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1、15Aluminium15.1IntroductionThisisprobablythemostabundantmetalontheearth,astheoxide,aluminaAl2O3,makesupthechiefpartallclaysandmanyotherrocks.ThemetalwasfirstisolatedasapowderbyWohler.Itwasnotuntilabout1854thatitwasobtainedonamanufacturingscale.Aluminumisaverylightmetal.Wei
2、ghingonlyabout2.7timesthatofwater.Anditisthereforeonlyaboutone-thirdtheweightofiron.Itisgoodconductorofelectricity,andalthoughinferiortocopperforthelongdistancetransmissionofelectricpowerowingtoitslightnessandlowercost.Itformsavaluablealloywithcopper,knownasaluminumbronze.
3、Toobtainthebronzeamixtureofcorundum(alumina),charcoalandgranulatedcopperisheatedinanelectricfurnace.Thecarbontakesuptheoxygenofthealumina,whilethecopperuniteswiththealuminumtoformagolden-coloredalloywhichhasgreatstrengthandelasticity.Thedevelopmentofthemotorandaircraftindu
4、striesledtotheintroductionofanumberofaluminumalloysofgreatvalueowingtotheirlightnessandstrength.Themostimportantoftheseare‘magnalium’,containingmagnesium,and‘duralumin’,whichisaluminumwithabout4percentofcopperandalittermagnesium.Otheralloyswithcopper,nickelandzincareusedin
5、theconstructionofmotor-carandaeroplaneparts.Alloysofaluminumandsilicon,withsmallamountsofothersubstances,areusedinshipbuilding,asafterheattreatmenttheyareverystrongandresistthecorrosiveactionofseawater.Aluminumhasbeenmadeformanyyearsbytheelectrolysisofalumina(preparedbauxi
6、te,Al2O3●2H2O)dissolvedinfusedcryolite(sodiumaluminumfluoridethecathode.Thecurrentisbroughtinbythickcarbonrodsformingtheanodewhichwhilecarbonmonoxidegasescapes.Asthemetalisremovedthesupplyofaluminaiskeptupbyaddingmorebauxitetothemoltenmixture.Intheproductionofaluminum,asin
7、somanyotherprocesses,thesourceofpoweristheenergyoffallingwater.FactorieshavebeenbuiltnearmanyofthegreatwaterfallsoftheworldsuchasNiagara.TheFallsoftheRhineatSchaffhausenandinEnglandatKinlochleveninArgyllshire,andinNorthWales.ThebauxiteusedischieflyfromthesouthofFrance,butu
8、sefuldepositsoccurringinthesouthernpartoftheUnitedStates,andAntrim,NorthernIreland.Therem
