processesforproducingmaterials.Introduction.Allofoursteel,copper,aluminumandsilicon(includingsemiconductorgradesilicon)ismadebyprocessesthatatsomepointusehightemperatures.Inproducingceramicparts,hightemperature“sintering”iscommon.Thispartofthecourseisthereforedevotedtosomeofthosehightemperatureoperations.[By“hightemperatures”ismeanttemperaturesbetweenabout400and15000C.]Earlierwelearnedthatmanyoxidescanbereducedtometalsbytheinexpensivereducingagentscarbonandhydrogenathightemperatures.However,asshownonthenextslide,manyoresexistassulfides.Oxideandsulfideores.Aluminumoccursinthelithosphereasanoxide.Ironasoxides(mostly).Copperasbothsulfidesandoxides.Nickel(ditto).Zincassulfides.Siliconasoxides.Leadassulfides.Goldandsilverasmetals.Magnesiumaschloride(inthehydrosphere).Theproblemwithsulfides...…isillustratedintheEllinghamdiagramforsulfides(nextslide)whichshouldbecontrastedwiththeEllinghamdiagramforoxides.Incontrasttotheoxidediagram,thelinesfortheinexpensivereducingagentscarbonandhydrogen(goingtotheirsulfides)liehighinthediagram.Consequentlythesulfidesofmostmetalscannotsimplybereactedwithcarbonorhydrogentoproducethemetal.Expressedanotherway,neithercarbonnorhydrogenhavesufficientaffinityforsulfurtobeusedtoremovesulfurfrommostmetalcompounds.Alternativeprocessesforsulfides....…areillustratedonthenextslide.Onepossibilityistooxidizethesulfidetoanoxideandthencarbonorhydrogencanbeusedtoreducetheoxide.Thisworksfineformetalsthathaveahighaffinityforoxygen(i.emetalsabouthalf-waydowntheEllinghamdiagramforoxides,orlower,zincisagoodexample)andiscarriedoutinanoperationknownas“roasting”.Analternativeroutecanbeusedformetalswithaloweraffinityforoxygen(e.gcopper);thisalternativereliesonoxidizingthesulfidetometal(ratherthanoxide)andisknownas“smelting”.Alternativeprocessesforsulfides(cont).Alternativeprocessesforsulfides(cont).ThepredominancediagramfortheCu-S-OsystemappearsinthenextslideandshouldbecontrastedwiththatforNishownearlierinthecourse.ForNi,whichhasafairlyhighaffinityforox...
