纳米材料和纳米结构第五讲.ppt

纳米材料和纳米结构Basedoninorganicpolymerizationreactions（无机聚合反应）
Usedtoprepareinorganicoxides,suchasglassesorceramics,especiallymulticomponentsystems（多组分体系）
Beabletocontrolthestructureonnanoscalefromtheearlieststagesofprocessing
Easytoobtainnanostructuredgrainswithcompositionalhomogeneity（组分均匀性）,higherpurity,lowerprocessingtemperaturesoverbothconventionalceramicprocessingandtraditionalglassmeltingbycontrollingthechemicaladditives（添加剂）andprocessing,butwithoutadoptingvacuumconditionsThesol-geltechniquetomaterialsynthesisisbasedonsomeorganicprecursors（先驱物）,andthegelsmayformbynetworkgrowthfromanarrayofdiscreteparticlesorbyformationofaninterconnected3-Dnetworkbythesimultaneoushydrolysisandpolycondensation（缩聚作用）oforganometallic（有机金属）precursors.ThesizeofthesolparticlesdependuponsomevariablefactorssuchaspH,solutioncomposition,andtemperatureetc..Bycontrollingtheexperimentalconditions,onecanobtainthenanostructuredtargetmaterialsintheformofpowderorthinfilm.Basedonthedifferenceoftheprecursorsused,thesol-gelprocessingisroughlydividedintothreegroups:
Silica（二氧化硅）sol-gelprocessing
Metalalkoxide（金属醇盐）processing
Pechini-typeprocessingThewholesilicasol-gelprocessingcouldbedividedintothreesteps:hydrolysisandpolycondensation,gelationanddrying.Thehydratedsilicatetrahedra（水合硅氧四面体）interactinacondensationreaction（缩合反应）,formingbonds:ThehydrolysisandpolycondensationreactionsinitiateatnumeroussiteswithintheTMOS+H2Osolutionasmixingoccurs.Whensufficientinterconnectedbondsareformedinaregion,theyrespondcooperativelyascolloidalparticlesorasol.Theshapeandsizeofpolymeric（聚合的）structuralunitsaredeterminedbytherelativevaluesoftherateconstantsforhydrolysis(kH)andpolycondensationreactions(kC)
Toreducetheparticlesize,kHshouldbelargerthanKC
Fasthydrolysisandslowcondensationfavorformationoflinearpolymers
Slowhydrolysisandfastcondensationleadtolarger,bulkier,andmoreramified（网眼状的）polymerskHincreaseslinearlywiththeconcentrationofH+orH3O+inacidicmedia
andwiththeconcentrationofOH-inbasicmedium;
Forbasicconditions,distri