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[物理学]

Theintensiveworkofmaterialsscientistsandsolid-statephysicistshasgivenrisetoaclassofsolidsknownasamorphousmetallicalloysorglassymetals.Thereisagrowinginterestamongtheoreticalandappliedresearchersalikeinthestructuralpropertiesofthesematerials.

Whenamoltenmetalormetallicalloyiscooledtoasolid,acrystallinestructureisformedthatdependsontheparticularalloycomposition.Incontrast,moltennonmetallicglass-formingmaterialswhencooleddonotassumeacrystallinestructure,butinsteadretainastructuresomewhatlikethatoftheliquid—anamorphousstructure.Atroomtemperaturethenaturallong-termtendencyforbothtypesofmaterialsistoassumethecrystallinestructure.Thedifferencebetweenthetwoisinthekineticsorrateofformationofthecrystallinestructurewhichiscontrolledbyfactorssuchasthenatureofthechemicalbondingandtheeasewithwhichatomsmoverelativetoeachother.Thus,inmetals,thekineticsfavorsrapidformationofacrystallinesstructurewhereasinnonmetallicglassestherateofformationissoslowthatalmostanycoolingrateissufficienttoresultinanamorphousstructure.Forglassymetalstobeformed,themoltenmetalmustbecooledextremelyrapidlysothatcrystallizationissuppressed.

Thestructureofglassymetalsisthoughttobesimilartothatofliquidmetals.OneofthefirstattemptstomodelthestructureofaliquidwasthatbythelateJ.D.BernaloftheUniversityofLondon,whopackedhardspheresintoarubbervesselinsuchawayastoobtainthemaximumpossibledensity.Theresultingdense,random-packedstructurewasthebasisformanyattemptstomodelthestructureofglassymetals.

CalculationsofthedensityofalloysbasedonBernal-typemodelsofthealloysmetalcomponentagreefairlywellwiththeexperimentallydeterminedvaluesfrommeasurementsonalloysconsistingofanoblemetaltogetherwithametalloidsuchasalloysofpalladiumandsiliconoralloysconsistingofironphosphors,andcarbon,althoughsmalldiscrepanciesremained.OnedifferencebetweenrealalloysandthehardspheresareainBernalmodelsisthatthecomponentsofanalloyhavedifferentsize,sothatmodelsbasedontwosizesofspheresaremoreappropriateforabinaryalloyforexample.Thesmallermetalloidatomsofthealloysmightfitintoholesinthedenserandom-packedstructureofthelargermetalatoms.

Oneofthemostpromisingpropertiesofglassymetalsistheirhighstrengthcombinedwithhighmalleability.Inusualmaterials,onefindsaninverserelationbetweenthetwoproperties,whereasformanypracticalapplicationssimultaneouspresenceofbothpropertiesisdesirable.Oneresidualobstacletopracticalapplicationsthatislikelytobeovercomeisthefactthatglassymetalswillcrystallizeatrelativelylowtemperatureswhenheatedslightly.

1.Theauthorisprimarilyconcernedwithdiscussing

[A]crystallinesolidsandtheirbehavioratdifferenttemperatures.

[B]moltenmaterialsandthekineticsoftheformationoftheircrystallinestructure.

[C]glassymetalsandtheirstructuralcharacteristics.

[D]metallicalloysandproblemsindeterminingtheirdensity.

2.Theauthor’sattitudetowardtheprospectsfortheeconomicutilizationofglassymetalsisoneof

[A]disinterest.

[B]impatience.

[C]optimism.

[D]apprehension.

3.Accordingtothetext,whichofthefollowingdeterminesthecrystallinestructureofametallicalloy?

[A]Atwhatratethemoltenalloyiscooled.

[B]Howrapidtherateofformationofthecrystallinephaseis.

[C]Howthedifferent-sizedatomsfitintoadenserandom-packedstructure.

[D]Whatthealloyconsistsofandinwhatratios.

4.Whichofthefollowingbestdescribestherelationshipbetweenthestructureofliquidmetalsandthestructureofglassymetals,asitispresentedinthetext?

[A]Thelatterisanillustrativeexampleoftheformer.

[B]Thelatterisalarge-scaleversionoftheformer.

[C]Theformerisastructuralelaborationofthelatter.

[D]Theformerisafairapproximationofthelatter.

5.Itcanbeinferredfromthetextthat,theoretically,moltennonmetallicglassesassumeacrystallinestructureratherthananamorphousstructureonlyiftheyarecooled

[A]veryevenly,regardlessoftherate.

[B]rapidly,followedbygentleheating.

[C]veryslowly.

[D]toroomtemperature.