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ID:51516557
大小:4.54 MB
页数:23页
时间:2020-03-25
《材料结构及其性能英文版).ppt》由会员上传分享,免费在线阅读,更多相关内容在PPT专区-天天文库。
1、One-DimensionalNanomaterials——CarbonNanotubesReporter:Teammates:WanjunWuYuanheWangBinbinYangYongzhu11423OutlineIntroductionStructureandPropertiesPreparationApplicationsIntroductionSumioIijimaCarbonnanotubes(CNTs)wasfirstdiscoveredbyIijimain1991CNTs:rollingupathingraph
2、enesheet.CNTsSWCNTsMWCNTsProductionMethods1.Arc-dischargemethod2.LaserVaporizationmethod3.ChemicalVaporDeposition(CVD)PreparationCVDmethodshavebeensuccessfullyappliedinmakingcarbonnanotubes.Thegrowthprocesswiththismethodinvolvesheatingacatalystmaterialtohightemperature
3、sinatubefurnaceandflowingahydrocarbongasthroughthetubereactorforaperiodoftime.Materialsgrownoverthecatalystarecollecteduponcoolingthesystemtoroomtemperature.parameters:hydrocarbons,catalysts:suchastransition-metalnanoparticlesgrowthtemperature.Leftdiagram:basegrowthmod
4、e.Rightdiagram:tipgrowthmodeCVDgrowthmechanismProcess:Dissociationofhydrocarbonmoleculescatalyzedbythetransitionmetal.Dissolutionandsaturationofcarbonatomsinthemetalnanoparticle.Precipitationofcarbonfromthesaturatedmetalparticleleadstotheformationoftubularcarbonsolidsi
5、nsp2structure.GrowthmechanismofacarbonnanotubeatanopenendbytheabsorptionofC2dimersandC3trimers(inblack),respectivelyTheadsorptionofaC2dimeroraC3trimerattheactivedanglingbondedgesitewilladdonehexagontotheopenend.Tubuleformationisfavoredoverotherformsofcarbon,becauseatub
6、econtainsnodanglingbondsandthereforeisinalowenergyform.SchematicexperimentalsetupsforothertwonanotubegrowthmethodsSingle-wallednanotubesgrownbylaserablationStructureandPropertiesTheuniquenessofthenanotubearisesfromitsstructureandtheinherentsubtletyinthestructure,whichi
7、sthehelicityinthearrangementofthecarbonatomsinhexagonalarraysontheirsurfacehoneycomblattices.Thehelicity(localsymmetry),alongwiththediameter(whichdeterminesthesizeoftherepeatingstructuralunit)introducessignificantchangesintheelectronicdensityofstates,andhenceprovidesau
8、niqueelectroniccharacterforthenanotubes.CNTssuperiormechanicalpropertieslowmassdensityhighelectronmobilitylargecurren
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