanocarbons,and how many carbon materials we are using daily.In 2 Fundamental Science of Carbon Materials,the c

97、oncept of carbon fami-lies is firstly introduced,and then structural characteristics and the textures,whichhave arisen from their characteristic structures,are explained.The detailed discus-sion on texture development in carbon materials(carbonization)is given,by sepa-rating novel techniques for car

98、bonization.Structure development in carbonmaterials with high-temperature treatment(graphitization)is discussed based ontheir nanotextures and a general view of graphitization process is given.Also,acceleration of the graphitization process is discussed separately.Pores havegiven characteristic func

99、tions to carbon materials and so one section is devoted tothe characterization and the control of pore structure in carbon materials.Theintroduction of foreign species,not only atoms but also molecules,into carbonmaterials is also explained in an independent section,which has been donethrough interc

100、alation,substitution,and doping.In 3 Engineering and Applications of Carbon Materials,different carbonmaterials are explained in ten sections by paying particular attention to theirpreparation and applications.Polycrystalline graphite,highly oriented graphite,glass-like carbons,carbon fibers,nanocar

101、bons,porous carbons including activatedcarbons,carbon-based composites,and intercalation compounds of natural graph-ite are explained on their definition,production processes,and applications in sep-arate sections.Two sections are devoted especially to carbon materials for energy131.4Construction an

102、d purposes of the present bookstorage and environment remediation because of the important roles of carbonmaterials in these application fields.The authors aim to give an overview on fundamentals of science and engineer-ing of carbon materials from the point of view on structure and texture.If there

103、aders can get a general view on carbon materials and the fundamental conceptsto understand and to study the carbon materials,the authors will have succeeded.In addition,the authors strongly recommend all readers to refer to the originalpapers and also related papers cited in the present book,in orde

104、r to understand inmore detail.It has to be emphasized here frankly that all published papers are notcited in the present book and many interesting and important papers are omittedhere.One carbon material has different aspects.For example,porous carbons areproduced through different processes,from ca

105、rbonization of thermosetting precur-sors associated with activation,through template method without activation,fromcarbon aerogels,from the carbonization of thermoplastic precursors,through exfo-liation of graphite via intercalation compounds,etc.The porous carbons thus pre-pared have a wide range o

106、f pores from micropores to macropores,and,as aconsequence,they have been applied in various fields,adsorbents of variousmolecules,molecular sieving,storage of methane and hydrogen,sorption of vis-cous heavy oils,electrodes of electric double-layer capacitors,etc.As anotherexample,exfoliated graphite

107、 has been used as the raw material for flexible graph-ite sheets,which are applied in various fields of industry,but it has recently beenfound to be a good sorbent for heavy oils,a support for various catalyst metals,and also a raw material for graphenes.Various carbon materials are explained indiff

108、erent chapters and sections in the present book because they have been usedin different fields,as explained on porous carbons and exfoliated graphite.Therefore,the readers are strongly requested to read through whole parts of thepresent book first,even though they may be interested in a specialized

109、carbonmaterial,and then to visit the sections,which are written on the specified carbonmaterial.References1 J.B.Donnet,T.K.Wang,S.Rebouillat,J.C.M.Peng,Carbon Fibers(1998)573.2 T.Noda,M.Inagaki,J.Non-Cryst.Solids 1(1969)285.3 J.C.Bokros,Chem.Phys.Carbon 5(1969)1.4 A.W.Moore,Chem.Phys.Carbon 11(1973)

110、69.5 J.Guilleray,R.L.R.Lefevre,M.S.T.Price,Chem.Phys.Carbon 15(1976)1.6 J.D.Brooks,G.H.Taylor,Symp.Carbon,Tokyo(1964)Paper III-14-1.7 J.D.Brooks,G.H.Taylor,Chem.Phys.Carbon 4(1968)243.8 J.C.Bokros,L.D.LaGrange,F.J.Schoen,Chem.Phys.Carbon 9(1972)103.9 S.Akihama,T.Suenaga,T.Banno,KICT Report No.53(198

111、4).10 M.Inagaki,Carbon 29(1991)287.14CHAPTER 1 Introduction11 F.L.Vogel,Bull.Am.Phys.Soc.21(1976)263.12 G.Pistoia,Lithium Batteries(1994)483.13 E.W.Kroto,J.R.Hearth,S.C.IBien,et al.,Nature 318(1985)162.14 R.C.Hadden,A.F.Hebard,M.J.Rosseinsky,et al.,Nature 350(1991)320.15 Y.Chai,T.Guo,C.Jin,et al.,J.

112、Phys.Chem.95(1991)7564.16 S.Iijima,Nature 354(1991)56.17 S.Iijima,T.Ichihashi,Nature 363(1993)603.18 D.S.Bethune,C.H.Kiang,M.S.deVries,et al.,Nature 363(1993)605.19 R.Bacon,J.Appl.Phys.31(1960)283.20 A.Oberlin,M.Endo,T.Koyama,J.Cryst.Growth 32(1976)335.21 K.S.Novoselov,A.K.Geim,S.V.Morozov,et al.,Sc

113、ience 306(2004)666.22 H.P.Boehm,R.Setton,E.Stumpp,Carbon 24(1986)241.23 M.Inagaki,L.R.Radovic,Carbon 40(2002)2279.24 M.Inagaki,K.Kaneko,T.Nishizawa,Carbon 42(2004)1401.15ReferencesCHAPTER2Fundamental Science ofCarbon Materials2.1 Carbon families2.1.1 Carbon?carbon bondsCarbon atoms can have three di

114、fferent hybrid orbitals,sp3,sp2and sp,and give avariety of combinations of chemical bonds.Fig.2.1 illustrates how these threehybrid orbitals of carbon atoms give a large family of organic molecules and howthe inorganic carbon materials,diamond,graphite,fullerenes and carbynes,resultfrom the extensio

115、n to giant molecules of these organic materials.This variety inchemical bonds gives an enormous number of hydrocarbons and constructs anenormous number of organic materials;CaC bond using sp2hybrid orbitals givesa series of aromatic hydrocarbons,benzene,anthracene,phenanthrene,etc.,CaCabonds using s

116、p3and sp hybrid orbitals give various aliphatic hydrocarbons,such as methane,ethane,propane,ethylene,acetylene,etc.As schematicallyshown in Fig.2.1,infinite repetition of CaC bond using sp3results in a three-dimensional network of carbon atoms,which is known to be diamond.The atomicpositions of carb

117、on in an organic compound named as adamantane are exactly thesame as those in diamond.Therefore,if we were able to polymerize adamantaneto a giant molecule,we may synthesize diamond through a chemical process,though it has not yet succeeded.A simple repetition of CaC bond with sp2hybridorbitals give

118、s flat planes of hexagons of carbon atoms,as benzene,anthracene,ovalene,and finally reaches graphite,where giant flat planes tend to stack witheach other due to interaction between-electron clouds resonated between neigh-boring carbon atoms in the same plane.If CaC bonds based on sp2hybrid orbi-tals

119、 compose pentagons of carbon atoms,a coranulene molecule is formed,beingassociated with five hexagons,which is somewhat curved.By the polymerizationof these coranulene molecules,various clusters of carbon atoms are formed andthe resultant carbon materials are called fullerenes,where carbon hexagons

120、haveto be located between pentagons,the smallest molecule is C60,consisting of 12pentagons and 20 hexagons of carbon atoms.The infinite repetition of CaCbonds with sp hybrid orbitals gives the carbon materials called carbynes,in whichcarbon atoms are making linear chains either with double bonds or

121、with therepetition of single and triple bonds.Materials Science and Engineering of Carbon:Fundamentals.DOI:http:/dx.doi.org/10.1016/B978-0-12-800858-4.00002-4 2014 Elsevier Inc.All rights reserved.172.1.2 Carbon familiesBased on the extension by the repetition of three kinds of CaC bonds to infinite

122、molecules,we may define a family of inorganic carbon materials,carbon family,consisting of diamond,graphite,fullerene and carbyne.In Fig.2.2,the structuralcharacteristics and the structural diversities in each family are summarized.Diamond consists of sp3orbitals,where chemical bonds extend in a thr

123、ee-dimensional direction and are purely covalent.It is very hard because of covalentC960Buckminster-fullerene C60CorannuleneOvaleneAnthraceneBenzene1,3-Butadiene1-buten-3-ynePropaneButadiyne(Polyyne)CarbyneDiamondCarbyneGraphiteFullerenesPropyneAdamantane(Methylacetylene)C CCFluoreneH2CCHHHHHH H HHH

124、H H HCCCHHHC C CCPropeneHHHsp2sp3Csp2HHHHHCCHHCC C CCCCCCHHHHHHHHHHHHCCCCCCCCCC CC(Cumulene)PolyacetyleneCC CC70FIGURE 2.1CaC bonds to form a large number of hydrocarbons and their extension to carbonfamilies.18CHAPTER 2 Fundamental Science of Carbon Materialsbond and electrical insulator because of

125、 high localization of electrons(no-electrons exist).In order to construct diamond crystal,periodical and regularrepetition of this CaC bond is required in a long range.Let us put our attentionon a couple of carbon atoms indicated as A and B in Fig.2.3a.The carbonatom A has to be connected with four

126、carbon atoms,including B,to make a tetra-hedron because of directional sp3 bonds.The atom B has also to be surroundedby four carbon atoms,including A.If we look down these two tetrahedra centeredDIAMONDHexagonal graphiteRhombohedral graphiteCubic diamondHexagonal diamondDiamond-like carbonVariety of

127、 stacking sequences from regular to randomVarious texturesSubstitutionSubstitutionSubstitutionSubstitutionAdditionInter-calationIntercalationDoping in intersticesDoping intersticesDoping into sphereMultiwalledCumulene-typePolyyne-typec60,c70,c76,c240,c960,GRAPHITEFULLERENECARBYNEFIGURE 2.2Carbon fam

128、ilies and their diversity.FIGURE 2.3Mutual relations between two tetrahedra of carbon atoms in diamond.192.1Carbon familiesby A and B atoms along their connecting line,there are two possibilities inmutual relation between two basement planes consisting of three carbon atoms,which give two crystal st

129、ructures.If these two basement planes are rotated witheach other by 60?,as shown in Fig.2.3b,the resultant diamond crystal belongs tocubic crystal system(cubic diamond;Fig.2.3c).If there is no rotation betweenthese two basement planes(Fig.2.3d),diamond crystal in hexagonal system is theresult(hexago

130、nal diamond,Fig.2.3e).Most diamond crystals,which are eithernaturally occurred or synthesized,are cubic.Inthecasewherelong-rangeperiodicitywasnotattainedbetweeninterconnected two tetrahedra,in other words,in the case of random rotationbetween these two basement planes of tetrahedra,an amorphous stru

131、cture is theresult.Because of random rotation between tetrahedra,some carbon atoms cannotmake a chemical bond with neighboring carbon atoms,most of which are sup-posed to be connected with hydrogen atoms to be stabilized.The materials areobtained as thin films,mainly because random repetition of tet

132、rahedra is difficultto keep at a long distance,and called diamond-like carbon(DLC).Some of theseare as hard as diamond crystal,because principal CaC bonds are sp3bonding,and contain a relatively large amount of hydrogen.Carbon family having sp2bonding is represented by graphite,where the flatlayers

133、of hexagons of carbon atoms bound by using sp2orbitals are stackedparallel by using-electron clouds with a regularity of ABAB.,which belongsto a hexagonal crystal system.A stacking regularity of ABCABC.is also possi-ble,which belongs to a rhombohedral crystal system,but it occurs only locally byintr

134、oducing stacking faults due to shearing stress during grinding,for example.Inaddition,the parallel stacking of the layers without any regularity occurs mostlyin the carbon materials prepared at low temperatures as 1300?C,where the layersof hexagons are usually small in size and also a few number of

135、layers are stackedin parallel.This random stacking of layers is called turbostratic structure.Sincethis turbostratic structure can be partly transformed to regular stacking of layersby the heat treatment at high temperatures,a wide range of diversity in structurein the graphite family was caused.The

136、 graphite family can have various texturesin different scales mainly because the basic structural unit is the stacked flatplanes of carbon hexagons which are highly anisotropic.Structure and textures incarbon materials classified into the graphite family will be discussed in moredetail in Section 2.

137、2,because most carbon materials,which are used in our livesand also in industries,belong to graphite family.Bonding nature in fullerene particles is also sp2hybrid,but different fromgraphite in the fact that some sp2bonds are curved to construct pentagons ofcarbon atoms.The particle of buckminsterfu

138、llerene C60is composed of 12 penta-gons and 20 hexagons of carbon atoms.The addition of hexagons into C60tomake all pentagons apart from each other and to keep closed cluster morphologyleads to giant fullerenes,as shown in the upper line of Fig.2.4.Another way toincrease the number of hexagons is to

139、 make two groups of six pentagons apartfrom one another,which results in single-wall carbon nanotube,as shown20CHAPTER 2 Fundamental Science of Carbon Materialsschematically in the lower line of Fig.2.4.In this carbon family,a variety ofstructure is mainly due to the number of carbon atoms consistin

140、g of fullerene par-ticles and relative location of 12 pentagons.Carbynes have been supposed to be carbon atoms bound linearly by sp bond,where two electrons have to be resonated,giving two possibilities,i.e.,an alter-native repetition of single and triple bonds(polyyne)and a simple repetition ofdoub

141、le bonds(cumulene)(Fig.2.1).Its detailed structure is not yet clarified,butsome of the proposed structural models are illustrated in Fig.2.5,where someFIGURE 2.4Buckminsterfullerene to either giant fullerenes or single-wall carbon nanotube.FIGURE 2.5Structural models for carbines.212.1Carbon familie

142、snumber of carbon atoms make a line with sp hybrid orbitals and these lines gatherby van der Waals interaction between-electron clouds to make a layer,and thenthese layers are stacked.Three models resemble each other and the last model(Fig.2.5c),where foreign atoms are intercalated,seems to be the m

143、ost realistic.In this carbyne family,the variety in structure is mainly due to the number ofcarbon atoms making a line,in other words,the thickness of layers consisting oflinear carbon chains,and the density of chains in a layer.The synthesis of graphdiyne has been reported,which is constructed by r

144、epla-cing one-third of the carbon?carbon bonds in graphite with two acetylenic lin-kages.Since graphdiyne is supposed to be a flat layer consisting of sp and sp2bonds,it might be able to be classified to a new carbon family after enough accu-mulation of experimental evidences of their presence and t

145、o be an alternative ofgraphene.Each carbon family also shows various possibilities for accepting foreignatoms.Diversities in foreign atom acceptance are summarized in Fig.2.2.Thepossibility to accept foreign atoms into diamond structure is restricted to the sub-stitution of carbon atoms by either bo

146、ron or nitrogen.The possibilities to acceptforeign atoms into graphite structure are substitution of carbon atoms in funda-mental hexagonal layers and the intercalation into the space between hexagonallayers(gallery).In the fullerene family,various possibilities to accept foreignatoms,i.e.,insertion

147、 into either the interstices among fullerene particles or theinner space of a particle,and addition of atoms and radicals onto the surface offullerene particle,in addition to the substitution of carbon atoms by either boronor nitrogen,as occurs in diamond and graphite families.In carbyne family,inte

148、r-calation among layers of carbon chains,doping into the space between carbonchains in a layer and also substitution of carbon atoms in the chain are consid-ered.The intercalation of either an iron or potassium atom,as shown in Fig.2.5c,was reported to stabilize the carbyne structure.2.1.3 Structura

149、l relation to neighboring atomsCrystalline structures of the compounds of other atoms neighboring to carbon thePeriodic Table,i.e.,B4C,C3N4,SiC,BN,are shown in Fig.2.6,in relation tothe structural modifications of carbon described above.The compound SiC hasthe same crystal structures as cubic and he

150、xagonal diamond,which have to becalled zincblende-type and wurtzite-type structures,respectively,because it is abinary compound of C and Si.From the comparison of these two structures ofzincblende and wurtzite of ZnS(Fig.2.7)to those cubic and hexagonal diamonds(Fig.2.3),respectively,the similarity

151、is clear;if all constituent atoms in zincble-nde and wurtzite structures were carbon,the former corresponds to cubic diamondstructure and the latter to a hexagonal diamond one.This structural similarity isexplained by the rule that an equi-number of electrons in the outermost orbitalgives the same c

152、rystal structure,in the present case the total number of electronbeing eight(average four per atom,the same as carbon).22CHAPTER 2 Fundamental Science of Carbon MaterialsBN,whose constituent atoms,B and N,locate in the neighboring III and Vgroups in the Periodic Table,respectively,can have a layered

153、 structure,similar tographite,as shown in Fig.2.8.It consists of a layer composed of hexagons ofB and N atoms,a B atom in a layer is neighbored by N atoms in the upper andthe lower layers,the stacking sequence being expressed by AA.in the referenceto graphite structure as will be shown in Fig.2.9.Th

154、erefore,no structural modifi-cation is possible in this layered structure,as hexagonal and rhombohedral modi-fications in graphite.This layered structure of BN can transform to eitherzincblende or wurtzite structure under high pressure,corresponding to cubic andhexagonal diamond structures,respectiv

155、ely.BN with zincblende type structure isa super hard material,which has an advantage for cutting iron because no carbonatoms are contained.The compound between B and C,B4C,is also one of the hard materials.Thecompound between C and N,C3N4,was theoretically predicted to be a super hardFIGURE 2.6Struc

156、tural relations to neighboring atoms.FIGURE 2.7Zincblende and wurtzite type structures of ZnS.232.1Carbon familiesFIGURE 2.8Boron nitride BN with layered structure.cABA00a1a200000000000000000000000000001213231213231213131313131323AACBRhombohedralcellHexagonal cell23232323132323FIGURE 2.9Crystal stru

157、ctures for two modifications of graphite.24CHAPTER 2 Fundamental Science of Carbon Materialsmaterial and has been studied on its synthesis.Atoms B and N are known to sub-stitute carbon atoms in the structures of carbon materials.The compound betweenSi and N,Si3N4,attracted the attention of ceramists

158、 as a high-temperature struc-ture material.Silicon Si,which locates in the same group as carbon,but in the third row ofthe Periodic Table,cannot have layered structure,like graphite,and has cubic dia-mond structure.Such kind of structural anomalies,i.e.,only carbon atoms canhave layered structure gr

159、aphite,has often been observed in the atoms belongingto the top row in each group of the Periodic Table.2.2 Structure and texture of carbon materials2.2.1 StructureThe fundamental unit of the structure of carbon materials in graphite family is ahexagonal carbon layer.Regular stacking of these layers

160、 give graphite crystal,hexagonal graphite with ABAB.stacking regularity 1,2 and rhombohedralgraphite with ABCABC.regularity 3,4.The unit cells and equivalent pointsfor these two crystal modifications are shown in Fig.2.9.Rhombohedral graphiteis often expressed in a hexagonal system,because of easy c

161、omparison withhexagonal graphite,and so two unit cells in rhombohedral and hexagonal systemsare shown in Fig.2.9b,together with equivalent points for each unit cell,wherethick lines indicate rhombohedral unit cell and double lines hexagonal unit cell.The distance between neighboring carbon atoms in

162、the layer planes is 0.1412 nmand the spacing between neighboring layers is 0.3354 nm 5.The structural relation between hexagonal and rhombohedral graphites isexplained in Fig.2.10.In hexagonal graphite,the second layer(denoted as Bposition)is displaced by(2/3,1/3)along a1 and a2 axes from the first

163、layer(denoted as A position).With further displacement by(1/3,2/3)for the thirdlayer,the total displacement becomes unity in two directions,that is,exactly thesame position as the first layer A(Fig.2.10a).Therefore,it is said that AB stack-ing belongs to the hexagonal crystal system.For the third la

164、yer,however,it ispossible to displace again by(2/3,1/3),which is the same displacement betweenA and B.The third layer is not in the same position as either the first layer A orthe second layer B,and so is denoted as layer C.The repetition of the same dis-placement(2/3,1/3)in the fourth layer coincid

165、es to the first layer A,giving ABCstacking,which belongs to the rhombohedral crystal system.In addition to these regularly stacked structures,random stacking is possiblein many carbon materials,which is called turbostratic structure,as shown inFig.2.10b 6.This turbostratic stacking is often observed

166、 in the carbon materialsprepared at relatively low temperatures as 1300?1500?C,where the size of layeris small and only a few layers are stacked in parallel.By heating these carbons tohigh temperatures up to 3000?C,both the size and the number of stacked layers252.2Structure and texture of carbon ma

167、terialsusually increase and also the regularity in stacking is improved.The heattreatment at intermediate temperatures gives partial improvement in stacking reg-ularity.As a consequence,a wide range of structure from completely turbostraticstacking to pure ABAB stacking is possible through the inter

168、mediates with vari-able ratios of these two stacking regularities.The formation of intermediate struc-ture depends primarily on the starting materials(precursors)and the heattreatment temperature(HTT).In turbostratic structure,two kinds of displacementare possible,displacive and rotational,though it

169、 is difficult to differentiate them.Recently,the presence of displacive turbostratic stacking was shown throughdetailed analysis of scanning tunneling microscope(STM)images 7.X-ray powder diffraction gives useful information to study the structure ofcarbon materials.In Fig.2.11a,X-ray powder diffrac

170、tion pattern for naturalgraphite with high crystallinity is shown.The diffraction lines for graphite haveto be classified into three groups,the lines with 00l,hk0 and hkl indices,mainlybecause of the strong anisotropy in structure.The lines with 00l indices are due toFIGURE 2.10Graphitic and turbost

171、ratic structures shown by stacking of two hexagonal carbon layers.26CHAPTER 2 Fundamental Science of Carbon Materialsthe reflection from basal plane(hexagonal carbon layers),where only even indexof l is allowed because of the extinction rule due to ABAB stacking sequence oflayers.The lines with hk0

172、indices are due to the diffraction from the crystalplanes perpendicular to the basal planes and the lines with hkl indices come fromthe planes declined to basal plane,where three-dimensional structure has to beestablished with graphitic stacking of layers.Therefore,hkl lines are called three-dimensi

173、onal lines.On the other hand,powder pattern which is given by low-temperature-treatedcarbons is quite different from natural graphite,as shown on a petroleum cokeheat-treated up to 1000?C in Fig.2.11b because it consists of turbostratic stackingof small layers.The diffraction pattern is characterize

174、d by very broad 00l lines,unsymmetrical hk lines,and no hkl lines due to random turbostratic stacking of alimited number of layers.The diffraction lines due to the planes perpendicular tolayer planes are missing l index because of no regularity in the direction alongthe normal to layers,in other wor

175、ds,two-dimensional structure,and so expressed10 and 11 in Fig.2.11b.The rhombohedral structure of graphite was shown to form by applying shear-ing force,such as grinding 8,9.It gives additional diffraction lines,because ofABC stacking regularity,different from hexagonal graphite(AB stacking).InFig.2

176、.12a,change in diffraction pattern around 44?in 2 with grinding is shown10.With increasing grinding time,additional diffraction lines appear because ofthe introduction of stacking faults,which can be indexed to be 101 and 102 linesbased on rhombohedral structure in hexagonal system.The amount of rho

177、mbohe-dral stacking formed,Rh,was calculated from the intensity ratio of 101 line forrhombohedral to that for hexagonal modifications and plotted against the grindingtime in Fig.2.12b.The value of Rh saturates at around 33%,which seems to bereasonable because of the assumption that the rhombohedral

178、stacking is formeddue to the introduction of stacking fault in the crystallites with hexagonal stacking11.Further increase in grinding time results in increasing structural defects and002(a)Natural graphite(b)Petroleum coke heat-treated at 1000 C101004100102104103110112006105002203040506070809020304

179、050607080902(CuK)/2(CuK)/1000411FIGURE 2.11X-ray powder patterns for graphite and low-temperature-treated carbon.272.2Structure and texture of carbon materialsso all diffraction lines become broad,as shown by 004 line,together with 100line for hexagonal modification and 101 line for rhombohedral one

180、,in Fig.2.12c.After 60 h grinding,100 line becomes broad and unsymmetrical,and so the intro-duction of too much amount of stacking faults leads to turbostratic structure.For graphite,hexagonal carbon layer looks triangular under scanning tunnelingmicroscope(STM),as shown in Fig.2.13a,in other words,

181、only carbon atomsdesignated by in Fig.2.10a are detected under STM,because of the interactionwith lower-lying atoms in the position.In turbostratic structure,however,thereis no interaction with lower-lying atoms,because of no regular stacking,and sohexagons of carbon layers are observed,as shown in

182、Fig.2.13b 7.2.2.2 Structure development with heat treatment(carbonization and graphitization)Structure in carbon materials is known to depend strongly on the temperature thatthey experienced.In order to get carbon materials,in which carbon atoms areprincipal constituents,we have to heat-treat some o

183、rganic polymers,i.e.,carbonprecursors,in inert atmosphere.The process during the changes from organic pre-cursors to inorganic carbon materials is composed of pyrolysis,cyclization,aro-matization,polycondensation and carbonization of the organic precursor,anddepends strongly on the carbon precursors

184、 and on the conditions of heat treatment(temperature,heating rate,atmosphere,etc.).In addition,these are usuallyFIGURE 2.12Formation of rhombohedral modification with grinding of natural graphite 10.28CHAPTER 2 Fundamental Science of Carbon Materialsoverlapped with each other in most carbon precurso

185、rs.Therefore,often we callthe whole process from the precursor to the carbon material carbonization.Thegeneral scheme of the carbonization process is shown by indicating main out-gascomponents and changes in residues in Fig.2.14,although it strongly depends onthe carbon precursors.In the beginning o

186、f pyrolysis,aliphatic molecules with low molecular weightsand then low-molecular-weight aromatics are released as gases,mainly becausesome of CaC bonds in organic molecules are weaker than CaH bonds.Cyclization and aromatization proceeded in the residues,associated with therelease of low-molecular-w

187、eight hydrocarbons,and then polycondensation of aro-matic molecules occurs.Around 600?C,mainly foreign atoms such as oxygen andFIGURE 2.13STM image of hexagonal carbon layers in graphitic and turbostratic stackings.(Courtesy by Prof.K.Oshida of Nagano Nat.Coll.Tech.)FIGURE 2.14Carbonization process.

188、292.2Structure and texture of carbon materialsnitrogen are released as CO2,CO and(CN)2,together with methane CH4.In thisstage the residues are either gas,solid or liquid phases depending on the startingprecursors.Above 1000?C,out-gas is mainly H2because of polycondensation ofaromatics and the residu

189、es may be called carbonaceous solids,which still containhydrogen.Above 1300?C,almost all foreign atoms,mainly hydrogen,go out andthe residual solids are carbon materials.The details of carbonization process ofvarious precursors are discussed in the Section 2.3.In this carbonization process,a scheme

190、of preferred orientation of fundamentalstructural units,i.e.,hexagonal carbon layers,is established,which is nanotextureexplained in Section 2.2.3.Therefore,this carbonization process is the mostimportant for the preparation of carbon materials.However,carbon layers are stillsmall and in most cases

191、are stacking randomly(turbostratic structure).In order tomake these carbon layers grow and stack with graphitic regularity,heat treatmentat a high temperature above 2500?C is required.In some cases,graphitic structuredevelops,and so this process has been called graphitization.However,it doesnot occu

192、r always,the development of graphitic structure depending strongly onthe nanotexture formed during the carbonization process.During the carbonization and graphitization processes,the structure changesfrom starting organic precursor through carbon to graphite and,as a consequence,the properties of th

193、e materials change markedly.In Fig.2.15,the change inenergy band structure from an aromatic hydrocarbon through coke to polycrystal-line graphite is schematically shown as a function of HTT 12,13.Starting aro-matic hydrocarbon is a molecular crystal with a wide band gap E,it being aninsulator.The ca

194、rriers for electrical conduction in carbons heat-treated at lowtemperatures below 700?C are supposed to be electrons,of which mobility israther low.Above 1300?C,hydrogen atoms remained in the carbon starts todepart and leave electron traps,most of which may locate at the edge of the hexa-gonal carbo

195、n layer.As a consequence,the Fermi level is lowered and the concen-tration of positive holes increases which leads to the pronounced changes inFIGURE 2.15Scheme of changing in energy band structure with HTT 12.30CHAPTER 2 Fundamental Science of Carbon Materialselectromagnetic properties of carbon ma

196、terials.Around 2000?C,Fermi level startsto rise,because of healing of electron traps by high-temperature treatment.Alsothe band gap between the valence and conduction bands becomes small with theincrease in HTT,because of the growth of crystallites(layer size along a-axis andparallel stacking along

197、c-axis)and improvement of stacking regularity,and so therelative concentration of electron increases.In the carbons with highly developedgraphite structure,the valence and conduction bands overlap slightly andthe concentrations of two carriers,negative electrons and positive holes,arecomparable with

198、 each other,just as in graphite crystal.Even though the values ofelectromagnetic parameters approach those of graphite,it cannot reach the exactvalues measured on a single crystal of graphite.2.2.3 NanotextureIn the graphite family,the fundamental structural unit is a layer of carbon hexa-gons,which

199、 has a strong anisotropy because the bonds in the layer are covalentand those between the layers are van der Waals-like.As a consequence,these ani-sotropic layers tend to be oriented during their agglomeration to form certainmorphologies as carbon solids.Therefore,the way to agglomerate gives differ

200、entschemes and different degrees of preferred orientation of layers,and results in avariety of carbon materials,in addition to the mixing ratio of ABAB and turbos-tratic stacking.A classification based upon the scheme of preferred orientation of anisotropiclayers and its degree has been proposed,as

201、illustrated in Fig.2.16 14,15.Sincethese are the textures constructed by fundamental structure units in nano-size,they are called nanotextures.Firstly,random and oriented nanotextures are differentiated and then the latteris classified by the scheme of orientation,parallel to the reference plane(pla

202、narorientation),along the reference axis(axial orientation)and around the referencepoint(point orientation).The extreme case of planar orientation,i.e.,perfect orientation with large-sized planes,is a single crystal of graphite.The plates of so-called highly orientedpyrolytic graphite(HOPG)have a ve

203、ry high degree of planar orientation of hex-agonal carbon layers,but the size of layers is not so large,in other words,in thedirection perpendicular to the plate the structure is close to perfect orientation butin the parallel direction it is polycrystalline.Various intermediates between per-fect pl

204、anar orientation and random orientation are found in pyrolytic carbons andcoke particles depending on the preparation conditions and the temperature ofheat treatment.Various highly oriented graphite materials,kish graphite,variouspyrolytic carbons and carbon films derived from some precursor polymer

205、s,weredeveloped(see Section 3.2).In cokes the improvement in planar orientation oflayers with HTT was demonstrated through high-resolution transmission electronmicroscopy(HR-TEM).In Fig.2.17,the change in 002 lattice fringes observedby HR-TEM with HTT is shown 16.312.2Structure and texture of carbon

206、 materialsAxial orientation of layers is found in various fibrous carbon materials,inother words,fibrous morphology of carbon materials is possible because of thisaxial orientation scheme.In this orientation scheme,the co-axial and radial align-ments of layers relative to the reference axis are poss

207、ible.The co-axial alignmentof layers is realized in multi-walled carbon nanotubes and some carbon fibers,typical axial orientation being formed in vapor-grown carbon fibers.The radialalignment of layers can be found in one of mesophase-pitch-based carbon fibers,FIGURE 2.17Changes in 002 lattice frin

208、ges of a coke with HTT.(Courtesy of Mme.A.Oberlin.)FIGURE 2.16Classification of nanotextures in carbon materials 14.32CHAPTER 2 Fundamental Science of Carbon Materialshaving radial texture in the cross-section of the fibers.In carbon nanofibers,mostof which are grown through a chemical vapor deposit

209、ion process using fine cata-lyst particles,different orientation schemes along their axis are formed,from par-allel(tubular type)to perpendicular(platelet type)through herring-bone type orcup-stacked type,as shown in Fig.2.18.These fibrous carbon materials will bediscussed in more detail in Section

210、3.4.In point orientation,concentric and radial alignments have also to be differen-tiated.The extremes of concentric point orientation are a family of fullerenes,asshown in Fig.2.4.It can also be found in carbon black particles formed by minutehexagonal carbon layers.Carbon blacks are industrially p

211、roduced in a largeamount,of which sizes are from few tens to a few hundred nanometers,in whichminute-layer planes are preferentially oriented along the surface of spherical parti-cles,as shown in Fig.2.19 by 002 lattice fringe image and shown schematicallyin Fig.2.20a.Radial alignment of layers to f

212、orm spheres is found in the carbonspherules,which are formed from a mixture of poly(ethylene)and poly(vinylchloride)by pressure carbonization 17,as will be explained in Section 2.4.3.The structure of mesophase sphere is close to radial point orientation scheme,but in its center the orientation of la

213、yers is not radial 18,19.In Fig.2.20,themodels of nanotexture for carbon black particle 20,mesophase sphere 18 andcarbon spherule 21 are compared.The texture with random orientation occurs in glass-like carbons and carbonmaterials just after carbonization of precursor polymers(e.g.,phenol resin).Fun

214、damental structural units composed of most glass-like carbons are so smallas to be difficult to observe under TEM.Therefore,the discussion on their nano-texture was often performed on the basis of the TEM observations on theirhigh-temperature-treated ones,where layers became somewhat larger.Threenan

215、otexture models shown in Fig.2.21 have been proposed 22?24.In the shellFIGURE 2.18Schematic illustration of nanotextures in carbon nanofibers.332.2Structure and texture of carbon materialsFIGURE 2.20Nanotexture models for spherical carbon materials.FIGURE 2.21Nanotexture models of glass-like carbon

216、heat-treated at a high temperature.FIGURE 2.19002 lattice fringes in the particles of carbon black.(Courtesy of Dr.T.Nakata of Tokai Carbon Co.,Ltd.)34CHAPTER 2 Fundamental Science of Carbon Materialsmodel 24(Fig.2.21),hexagonal layers are locally oriented in concentric schemeto make closed pores.By

217、 taking into consideration the presence of a large amountof closed micropores and gas impermeability of glass-like carbons,this model isbelieved to be realistic,which will be discussed in more detail in Section 3.3.2.2.4 Microtexture(agglomeration)Most particles with planar and axial orientation,for

218、 example,coke particles andfibers,are also anisotropic and so their agglomeration can create further variety intexture.Therefore,it is necessary that the texture formed by the preferred orienta-tion of the constituent particles,particles themselves having anisotropy,has to betaken into consideration

219、 and differentiated from nanotexture discussed in theprevious section.The texture due to the preferred orientation of anisotropic parti-cles may be called microtexture,because the particles are often in micrometeror millimeter sizes.This microtexture is usually formed during the forming pro-cess of

220、bulky carbon materials.For example,in large-sized graphite electrodes formetal refining(Fig.1.2a)the particles of needle-like coke tend to be orientedalong the rod axis during their forming process through extrusion with binderpitch(more detailed explanation will be presented in Section 3.1).To prep

221、are thecarbon-fiber-reinforced plastics for fishing rods,for example,constituent carbonfibers have to be oriented along the rod axis in order to get high strength andhigh Yongs modulus(more details are presented in Section 3.6.2.3 Carbonization(nanotexture development)2.3.1 Formation processes of ca

222、rbon materialsAs discussed above(Section 2.2.2 and Fig.2.14),the precursors are carbonized tosolidcarbonmaterialsbyheattreatmentuptoatemperaturearound1000?1500?C.During this carbonization process,the precursor passes througheither gas,liquid or solid phase.In Table 2.1,carbonization processes are cl

223、assi-fied on the basis of the intermediate phases and the representative carbon materialsformed through the process are listed.The products of carbonization and carbons,are often classified into two categories,graphitizing and non-graphitizing,whichmeans whether the carbon can be converted to graphi

224、te through the treatment athigh temperature under atmospheric pressure.These terms,graphitizing and non-graphitizing(graphitizable and non-graphitizable or soft and hard are also used),are convenient to predict graphitizability of the carbon,so that they are frequentlyused to show the characteristic

225、s of carbon materials.However,it has to be takeninto consideration that carbon materials cannot be divided clearly into thesetwo categories,many carbons showing intermediate behavior,as shown inSection 2.4.From hydrocarbon gases,different carbon materials have been produced,thisprocess being gas pha

226、se carbonization(Section 2.3.2),because hydrocarbon352.3Carbonization(nanotexture development)molecules decompose in gaseous phase to deposit as a solid carbon.Dependingmostly on the concentration of hydrocarbon gases,various carbon materials areproduced:carbon blacks,pyrolytic carbons,carbon fibers

227、 and nanofibers,carbonnanotubes and fullerenes.On the other hand,most of thermosetting resins,such as phenol,furfurylalcohol,and celluloses,can be converted to carbon materials without any markedchanges in morphology,solid phase carbonization(Section 2.3.3).When the car-bonization of most of these p

228、recursors proceeds rapidly,the resultant carbonmaterials are porous.If the carbonization is performed so slowly that the resultantcarbonaceous solids could shrink,so-called glass-like carbons are produced,which contain a large amount of closed pores.Table 2.1Carbonization Processes for the Productio

229、n of Various Carbon MaterialsCarbonizationProcessPrecursorsCarbonMaterialsCharacteristicsGas phasecarbonizationHydrocarbon gasesdecomposition inspaceCarbon blacksFine particles,so-calledstructureHydrocarbon gases,deposition onsubstratePyrolytic carbonsVarious textures,preferred orientationHydrocarbo

230、n gases,with metal catalystsVapor-growncarbon fibersCarbonnanofibersFibrous morphology,various nanotexturesCarbon vaporCarbonnanotubesTubular,single-wall&multi-walledCarbon vaporFullerenesSpherical,molecularnatureHydrocarbon gasesDiamond-likecarbonThin film,sp3bond,amorphous structureSolid phasecarb

231、onizationPlants,coals&pitchesActivatedcarbonsHighly porousadsorptivityFurfuryl alcohol,phenol resin,cellulose,etc.Glass-like carbonAmorphous structure,gas impermeability,conchoidal fracturesurfacePoly(acrylonitrile),pitch,cellulose&phenol resin withstabilizationCarbon fibersFibrous morphology,high m

232、echanicalpropertiesLiquid phasecarbonizationPitch,coal tarCokesCokes with binderpitchesGraphite blocksVarious densities,various degrees oforientation36CHAPTER 2 Fundamental Science of Carbon MaterialsPolycrystalline graphite blocks(one of the classic carbons;Section 3.1)are indus-trially produced by

233、 forming the coke particles using a pitch as a binder and then car-bonizing and graphitizing at high temperatures.The cokes are also produced frompitches.In the case of most pitches,their carbonization process is classified intoliquid phase carbonization(Section 2.3.4),because all of them transform

234、to viscousliquid during heat treatment to be carbonized even though they are solids at roomtemperature.To produce graphite blocks,the coke particles are used as fillers inorder to avoid a large amount of volatiles,which may introduce some shape distor-tion and crack in the products,and also may redu

235、ce the density.Since these coke par-ticles are not sintered to form blocks,a binder has to be used,pitches having beenoften selected,which give similar carbon residues after carbonization with relativelyhigh yield.Therefore,the production of graphite blocks is based on liquid phasecarbonization in t

236、wo steps;in the process of the filler coke preparation and in thecarbonization of the binder pitch in the formed blocks.The carbonization process is the most important process for the production ofcarbon materials because the nanotexture of carbon materials,which has the deter-mining effect on struc

237、tural change at high temperatures and consequently on theirproperties,is principally established during this process,as explained below.Thecarbons in which graphitic structure develops markedly at high temperatures above2500?C has been called graphitizing carbons and those showing no appreciabledeve

238、lopment of graphitic structure called non-graphitizing carbons,though manycarbons have intermediate behavior between graphitizing and non-graphitizing.Graphitization behavior of various carbons is discussed in Section 2.5.2.3.2 Gas phase carbonizationThe carbon materials produced by gas phase carbon

239、ization depend strongly on theconcentration of the precursor hydrocarbon gases.Under a high concentration ofthe precursors,various carbon blacks,which is one of classic carbons and havethe nanotexture of point orientation,are produced in an industrial scale.Under alow precursor concentration with so

240、me solid substrates,however,pyrolyticcarbons are formed,which is one of new carbons developed in the beginning ofPeriod II of carbon history(Table 1.1)and have the nanotexture of planar orien-tation.Some fine metallic particles have been found to catalyze the carbonizationof hydrocarbon gases to giv

241、e the fibrous carbon materials,nanofibers,which maybe classified as nano-sized carbons and have the axial orientation nanotexture.Some of these nanofibers can be converted to carbon nanotubes by a high-temperature treatment.So-called vapor-grown carbon fibers were developed inthe beginning of Period

242、 II(Table 1.1)and have different characteristics in com-parison with other carbon fibers,such as PAN-based carbon fibers.After thefinding of carbon nanotubes,it was recognized that the center of these vapor-grown carbon fibers consists of carbon nanotubes.Through carbon vapor which isformed by arc d

243、ischarging between carbon electrodes,carbon nanotubes werefound to be formed.372.3Carbonization(nanotexture development)a.Carbon blacksCarbon blacks are formed through incomplete combustion of either gaseous ormist-like hydrocarbons and are very important industrial products 25.Theywere used as a co

244、lorant in inks in the third century AD and are used now for rein-forcement of rubbers in large amounts.Carbon blacks are classified on the basesof reaction process and raw materials into furnace blacks,channel blacks,lampblacks,thermal blacks and acetylene blacks,as summarized in Table 2.2.Theyare c

245、haracterized by spherical primary particles,which are in different sizes andcoalesced into aggregates(secondary particles)more or less,as shown by trans-mission electron microscope(TEM)images in Fig.2.22.The aggregation ofprimary particles into the secondary particles is very important for the perfo

246、r-mance of carbon blacks,particularly for the reinforcement of rubbers and is oftencalled structure in industry.The mechanism of the formation of carbon black particles was discussed indetail in the literature 26.The formation of oil droplets due to pyrolysis andTable 2.2Production Methods and Raw M

247、aterials of Carbon BlacksReaction ProcessCarbon Black FormedMain Raw MaterialsIncomplete combustionOil furnace blackCreosote oilGas furnace blackNatural gasChannel blackNatural gasLamp blackHeavy oilsPyrolysisThermal blackNatural gasAcetylene blackAcetyleneFIGURE 2.22TEM images of carbon blacks.(Cou

248、rtesy of Dr.T.Nakata of Tokai Carbon co.Ltd.)38CHAPTER 2 Fundamental Science of Carbon Materialspolymerization/condensation of organic molecules in the space of the furnaceseems to be important in order to interpret structure.However,it is very difficultto determine the mechanism because of the form

249、ation reaction in a millisecond ata high temperature such as 1300?1500?C.Furnace blacks are produced from either mists of creosote oil or natural gasconsisting mainly of methane by their incomplete combustion in the furnace.Their yield and quality are predominantly governed by the temperature of com

250、-bustion(usually 1260?1420?C),which is regulated by the mixing ratio of hydro-carbon gas with air and their turbulence conditions.The size of primary particleshas a rather broad distribution,the carbon black with the smaller particles havingthe narrower size distribution,as shown in Fig.2.23.The agg

251、regation of theseprimary particles,structure,is particularly developed in furnace blacks,thisbeing the main reason why they have been used to reinforcement of rubbers.Fig.2.24a shows a TEM image of 002 lattice fringes for the coalesced partbetween primary particles of a furnace black.The concentric

252、point orientation ofhexagonal carbon layers is clearly observed on the surface of the particles,but atthe center the layers look randomly oriented.Even at the neck between two pri-mary particles,the orientation of layers along the surface is observed.This struc-ture of carbon blacks was evaluated by

253、 measuring the absorption of either linseedoil or dibutylphthalate(DBP)and also by analyzing their TEM images.Channel blacks are formed by impingement of natural gas flames on channelirons.Lamp blacks are manufactured by burning aromatic oils in shallow,openpans with limited air supply,which have be

254、en used mainly for inks.Thermal blacks are produced by thermal decomposition of natural gas,whileacetylene blacks are formed through an exothermic decomposition of acetylenegas at a relatively high temperature such as 2400?C.In thermal blacks,the size of30N110N220N330N550N77420Frequency/%100102030Si

255、ze of primary particles/nm4050607080FIGURE 2.23Size distribution of primary particles of furnace blacks.(Courtesy of Dr.T.Nakata of Tokai Carbon Co.,Ltd.)392.3Carbonization(nanotexture development)their primary particles is usually large,as shown in Fig.2.22a and almost noaggregation is observed,i.e

256、.,no structure,as shown by TEM image of 002 latticefringes in Fig.2.24b.In most of the large particles of thermal blacks,concentricpoint orientation of hexagonal carbon layers is observed clearly,even at thecenter of the particles.Acetylene blacks are produced by pyrolysis of acetylene gas,which hav

257、e highstructure,as shown in Fig.2.25a.By using similar conditions to furnace blacks,carbon blacks with developed structure as comparable with acetylene black(named Ketjenblack),as shown in Fig.2.25b,are produced 27.They are oftenused as electric conductive additives for the electrodes of lithium-ion

258、 batteriesand various electrochemical capacitors.FIGURE 2.24TEM image of 002 lattice fringes of furnace and thermal blacks.(Courtesy of Dr.T.Nakata of Tokai Carbon Co.,Ltd.)FIGURE 2.25TEM images of acetylene black and Ketjenblack 27.40CHAPTER 2 Fundamental Science of Carbon Materialsb.Pyrolytic carb

259、onsIf a substrate is inserted into the combustion flame of hydrocarbon gas,carbondeposition occurs on the surface of the substrate.In order to control the structureof the carbon deposits formed on the substrate,the deposition conditions have tobe controlled.Methane and propane have usually been empl

260、oyed as precursorgases.This process is a kind of chemical vapor deposition(CVD)and the pro-ducts are called pyrolytic carbons.Practically,the deposition of pyrolytic carbons has been performed on bothstatic and dynamic substrate;in the former case the substrate was placed in thefurnace,which is heat

261、ed either by direct passing of electric currents(cold-walltype apparatus)or from the surroundings(hot-wall type apparatus),and in thelatter case the small substrate particles are fluidized in the furnace.When thestatic substrate is heated by passing electric current through itself,the depositiontemp

262、erature,in other words the temperature of the surface of deposited carbon,changes with increasing thickness of pyrolytic carbon formed.If the temperatureof the surface of the substrate is controlled to be constant,the temperature of theinside becomes higher and even compressive stress arises,which m

263、odifies thestructure of formed pyrolytic carbons.The factors controlling the structure andproperties of pyrolytic carbons are(1)precursor hydrocarbon gas and its concen-tration,(2)deposition temperature,(3)contacted time between hydrocarbonmolecule and substrate heated at a high temperature,which de

264、pends strongly onflow rate of gas and size of the furnace,and(4)the geometrical arrangement ofthe furnace,particularly the physical surface area of the substrate relative to thevolume occupied by decomposition gas 28,29.When the static substrate isheated by passing the electric current,not only the

265、surface of the substrate butalso the surrounding space has to reach a temperature enough for the decomposi-tion of hydrocarbon precursor gases(hot sheath).The size of this hot sheathdepends strongly on the flowing rate of gases.In Fig.2.26,bulk density of pyrolytic carbons prepared from propane andm

266、ethane is plotted against deposition temperature 30.Both methane and propane2.52.0Density/g/cm31.51.08001,2001,600Deposition temperature/C2,000Methane 1.7102 TorrMethane 4 TorrPropane 15 TorrFIGURE 2.26Dependences of bulk density of pyrolytic carbon on deposition temperature as a functionof precurso

267、r gas and its pressure 30.412.3Carbonization(nanotexture development)gases give relatively low bulk density at the temperature of 1400?2000?C,whichis mainly due to the formation of carbon black particles,which are incorporatedinto the pyrolytic carbon deposited.In order to prepare pyrolytic carbon w

268、ith highdensity in this temperature range,the pressure of precursor gas,methane inFig.2.26,has to be very low.Below 1400?C and above 2000?C,bulk densitydoes not depend on the pressure of precursor gas,but these temperature rangesare not practical,because the deposition rate is very low,below 1400?C,

269、and highenergy consumption and special materials for the furnace construction arerequired above 2000?C.In Fig.2.27,optical micrographs of two different textures are shown on thecross-sections perpendicular to the deposition plane of the pyrolytic carbon,consisting of so-called growth cones 31.In Fig

270、.2.27a,growth cones seem tostart at the surface of substrate and grow larger with the proceeding of the deposi-tion,which has been called singularly nucleated.The nucleation points for eachgrowth cone are supposed to be due to the roughness of the substrate surface.InFig.2.27b,however,growth cones a

271、re small and thin,and look to be generatedeven in the course of the deposition,which has been called regeneratively nucle-ated or continuously nucleated.In this texture,the nucleation was supposed tooccur from the soot-like small particles,which are formed in the gas phase duringdeposition.The pyrol

272、ytic carbons with such regeneratively nucleated texture usu-ally give low bulk density.The decrease in bulk density at certain depositiontemperature with relatively high concentration of hydrocarbons,as shown inFig.2.26,is mainly due to this co-deposition of soot-like particles into pyrolyticcarbon

273、with regeneratively nucleated texture.Reduction of partial pressure of theprecursor hydrocarbons is experimentally shown to be effective to suppress theformation of these soot-like particles,resulting in a high bulk density and thechange in optical texture to a singularly nucleated one 30,and also e

274、ffective toshift the temperature giving density minimum to lower 31.FIGURE 2.27Optical micrographs of the cross-section perpendicular to the deposition plane of pyrolyticcarbons 31.42CHAPTER 2 Fundamental Science of Carbon MaterialsVarious optical textures under polarized light were observed on the

275、surfaceparallel to the deposition plane,i.e.,perpendicular to the growth cones.They areusually classified into four groups,granular,columnar,laminar and isotropic.Granular texture corresponds to regeneratively nucleated texture in the cross-section and columnar to singularly nucleated.Similar optica

276、l textures were observed on the pyrolytic carbons deposited inthe spaces among carbon fibers to produce carbon fiber/carbon composites(carbon/carbon composites)32,33 and also on those deposited on small particlesof uranium oxides in fluidized bed for the preparation of fuel particles for nuclearreac

277、tors 34.Three optical textures observed in carbon fiber/carbon compositesare shown in Fig.2.28.The textures classified into columnar and laminar are fur-ther divided by the size of the regions,which show homogeneous optical nature,such as rough and smooth columnar.Optical texture of the pyrolytic ca

278、rbonsformed in carbon/carbon composites is known to be governed predominantly bythe conditions of the deposition,geometry of deposition furnace,area of deposi-tion surface of the substrate,deposition temperature,gas used,gas pressure,flow-ing rate of gas,etc.34.Preparation and properties of carbon/c

279、arbon compositesare discussed in Section 3.6.2.This deposition process was successfully applied to the fine particles flowingin a gas stream,in order to produce the carbon-coated nuclear fuel particles ofuranium compounds 28.One example of construction of the cross-section of theparticle is illustra

280、ted in Fig.2.29,where the carbon layers with well-oriented andrandom texture are formed on purpose by controlling deposition conditions.Itwas successfully employed also to the carbon coating of the substrate withcomplicated shape;a marked example is a heart valve 29.FIGURE 2.28Optical textures of py

281、rolytic carbon deposited among the fibers.(Courtesy of Prof.E.Yasuda of Tokyo Inst.Tech.)432.3Carbonization(nanotexture development)c.Vapor-grown carbon fibers and nanofibersVapor-grown carbon fibers(VGCFs)were deposited on a substrate from benzenevapor in a flow of high-purity hydrogen gas using a

282、catalyst of fine particle ofiron 35?37.The formation process of the fibers was studied in detail 38.The growing process of VGCF is divided into three steps,as shown inFig.2.30.The first step is the nucleation period,corresponding to the temperatureof the furnace of 950?1000?C,where iron compounds(ox

283、ides or metal)arereduced to form fine iron particles and their surfaces are covered by carbon pro-duced from benzene vapor.The appearance of the surface of the substrate at thefirst step is shown in Fig.2.31a.In this step,the embryo for the carbon fibers isformed,in which fine iron particle is embed

284、ded.In the second step,the length of very thin fibers increases rapidly(elongationstep).They are so thin that they look transparent under scanning electron micro-scope(SEM),as shown in Fig.2.31b.The detailed TEM observation using differ-ent techniques,bright-field,different dark-fields,lattice fring

285、e images andselected-area electron diffraction,showed that in the fibers formed in this step thehollow tubes consisting of a limited number of carbon layers are formed,atthe top of which a very fine iron particle is always included 39.TEM image ofthe tubes formed in this step is shown in Fig.2.32a,w

286、here even the tube consist-ing of a single layer(single wall carbon nanotube)is observed.This TEM imagealso suggests that the deposition of carbon consisting of small layers occurs onthe surface of the thin tube.The third step is the step to increase the thickness of the fiber(thickening step),as sh

287、own in Fig.2.31c.The high-resolution TEM observation shows that the resul-tant VGCF composes of the hollow tube and oriented small layers(Fig.2.32b).The detailed analysis shows that the wall of hollow tube consists of few straightlayers and that small layers preferentially orient parallel to the tub

288、e surface,asHigh-density columnar pyrolytic carbon layer(45m)High-density isotropic pyrolytic carbon layer(30m)Porous isotropic pyrolytic carbon layer(60m)Diameter of the particle 920 m SiC layer(25m)UO2fuel core600mFIGURE 2.29Construction of nuclear fuel particle coated by pyrolytic carbon layers w

289、ith different opticaltextures 28.44CHAPTER 2 Fundamental Science of Carbon Materialsshown in Fig.2.33 39.On the part of hollow tube wall,ten lattice fringes areobserved,because layers are located perpendicular to the electron beams in micro-scope and are aligning along the fiber axis.On the other ha

290、nd,layers deposited onthe hollow tube wall are small,but preferentially orient along the fiber axis.The formation of the same VGCFs was reported by using different precursorhydrocarbon gases,carrier gases,catalyst metals and deposition conditions40?44.In order to get a high yield of VGCFs,floating c

291、atalyst method wasdeveloped,instead of the method where the catalysts were seeded on the surfaceof substrate(seeding catalyst method)45(refer to Section 3.4.2.d).The formation mechanism of VGCFs was also discussed in various references38,39,46.In Fig.2.34,growth models for two methods,seeding and fl

292、oatingcatalyst methods,are shown.11001050100070Nucleation stepTemperatureThickening stepLength of fibersDiameter of fibersDiameter of fibers/mElongationstep605040Length of fibers/mmTemperature/C3020100123Tim/h40510152025FIGURE 2.30Processes of the growth of vapor-grown carbon fibers.(Courtesy of Pro

293、f.M.Endo of Shinshu Univ.)452.3Carbonization(nanotexture development)Since most vapor-grown carbon fibers changed to well-graphitized carbonfibers and they could be prepared without the coexistence of other forms of car-bons,like carbon blacks,huge numbers of works to prepare fibrous carbonsthrough

294、the decomposition of various gases,not only hydrocarbons but also CO,under different conditions were performed,aiming to prepare carbon nanotubes ina high purity with a high yield 47?54.These fibrous carbons are called nanofi-bers,differentiating from carbon nanotubes and also from vapor-grown carbo

295、nfibers.In Fig.2.35,fibrous carbons formed from CO gas are shown 50.Thenanotexture of these fibrous carbons showed a wide diversity from tubular toplatelet,as shown in Fig.2.18.By selecting the decomposition conditions,carbonhelical microcoils with controlled pitch were prepared 55.The fibrous carbo

296、nsFIGURE 2.31SEM images on different steps for the growth of vapor-grown carbon fibers.(Courtesy by Prof.M.Endo of Shinshu Univ.)FIGURE 2.32002 lattice fringe images of vapor-grown carbon fibers in the second and third steps.(Courtesy by Prof.M.Endo of Shinshu Univ.)46CHAPTER 2 Fundamental Science o

297、f Carbon Materialswith the appearance as many cups are stacked in one direction,cup-stacked nano-fibers,as shown in Fig.1.10,were prepared in a similar process 56.The carbonmaterials with fibrous morphologies are summarized in Section 3.4.d.Carbon nanotubesCarbon nanotubes were found in the carbon d

298、eposits on the graphite anode duringarc discharge in He atmosphere 57.The temperature at the graphite electrodewas estimated to reach up to 2500?C.The hollow tube at the center of carbonnanotubes thus obtained showed a wide range of diameter from 1?50 nm andtheir wall consisted of different numbers

299、of carbon layers.Most of them areclosed at the end 58,the smallest diameter being the same as the size of thesmallest fullerene C60.The carbon nanotubes of single wall were found later59,60.In Fig.2.36,TEM image of carbon nanotube is shown.By selecting thearc discharging conditions between graphite

300、electrodes,a relatively high yield ofcarbon nanotubes was reported 61.Under very similar conditions of arc discharging,fibrous carbons wereobtained in 1960,of which the structure was understood to be a scroll ofFIGURE 2.33Lattice fringe image of vapor-grown carbon fibers.(Courtesy by Prof.M.Endo of

301、Shinshu Univ.)472.3Carbonization(nanotexture development)FIGURE 2.34Illustration of the growth of vapor-grown carbon fibers by seeding and floating catalystmethods 46.FIGURE 2.35Fibrous carbons obtained from CO at 500?C.(Courtesy of Mme A.Oberlin.)48CHAPTER 2 Fundamental Science of Carbon Materialsh

302、exagonal carbon layers and so-called graphite whisker 62.Similar carbonnanotubes,even single wall nanotube,were formed at the beginning of the forma-tion of vapor-grown carbon fibers(see Fig.2.32a)39.In the preparation of carbon nanotubes by arc discharge,they are formedtogether with other forms of

303、carbons,such as carbon blacks and pyrolyticcarbons.Therefore,the purification process is unavoidable in order to have nano-tubes in high purity.Also the control of diameter and length of carbon nanotubesis difficult in the arc discharge process.By CVD process using catalysts(catalyticCVD),however,ca

304、rbon nanotubes were successfully grown vertically on thesubstrate 63?67.In Fig.2.37,single-wall carbon nanotubes grown vertically tothe substrate(called either forest or array)are shown,being synthesized bycatalytic CVD process using ethylene gas with a small amount of water vapor66.The growth rate

305、of carbon nanotubes was very fast,2.5 mm length for10 min CVD without formation of other forms of carbon 65?67.Arrays ofmulti-walled carbon nanotubes were also synthesized 63,64.The conditions ofCVD,including precursors,water vapor content,etc.,were studied in detail.e.FullerenesThe carbon cluster C

306、60was firstly found in the soot formed by laser ablation in Heatmosphere 68,69 and named as buckmisterfullerene.C60was also found in thesoot formed through the vaporization of carbon vapor from the graphite rod heatedat high temperatures in He atmosphere 70.Also in the carbon deposits formedby arc d

307、ischarge between graphite electrodes a relatively high concentration offullerenes were found 71.This carbon cluster C60could be isolated using the sol-vents,such as benzene,carbon disulfide,etc.72.By the solvent fractionation,the formation of carbon clusters with different sizes,such as C70,C82,.C96

308、0,is confirmed and this series of clusters is called fullerenes.The cluster C60FIGURE 2.36TEM image of carbon nanotube.(Courtesy of Prof.M.Endo of Shinshu Univ.)492.3Carbonization(nanotexture development)can also be separated from the soot by vaporization at around 400?C in vacuum.For the formation

309、of these fullerenes,the atmosphere of different gases isexamined,but helium atmosphere resulted in a relatively high yield of fullerenesin most cases.The formation mechanism of these fullerene clusters was discussed in theliterature 73,74.A model named ring-stacking model is illustrated in Fig.2.38,

310、C60molecule being formed by the stacking of carbon clusters of different sizes(different number of carbon atoms)75.The synthesis of C60through a chemical route has been tried,but not yet suc-ceeded 75.It was started from trindane C15H18,where three pentagons werebonded around the hexagon,as shown as

311、 A in Fig.2.39,and tried to polymerizethem.The dimmer(B)and trimmer(C)were successfully synthesized,but no tet-rammer(D),i.e.,C60,was obtained.The trimmer had caged morphology and wassaid to be very stable.The first chemical synthesis of C60has been done by flushvacuum pyrolysis at 1100?C.However,C7

312、0or higher fullerenes are not yetsynthesized.FIGURE 2.37Carbon nanotubes synthesized by catalytic CVD 66.50CHAPTER 2 Fundamental Science of Carbon Materialsf.GraphenesThe chemical vapor deposition process is one of preparation methods forgraphene 76.Graphene grown on polycrystalline Pt foil by ambie

313、nt pressureCVD with a low concentration of methane at 1040?C is shown in Fig.2.40 77.The graphene thus synthesized has hexagonal morphology with high crystal per-fection and is grown to millimeter-size during 180 min.2.3.3 Solid phase carbonizationIn the process of solid phase carbonization,the diff

314、erence in heating rate givesmany different carbon materials.Most thermosetting resins do not pass throughliquid state during their pyrolysis and carbonization.When these thermosettingresins are heated very slowly,the carbonized products shrink homogeneously bykeeping their forms and give glass-like

315、carbons,which have the nanotexture ofrandom orientation and contain a large amount of closed pores.Glass-like carbonsFIGURE 2.38Ring-stacking model for the formation of buckminsterfullerene C6075.FIGURE 2.39Trial to synthesize C60by polymerization 75.512.3Carbonization(nanotexture development)are on

316、e of the new carbons developed in the beginning of Period II(refer toTable 1.1).When the thermosetting resins were rapidly heated,a number ofcracks were formed in most of the carbonized products and became small frag-ments,in which many open micropores were easily created by oxidation(activa-tion)to

317、 give activated carbons,one of classic carbons.Thin films of polyimidesand some other polymers do not pass apparently through liquid phase during car-bonization process.Partial oxidation of organic fibers to prevent their softeningduring pyrolysis and carbonization processes(called stabilization)is

318、an essentialprocess to produce PAN-based and pitch-based carbon fibers.The process forthermosetting resins to form glass-like and porous carbons,including polyimideto form carbon films,may be intrinsic solid phase carbonization.On the otherhand,the process for PAN-and pitch-based carbon fibers may b

319、e extrinsic solidphase carbonization because these precursors PAN and pitch,which are intrinsi-cally carbonized in liquid state,are changed by the process of stabilization.a.Activated carbonsActivated carbons contain a large amount of open nano-sized pores(nanopores),which are usually evaluated by B

320、ET surface area.They have been used as adsor-bents since prehistoric age,and are now used in a much wider field,from ourdaily lives to various industries not only for manufacturing some products butalso for the treatment of waste.For their predominant applications as adsorbents,pore structure is the

321、 most important property to be controlled 78?80.Forthe pore development,partial oxidation of carbonized materials under a controlledcondition,which has been called activation,was usually carried out.For carbonprecursors,not only natural biomasses,such as plants and woods,but also pitchesand resins h

322、ave been used.In Fig.2.41a,SEM micrograph of a carbon preparedfrom coconut shell is shown,which are used as a filter in tobacco.Fig.2.41b is aFIGURE 2.40Graphene formed on Pt substrate via CVD of methane 77.52CHAPTER 2 Fundamental Science of Carbon MaterialsSEM of charcoal,where homogeneous sizes of

323、 pores are aligned in a relativelyregular way.These pores observed under SEM are macropores,which are origi-nated from the cell structure in the precursor plants,and are not effective foradsorption of various molecules.However,the presence of these macroporesbefore activation is preferable for creat

324、ing micropores on the wall.Various wastedmaterials,such as sawdust from woods,wasted cotton,etc.,are able to convert toactivated carbons.For activation,different processes were employed,oxidation using dilutedoxygen gas,air,water vapor,etc.(physical activation),and oxidation using ZnCl2and KOH(chemi

325、cal activation).Recently great success to get a high surface areareaching to about 3600 m2/g was obtained by using KOH for activation 81.During the activation process,the creation of micropores of size 0.4?2 nm is themost important.In most carbon materials,however,macropores(the size of.50 nm)and me

326、sopores(2?50 nm)are coexistent with micropores,as shownschematically in Fig.2.42a.In other words,macropores and mesopores had to beformed during the activation process in order to develop a large amount ofFIGURE 2.41SEM images of a carbon prepared from coconut shell and charcoal.(Courtesy of Dr.A.Yo

327、shida of Tokyo City Univ.)FIGURE 2.42Schematic illustrations of pore structure.532.3Carbonization(nanotexture development)micropores,and these pores also play an important role for adsorption as path-ways for adsorbates.For the carbons prepared from natural plants,many macro-pores are already formed

328、 during carbonization as a memory of cell structure ofthe original plants,as shown in Fig.2.41,which seems to make micropore devel-opment by activation easier.In so-called activated carbon fibers,on the other hand,micropores are exposed tothe surface of thin carbon fibers,as schematically shown in F

329、ig.2.42b.Such a directexposure of micropores gives an advantage of fast adsorption/desorption 82.Pore size distribution in activated carbons is important,as well as pore volume(porosity),for practical applications,for example,for the adsorption of liquidmaterials relatively large pores in a few nano

330、meter size(mesopores),are desired,but for that of gaseous materials small pores(micropores)are effective.Theactivated carbons for molecular sieving must have sharp pore size distribution atthe size suitable for target molecules.In Fig.2.43,some examples of pore sizedistributions for different applic

331、ations.Recently,the cores of kenaf plant(Hibiscus cannabinus)were found to give ahigh BET surface area,as high as 2700 m2/g,by the carbonization in inert atmo-sphere,without any activation process 83.This high surface area was supposedto be due to the departure of metallic impurities(mostly K),which

332、 were origi-nally included in the cores,during carbonization.The development of pores and the control of their sizes in carbon materialswill be discussed in detail in Section 2.7 and also in Section 3.5.Also,pore devel-opment without activation was carried out by the selection of suitable precursors

333、with different techniques,which are explained in Section 2.4.1010.10.010.1110Pore diameter/nmActivated carbonfor molecular sievingActivated carbonfor gas phase adsorptionActivated carbonfor liquid phase adsorptionPore volume/ml/gFIGURE 2.43Pore size distributions of activated carbons for different applications.54CHAPTER 2 Fundamental Science of Carbon Materialsb.Glass-like carbonsGlass-like carbon