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1、NanoStructuredMaterials,Vol.11,No.8,pp.1219±1229,1999ElsevierScienceLtdPergamonCopyright©2000ActaMetallurgicaInc.PrintedintheUSA.Allrightsreserved.0965-9773/99/$±seefrontmatterPIIS0965-9773(99)00412-2NOVELSYNTHESISOFAl13-CLUSTERBASEDALUMINAMATERIALSM.Wangan
2、dM.MuhammedMaterialsChemistryDivision,DepartmentofMaterialsScienceandEngineering,RoyalInstituteofTechnology,SE-10044Stockholm,Sweden(ReceivedOctober30,1999)(AcceptedNovember5,1999)71AbstractÐThepolyoxocationAl13O4(OH)24(H2O)12,knownasanAl13cluster,hasbeensy
3、nthesizedbycontrolledohydrolysisofaluminum(III)aqueoussolutionat70C,andpHbetween5.0and6.0.Theformationofthe7127polyoxocationAl13O4(OH)24(H2O)12insolutionwasexperimentallyconfirmedbyAlNMR.TheAl13cluster-containingpowderwasobtainedbyprecipitatingthepolyoxoalu
4、minateionfromthesolutionbytheadditionofasuitablesalt,e.g.sodiumsulphateorammoniaoxalate.TheobtainedpowderwascharacterizedbyTGA,XRD,andSEM.Itwasfoundthatthesulfate-precipitatedpowderhadthreedifferentcrystalstructures,i.e.monoclinicfiber,monoclinicrectanglesh
5、apedcrystalandtetrahedralshapedcrystal,whiletheoxalatepowderobtainedfromtheoxalateprecipitationwasaspherical-particlespowderwithparticlesizearound200nm.XRDoftheAl13-sulfateshowedthatthepowderconsistedofacubicphasewithaunitcellsizeof17.9Å.Aftercalcinationoft
6、heAl13-sulfateandAl13-oxalatesaltsat1000°C,thepowderwasconvertedtoa-alumina.Thea-aluminapowderobtainedfromtheoxalateroutewasabout100to200nmindiameter.©2000ActaMetallurgicaInc.IntroductionAluminabasedceramicmatrixcomposites(CMC),haveseveralusefulapplications
7、,e.g.,incuttingtools,heatexchangers,enginecomponents,marinehardware,andpumps,etc[1±6].Thecompositionrangevariesfromvirtuallypureoxidewithnoadditionstoalumina-basedcompositescontainingmanyotherconstituentstomeetthedifferentrequiredpropertiesandapplicationreq
8、uirements[1±4].Thesizeandhomogeneityofalumina-basedcomposites,aretwoimportantfactors,whichgreatlyinfluencethepropertiesoftheceramicmaterial[5,6].Furthermore,thedecreaseoftheparticlesizetothenanophasere
