1141_Nanocorundum—advanced-synthesis-and-processing

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1、NanoStructuredMaterials,Vol.11,No.8,pp.1141±1153,1999ElsevierScienceLtdPergamonCopyright©2000ActaMetallurgicaInc.PrintedintheUSA.Allrightsreserved.0965-9773/99/$±seefrontmatterPIIS0965-9773(99)00405-5NANOCORUNDUMÐADVANCEDSYNTHESISANDPROCESSINGA.Krellan

2、dH.MaFraunhoferInstituteofCeramicTechnologiesandSinteredMaterials(IKTS),01277Dresden,Germany(ReceivedJuly22,1999)(AcceptedNovember21,1999)AbstractÐInorganicandorganicapproachesforthesynthesisofnanocorundumpowdersandproductsaredescribedonascaleof50gbatc

3、hes.Themedianparticlesizeofthevolumedistributionofredispersedpowdersisabout50nmaftercalcinationatT,950°C.Akeyissueofadvancedprocessingisthepreparationofdensesinteredbodiesatasinteringtemperature,1300°Cwithasubmicrometergrainsize;thebodiesarelargeenough

4、toenablethemeasurementofaVickersmacrohardness.21GPaatatestingloadof10kg.Poroussinteredcorundumbodieswithanaverageporesizebetween15and60nmandaporosityofabout40±55%havebeenproducedwithintheframeworkofthedescribedsynthesisbybothpowderorsol/geltechnologies

5、fortheuseaschemicallyhighlystablefiltrationmembranesorascatalystsupports.Otherapplicationsareamorphousorcrystallinenanoporousproductswithaverageporesizesofabout1nm.©2000ActaMetallurgicaInc.IntroductionAluminaisoneofthemostimportantceramicsforstructural

6、applications,preferentiallyinthechemicallymoststableformofcorundum(}-Al2O3).Decreasinggrainsizeshavebeenshowntoimprovethehardnessandwearresistanceofdensesinteredproducts(1)aswellastheirstrengthifadvancedshapingapproachesavoiddefectsastheyareusuallyasso

7、ciatedwiththeincreasingtendencyoffine-grainedrawpowderstoagglomerate(2).Anothermotivationtodevelopextremelyfinegrainedcorundumpowderscomesfromtheincreasingmarketforporousaluminaceramicsusedforultrafil-trationmembranesandcatalystsupports.Inalltheseappli

8、cationscorundum(a-Al2O3)isthepreferredphasebecauseoftworeasons:(i)itischemicallymuchmoreresistantthantransitionalaluminaphases,and(ii)allapproachesstartingwithmetastablealuminasortheirprecursorsfacetheproblemofasequenceofnucleationcontr