千里之行，始于足下讓知識帶有溫度。第第2頁/共2頁精品文檔推薦材料專業英語課件：ClassificationofMaterials材料專業英語課件：ClassificationofMaterials

BasicClassificationsandEngineeringMaterials

Solidmaterialshavebeenconvenientlygroupedintothreebasicclassifications：metals，ceramicsandpolymers．Thisschemeisbasedprimarilyonchemicalmakeupandatomicstructure,andmostmaterialsfallintoonedistinctgroupingoranother，althoughtherearesomeintermediates.Inaddition，therearethreeothergroupsofimportantengineeringmaterials—composites，semiconductor，andbiomaterials．Compositesconsistofcombinationsoftwoormoredifferentmaterials，whereassemiconductorsareutilizedbecauseoftheirunusualelectricalcharacteristics；biomaterialsareimplantedintothehumanbody．Abriefexplanationofthematerialtypesandrepresentativecharacteristicsisofferednext．

Metals：Metallicmaterialsarenormallycombinationsofmetallicelements．Theyhavelargenumbersofnonlocalizedelectrons；thatis，theseelectronsarenotboundtoparticularatoms.Manypropertiesofmetalsaredirectlyattributabletotheseelectrons．Metalsareextremelygoodconductorsofelectricityandheat，andarenottransparenttovisiblelight：apolishedmetalsurfacehasalustrousappearance．Furthermore，metalsarequitestrong，yetdeformable，whichaccountsfortheirextensiveuseinstructuralapplications．

Ceramics：Ceramicsarecompoundsbetweenmetallicandnonmetallicelements：theyaremostfrequentlyoxides,nitrides，andcarbides．Thewide

rangeofmaterialsthatfallswithinthisclassificationincludesceramicsthatarecomposedofclayminerals，cement，andglass.Thesematerialsaretypicallyinsulativetothepassageofelectricityandheat，andaremoreresistanttohightemperaturesandharshenvironmentsthanmetalsandpolymers．Withregardtomechanicalbehavior，ceramicsarehardbutverybrittle．

Polymers：Polymersincludethefamiliarplasticandrubbermaterials．Manyofthemareorganiccompoundsthatarechemicallybasedoncarbon，hydrogen，andothernonmetallicelements；furthermore，theyhaveverylargemolecularstructures．Thesematerialstypicallyhavelowdensitiesandmaybeextremelyflexible．

Composites：Anumberofcompositematerialshavebeenengineeredthatconsistofmorethanonematerialtype．Fiberglassisafamiliarexample，inwhichglassfibersareembeddedwithinapolymericmaterial.Acompositeisdesignedtodisplayacombinationofthebestcharacteristicsofeachofthecomponentmaterials．Fiberglassacquiresstrengthfromtheglassandflexibilityfromthepolymer．Manyoftherecentmaterialdevelopmentshaveinvolvedcompositematerials．

Semiconductors：Semiconductorshaveelectricalpropertiesthatareintermediatebetweentheelectricalconductorsandinsulators．Furthermore，theelectricalcharacteristicsofthesematerialsareextremelysensitivetothepresenceofminuteconcentrationsofimpurityatoms，whichconcentrationsmaybecontrolledoververysmallspatialregions．Thesemiconductorshavemade

possibletheadventofintegratedcircuitrythathastotallyrevolutionizedtheelectronicsandcomputerindustriesoverthepasttwodecades．

Biomaterials:Biomaterialsareemployedincomponentsimplantedintothehumanbodyforreplacementofdiseasedordamagedbodyparts．Thesematerialsmustnotproducetoxicsubstancesandmustbecompatiblewithbodytissue(i．e．mustnotcauseadversebiologicalreactions)．Alloftheabovematerials--metals，ceramics，polymers，compositesandsemiconductors--maybeusedasbiomaterials．Forexample，someofthebiomaterialssuchasCF／C(carbonfibers／carbon)andCF／PS(polysulfone)areutilizedinartificialhipreplacements．

AdvancedMaterials

Materialsthatareutilizedinhigh-technology(orhigh-tech)applicationsaresometimestermedadvancedmaterials．Byhightechnologywemeanadeviceorproductthatoperatesorfunctionsusingrelativelyintricateandsophisticatedprinciples；examplesincludeelectronicequipment(VCRs，CDplayers，etc．)，computers，fiberopticsystems，spacecraft，aircraft，andmilitaryrocketry．Theseadvancedmaterialsaretypicallyeithertraditionalmaterialswhosepropertieshavebeenenhancedornewlydeveloped，high—performancematerials．Furthermore，theymaybeofallmaterialtypes(e．g．metals，ceramics，polymers)，andarenormallyrelativelyexpensive．

ModernMaterialsNeeds

Inspiteofthetremendousprogressthathasbeenmadeinthedisciplineofmaterialsscienceandengineeringwithinthepastfewyears，therestillremaintechnologicalchallenges，includingthedevelopmentofevenmoresophisticatedandspecializedmaterials，aswellasconsiderationoftheenvironmentalimpactofmaterialsproduction．Somecommentisappropriaterelativetotheseissuessoastoroundoutthisperspective．

Nuclearenergyholdssomepromise，butthesolutionstothemanyproblemsthatremainwillnecessarilyinvolvematerialsfromfuelstocontainmentstructuresandfacilitiesforthedisposalofradioactivewaste．

Significantquantitiesofenergyareinvolvedintransportation．Reducingtheweightoftransportationvehicles(automobiles，aircraft，trains，etc．)，aswellasincreasingengineoperatingtemperatures，willenhancefuelefficiency．Newhighstrength，low—densitystructuralmaterialsremaintobedeveloped，aswellasmaterialsthathavehigher—temperaturecapabilities，foruseinenginecomponents．

Furthermore，thereisarecognizedneedtofindnew，economicalsourcesofenergy，andtousethepresentresourcesmoreefficiently．Materialswillundoubtedlyplayasignificantroleinthesedevelopments．Forexample，thedirectconversionofsolarenergyintoelectricalenergyusessiliconmaterials．Toensureaviabletechnology，materialsthatarehighlyefficientinthisconversionprocessyetlesscostlymustbedeveloped．

Additionally，environmentalqualitydependsonourabilitytocontrolairandwaterpollution．Pollutioncontroltechniquesemployvariousmaterials．Inaddition,materialsProcessingandrefinementmethodsneedtobeimprovedsothattheyproducelessenvironmentaldegradation，thatis，lesspollutionandlessdespoilageofthelandscapefromminingofrawmaterials．Also，insomematerialsmanufacturingprocesses，toxicsubstancesareProduced，andtheecologicalimpactoftheirdisposalmustbeconsidered.

Manymaterialsthatweusearederivedfromresourcesthatarenoenewable，thatisnotcapableofbeingregenerated．Theseincludepolymers，forwhichtheprimerawmaterialisoil，and