材料科学与工程专业英语2

材料科学与工程专业英语2

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时间:2019-10-23

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1、材料科学与工程专业英语2Solidmaterialsareconvenientlydividedintothreebasictypes:metals,ceramics,andpolymers・Thisclassificationisfirstbasedonchemicalcompositionandatomicstructure,andmostofthematerialfallsintoadistinetcategory,althoughtherearemanyintermediates・Inaddition,ther

2、earethreeotherimportantengineeringmaterials一compositematerials,semiconductormaterialsandbiologicalmaterials・Compositesconsistoftwoormorethantwodifferentmaterials,however,semiconductorsareusedbecauseoftheirunusualelectricalproperties;biologicalmaterialsaretranspl

3、antedintohumanbodies・Asimpleexplanationofthematerialtypeandtheirspecialfeatureswillbegivenlater・Metalmaterialisusuallymadeupofmetalelements・Theyhavealargenumberofirregularlymovingelectrons.Thatis,theseelectronsarenotboundtoaparticularatom.Manyofthepropertiesofme

4、talsaredirectlyattributabletotheseirregularlymovingelectrons・Metalsareverygoodelectricalandheatconductors,whichareopaquetovisiblelight;apolishedmetalsurfacewithabrilliantsurface・Inaddition,metalsareveryhardanddeformable,andthispropertyexplainstheirwidespreadusei

5、nstructuralapplications.Ceramicsarecompoundsbetweenmetalsandnonmetallicelements:theyareusuallyoxides,nitrides,andcarbides・Thewiderangeofmaterialsfallingintothiscategoryincludesceramics,consistingofclayminerals,cementandglass・Thesematerialsaretypicalelectricaldnd

6、thermalinsulators,andtheyaremoreresistanttoheatandharshenvironmentsthanmetalsandpolymers・Asfarasmechanicalperformanceisconcerned,ceramicsarehardbutbrittle・Polymersincludecommonplasticsandrubbermaterials・Mostofthemareorganiccompoundsthatcombinecarbon,hydrogen,and

7、othernonmetallieelementsinachemicalway.Asaresult,theyhaveverylargemolecularstructures・Thesematerialsareusuallyoflowdensityandmaybeverysoft・Manycompositesareusedforengineeringpurposes・Theyconsistofatleastonetypeofmateria1.Glassfiberisafamiliarexampleofglassfibers

8、embeddedinpolymermaterials・Inordertocombinethebestfeaturesofeachcomponentmaterial,acompositematerialisdevised・Glassfibersobtainstrengthfromglassandobtainsoftnessfromp

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