




下载本文档
版权说明:本文档由用户提供并上传,收益归属内容提供方,若内容存在侵权,请进行举报或认领
文档简介
ChapterofMetalsand8.1MetallicBondinginthesolidFormetals,theatomshavelowelectron-negativitiesandelectronionizationpotentials;thereforetheelectronsaredelocalizedoveralltheatoms.Wemaythinkofthestructureofametalasanarrangementofpositiveatomcoresinaseaofelectrons. izethebondinginametalitmakessensetopackasmanyatomsaroundeachotheras izethenumberofthenearestneighbors(CN)andminimizethevolume.8.1MetallicBondinginthesolid•Highelectrical•Highthermal•HighreflectivityofvisibleThe“free-electron”modelofthemetallicbond(Asimplemodelformetals)TheFreeElectronConsiderametalsuchasNa,MgorAltobeessentiallyaboxinwhichthevalenceelectronsofthemetalareThepotentialwithintheboxistakentobeuniformandmuchlowerthanthatinthesurroundingmedium.(V=0)ConsidertheinteractionbetweenelectronstobeTreatquantummechanicallyasaparticleinaSolutionstoathreedimensionalparticleinabox28 V(周期性平面波:(xl) 1(x,y,z)()2l
(nxxnyynzh2hE
n2)
n2h2
n22ml
2ml•where,n•where,nx,ny,nzcanbepositive,zero,xyz《结构化学基础 Solutionstoathreedimensionalparticleinabox
E2ml
(nx
nz)
2ml在微观范围内,能级分Therearefourquantumnumbernx,ny,n在微观范围内,能级分Wecanhavetwoelectronsperuniquecombinationofnx,nyandn20,简并态1,ms=1/2,1/2,2电子Foralargeboxtheenergylevelsaregoingtobeclosetogether,considerenergylevelsasformingacontinuousbandHowmanyenergylevelsdowehavewithenergylessthansomeFermienergylevelEFistheuppermostfilledenergyFermienergylevelEFistheuppermostfilledenergylevelofaconductorat0K.eg.MetalNa:EF=3.15eV EF=3.2••At0K,ElectronsfilltheorbitalsfromthelowestenergylevelfirstuntiltheFermienergylevelEF0K时,导体中电子所占据最高能级)•AllenergylevelslowerthanEFarefilled,andallthosehigherthanEFareempty.•WhenT>0K,somefreeelectronscanbeactivatedtotheenergylevelhigherthanEF.8.1.2Bondtheoryof(Theoryofsolidsusingmolecular••Considertheelectronsinmetalsmovinginapotentialfieldsofthemetalatoms(V≠0,V(x)=V(x+l
2V]•Considera•Considerasolidtobealargemoleculeandmolecularorbitaltheory.Bandsresultfromtheoverlapofatomicorbitals(LCAO-MO) Energiesofthe2s(valence)molecularorbitalsforclustersoflithiumatomsfilledwith1valenceelectronperatom:Forasolid,Nissolarge(>1020)thattheMOenergiesformacontinuousPartiallyfilledbondmeansnoenergygapbetweenthehighestfilledorbital(HOMO)andthelowestunfilledorbitalElectronscanbemovedeasilyfromfilledtoemptyorbitalsbyanelectricfield,solithiummetalconductselectricity.Electronsincomple yfilledbandscan’tbemovedbyelectricfields,andthereforearepoorelectricalconductors(insulatorsorsemiconductors)Berylliumhas2valenceelectronsperatom,justenoughto yfillthe2sband,soBeshouldbeanelectricalBemetalisanelectricalconductor!Wheredidthetheorygoconsiderboth2sand2p(valence)molecularorbitalsofberylliumTheoverlap 2sand2pbandsformasinglebandthatispartiallyfilled.ThusBemetalisanelectricalconductor.Band
Empty
Conduction
Filled••能带较宽个能带按能量高低排为能带结构每个能带具有一定的能量范 间轨 少的每个能带具有一定的能量范 较窄,轨 多的外层原子轨道形成
SiEg=1.1ev;GeEg=0.72evGaAsEg=1.4ScanningTunnelingMicroscope(STM)ImageofIroninthe(110)planeAnactualSTMimageofaNiNotethehexagonalarrangementofClosepackingspheresandthestructureofpureClosepackingofhard MetallicsolidscanbemodeledashardLimitationsforpackingarepurelyResultsinhighestpossibledensityofspheres(12nearestneighbors)Thetwomostcommonclose-packedABABstructureofhexagonalclosepacking(HCP,TypeABCABCstructureofcubicclosepacking orFCC,Typeabplanea
cplanebplaneaplanecplaneHexagonal/CubicClosePackingandunitABABAB…Closeab aa
Unit(0,0,0)(1/2,(0,1/2,1/2)ABCABC…ClosecHexagonalclosepacked(hcp,TypeUnit
FaceCenteredCubic(FCC) ,TypeA1)
bplaneaplanecplane8.2.2.PackingEfficiencyand Usingalittlegeometryandsomediagramswecanshowthat74%oftheunitcellofacubicclosepackedstructureisfilledwithhardspheres,26%isemptyEmpty TwopossibletypesofOctahedralCoordinationNumber(C.N.)isPackingefficiencyofFCCstructure a4R2
a3 2R)3
R) coefficient
16
OctahedralholesinFCC ,FoundbetweentwoparalleltrianglesofNspheresresultinNoctahedralWithinWithinaunit 12*1/4+1=4octahedralTetrahedralholesinFCCWithinaunit tetrahedralWithinaunit tetrahedralTwopossibletypesof-upand-NholesofeachtypesforNNspheresresultin2NtetrahedralHCPstructure: octahedralholesinHCP tetrahedralholesinHCPa2
2+8/4=WithinaWithinaunitcell:22octahedralNspheresresultinNoctahedralWithinaunitcell:2 tetrahedralNspheresresultin2Ntetrahedral8.2.3.NonClosePacked BCCand4R a3(4R)36433 33 2(4R3)8BCC(bcpor-Bodycentered
68%packing
Vsphere
8R3 64
a223a2BCCstructure(bcp,a223a2 Holes Withinaunit26distortedoctahedralholes(1/412+1/212distortedtetrahedralholesSCandSC, -Simplecubic52%packing
DC, -Thediamond34%packingMorecomplex,lesssymmetricstructuresaretypicallydistortionofthesepackingsystemsSCand4148Ca,Sr,Ba224Zn,Cd2168111 8.38.3StructuresofpureA.structuresofpure B.AtomicradiiofTheTheatomicradiiofthemetalswereobtainedbyhavingthedistanceofclosestcontactAtomicradiiofmetalschangeswithbondinmetalliccrystal,rMg=1.60inioniccrystal,rMg2+=0.78Atomicradiiofmetalschangeswithcoordination86421ThestructuresandpropertiesofAlloy:asubstancethatcontainsamixtureofelementsandhasmetallicproperties,maybedividedintothreemajorcategoriessubstitution:additivesdisplacelatticepointsInterstitial:additivesoccupyholes(填隙合金Completefillingofholes:beginstoformnewlatticeSolidsolutions(固溶体SignificantcommonCrystalAtomicradii radiiandcrystalstructurearerequiredsothatthelatticeisnotexcessivelydistortedElectronegativitysimilarityrequiredotherwiseintermetallicbondsform
structuraltypeofCu,Ag,Au,Ni,-Co,-Fe,Pt,Ir,bcp-Fe,V,Mo,OrderordisorderofthemetalliccF:ThestructureofsolidsolutioncanbecF:cP:a=3.753
a=b=3.960Åc=3.667ÅMetalliccompound(金属化合物SignificantdifferencesCrystalAtomicCharacteristicsofthemetallicThestructureisdifferentfromthepureEachtypeofmetaloccupyingoneofthe ExampleA:thestructureofthealloyMg:Mg:dcpackingCu:halftetrahedralElectronegativity:Mg CuRadius:Mg1.60;CuEachunitCu:DistanceDistancebetweenMg-几何上有效的填充空间是其稳定存在的(71.0%AB2laves (164种合金
•化学式主要为AB2•化学式主要为AB2positionof rΑ/rB:Radius:MgCu1.90;Ni1.91;ZnCu1.28;Zn1.39;NiExampleB:thestructureofthealloyatoms/unitatoms/unitCu:1/2Ca:1/8oneCaCu5/unitC.N.ofElectronegativity:Ca1.00;Cu1.90;Radius:Ca1.97;Cu1.28ElectronegativityLa1.10;Ni1.91;CoRadius:La1.82;Ni1.24;Co ExampleB:thestructureofthealloyLaNi5LaNi5,LaCo5,CeCo5havesamestructuresasCaCu561022~71022hydrogen>4.21022hydrogenatom(liquidOtherreservoirsforhydrogen:AlloyMn-Ti(lavesphase)HavecapacityHavecapacitytostoreInterstitialmetalliccompounds(金属填隙化合物•Interstitial•InterstitialAlloyformedwhensomeoftheholesinclosestpackedstructurearefilledwithsmallerRequiressmallatomadditivesthatfitwithinlatticemaybestoichiometricor dramaticallychangethephysicalpropertiesofthematerialExample:steelisaninterstitialalloyofironandcarbonrC/rFe=0.70/1.40=0.50>Thestructureandpropertiesofsteelandpurepureiron(<0.02%C) A2(bcp)structure:-(纯铁 -Feand-A1(fcc) -Steelisanalloysystemconsistingofironandcarbon。harderandstronger0.02%~2%C(0.25%低C2.0%C高C钢or铸铁castIron-soft,ductile,Steel-harder,stronger,lessductilethanpuremorecarbon,hardersteel(0.2%~StructureofFerrite(铁素体):asolidsolutionofCin-Fe(BCC).Sincethesizeoftheoctahedralholesisverysmallin-Fethesolubilityisverylow(thehighestsolubilityis0.02(pureiron纯铁)Austenite:aninterstitialsolidsolutionofCin-Fe(about0.8%byweight,atomratioFe:C=27:1,1Catom/6~7Feunit)Cementite(渗碳体 Fe3C orthorhombic:Martensite:asupersaturatedsolidsolutionofCin-Fe(about1.6%byweight,byfastcoolingofaustenite) Ferrite(0.02%Cin-Fe(BCC)
(0.8%Cin
温馨提示
- 1. 本站所有资源如无特殊说明,都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
- 2. 本站的文档不包含任何第三方提供的附件图纸等,如果需要附件,请联系上传者。文件的所有权益归上传用户所有。
- 3. 本站RAR压缩包中若带图纸,网页内容里面会有图纸预览,若没有图纸预览就没有图纸。
- 4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
- 5. 人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对用户上传分享的文档内容本身不做任何修改或编辑,并不能对任何下载内容负责。
- 6. 下载文件中如有侵权或不适当内容,请与我们联系,我们立即纠正。
- 7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
最新文档
- 2024年事业单位考试四川省遂宁市A类《职业能力倾向测验》模拟试题含解析
- 2025年遵义市税务系统遴选面试真题附详解含答案
- 慢病防治知识讲座参考课件
- 林长制智慧林长综合管理平台建设方案
- 辽阳市弓长岭区文职辅警招聘考试真题
- 老年健康管理内容课件
- 老师的视频课件大全
- 高效智能仓储租赁服务协议
- 采矿权出让与矿产资源保护责任书范本
- 矿山股权转让与矿区环境保护责任书
- 保山2025年云南保山市中心血站招聘编外工作人员笔试题库附带答案详解
- 弘扬家风文化班会课件
- 吐鲁番采油厂玉果油田滚动建产工程环境影响报告书
- 2025年6月英语四级真题及参考答案
- 浙江省2024-2025学年高二下学期数学学考模拟考(三)(含答案)
- 电大:理论联系实际谈一谈如何维护政治安全?参考答案
- 2025年下半年佛山市图书馆招考工作人员易考易错模拟试题(共500题)试卷后附参考答案
- 社区社会工作课件
- 医药代表关键客户管理策略
- 2025年人教版小学小升初科学模拟试卷(含答案解析)
- 浙江省杭州市拱墅区2025年中考英语一模试卷(含笔试答案无听力答案、原文及音频)
评论
0/150
提交评论