工程材料科学与设计(原书第2版)课后习题答案(4—8)

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1、SolutionstoChapter41.FIND:Whatmaterialhasapropertythatishugelyaffectedbyasmallimpuritylevel?SOLUTION:Electricalconductivityspansawiderange.Incorporationofafewpartspermillionimpuritiescanchangeelectricalconductivityordersofmagnitude.Smallcracksinbrittlematerialsdecreasetheirtensilestrengthbyorder

2、sofmagnitude.Smalladditionsofimpuritycanchangethecolorofgems.COMMENTS:Thesearebutafewexamples.2.COMPUTE:Thetemperatureatwhichthevacancyconcentrationisonehalfthatof25oC.GIVEN:EQUATION:whereCv=vacancyconcentrationQfv=activationenergyforvacancyinformationR=gasconstant8.314J/mole-KT=absolutetemperat

3、ureInthepresentproblemandT1=35+273=308KT2=25+273=298KalsoCv(35oC)=2Cv(25oC)Thus,SolvingforQfvwegetQfv=52893.5J/mole.UsingthisvalueofQfv,theCv(25oC)canbecalculatedTheproblemrequiresustocalculatethetemperatureatwhichthevacancyconcentrationis½Cv(25oC).½Cv(25oC)=2.675x10-10ThusforsolvingT,weget:T=28

4、8.63Kor15.63oC.3.COMPUTE:GIVEN:EQUATION:Dividing(1)by(2)weget:SolvingforQ,weget:Q=22033.56J/mole=exp(-7.511)=5.46x10-4TheproblemrequirescomputingatemperatureatwhichCv=3Cv(80oC).3Cv(80oC)=3x5.46x10-4=1.63x10-3solvingforT,weget:T=413.05Kor140.05oC4.5.FIND:AreAlandZncompletelysolubleinsolidsolution

5、?IfAl-ZnsystemobeysalltheHume-Rotheryrules.Thenitisexpectedtoshowcompletesolubility.(i)TheatomicradiiofAlandZnare0.143nmand0.133nmrespectively.Thedifferenceintheirradiiis7.5%whichislessthan15%.(ii)TheelectronegativitiesofAlandZnare1.61an1.65respectivelywhicharealsoverysimilar.(iii)Themostcommonv

6、alenceofAlis+3and+2forZn.(iv)AlhasanFCCstructurewhereZnhasaHCPstructure.ItappearsthatAl-Znsystemobeys3outof4Hume-Rotheryrules.Inthiscasetheyarenotexpectedtobecompletelysoluble.6.SHOW:TheextentofsolidsolutionformationinthefollowingsystemsusingHume-RotheryRules.(a)AlinNiSize:r(Ni)=0.125nm;r(Al)=0.

7、143nmdifference=14.4%Electronegativity:Al=1.61;Ni=1.91MostCommonValence:Al3+;Ni2+CrystalStructure:Al:FCC;Ni:FCCThecrystalstructureofAlandNiarethesameandthemostcommonvalenciesarealsocomparable.However,thesizedifferenceisclose