陶瓷材料制备2.pdf

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1、Precursorsforsol-gelHydrolysisbehaviorofvariousyttriumprecursorsHydrolysisratioh=[HO]/M2LigandCompoundremoved0.131015CrystallineAmorphousAmorphousYO(OPri)OPri513precipitateprecipitateprecipitateTransparentgelTransparentgel[Y(OR)]NoeffectOCHOMe310(t=15min)(t=15min)2

2、4AcidiccatalysisacacfirstY(OAc)(acac)NoeffectNoprecipitate224(precipitate)ThenOAcFibersY(OR)(acac)NoeffectNoprecipitateOCHOMe354after≈7days24L.G.Hubert-Pfalzgrafetal.,MRSSymp.Proc.,Vol.180,1990,p73.Precursorsforsol-gelRolesofacetylacetone:(1)decreasinghydrolysisrat

3、e;(2)modifiertocauselinear-chainpolymerization(1-Drubberypolymers).HCCHCH33CCOOTi(OPri)+2acacPriO-Ti-O-Pri+2PriOH4OOCCHCCHCH33Precursorsforsol-gelOtherorganicchelatingagentstocauserubberypolymerization:(1)ethylenediamine(en);(2)diethylenetriamine(DETA);(3)aceticaci

4、d.iiiiTi(OPr)+AcOH→[Ti(OPr)(OAc)H]→Ti(OPr)(OAc)+PrOH43CH3COOPriOOPriOPriAlesshydrolyzablebidentatedbridgingalkoxideisyeldedandTiTiPriOOPriOPrihenecethegelationtimeOOincreases.CCH3Multicomponentoxidespreparationbysol-gelThehydrolysisratesofdifferentprecursorsshouldb

5、ematchedinordertogetahomogeneousgel:(1)Usingchelatingorganicligandstocontrolthehydrolysisrateofthemorereactivealkoixdes;(2)Adoptingprehydrolysisoflessreactivealkoxides;(3)Usingcomplexalkoxidesasprecursors.6.4StöberprocessandOstwaldripening•Ostwaldripening:Smallpart

6、iclesdissolvefasterthanlargerparticles.Astheprocessisdynamicandreversible,smallerparticlesmaybedissolvedtofeedgrowthofthelargerparticles.•Thegrowthstopswhenthedifferenceinsolubilitybetweenthelargestandsmallestparticleisafewppm.•Itisthereforepossibletopreparespheric

7、al,non-porous,highlymonodispersesilicaparticles(Stöberparticles)whichhavediametersofseveral100nmfromagel.W.Stöber,A.Fink,andE.Bohn.1968.J.ColloidInterfaceSci.,26,62OriginofOstwaldripeningP(r)2γVln=lvmKelvinequation(Liq-Vapinterface)PRTr0C(r)2γVln=slmOstwald-Freundl

8、ichequation(Liq-C(∞)RTrsolidinterface)V=molarvolumemγ=surfacetensionr=radiusGibbs-Thomsonequation:Au4γslΔT(r)=T−T(r)=TmmBmmBHρrfsT=Bulkmeltingtem