2020年材料专业英语课件： CLASSIFICATION OF MATERIALS.doc

材料专业英语课件： Classification of Materials BasicClassificationsandEngineeringMaterials Solidmaterialshavebeenconvenientlygroupedintothreebasicclassifications：metals，ceramicsandpolymersThisschemeisbasedprimarilyonchemicalmakeupandatomicstructure,andmostmaterialsfallintoonedistinctgroupingoranother，althoughtherearesomeintermediates.Inaddition，therearethreeothergroupsofimportantengineeringmaterialsposites，semiconductor，andbiomaterialsCompositesconsistofbinationsoftwoormoredifferentmaterials，whereassemiconductorsareutilizedbecauseoftheirunusualelectricalcharacteristics；biomaterialsareimplantedintothehumanbodyAbriefexplanationofthematerialtypesandrepresentativecharacteristicsisofferednext Metals：MetallicmaterialsarenormallybinationsofmetallicelementsTheyhavelargenumbersofnonlocalizedelectrons；thatis，theseelectronsarenotboundtoparticularatoms.ManypropertiesofmetalsaredirectlyattributabletotheseelectronsMetalsareextremelygoodconductorsofelectricityandheat，andarenottransparenttovisiblelight：apolishedmetalsurfacehasalustrousappearanceFurthermore，metalsarequitestrong，yetdeformable，whichaountsfortheirextensiveuseinstructuralapplications Ceramics：Ceramicsarepoundsbetweenmetallicandnonmetallicelements：theyaremostfrequentlyoxides,nitrides，andcarbidesThewide rangeofmaterialsthatfallswithinthisclassificationincludesceramicsthatareposedofclayminerals，cement，andglass.Thesematerialsaretypicallyinsulativetothepassageofelectricityandheat，andaremoreresistanttohightemperaturesandharshenvironmentsthanmetalsandpolymersWithregardtomechanicalbehavior，ceramicsarehardbutverybrittle Polymers：PolymersincludethefamiliarplasticandrubbermaterialsManyofthemareorganicpoundsthatarechemicallybasedoncarbon，hydrogen，andothernonmetallicelements；furthermore，theyhaveverylargemolecularstructuresThesematerialstypicallyhavelowdensitiesandmaybeextremelyflexible Composites：AnumberofpositematerialshavebeenengineeredthatconsistofmorethanonematerialtypeFiberglassisafamiliarexample，inwhichglassfibersareembeddedwithinapolymericmaterial.ApositeisdesignedtodisplayabinationofthebestcharacteristicsofeachoftheponentmaterialsFiberglassacquiresstrengthfromtheglassandflexibilityfromthepolymerManyoftherecentmaterialdevelopmentshaveinvolvedpositematerials Semiconductors：SemiconductorshaveelectricalpropertiesthatareintermediatebetweentheelectricalconductorsandinsulatorsFurthermore，theelectricalcharacteristicsofthesematerialsareextremelysensitivetothepresenceofminuteconcentrationsofimpurityatoms，whichconcentrationsmaybecontrolledoververysmallspatialregionsThesemiconductorshavemade possibletheadventofintegratedcircuitrythathastotallyrevolutionizedtheelectronicsandputerindustriesoverthepasttwodecades Biomaterials:BiomaterialsareemployedinponentsimplantedintothehumanbodyforreplacementofdiseasedordamagedbodypartsThesematerialsmustnotproducetoxicsubstancesandmustbepatiblewithbodytissue(iemustnotcauseadversebiologicalreactions)Alloftheabovematerials-metals，ceramics，polymers，positesandsemiconductors-maybeusedasbiomaterialsForexample，someofthebiomaterialssuchasCFC(carbonfiberscarbon)andCFPS(polysulfone)areutilizedinartificialhipreplacements AdvancedMaterials Materialsthatareutilizedinhigh-technology(orhigh-tech)applicationsaresometimestermedadvancedmaterialsByhightechnologywemeanadeviceorproductthatoperatesorfunctionsusingrelativelyintricateandsophisticatedprinciples；examplesincludeelectronicequipment(VCRs，CDplayers，etc)，puters，fiberopticsystems，spacecraft，aircraft，andmilitaryrocketryTheseadvancedmaterialsaretypicallyeithertraditionalmaterialswhosepropertieshavebeenenhancedornewlydeveloped，highperformancematerialsFurthermore，theymaybeofallmaterialtypes(egmetals，ceramics，polymers)，andarenormallyrelativelyexpensive ModernMaterialsNeeds Inspiteofthetremendousprogressthathasbeenmadeinthedisciplineofmaterialsscienceandengineeringwithinthepastfewyears，therestillremaintechnologicalchallenges，includingthedevelopmentofevenmoresophisticatedandspecializedmaterials，aswellasconsiderationoftheenvironmentalimpactofmaterialsproductionSomementisappropriaterelativetotheseissuessoastoroundoutthisperspective Nuclearenergyholdssomepromise，butthesolutionstothemanyproblemsthatremainwillnecessarilyinvolvematerialsfromfuelstocontainmentstructuresandfacilitiesforthedisposalofradioactivewaste SignificantquantitiesofenergyareinvolvedintransportationReducingtheweightoftransportationvehicles(automobiles，aircraft，trains，etc)，aswellasincreasingengineoperatingtemperatures，willenhancefuelefficiencyNewhighstrength，lowdensitystructuralmaterialsremaintobedeveloped，aswellasmaterialsthathavehighertemperaturecapabilities，foruseinengineponents Furthermore，thereisarecognizedneedtofindnew，economicalsourcesofenergy，andtousethepresentresourcesmoreefficientlyMaterialswillundoubtedlyplayasignificantroleinthesedevelopmentsForexample，thedirectconversionofsolarenergyintoelectricalenergyusessiliconmaterialsToensureaviabletechnology，materialsthatarehighlyefficientinthisconversionprocessyetlesscostlymustbedeveloped Additionally，environmentalqualitydependsonourabilitytocontrolairandwaterpollutionPollutioncontroltechniquesemployvariousmaterialsInaddition,materialsProcessingandrefinementmethodsneedtobeimprovedsothattheyproducelessenvironmentaldegradation，thatis，lesspollutionandlessdespoilageofthelandscapefromminingofrawmaterialsAlso，insomematerialsmanufacturingprocesses，toxicsubstancesareProduced，andtheecologicalimpactoftheirdisposalmustbeconsidered. Manymaterialsthatweusearederivedfromresourcesthatarenoenewable，thatisnotcapableofbeingregeneratedTheseincludepolym