2材料科学基础英文版8

会计学12材料科学基础英文版8AssessmentStructureWrittenexamination(50%)Oralpresentation(20%,anytopicsinChapter7–MechanicalProperties,4studentsasagroup,15minutes)Report(20%,anytopicsinmaterialsscienceandengineering)Assignment(10%)第1页/共27页OutlineIntroductionAtomicbondinginsolidsStructuresofmetalsandceramicsImperfectionsinsolidsDiffusionMechanicalpropertiesDeformationandstrengtheningmechanismsFailurePhasediagramsandphasetransformationsTypesandapplicationsofmaterials第2页/共27页ChapterOne

IntroductionMaterialsscienceandengineering(MSE)WhystudymaterialsscienceandengineeringClassificationofmaterialsAdvancedmaterials第3页/共27页WhatismaterialsscienceandengineeringMaterialsscience Concernedwiththerelationshipbetweencomposition,structureandpropertiesofmaterialsMaterialsengineering Concernedwithdesigningorengineeringthestructuretoproduceapredeterminedsetofproperties Thestructureofamaterialdependsonwhatcompositionithasandhowitisprocessed.Also,theperformanceofamaterialisafunctionofitspropertiesMSE:Composition-processing-structure-properties-performancerelationship第4页/共27页Whystudymaterialsscienceandengineering Allappliedscientistsandengineersinanyengineeringareas:designproblemsinvolvingmaterialsToselectarightmaterialfrommanythousandsaccordingtoserviceconditionsandpropertyrequirements,weneedtohavetheknowledgeofMSE Tomodifyexistingmaterialsanddevelopnewmaterials,weneedtoknowMSE第5页/共27页ClassificationofmaterialsIntermsofchemicalmakeupandatomicstructure

Metals;Ceramics;Polymers1)Metallic:combinationsofmetallicelementsFreeelectrons–goodelectricalandthermalconductivitiesStrongbutdeformable–extensiveuseinstructuralapplications2)Ceramic:compoundsbetweenmetallicandnonmetallicelements–oxides,nitrides,andcarbidesVeryinsulativetoelectricityandheat–verylowelectricalandthermalconductivitiesHighlyresistanttohightemperaturesandcorrosiveenvironmentsVeryhardbutverybrittle3)Polymeric:organiccompoundsbasedoncarbon,hydrogenandothernonmetallicelements–plasticsandrubbersNormallylowdensityandrelativelyflexible第6页/共27页Additionaltypesofmaterial

Composites;Semiconductors;andBiomaterialsTheyoriginatefromthethreebasics(metals,ceramicsandpolymers),buttheyhavespecialusesandfunctions1)CompositesComposedofmorethanonematerialtype–one:matrix;other(s):reinforcingadditionMatrix–polymeric,metallic,orceramicmaterialsReinforcingaddition:glassfibers,carbonfibers,ceramicfibers(e.g.basaltfibers)ornanoparticles(e.g.SiC,SiN,etc)Designedtodisplayacombinationofthebestpropertiesofeachofthecomponents2)SemiconductorsElectricalpropertiesbeingintermediatebetweenconductorsandinsulatorsandbeingverysensitivetotheircompositionandenvironmentalconditions(e.g.,functionalceramics:microwavedielectricceramics,ferroelectricandpiezoelectricceramics)3)BiomaterialsUsedforcomponentsimplantedintothehumanbodyforreplacementofthediseasedordamagedbodyparts第7页/共27页AdvancedmaterialsMaterialsusedinhightechnologyelectronicequipment,computers,spacecraft,aircraft,nuclearequipment,etc.Including:Traditionalmaterialswhosepropertiesareenhancedbysomemodifications(newprocessingtechnology)Newlydevelopedmaterials第8页/共27页ChapterTwo

AtomicbondinginsolidsIntroductionPrimaryinteratomicbondsSecondarybondsCondensedstatesofmatterInteratomicforces第9页/共27页Atomicbondinginsolids–Introduction(1)Tounderstandtheoriginofsomematerialproperties,e.g.themodulusofelasticity–needtolookatmaterialsontheatomiclevel

Twoimportantthings:Theforcewhichholdstwoatomstogether(theinteratomicbond),workinglikealittlespringThespring-likebondbetweentwoatoms第10页/共27页Atomicbondinginsolids–Introduction(2)2)Thewaysinwhichatomspacktogether(atompacking)–determiningthenumberoflittlespringsperunitareaandthebond-angleAtompackingandbond-angle第11页/共27页Thewaysinwhichatomscanbeboundtogetherinclude:Atomicbondinginsolids–Introduction(3)Primarybondsionic,covalent,andmetallicbonds-strong(2)SecondarybondsVanderWaalsandhydrogenbonds-weak第12页/共27页Primaryinteratomicbonds(1)AllceramicsandmetalsareboundtogetherbyprimarybondsIonicandcovalentbondsinceramicmaterialsMetallicbondsinmetallicmaterialsBothprimaryandsecondarybondsinpolymericmaterials

e.g.,inliquidN2,N-NN-N第13页/共27页Primaryinteratomicbonds(2)1)IonicbondsSodiumchloride:NaClCl-FormationofanionicbondbetweenasodiumatomandachlorineatomBondingenergy:Ubonding=Ui–(UA+UR)Ui=energyofisolatedions第14页/共27页Primaryinteratomicbonds(3)Theformationofanionicbond,viewedintermsofenergyUbonding第15页/共27页Primaryinteratomicbonds(4)2)CovalentbondsThebondisformedbysharingofelectronsbetweenadjacentatomse.g.Methane(CH4)TheformationofcovalentbondsinCH4第16页/共27页Primaryinteratomicbonds(5)Bondenergy:Ub=-A/rm+B/rn(m<n)Theformationofacovalentbond,viewedintermsofenergyUbonding第17页/共27页Primaryinteratomicbonds(6)

Compound–partiallyionicbondingandpartiallycovalentbondingDegreeofeitherbondingtype–differenceintheelectronegativityofcomponentatomsForacompoundcomposedoftwoelementsAandB

%ioniccharacter={1-exp[-(0.25)(XA-XB)2]}100XAandXB–electronegativitiesofelementsAandB Increasingwithincreasingelectronegativitydifference第18页/共27页3)MetallicbondsDominantinteratomicbondinginmetalsMetalioncores+freeelectrons(valenceelectrons)Primaryinteratomicbonds(7)Bondinginametal第19页/共27页Secondarybonds(1)Muchweakerthanprimarybonds,butimportantLinksbetweenpolymermolecules–solidsKeepwaterliquidatroomtemperature;water–boilat–80oCwithoutthemTwotypesofsecondarybondsVanderWaalsbondsHydrogenbonds

第20页/共27页Secondarybonds(2)VanderWaalsbonds

Describeadipolarattractionbetweenunchargedatomswithstableelectronstructuresorbetweenmoleculesinmolecularstructurese.g.inertgaseshelium(He),neon(Ne),argon(Ar),andH2,N2,F2;whentheyareintheliquidstate,theiratomsormoleculesarebondedbyVanderWaalsbondsReason:

Electronicchargeonanatomisalwaysinmotion;ontheaverage–sphericallysymmetricrelativetothenucleus,butatanyinstant–unsymmetric–dipolemomentTwodipolesontwoadjacentatomsattracteachotherBondenergy:第21页/共27页Secondarybonds(3)VanderWaalsbonding–theatomsareheldtogetherbythedipolechargedistributionTypicalexample:liquidnitrogenat–198oC–covalentlybondedN2moleculesaregluedtogether