第1页共63页编号:时间:2021年x月x日书山有路勤为径,学海无涯苦作舟页码:第1页共63页1.MetalsandTheirUseItisknownthatmetalsareveryimportantinourlife.Metalshavethegreatestimportanceforindustry.Allmachinesandotherengineering[]constructionshavemetal[]parts;someofthemconsistonlyofmetalparts.Therearetwolargegroupsofmetals:1)Simplemetal-moreorlesspurechemicalelements[]2)Alloys[]-materialsconsistingofasimplemetalcombinedwithsomeotherelements.Abouttwothirdsofallelementsfoundintheeartharemetals,butnotallmetalsmaybeusedinindustry.Thosemetalswhichareusedinindustryarecalledengineeringmetals.Themostimportantengineeringmetalisiron[],whichintheformofalloyswithcarbon[]andotherelements,findsgreaterusethananyothermetal.Metalsconsistingofironcombinedwithsomeotherelementsareknownasferrous[]metals;alltheothermetalsarecallednonferrous[]metals.Themostimportantnonferrousmetalarecopper[],aluminum[],lead[],zinc[],tin[],butallthesemetalsareusedmuchlessthanferrousmetals,becausetheferrousmetalsaremuchcheaper.Engineeringmetalsareusedinindustryintheformofalloysbecausetheproperties[]ofalloysaremuchbetterthanthepropertiesofpure[]metals.Onlyaluminummaybelargelyusedintheformofsimplemetal.Metalshavesuchagreatimportancebecauseoftheirusefulpropertiesortheirstrength,hardness,andtheirplasticity[].Differentmetalsareproducedindifferentways,butalmostallthemetalarefoundintheformsofmetalore[](ironore,copperore,etc[etcetra].)Theoreisamineral[]consistenceofametalcombinedwithsomeimpurities[].Inordertoproduceametalfromsomemetalore,wemustseparatetheseimpuritiesfromthemetalthatisdonebymetallurgy[].2.PlasticsandOtherMaterialsPlastics[]havespecificpropertieswhichmaymakethempreferable[]totraditionalmaterials[]forcertainuses.Incomparison[]withmetals,forexample,plasticshavebothadvantagesanddisadvantages.Metalstendtobecorroded[]byinorganic[]acids[],suchassulphuric[]acidandhydrochloric[]acid.Plasticstendtoberesistanttotheseacids,butcanhavedissolvedordeformedbysolvent[],suchascarbontetrachloride[],whichhavethesamecarbonbaseastheplastics.Colormustbeappliedtothesurfaceofmetals,whereasitcanbemixedinwithplastics.Metalsaremorerigid[]thanmostplasticswhileplasticsareverylight,withaspecific[]gravitynormallybetween0.9and1.8.Mostplasticsdonotreadily[]conduct[]heatorelectricity[].Plasticssoftenslowlyandcaneasilybeshaped[]whentheyaresoft.塑料具有特殊的性能。对于某种用途而言,这些性能使得塑料比传统材料更为可取。例如,跟金属相比较,塑料既有优点也有缺点。金属易受到无机酸的腐蚀,如硫酸和盐酸,塑料能抵抗这些酸的腐蚀,但可被溶剂所洛解或引起变形,例如溶剂四氯化碳与塑料具有同样的碳基。颜色必定只能涂到金属的表面。而它可以跟塑料混合为一体。金属比大多数塑料刚性要好,而塑料则非常之轻,通常塑第2页共63页第1页共63页编号:时间:2021年x月x日书山有路...