陶瓷材料制备1.pdf
?6.1 Introduction?6.2 Solid state reactions for ceramic synthesis?6.3 Wet-chemical routes to ceramics(spray/co-precipitation/complexation/sol-gel process)?6.4 Stber process and Ostwald ripening?6.5 Pechini method?6.6 Glycine-nitrate pyrolysis(GNP)method?6.7 Other wet-chemical methodsChapter 6:Ceramic synthesis and processing1.Introduction.The process(microstructure,homogeneity)The process(microstructure,homogeneity)2.Characteristics of powders.Definitions;particle sizeDefinitions;particle size3.Interaction between powder particles.DLVO theory;suspension stabilityDLVO theory;suspension stability4.Preparation of powders and coatings.Solid state reactions;nucleation Solid state reactions;nucleation crystal growthcrystal growth5.Treatments of powders.Milling,mixing,granulationMilling,mixing,granulation6.Compaction processing.Pressing,extrusion,etcPressing,extrusion,etc7.Thermal processing.Drying,binder burnDrying,binder burn-outout8.Sintering.Solid state sintering;liquid phase sinteringSolid state sintering;liquid phase sinteringLouis Winnubsts Lecture notesCeramic Processing andMicrostructures6.1 Introduction6.1 IntroductionCeramic MaterialsCeramic MaterialsA long history and a great futureA long history and a great futureCeramicsCeramicsUniversiteit Twente Ceramics are inorganic(non-metallic)materials,which are able to withstand elevated temperatures(in excess of 500 C)They are availabe as bulk or as coatings or as powders.For bulk ceramics(in most cases also for coatings)a powder is brought into a form and subsequently a high temperature treatment is given(1000oC)several hours Milling and calcinationsteps repeated several times Powder Simple,cheap processSimple,cheap process Homogeneity,morphology?Homogeneity,morphology?better calleddispersantMilling/mixingMilling/mixingPlanetary millPlanetary millRoller benchRoller benchAttritor mill)():(29.42rpmmunitDVc=V=6575%VcSolid State ReactionsSolid State Reactions Direct reaction of solids to form the final product.In Direct reaction of solids to form the final product.In principle,no decomposition is involved.principle,no decomposition is involved.Solids do not react with solids at room temperature Solids do not react with solids at room temperature even if thermodynamics is favorable.even if thermodynamics is favorable.High temperature must be used.High temperature must be used.SolidSolid-solid reactions are simple to perform,starting solid reactions are simple to perform,starting materials are often readily available at low cost and materials are often readily available at low cost and reactions are reactions are“cleanclean”i.e.do not involve other chemical i.e.do not involve other chemical elements.elements.DisadvantagesDisadvantages include the need for high temperatures,include the need for high temperatures,the possibility of nonthe possibility of non-homogeneity,contamination from homogeneity,contamination from containers etc.containers etc.Solid State Reactions:exampleSolid State Reactions:exampleSynthesis of YBCO,YBaSynthesis of YBCO,YBa2 2CuCu3 3OO7 7-x x Direct reaction between YDirect reaction between Y2 2OO3 3,BaO,BaO2 2,CuOCuO(Reaction(Reaction between three solid components)between three solid components)?Grind to obtain Grind to obtain large surface area large surface area?Press into pellets(contact)Press into pellets(contact)?Heat Heat in alumina boat,temperature profile:in alumina boat,temperature profile:Other precursors may be used,e.g.BaCO3,which may be decomposed to fine grained BaO during the reaction.(+nitrates etc.)Decomposition must be performed in a controlled manner in order to avoid violent decomposition(i.e.choosing an appropriate temperature)Solid State Reactions:general aspectsSolid State Reactions:general aspectsIons in solids are not mobile at low temperatures.At high temperatures,as a rule of thumb,at 2/3 of Tm(of one component)the diffusion is sufficient to achieve solid state reactions.Formation of BaTiO3by reacting BaCO3and TiO2is an example of a seemingly simple reaction but is more complex than expected.BaCO3is decomposed to reactive BaO:(Rock salt,ccp of the oxide anions,Ba2+in octahedral sites),TiO2(Rutile,hcp of oxide ions,Ti4+in half of the octahedral sites)At least three stages are involved in formation of BaTiO3from BaO and TiO2.BaO react with the surface of TiO2,forming nuclei and a surface layer of BaTiO3.Reaction between BaO and BaTiO3to form Ba2TiO4.This is a necessary phase for increasing migration of Ba2+ions.Ba2+ions from the Ba-rich phase migrate into the TiO2phase and form BaTiO3.PowderPowder preparationpreparationSolid State Reaction(SSR)Solid State Reaction(SSR)Few processing stepsFew processing steps?LowLow chemicalchemical homogeneityhomogeneity?LargeLarge irregularirregular particlesparticlesWet chemicalWet chemical BetterBetter morphologymorphology Chemical homogenousChemical homogenous?More processing stepsMore processing steps323232242242322222BaCOTiOBaCO TiOBaCO TiOBa TiOCOBa TiOTiOBaTiO+=+=Solid stateSolid state preparation of preparation of BaTiOBaTiO3 3 perovskiteperovskite powder powder A=BaM=TiSolid State Reactions:general aspectsSolid State Reactions:general aspectsReaction rates depends on:Area of contact between the reacting solids,i.e.surface area and“density”(How to increase surface area?)The rate of nucleation(How to increase rate of nucleation?)Rates of diffusion of ions(and other species)(How to increase?)Disadvantages,e.g.:Nucleation and diffusion related problems(high temperature)Formation of undesired phases(reaction paths)(e.g.BaTi2O5)Homogeneous distribution,especially for dopants,is difficultDifficult to monitor the reaction directly,in-situ?Separation of phases after synthesis is difficultReaction with containers/cruciblesVolatility of one or more of the componentsPrecursor solutionDrying,CalciningPowderPowder preparationSol-GelGelation-Precipitation-Pyrolyis(Citrate,EDTAPechini,Bilcher)ComplexationChemicalDirectEmulsionCo-PrecipitationSpraying techniques-Spray drying-Freeze dryingDispersionPhysicalImmobilisation step6.3 Wet chemical routes6.3 Wet chemical routesPrecursor solutionDrying,CalciningPowderPowder preparationSol-GelGelation-Precipitation-Pyrolyis(Citrate,EDTAPechini,Bilcher)ComplexationChemicalDirectEmulsionCo-PrecipitationSpraying techniques-Spray drying-Freeze dryingDispersionPhysicalImmobilisation stepDispersion6.3.1 6.3.1 Spray techniquesSpray techniques Make small droplets of the precursor solutionMake small droplets of the precursor solution Disperse droplets in a second phase Disperse droplets in a second phase Each droplet is a separate Each droplet is a separate“containercontainer”Liquid is removed from the Liquid is removed from the“containercontainer”(spray/freeze drying)(spray/freeze drying)Only Only inhomegeneitiesinhomegeneities within the dried dropletwithin the dried droplet CalcinationCalcination?solid state reactionsolid state reactionDroplet generation by ultrasonic methods:?Spray roasting or liquid aerosol thermolysisSpray roastingSpray roastingDispersionPrecursor solution(metal salts)Nebulization(ultrasonic)DryingCalcination Control of homogeneity at Control of homogeneity at small levelsmall level Droplet size a/o dependent Droplet size a/o dependent on frequencyon frequencySpray roastingSpray roastingUltrasonic Ultrasonic nebulationnebulation of precursor solutionof precursor solutionDroplet size dDroplet size dg g:Water:Water:750 kHz:5 750 kHz:5 mm2.5 MHz:2 2.5 MHz:2 mm324Fdg=:surface tension:surface tension:density of liquiddensity of liquidF:F:(ultrasonic)frequency(ultrasonic)frequencyDispersionFinal particle size Final particle size d dp p:of a dof a denseense particleparticleddMMCpgi=003MM0 0:molecular weight:molecular weight of of oxideoxideMMi i:molecular weight:molecular weight of of saltsaltC:concentration in precursor solutionC:concentration in precursor solution 0 0:density of oxidedensity of oxideDevelopment of morphology during dryingDevelopment of morphology during dryingSpray roastingSpray roastingDispersionHollow particles caused by:Hollow particles caused by:Too slow drying:Too slow drying:TemperatureTemperature Solubility of productSolubility of product?DispersionSpray roastingSpray roastingPrecursor solutionDrying,CalciningPowderPowder preparationSol-GelGelation-Precipitation-Pyrolyis(Citrate,EDTAPechini,Bilcher)ComplexationChemicalDirectEmulsionCo-PrecipitationSpraying techniques-Spray drying-Freeze dryingDispersionPhysicalImmobilisation step6.3.2 Co6.3.2 Co-precipitation routeprecipitation route6.3.2.1 6.3.2.1 NanoNano-structured structured zirconiazirconia powders powders prepared by prepared by direct precipitationdirect precipitationWeakly agglomerated powderMetal salt solution(ZrCl4+YCl3)Hydrolysis in excess ammonia(pH 12)Water/Ethanol washing(control agglomeration)DryingCalciningNucleation burstAmorphous metal hydroxideWhat is happening during calcining?Adsorbed solvent is removed(1)Crystalline oxide powder is formed(2)DifferantionalDifferantional Thermal Analysis Thermal Analysis(DTA)of dried(DTA)of dried Zr,YZr,Y-hydroxide gelhydroxide gel12NanoNano-structured structured zirconiazirconia powders powders prepared by direct precipitationprepared by direct precipitationWeakly agglomerated powderDense zirconiaGrain size:125 nm Deep drawing Deep drawing at 1210 at 1210 C C3Y-TZP Ts=1100 oCMetal salt solution(ZrCl4+YCl3)Hydrolysis in excess ammonia(pH 12)Water/Ethanol washing(control agglomeration)DryingCalciningNucleation burstAmorphous metal hydroxideT Ts s=1300=1300 C CGrain size:Grain size:250 nm250 nmCalcined powder(550 oC)Crystallite size:8 nmDeep Drawing of ZirconiaDeep Drawing of Deep Drawing of ZirconiaZirconiaDisplacement:0.6 mm/minB1:Grain Size 250 nmC1:Grain Size 125 nmB1:fractures at 6 mmC1:deforms to 10 mm!Deformation temperature:1210 CProperty is a function of grain sizeProperty is a function of grain size Deformed at Height C1 C2 C3 1210oC(0.6 mm/min)1150oC(0.6 mm/min)1160oC(0.3 mm/min)10 mm 4 mm(f)8 mm Deep Drawing of Zirconia(Grain size:125 nm)(Super)plastic behaviour is possible if:Ceramic grain size is sufficient small(Super)plastic behaviour is possible if:Ceramic grain size is sufficient small Precursor solutionDrying,CalciningPowderPowder preparationSol-GelGelation-Precipitation-Pyrolyis(Citrate,EDTAPechini,Bilcher)ComplexationChemicalDirectEmulsionCo-PrecipitationSpraying techniques-Spray drying-Freeze dryingDispersionPhysicalImmobilisation step6.3.2.2 6.3.2.2(Co(Co-)precipitationprecipitationbyby reactionreaction betweenbetween emulsionemulsion dropletsdroplets100 nmsurfactantsurfactant layerlayerwaterwateroiloilw/o emulsion 1w/o emulsion 2ammoniametal ionsmetal hydroxidemetal oxidehydrate in oilparticle dispersionazeotropicdistillationNonNon-agglomerated/agglomerated/-aggregated powderaggregated powderPrepared by direct precipitationPrepared by direct precipitation共沸共沸DiDABDiDAB:(C:(C1212H H2525)2 2(CH(CH3 3)2 2N N+BrBr-D Didodecylidodecyl dimethylammoniumdimethylammonium bromidebromideArkopalArkopal 4040:C:C9 9H H1919-O(O(-CHCH2 2-CHCH2 2-O)O)4 4-H HN Nonylphenolonylphenol tetratetra(ethyleneglycolethyleneglycol)etherethermetal ionsmetal ionsammoniaammoniaW/O emulsion 1 W/O emulsion 1 W/O emulsion 2W/O emulsion 2metal hydroxidemetal hydroxideazeotropicazeotropicdistillationdistillationmetal hydroxide metal hydroxide in oilin oilNanoNano-structured oxide coatings structured oxide coatings via emulsion precipitationvia emulsion precipitation0.10.1-0.8 0.8 mm“micro reactors”LiNiOLiNiO2 2Formed by Reverse Formed by Reverse MicroemulsionMicroemulsionCyclohexane1-hexanol+PolyoxyleneOctylphenyl ether(OP-10)1M LiNO3+1M Ni(NO3)2Cyclohexane:OP-10:1-heaxanol=10:2:3(v/v)Water:oil=1:10250C inkeroseneTamkang J.Sci.Eng.7(2004)199-204OP-10乳化剂是含有10个乙氧基的辛烷基酚聚氧乙烯醚，(Po1yoxyethylene octylphenolether）又称烷基酚聚氧乙烯(10)醚Alkylphenol polyoxyethylene(10)ether，简称为TX-10、OP-10。DiDABDiDAB:(C:(C1212H H2525)2 2(CH(CH3 3)2 2N N+BrBr-D Didodecylidodecyl dimethylammoniumdimethylammonium bromidebromideArkopalArkopal 4040:C:C9 9H H1919-O(O(-CHCH2 2-CHCH2 2-O)O)4 4-H HN Nonylphenolonylphenol tetratetra(ethyleneglycolethyleneglycol)etherethermetal ionsmetal ionsammoniaammoniaW/O emulsion 1 W/O emulsion 1 W/O emulsion 2W/O emulsion 2metal hydroxidemetal hydroxideazeotropicazeotropicdistillationdistillationmetal hydroxide metal hydroxide in oilin oilNanoNano-structured oxide coatings structured oxide coatings via emulsion precipitationvia emulsion precipitation0.10.1-0.8 0.8 mm“micro reactors”coating coating on silicon on silicon waferwaferspin coatingspin coatingDiDABDiDAB:(C:(C1212H H2525)2 2(CH(CH3 3)2 2N N+BrBr-D Didodecylidodecyl dimethylammoniumdimethylammonium bromidebromideArkopalArkopal 4040:C:C9 9H H1919-O(O(-CHCH2 2-CHCH2 2-O)O)4 4-H HN Nonylphenolonylphenol tetratetra(ethyleneglycolethyleneglycol)etherethermetal ionsmetal ionsammoniaammoniaW/O emulsion 1 W/O emulsion 1 W/O emulsion 2W/O emulsion 2azeotropicazeotropicdistillationdistillationT T 600600 C Ccoating coating on silicon on silicon waferwaferZrOZrO2 2coating on silicon wafercoating on silicon wafer(grain size:(grain size:10 nm)10 nm)10 nmNanoNano-structured oxide coatings structured oxide coatings via emulsion precipitationvia emulsion precipitationnonnon-agglomerated agglomerated nanonano particles?particles?NanoNano-structured oxide structured oxide powderspowders via via reverse reverse micromicroemulsionemulsion precipitationprecipitationZarur&Ying,Nature 403(2000)65-67.BaO6Al2O3(BHA)Barium hexaaluminateBHA nanowhiskerCHEM.COMMUN.,2003,187618776.3.2.3 Processes involved in6.3.2.3 Processes involved inprecipitationprecipitationProcesses which may be involved in precipitation:*Nucleation*Crystal growth*Ostwald ripening*Recrystallization*Coagulation*AgglomerationIt is necessary to control each of these steps in order to e.g.form monodisperse particles with a well-defined and reproducible morphology.Monodisperse materials are interesting e.g.for formation of stable dispersions,uniform ceramics powders,pigments with reproducible colour,catalysts and nano-objects.The solvent is usually water,but may be other solvents or molten salts.Processes involved inProcesses involved in precipitationprecipitation?In solutions,concentration must be increasedDirect reaction of ions(e.g.adding bromine ions to a solution containing silver cations(AgCl)Redox reactions(e.g.reduction of HAuCl4with formaldehyde to give colloidal gold(Au)Precipitation by poor solvents(e.g.adding water to an ethanolicsolution of sulphur(S)Decomposition of compounds(e.g.adding acid to an aqueous solution of thiosulphate S2O32-to precipitate sulphur(S)Hydrolysis(TiCl4+H2O?TiO2)?Decomposition or removal of complexing agents:Precipitation and growth of large crystals of Ag2CO3from NH3(aq)?Temperature controlExample of precipitationAgBr particles fromprecipitationJ.E.Maskasky,J.Imaging Sci.1986,30,247.6.3.2.4 Synthesis of monodispersed colloids special precipitation(forced hydrolysis)AgBr particles fromprecipitationJ.E.Maska
