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1、1.MetalsandTheirUseItisknownthatmetalsareveryimportantinourlife.Metalshavethegreatestimportanceforindustry.Allmachinesandotherengineering[7endVi5niEriN]constructionshavemetal[5metl]parts;someofthemconsistonlyofmetalparts.Therearetwolargegroupsofmetals:1)Simpleme
2、tal-moreorlesspurechemicalelements[5elimEnt]2)Alloys[5AlCi]-materialsconsistingofasimplemetalcombinedwithsomeotherelements.Abouttwothirdsofallelementsfoundintheeartharemetals,butnotallmetalsmaybeusedinindustry.Thosemetalswhichareusedinindustryarecalledengineerin
3、gmetals.Themostimportantengineeringmetalisiron[5aiEn],whichintheformofalloyswithcarbon[5kB:bEn]andotherelements,findsgreaterusethananyothermetal.Metalsconsistingofironcombinedwithsomeotherelementsareknownasferrous[5ferEs]metals;alltheothermetalsarecallednonferro
4、us[5nCn5ferEs]metals.Themostimportantnonferrousmetalarecopper[5kCpE],aluminum[E5lju:minEm],lead[li:d],zinc[ziNk],tin[tin],butallthesemetalsareusedmuchlessthanferrousmetals,becausetheferrousmetalsaremuchcheaper.Engineeringmetalsareusedinindustryintheformofalloysb
5、ecausetheproperties[5prCpEti]ofalloysaremuchbetterthanthepropertiesofpure[pjuE]metals.Onlyaluminummaybelargelyusedintheformofsimplemetal.Metalshavesuchagreatimportancebecauseoftheirusefulpropertiesortheirstrength,hardness,andtheirplasticity[plAs5tisiti].Differen
6、tmetalsareproducedindifferentways,butalmostallthemetalarefoundintheformsofmetalore[C:(r)](ironore,copperore,etc[etcetra].)Theoreisamineral[5minErEl]consistenceofametalcombinedwithsomeimpurities[im5pjuEriti].Inordertoproduceametalfromsomemetalore,wemustseparateth
7、eseimpuritiesfromthemetalthatisdonebymetallurgy[me5tAlEdVi].2.PlasticsandOtherMaterialsPlastics[5plAstik,plB:stik]havespecificpropertieswhichmaymakethempreferable[5prefErEbl]totraditionalmaterials[mE5tIErIEl]forcertainuses.Incomparison[kEm5pArisn]withmetals,fore
8、xample,plasticshavebothadvantagesanddisadvantages.Metalstendtobecorroded[kE5rEud]byinorganic[7inC:5^Anik]acids[5AsId],suchassulphuric[sQl5fjuErik]acidandhydrochloric[
