材料科学基础辅导与习题-上交课件 05ch2-1VIP

06年4月6日美国“林肯”号核动力航空母舰战斗群访问香港1载有约7000名官兵，战斗机及轰炸机达60多架，包括先进的F/A-18E“超级大黄蜂”战斗机，隶属美国太平洋舰队。21988年3月下水，总长332.9公尺，舰宽40.8公尺，排水量约10万吨，由两台原子炉推动。34567德国产最新改装豪华奔驰SLK8203.04克拉的梨形白色钻石——千禧之星海洋之星——重5.51克拉的心形钻石是世界上最大的天然深蓝绿色彩钻9101112欧洲皇室的奢华卧房令人惊叹1314151617Fe3Al和FeAl型18负离子配位多面体19（a）叶腊石202.2.4M2X3结构

刚玉为天然α-Al2O3单晶体,呈红色的称红宝石,呈蓝色的称为蓝宝石.刚玉为三方晶系,6:4配位,单位晶胞较大,且结构较复杂:其中O2-的排列大体上为HCP结构,其中八面体间隙位置的

2/3被Al3+有规律地占据,空位均匀分布,这样六层构成一个完整周期

212223第二章 固体材料的结构固体材料的宏观使用性能和工艺性能取决于其微观的化学成分、组织和结构，而在化学成分、组织和结构中，晶体结构又是最关键的因素。§2-1原子结构与晶体中的原子结合§2-2元素的晶体结构§2-3合金相的晶体结构§2-4陶瓷的晶体结构§2-5高分子的链结构及聚集态结构24§2-1参考书包永千，金属学基础，冶金工业出版社，1986[美]唐纳德.R.阿斯克兰，材料科学与工程，宇航出版社，1988

赵品等，材料科学基础，哈尔滨工业大学出版社，1999

石德珂等，材料科学基础，机械工业出版社，199925§2-1BondinginSolids通常把材料的液态和固态称为凝聚态。在凝聚态下，原子间距离十分接近，便产生了原子间的结合力，使原子结合在一起，即形成了键。26BondinginSolids1.Manyofthephysicalpropertiesofsolidmaterialsisaconsequenceoftheforcesthatholdtheatoms,moleculesorionstogether,andthewayinwhichneighboringatoms,moleculesorionspacktogether.2.Therearefourtypesofsolids,basedontheintermolecularforcesthatholdthemtogether:molecularsolids,covalent-networksolids,ionicsolidsandmetallicsolids273.MOLECULARSOLIDSareheldtogetherbyintermolecular(i.e.non-covalent)forces;includingdipole-dipole,Londondispersionforces,andhydrogenbonds).Thesearerelativelyweakforces,somolecularsolidsaretypicallysoftandmeltatlowtemperatures.Sincetheintermolecularforcesareweak,theshapeofthemolecule,anditsinfluenceonpackingarrangements,hasabiginfluenceonthepropertiesofthesolid.284.COVALENT-NETWORKSOLIDSareatomsheldtogetherbyanetworkofcovalentbonds.Thesearestrongbondsandtherefore,thesesolidsaretypicallyhard,withhighmeltingtemperatures.Diamondisacovalent-networksolidofcarbonatoms.295.IONICSOLIDSareheldtogetherbyionicbonds.Thestrengthofthebonddependsupontheionicchargesoftheionsinvolved,aswellashowclosetogethertheycanpackinthesolid.Manyionicsolidsinvolvesimpleions(asopposedtomolecularions)andpackincubictypearrangements.Thesesolidsaretypicallyharderthanmolecularsolids,butnotashardascovalent-networksolids.Thisisbecausetheionicbondisstrongerthantheabovedescribedintermolecularforces,butweakerthancovalentforces.306.METALLICSOLIDSconsistentirelyofmetalatoms.Inthiscasethebondingisduetovalenceelectronsthataredelocalizedthroughouttheentiresolid.Themobilityoftheelectronsisthereasonwhymetalsaresuchgoodconductorsofelectricity.31§2-1BondinginSolids材料的许多性能在很大程度上取决于原子结合键。根据结合力的强弱可把结合键分为两大类。一次键：结合力较强（依靠外壳层电子转移或共享而形成稳定的电子壳层），包括离子键、共价键和金属键。二次键：结合力较弱（依靠原子之间的偶极吸引力结合而成），包括分子键和氢键。32PROPERTIESOFSOLIDSThephysicalpropertiesofcrystalsaredeterminedbythekindsofparticlestheyarecomposedof,andtheattractiveforcesthatoccurbetweenthoseparticles.Someexamplesofthevarietyofphysicalpropertieswhichweobservedinsolidsarelistedbelow;1.Diamondisanextremelyhardsubstance2.Graphiteisaverygoodlubricant3.Bothdryice(solidcarbondioxide)andicearesoft4.MetalsaregoodconductorsAllofthesepropertiesdependon;1.Thekindofintermolecularforces2.StrengthoftheintermolecularforcesWecandividecrystalsintotypes,basedonthetypeofintermolecularattractiveforces,whichexhibitsimilarproperties.33AtomicBondsTherearetwotypesofbondsPrimaryBonds:

Primarybondsarethestrongestbondswhichholdatomstogether.Thethreetypesofprimarybondsare:

MetallicBonds;

CovalentBonds;

IonicBondsSecondaryBonds:

Secondarybondsaremuchweakerthanprimarybonds.Theyoftenprovidea"weaklink"fordeformationorfracture.Exampleforsecondarybondsare:

HydrogenBonds;

Vander

WaalsBonds34IonicSolidsHeldtogetherbyionicbondsThestrengthoftheionicinteractionsdependsonthemagnitudeofthechargeoftheions.Thus,NaCl(singlechargeonbothions)hasameltingpointof801°C,whereasMgO(2+,2-chargeontheions)hasameltingpointof2852°C35IonicBonds

Atomsliketohaveafilledoutershellofelectrons.Sometimes,bytransferringelectronsfromoneatomtoanother,electronshellsarefilled.Thedonoratomwilltakeapositivecharge,andtheacceptorwillhaveanegativecharge.Thechargedatomsorionswillbeattractedtoeachother,andformbonds.ThecompoundNaCl,ortablesalt,isthemostcommonexample.36Figure4a.FormationofionicbondinNaCl.Figure4b.Na+andCl-ionsformedbyionicbondingmechanism3738IonicBondingMostcommonbondinginmetal-nonmetalcompounds.Atomsgiveup/receiveelectronsfromotheratomsinthecompoundtoformstableelectronconfigurationsBecauseofnetelectricalchargeineachion,theyattracteachotherandbondviacoulombicforces.39IonicBondingPropertiesofionicbondingnondirectional:magnitudeofbondisequalinalldirectionsaroundtheion.Highbondingenergies(~600-1500kJ/mol)reflectedinhighmeltingtemperaturesgenerallyhardandbrittlematerialsmostcommonbondingforceramicmaterialselectricallyandthermallyinsulativematerials40primarybonding：Ionicbonding1.离子键结合即为失掉电子的正离子（ⅠA、ⅡA族金属）和得到电子的负离子（ⅥA、ⅦA族非金属）依靠静电引力而结合在一起。41primarybonding：Ionicbonding2.无方向性。原因是离子周围的电子云是以核为中心球对称分布的，它在各个方向上与异性离子的作用力都是相同的。3.结合力较强，结合能很高，所以离子晶体大多具有高熔点、高硬度、低的热膨胀系数。而且由于不存在自由电子，所以离子晶体是不导电的，但在熔融状态下可以依靠离子的定向运动来导电。

42CovalentNetworkSolidsConsistofnetworksorchainsofmoleculesheldtogetherbycovalentbonds1.Covalentbondsarestrongerthanintermolecularforcesandcovalentsubstancesaresubsequentlyharderandhavehighermeltingtemperatures2.Diamondisacovalentstructureofcarbon.Itisextremelyhardandhasameltingtemperatureof3550°C43CovalentBondingStableconfigurationsareobtainedbythesharingofvalenceelectronsby2ormoreatoms.Typicalinnonmetalliccompounds(CH4,H20)Numberofpossiblebondsperatomisdeterminedbythenumberofvalenceelectronsinthefollowingformula:numberofbonds=8-(valenceelectrons)Bondsalsoareangledependent44CovalentBonds

Someatomsliketoshareelectronstocompletetheiroutershells.Eachpairofsharedatomsiscalledacovalentbond.Covalentbondsarecalleddirectionalbecausetheatomstendtoremaininfixedpositionswithrespecttoeachother.Covalentbondsarealsoverystrong.Examplesincludediamond,andtheO-OandN-Nbondsinoxygenandnitrogengases.

45CovalentBonding Propertiesofcovalentbondingcanbeeitherverystrongorveryweakbonds,dependingupontheatomsinvolvedinthebond.Thisisalsoreflectedinthemeltingtemperatureofthecompoundex: diamond(strongbond)--Tm>3350°C bismuth(weakbond)--Tm~270°Cmostcommonformofbondinginpolymers46Bismuthisawhite,crystalline,brittlemetalwithapinkishtinge.Bismuthisthemostdiamagneticofallmetals,andthethermalconductivityislowerthananymetal,exceptmercury.Ithasahighelectricalresistance,andhasthehighestHalleffectofanymetal(thatis,thegreatestincreaseinelectricalresistancewhenplacedinamagneticfield).bismuth47Cadmiumisasoft,bluish-whitemetalandiseasilycutwithaknife.Itissimilarinmanyrespectstozinc.Interestingly,acharacteristiccadmium"scream"isheardonbendingacadmiumbar.Cadmiumanditscompoundsarehighlytoxic.Silversolder,whichcontainscadmium,shouldbehandledwithcare.CalciumCadmium48Scanningelectronmicrographofundeformedcadmiumsinglecrystal49Cadmiumcrystalafterdeformationto100%strain50Highmagnificationimageofslipstepsincadmiumcrystalafterdeformationto200%strain.Thetensileaxisrunsapproximatelyfromthebottomleftcornertothetoprightcorneroftheimage51primarybonding：covalentbonding1.ⅣA、ⅤA、ⅥA族的亚金属大多以共价键相结合。它们一般具有3个以上价电子，当其结合时，相邻原子各给出一个电子作为二者共有，原子借共用电子对产生的力而结合。5253primarybonding：covalentbonding2.具有方向性。因为共价键除依赖电子配对外，还依赖于电子云的重叠，电子云重叠愈大，结合能愈大，结合能愈强。原子的结构表明，s轨道电子云呈球对称，其它轨道的电子云都有一定的方向性。为使电子云达到最大限度的重叠，共价键具有方向性。54primarybonding：covalentbonding3.延性和导电性都很差；具有高熔点、高硬度。例如金刚石具有最高的摩氏硬度，且熔点高达3750℃。55MetallicSolidsConsistentirelyofmetalatoms.Typicallyhexagonalclosepacked,cubicclosepackedorbody-centeredcubicstructures.Thesehavecoordinationnumbersofeither12or8.BondingisduetovalenceelectronswhicharedelocalizedthroughouttheentiresolidBondingisstrongerthansimpledispersionforces,butthereareinsufficientelectronstoformordinarycovalentbonds.ThestrengthofthebondingincreaseswiththenumberofelectronsavailableforbondingDelocalizationofelectronsisthephysicalbasisfortheabilityofmetalstocarryelectricalcurrent(electronsarefreetomoveaboutthemetalstructure)56MetallicSolidsThenucleusandinnercoreofelectronsareina"sea"ofdelocalized,mobilevalenceelectrons57MetallicBondsInametal,theouterelectronsaresharedamongalltheatomsinthesolid.Eachatomgivesupitsouterelectronsandbecomesslightlypositivelycharged.Thenegativelychargedelectronsholdthemetalatomstogether.Sincetheelectronsarefreetomove,theyleadtogoodthermalandelectricalconductivity.58Metallicbondandelectroncloud59MetallicBondingMostcommoninbondingofmetalsandtheiralloys.Proposedmodelofmetallicbondingmetalsusuallyhave,atmost,3valenceelectrons,allofwhichforman“electronsea”,whichdriftthroughtheentiremetal.Baseelectronsformnet-positiveioncores,whichattractthefreeelectronsfromthe“sea”asneededtomaintainneutrality.60MetallicBondingBondingmaybeweakorstrong,dependinguponatomsinvolved.Ex:Hgbondingenergy=68kJ/mol Wbondingenergy=850kJ/mol61primarybonding：Metallicbonding1.约占元素周期表中4/5的金属元素大多以金属键相结合。它们因外层电子较少，当相互靠近产生相互作用时，都易失去最外层电子而成为正离子。而脱离了每个原子的电子为相互结合的集体离子所共有，成为自由的公有化的电子云(或称电子气)而在整个金属中运动。电子云的分布可看作是球形对称的。金属正是依靠正离子与自由电子之间产生强烈的静电相互作用而结合。6263primarybonding：Metallicbonding2.良好塑性、固溶性、导电性、导热性、金属光泽、正的电阻温度系数及晶体中原子密集排列。(1)良好塑性：金属键没有方向性，正离子之间改变相对位置并不会破坏电子与正离子之间的结合力，因而金属具有良好的塑性；(2)固溶性：金属正离子被另一种金属正离子取代时也不会破坏结合键,即它们具有相互溶解性(称为固溶)；

(3)导电性：在外加电压作用下，自由电子可定向移动；

64(4)导热性：固态金属中，不仅正离子的振动可传递热能，而且电子的运动也能传递热能，故比非金属具有更好的导热性；(5)金属光泽：金属中的自由电子可吸收可见光的能量，被激发、跃迁到较高能级，因此金属不透明。当它跳回到原来能级时，将所吸收的能量重新辐射出来，使金属具有金属光泽；(6)正的电阻温度系数：随温度升高，正离子（或原子）本身振幅增大，阻碍电子通过，使电阻升高，因此金属具有正的电阻温度系数；(7)晶体中原子密集排列：金属键没有饱和性和方向性，故形成的金属晶体结构大多为具有高对称性的紧密排列。

65MolecularSolidsConsistofatomsormoleculesheldtogetherbyintermolecularforces(dipole-dipole,dispersionandhydrogenbonds)1.Theseforcesareweakerthanchemical(covalent)bonds.Thereforemolecularsolidsaresoft,andhaveagenerallylowmeltingtemperature2.Mostsubstancesthataregassesorliquidsatroomtemperatureformmolecularsolidsatlowtemperature(e.g.H2O,CO2)66ThepropertiesofmolecularsolidsalsodependsupontheshapeofthemoleculeBenzene(sixcarbonringwithasymmetricalstructure)packsefficientlyinthreedimensionsTolueneisrelatedtobenzenebuthasamethylgroupattachedtoonecarbonofthering.Itisnotsymmetricalanddoesnotpackefficiently.Itsmeltingpointislowerthanbenzene67SecondaryBondingVander

Waalsbondingweakbondsincomparisonwithotherformsofbonding(~10kJ/mol)evidentbetweenallatoms,includinginertgasesandespeciallybetweencovalentlybondedmolecules.Bondsarecreatedthroughbothatomicandmoleculardipoles68Vander

WaalsBonds

Vander

Waalsbondsareveryweakcomparedtoothertypesofbonds.Thesebondsareespeciallyimportantinnoblegaseswhicharecooledtoverylowtemperatures.Theelectronssurroundinganatomarealwaysmoving.Atanygivenpointintime,theelectronsmaybeslightlyshiftedtoonesideofanatom,givingthatsideaverysmallnegativecharge.Thismaycauseanattractiontoaslightlypositivelychargedatomnearby,creatingaveryweakbond.Atmosttemperatures,thermalenergyoverwhelmstheeffectsofVander

Waalsbonds.69VanDer

Waalsbondingisasecondarybonding,whichexistsbetweenvirtuallyallatomsormolecules,butitspresencemaybeobscuredifanyofthethreeprimarybondingtypesispresent.Secondarybondingforcesarisefromatomicormoleculardipoles.Inessence,anelectrondipoleexistswheneverthereissomeseparationofpositiveandnegativeportionsofanatomormolecule.Whenanelectronclouddensityoccursatonesideofanatomormoleculeduringtheelectronflightaboutthenucleus,VanDer

Waalsforcesaregenerated.Thiscreatesadipolewhereinonesideoftheatombecomeselectricallychargedandtheothersidehasdeficiencyofelectronsandisconsiderablychargedpositive.TheatomisdistortedasshowninFigure7.70Figure7.Vander

WaalsBond71SecondaryBonding：Molecularbonding1.（vander

Waalsbonding）范德瓦尔键是以弱静电吸引的方式使分子或原子团连接在一起的(即原子间的偶极吸引力)。72SecondaryBonding：Molecularbonding2.分子键键能很低，所以分子晶体的熔点很低。依靠它大部分气体才能聚合为液态甚至固态，当然它们的稳定性极差。例如，塑料易产生大的变形，液氮室温下汽化，水100℃下汽化等。73SecondaryBondingHydrogenbondingspecialtypeofsecondarybondbetweenmoleculeswithpermenantdipolesandhydrogeninthecompound.Ex:HF,H2O,NH3thesesecondarybondscanhavestrengthsashighas~50kJ/molandwillcauseincreasesinmeltingtemperatureabovethosenormallyexpected.74Hydrogenbondsarecommonincovalentlybondedmoleculeswhichcontainhydrogen,suchaswater(H2O).Sincethebondsareprimarilycovalent,theelectronsaresharedbetweenthehydrogenandoxygenatoms.However,theelectronstendtospendmoretimearoundtheoxygenatom.Thisleadstoasmallpositivechargearoundthehydrogenatoms,andanegativechargearoundtheoxygenatom.Whenothermoleculeswiththistypeofchargetransferarenearby,thenegativelychargedendofonemoleculewillbeweaklyattractedtothepositivelychargedendoftheothermolecule.Theattractionisweakbecausethechargetransferissmall.

75Figure6.Hydrogenbonds76SecondaryBonding:Hydrogenbonding1.氢键的本质与范德瓦尔键一样，只是在氢键中氢原子起了关键作用。氢只有一个电子，当它与一个电负性很强的原子（或原子团）X结合成分子时，氢原子的一个电子转移至该原子壳层上，氢离子则实质上成了一个裸露的质子，对另一个电负性较大的原子Y表现出较强的吸引力77SecondaryBonding：Hydrogenbonding氢键中的氢原子在两个电负性很强的原子（或原子团）之间形成一个桥梁，把两者结合起来，成为氢键。表达式为：X-H——YH与X为离子结合，与Y之间为氢键结合，通过氢键将X与Y结合起来，X与Y可以相同或不同。78Hydrogenbonding氢键的结合力较范德瓦尔键为强。在带有-COOH、-OH、-NH2原子团的高分子聚合物中常出现氢键，依靠它将长分子链结合起来。氢键在一些生物分子如