文件背景PPT

MSE120-1999Hightemperatureprocessesforproducingmaterials.(includingsemiconductorgradesilicon)ismadebyprocessesthatatsomepointusehightemperatures.Inproducingceramicparts,hightemperature“sintering”iscommon.Thispartofthecourseisthereforedevotedtosomeofthosehightemperatureoperations.[By“hightemperatures”ismeanttemperaturesbetweenabout400and15000C.]Earlierwelearnedthatmanyoxidescanbereducedtometalsbytheinexpensivereducingagentscarbonandhydrogenathightemperatures.However,asshownonthenextslide,manyoresexistassulfides.MSE120-1999Oxideandsulfideores.Aluminumoccursinthelithosphereasanoxide.Ironasoxides(mostly).Copperasbothsulfidesandoxides.Nickel(ditto).Zincassulfides.Siliconasoxides.Leadassulfides.Goldandsilverasmetals.Magnesiumaschloride(inthehydrosphere).MSE120-1999Theproblemwithsulfides...…isillustratedintheEllinghamdiagramforsulfides(nextslide)whichshouldbecontrastedwiththeEllinghamdiagramforoxides.Incontrasttotheoxidediagram,thelinesfortheinexpensivereducingagentscarbonandhydrogen(goingtotheirsulfides)liehighinthediagram.Consequentlythesulfidesofmostmetalscannotsimplybereactedwithcarbonorhydrogentoproducethemetal.Expressedanotherway,neithercarbonnorhydrogenhavesufficientaffinityforsulfurtobeusedtoremovesulfurfrommostmetalcompounds.MSE120-1999Ellinghamdiagramforsulfides.MSE120-1999EllinghamdiagramforoxidesMSE120-1999Alternativeprocessesforsulfides....…areillustratedonthenextslide.Onepossibilityistooxidizethesulfidetoanoxideandthencarbonorhydrogencanbeusedtoreducetheoxide.Thisworksfineformetalsthathaveahighaffinityforoxygen(i.emetalsabouthalf-waydowntheEllinghamdiagramforoxides,orlower,zincisagoodexample)andiscarriedoutinanoperationknownas“roasting”.Analternativeroutecanbeusedformetalswithaloweraffinityforoxygen(e.gcopper);thisalternativereliesonoxidizingthesulfidetometal(ratherthanoxide)andisknownas“smelting”.MSE120-1999Alternativeprocessesforsulfides(cont).MSE120-1999Alternativeprocessesforsulfides(cont).ThepredominancediagramfortheCu-S-OsystemappearsinthenextslideandshouldbecontrastedwiththatforNishownearlierinthecourse.ForNi,whichhasafairlyhighaffinityforoxygen,theareaofthepredominancediagramwherethemetalexistsissmall.Forcopperitisquitelargeanditispossibletoengineertheoxidationofcoppersulfidetooperateinthemetalpredominantregion.Wewillreturntocoppersmeltinglater.Butfirstlet’slookatroasting.MSE120-1999Cu-O-Spredominancediagram.MSE120-1999Ni-O-Spredominancediagram.MSE120-1999Roasting.Theobjectiveisusuallytoremove(ordiminish)thesulfurcontentofaconcentratebyoxidation.E.gforaleadconcentrate:2PbS+3O2=2PbO2+SO2Suchreactionsaretypicallyexothermicandtheheatproducedisusuallysufficienttobringthereactantsuptoreactiontemperature.Theequipmentisillustratedinthenextfourslides(seereaderfordetails).MSE120-1999Roasting(cont).MSE120-1999Roasting(cont).MSE120-1999Roasting(cont).MSE120-1999Roasting(cont).MSE120-1999Roasting(cont).Althoughtheobjectiveofroastingistoproduceoxidefromsulfide,thereexiststhepossibilityofproducingsulfates,asillustratedforthePb-O-Ssysteminthenextslide.Goodcontroloftemperatureandgascompositionarerequiredtoavoidsulfateformation.Whichofthefourreactorsillustratedmightbemostsuitableforthis?MSE120-1999Predominancediagram,Pb-S-OMSE120-1999Calcining...…..isthetermusedforthermaldecompositionofsolids,e.g.CaCO3=CaO+CO2andisfrequentlydoneinrotarykilns.Thesetypesofreactionsareusuallyendothermicandfuelmustbeburnttosustainthem.Bothroastingandcalciningareshrinkingcoretypereactions(seenextslide)MSE120-1999Morphologyofroastingandcalciningreactions.Theseareidealizationsofhowreactionproceeds.Nowtoreturntotheoverallschemeofprocessingoxidesandsulfides.MSE120-1999Generalschemeforprocessingoxidesorsulfides.MSE120-1999Reduction….…isthetechnologybywhichoxidesareturnedintometals.Theoxidescouldbenaturallyoccurringortheycouldbeproducedbyroastingsulfides.Thereadergivesyoumuchinformationonthereductionofzincoxidebutthismethodofproducingzincisbecomingobsoletesowewillnottreatitinclass.However,pleasereadsection8.5.1onzincproduction(aswellastheotherpartsofthischapter);itcontainssomeinterestingthermodynamics/kinetics.Themainindustrialunitwherereduction(ofironoxidestometal)iscarriedoutis….MSE120-1999….Theironblastfurnace.MSE120-1999Theironblastfurnace(cont).Thestructureisofsteelwitharefractorybricklining(inertoxidesintheupperregionofthefurnacecarbonblocksinthehearth).About15minsidediameter(atitswidest)and50mhigh.Producingabout4,000tonsmoltenironperday.Mostofthefurnaceisfilledwithadescendingandreactingmixtureofcoke,ironoreandlimestonewhicharefedinatthetop.Surroundingthefurnaceatthebottomisagasmain(“bustlepipe”)carryingpreheatedair(the“blast”)tothefurnace.Theairflowsintothebottomofthefurnace(the“bosh”)throughpipescalled“tuyeres”.Thisairburnspartofthecoke,producingtheheatneededforendothermicreactionsandforbringingthesolidsuptothehightemperaturewheretheyreact.Alsocarbonmonoxideisproducedandthistoocanreduceoxides.Periodicallythemoltenironistappedfromthefurnaceandthemo