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1、StyleofmaterialsMaterialsmaybegroupedinseveralways.Scientistsoftenclassifymaterialsbytheirstate:solid,liquid,orgas.Theyalsoseparatethemintoorganic(onceliving)andinorganic(neverliving)materials.Forindustrialpurposes,materialsaredividedintoengineeringmaterialsornonengineeringmaterials.Engineerin
2、gmaterialsarethoseusedinmanufactureandbecomepartsofproducts.Nonengineeringmaterialsarethechemicals,fuels,lubricants,andothermaterialsusedinthemanufacturingprocess,whichdonotbecomepartoftheproduct.Engineeringmaterialsmaybefurthersubdividedinto:①Metal②Ceramics③Composite④Polymers,etc.MetalsandMet
3、alAlloysMetalsareelementsthatgenerallyhavegoodelectricalandthermalconductivity.Manymetalshavehighstrength,highstiffness,andhavegoodductility.Somemetals,suchasiron,cobaltandnickel,aremagnetic.Atlowtemperatures,somemetalsandintermetalliccompoundsbecomesuperconductors.Whatisthedifferencebetweenan
4、alloyandapuremetal?Puremetalsareelementswhichcomefromaparticularareaoftheperiodictable.Examplesofpuremetalsincludecopperinelectricalwiresandaluminumincookingfoilandbeveragecans.Alloyscontainmorethanonemetallicelement.Theirpropertiescanbechangedbychangingtheelementspresentinthealloy.Examplesofm
5、etalalloysincludestainlesssteelwhichisanalloyofiron,nickel,andchromium;andgoldjewelrywhichusuallycontainsanalloyofgoldandnickel.Whyaremetalsandalloysused?Manymetalsandalloyshavehighdensitiesandareusedinapplicationswhichrequireahighmass-to-volumeratio.Somemetalalloys,suchasthosebasedonaluminum,
6、havelowdensitiesandareusedinaerospaceapplicationsforfueleconomy.Manyalloysalsohavehighfracturetoughness,whichmeanstheycanwithstandimpactandaredurable.Whataresomeimportantpropertiesofmetals?Densityisdefinedasamaterial’smassdividedbyitsvolume.Mostmetalshaverelativelyhighdensities,especiallycompa
7、redtopolymers.Materialswithhighdensitiesoftencontainatomswithhighatomicnumbers,suchasgoldorlead.However,somemetalssuchasaluminumormagnesiumhavelowdensities,andareusedinapplicationsthatrequireothermetallicpropertiesbutalsorequirelowweigh
