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1、CHAPTER1IntroductiontoCarbonCarbonfibersrefertofiberswhichareatleast92wt.%carbonincomposition[l].Theycanbeshortorcontinuous;theirstructurecanbecrystalline,amorphous,orpartlycrystalline.Thecrystallineformhasthecrystalstructureofgraphite(Figurel.l),whichconsistsofsp2hybridizedcarbonatomsarrangedt
2、wo-dimensionallyinahoneycombstructureinthex-yplane.Carbonatomswithinalayerarebondedby(1)covalentbondsprovidedbytheoverlapofthesp2hybridizedorbitals,and(2)metallicbondingprovidedbythedelocalizationofthepzorbitals,Le.,the7relectrons.Thisdelocalizationmakesgraphiteagoodelectricalconductorandagoodt
3、hermalconductorinthex-yplane.ThebondingbetweenthelayersisvanderWaalsbonding,sothecarbonlayerscaneasilyslidewithrespecttooneanother;graphiteisanelectricalinsulatorandathermalinsulatorperpendiculartothelayers.Duetothedifferencebetweenthein-planeandout-of-planebonding,graphitehasahighmodulusofelas
4、ticityparalleltotheplaneandalowmodulusperpendicu-lartotheplane.Thus,graphiteishighlyanisotropic.Thehighmodulusofacarbonfiberstemsfromthefactthatthecarbonlayers,thoughnotnecessarilyflat,tendtobeparalleltothefiberaxis.Thiscrystallographicpreferredorientationisknownasafibertexture.Asaresult,acarbo
5、nfiberhasahighermodulusparalleltothefiberaxisthanperpendiculartothefiberaxis.Similarly,theelectricalandthermalconductivitiesarehigheralongthefiberaxis,andthecoefficientofthermalexpansionisloweralongthefiberaxis.Thegreaterthedegreeofalignmentofthecarbonlayersparalleltothefiberaxis,Le.,thestronge
6、rthefibertexture,thegreaterthec-axiscrystallitesize(I,=),thedensity,thecarboncontent,andthefiber’stensilemodulus,electricalconductivity,andthermalconductivityparalleltothefiberaxis;thesmallerthefiber’scoefficientofthermalexpansionandinternalshearstrength.ThecarbonlayersingraphitearestackedinanA
7、Bsequence,suchthathalfofthecarbonatomshaveatomsdirectlyaboveandbelowtheminadjacentlayers(Figure1.1).NotethatthisABsequencediffersfromthatinahexagonalclosepacked(HCP)crystalstructure.Inacarbonfiber,therecanbe34CARBONFIBERCOMPOSITES
