合金固溶体形成的Hume-Rothery规则

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1、Metalsandalloys.Hume-Rotheryrules.1.Threetypesofmetals.2.Alloys.Hume-Rotheryrules.3.Electricalresistanceofmetallicalloys.4.Applicationsofmetallicalloys.5.Steels.Superalloys.6.Electromigrationinthinwires.ThreetypesofmetalsMetalssharecommonfeaturesthatdefinethemasaseparateclasso

2、fmaterials:•Goodthermalandelectricalconductors(Why?).•Electricalresistanceincreaseswithtemperature(Why?).•Specificheatgrowslinearlywithtemperatureatlow(Why?).temperatures.•Goodreflectivityininfraredand,forsomemetals,invisiblelight(Why?).•Highmolardensitiesandstructureswithlarg

3、enumberofnearestneighbors(Why?).Propertiesofmetalsarelargelydefinesbytheirelectronstructure.Forsp-bondedmetalsassumingonecanassumethatthemacroscopicpropertiesaretheenergyofelectrongas(seelecturenotesofthefallsemester).EnergyofanelectrongaswithFermienergyEF:2233Nhæ3pNöU=nE=ç÷Fç

4、÷510mèVøæ¶UöPressureofelectrongas:P=-ç÷è¶VøS2æ¶Pöæ¶Uö2nEFBulkmodulus:B=-Vç÷=-Vç÷=ç2÷è¶VøSè¶VøS3Thisderivationdoesnotincludetheattractionforcebetweenthelatticeandtheelectronsandcoulombrepulsion.sp-bondedmetalsfollowSommerfeldmodel.sp-bondedmetalsarequitedifferent:Ia–metalsareso

5、ft,IIa–metalsarehard,IIIaandIVa–metalsaresoft.Mostofthesemetalsaregoodconductors.Transitionmetals.Propertiesoftransitionmetalsstronglydependsonthenumberofdelectrons!CohesiveenergyBulkmodulus.Meltingtemperaturesandelasticconstantfollowthesamepattern.Thebehaviorreflectsthestreng

6、thofthed-orbitalinteractions.RareEarthMetals.f-orbitalsarelocalizedandinteractionbetweenf-orbitalsofdifferentatomsisweak.MostoftheREmetalsaretrivalent(exceptionCe4+,Sm2+,Eu2+).MostofREmetalsarepoorelectricalconductorsduetomagneticscattering(interactionofconductingelectronsofwi

7、thmagneticspinmomentsf-electrons).AtlowtemperaturesresistivityofREmetalsincreaseswithtemperature(Kondoeffect).MeltingpointsofREmetalsarehigherthanthoseofsp-bondedonesbutlowerthatthemeltingpointsoftransitionmetals.EffectiveelectronmassinREmetalsis10-100timeslargerthanthatofafre

8、eelectron(Why?).Alloys.Reminder:Analloyisaphasecomprisingofon