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