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1、SOLGELTECHNOLOGY1.IntroductionSolgeltechnologyisafieldofgrowingimportanceandthesubjectoftextbooks(1,2).Inpractice,althoughorganicgelsexist,thisfieldreallydesignatesagroupofprocessingtechniquestosynthesizematerialsinwhichonecomponentatleastisinorganic.Neverth
2、eless,alargevarietyoforganicinorganichybridorevenbiochemicalinorganichybridmaterialsarenowbeingdeveloped.Whenmadebysolgelprocessing,allthesematerialsareachievedafterasuccessionoftransformationsbeginningwithchemicalcompoundsknownasprecursors.Thefirstchemical
3、step,whichiscarriedoutinliquidmediumatnearroomtempera-ture,transformstheseprecursorstoadispersedcolloidalstate.Thelattercanbeeitherasolorapolymericsolution.Inthesecondstep,thepreviousdispersedcolloidalstateismadetotransformtoaninterconnectedcolloidalstatek
4、nownasagel.Inathirdstep,agelusuallyneedstobedried.Finally,itmaypossiblybetransformedtoadenseceramicbythermaltreatmentathighertemperatures.2.OverviewofSolGelTechnology2.1.MainDefinitions.Adispersedcolloidisadividedstateofsolidmat-ter,suchthateachindividualco
5、lloidalparticlecanbemaintainedinsuspension,eitherinaliquidorinagas.Thedrivingforceresponsibleforsuchasuspendedstateisprovidedbythelocalthermalenergy,thatistosaythelocaltemperature,whichkeepsthecolloidalparticlesunderconstantandrandomagitationknownasBrownia
6、nmotion.Thisthermaldrivingforcemustbeofamagnitudelargerthantheactionofgravity,whichmeansthateachparticlemusthaveaverysmallmass.Inpractice,thisconditioncanbesatisfiedwitharangeofparticleswithverydifferentshapes.Colloidalparticlesareoftennearlysphericalwithas
7、izethatdependsonthenatureofthematerial,typically<0.2mmwithoxides.Ortheycanbeplate-likeparticleswithanextentintheplatethatcanexceed1mmwhilethethicknessistypically<0.1mm,suchasoccurringinsomeclaysuspen-sions.Ortheycanbemorelinearpolymericmoleculesoftenobserv
8、edinorganicchemistry,withanindividualmasssimilartothatoftheprevioussphericaloxideparticles.Inbothformerexamples,asoldesignatesastablesuspensionofcolloi-dalparticleswithinaliquid,whileinthethirdoneitdesignates
