醇类添加剂对冷冻浇注陶瓷的多孔结构及形貌的影响

Effectofalcoholadditivesontheporestructureandmorphologyofthefreeze-castceramics#ZENGJing,ZHANGYan,ZHOUKechao,ZHANGDou**510152025303540

(StateKeyLaboratoryofPowderMetallurgy,CentralSouthUniversity,ChangSha410083)Abstract:Theporousaluminaceramicswithlamellarstructurewerefabricatedsuccessfullybyfreezecasting.Theviscositiesofaluminaslurries,porestructures,porositiesandmechanicalpropertiesofthesinteredceramicswereinvestigatedbyintroducingbothtypesofalcoholsaswatersolidificationmodifierintotheinitialslurries,suchasethanoland1-propanol.Withtheadditionofethanolor1-propanol,theviscositiesofslurriesandporositiesofsinteredceramicsincreased.Thecompressivestrengthsofthesinteredporousaluminaceramicswereimprovedduetoagoodconnectivitybetweenlamellaewiththeadditionofbothtypesofalcohols.Thelowestporositiesof68.52%and73.72%andhighestcompressivestrengthsof18.2MPaand15.0MPawereobtainedbytheadditionof30wt.%ethanoland1-propanol,respectively.Keywords:Inorganicnonmetallicmaterials;Aluminaceramic;porousmaterial;ethanol;1-propanol0IntroductionPorousmaterialshaveattractedmuchattentionduetotheirsuperiorfunctionsandawiderangeofapplicationsvaryingfrombonesubstitutestopartfortheautomotiveindustryincludingceramicfilters,catalystsupport,porouselectrode,gasdistributorsandbiomaterialsinsulator[1-3].Nowadays,variousfabricationtechniquesofporousceramicshavebeendevelopedsuchasgelcasting[4],directfoaming[5],polymerfoamreplication[6]andfreezecasting[7].Freezecastingasasimple,versatile,low-cost,environmentallyfriendlyandcomplex-shape-foamingmethodiswidelyusedtoprepareporousmaterialswithalignedpores[4,8].Duringthefreezecastprocess,theceramicslurryispouredintoamould,andfrozenunderacertainfreezingtemperatureformingalamellarstructureandpushingtheceramicparticlesintospacesbetweenadjacentfrozenlamellae,followedbyfreezedryingundervacuumbysublimationoficetopreventthegenerationofcracks,shrinkageandwarpofthegreenbodywhichusuallyexistincommondrying[9].Recently,manyresearchesonaluminaporousmaterialbyfreezecastingwiththeadditionofadditiveswereinvestigated,exhibitingastrongcorrelationbetweenthekindandconcentrationoftheemployedadditivesandthemorphologyandmechanicalpropertiesofice-templatedporousceramics.Kohetal.[10]investigatedtheeffectofpolystyrene(PS)additionasorganicbinderonthefreezingbehaviorofaverydilutealumina/campheneslurryforthefabricationofultra-highporosityceramicswithalignedporechannels.Itisknownthatmanycryoprotectants,alsoknownasantifreezeagentsshowconsiderabledecreaseoffreezingpoints[11]andseveralpossiblecryoprotectantshavebeenconsideredtomodifytheformationofgreenbodiesforobtainingdensealuminaparts[12].Forexample,Sofieetal.[4]reportedthattheglyceroladditiveresultedinthebodieswithauniformmicrostructureofthealuminaceramic.Sinceethanolor1-propanolcanactasorganicbinderandcryoprotectants[13],ourworkwastoadddifferentalcoholsaswatersolidificationmodifierandexploretheirinfluenceontherheologicalpropertiesofaqueousslurriesandthemicrostructuresoffreeze-castceramics,andtocharacterizethemechanicalpropertiesofporousceramics.Foundations:SpecializedResearchFundfortheDoctoralProgramofHigherEducation(Nos.20210162130003and20210162110044),theNationalNaturalScienceFoundationofChina(Nos.51172288and51072235)Briefauthorintroduction:ZENGJing,〔1990〕,female,masterstudent,functionmaterial.Correspondanceauthor:ZHOUKechao,(1962),male,professor,functionmaterial.E-mail:zhoukc2@-1-1Experimentalprocedures1.1Materials

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Commerciallyavailablealuminapowder(AES-11,SumitomoChemicalCo.Ltd.,Tokyo,Japan)withanaverageparticlesizeof0.5µmandthepurityof99.8%andthedeionizedwaterwereusedasthestartingmaterialandfreezingvehicle,respectively.Ammoniumpolyacrylate(HydroDisperA160,ShenzhenHighrunChemicalIndustryCo.Ltd.,P.R.92China)andPVA(420,KurarayCo.Ltd.,Japan)wereusedasthedispersantandbinder,respectively.Inaddition,ethanol(TianjinHengxingChemicalIndustryCo.Ltd.,P.R.China)and1-propanol(TianjinKermelChemicalIndustryCo.Ltd.,P.R.China)wereusedasadditives.1.2PreparingprocessingThedeionizedwater,ammoniumpolyacrylate(1wt.%ofaluminapowder),acertainamountofaluminapowder,PVAbinder(1wt.%ofaluminapowder),avariousconcentration(10wt.%,30wt.%ofthedeionizedwater)ofethanolor1-propanolwereaddedtothemixingcontainersandball-mixedatroomtemperaturefor24hwithzirconiaballs,followedbyde-airedthroughstirringinavacuumdesiccatorstoremoveairbubblescompletely.Theinitialsolidconcentrationofaluminaslurrywaskeptas10vol.%.Theslurrycontainingsamesolidcontentwithoutanyalcoholswasalsopreparedforthecomparisonpurpose.Thentheslurrywaspouredintoatransparentcylindricalpolydimethylsiloxane(PDMS)mouldwith10mmindiameterand15mminheight.Thenthemouldwastransportedtoacoppercoldfingerplacedinaliquidnitrogencontainer.Thefrozenbodieswerethentakenoutofthemouldandputintoavacuumchamberwithpressureunder10Paandtemperatureunder-53°Cofafreeze-drier(FD-1A-50,BeijingBoyikangMedicalEquipmentCo.China)forfreezedryingfor24h.Thegreenbodiesweresinteredat1500°Cinairfor2h,withheatingrateof5°Cmin-1andcoolingnaturallytoroomtemperatureinfurnace.1.3CharacterizationTheviscositiesoftheceramicslurrieswereinvestigatedbyarheometer(AR2000,TAInstrument,NewCastle,DE)atashearratefrom1to500s-1at25°Cbytheuseofastainlesssteelparallel-plateconfiguration(diameter:40mm,gap:500µm).Thesintereddensity,whichwasmeasuredthroughArchimedesprinciple,wasdividedbythetheoreticaldensityofalumina,3.98g/cm3,toobtaintherelativedensitytoderivethetotalporosity.Everypointwasmeasuredbyatleastthreetimes.Environmentalscanningelectronmicroscopy(ESEM,Quantan200,JEOL,Tokyo,Japan)wasusedtomeasurethemicrostructuresonfracturesurfacesofthesinteredbodiescoatingwithathinlayerofgold.Todeterminethecompressivestrengthofthesinteredbody,anElectronicUniversalTestingMachine(KD11-2,ShenzhenKEJALITechnologyCo.Ltd.,China)wasusedatacrossheadspeedof0.2mm/min.2ResultsandDiscussion2.1TheviscositiesoftheslurriesFig.1showstheeffectsofthealcoholconcentrationsontheviscositiesof10vol.%solidloadingslurriesattheshearratefrom1to500s-1.Allviscositiesofaluminaslurrieswerelowwitharangeofadditiveconcentrationsfromnoneto30wt.%.Withtheincreaseoftheshearrate,theviscositiesofallslurriesdecreasedandshowedtheshearthinningbehavior.Itisobviousthattheslurrieswithethanolor1-propanolshowedhigherviscositiesthanthosewithouttheaddition-2-

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ofalcohols,similartothetrendobtainedbyZhangetal.[14].Withtheincreaseoftheconcentrationofbothtypesofalcoholsfromnoneto30wt.%,theviscositiesofbothslurriesincreasedatthesameshearrate.Theslurrieswithoutandwiththeadditionof1-propanolshowedlittledifferenceinviscosityatallshearrates.Theviscosityofslurrywith30wt.%ethanolwasnearly5-10timeshigherthantheonewithoutanyadditive.35none30252015105

10wt.%ethanol30wt.%ethanol10wt.%1-propanol30wt.%1-propanol0

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Fig.1.Viscositiesofaluminaslurriespreparedusing10vol.%solidsloadingwithdifferentalcoholadditionsattheshearratefrom1-500s−12.2MicrostructureFig.2.showstheSEMmicrographsofsinteredporousAl2O3ceramicspreparedfrom10vol.%solidsloadingslurrieswithdifferentconcentrationsofethanolrangingfrom10to30wt.%.Theporousarchitecturewithlamellarchannelsoflong-rangeorderasthereplicaoftheethanol-watermixturedendritescanbeapproximatelyfoundparalleltothemacroscopicicegrowthdirection,asshowninFig.2(A)and(C).Withtheincreaseoftheethanolconcentration,thelamellarporewidthdecreasesasaresultofvariationofviscositywhichcorrespondingwelltoourpreviousreportusinghydroxyapatiteastherawmaterial[15].Duringthesolidificationoftheaqueousslurrywiththeadditionofethanol,mostceramicparticlesintheslurrywererejectedbythegrowingdendritesandbecameintensivebetweenthedendritearmsortheneighboringdendrites.Inthedirectionofperpendiculartotheicetop(Fig.2(B)and(D)),thisphenomenoncanbeobservedmoredirectly.Connectionsinasmallbondingareabetweentheceramicadjacentlamellaewithporesizeof10-80μmwereobservedwiththeadditionof10wt.%ethanol.Whiletheconcentrationwasupto30wt.%,anearlydenseceramicwallwiththeporesizeof5-10μmwasachieved.-3-viscosity,mPa·sShearrate,sviscosity,mPa·sShearrate,s

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Fig.2.SEMmicrostructureofporousaluminaceramicspreparedbyvariousethanolconcentrationsof10wt.%(AandB),30wt.%(CandD).Theleftandrightimagesshowtheporesformedparallelandperpendiculartotheicefront.Fig.3.showstheSEMmicrographsofsinteredporousAl2O3ceramicspreparedfrom10vol.%solidsloadingslurrieswithdifferentconcentrationsof1-propanolrangingfrom10to30wt.%.Withtheadditionof10wt.%1-propanol,thelong-rangeorderedporestructureasthereplicaofthe1-propanol-watermixturedendriteswasmoreeasilyobservedinthedirectionbothparallelandperpendiculartotheicefrontasshowninFig.3(A)and(B).Withtheincreaseof1-propanolconcentration,thewellalignedporesstructuredisappearedbuttheadjacentceramiclamellaejointtogether.Meanwhile,atwistduetothegrowingof1-propanol-watermixturedendriteandanearlydensestructurecanbeobtained.Fig.3SEMmicrostructureofporousaluminaceramicspreparedbyvarious1-propanolconcentrationsof10wt.%(AandB),30wt.%(CandD).Theleftandrightimagesshowtheporesformedparallelandperpendiculartotheicefront.130-4-Tab.1Freezingpoints(℃)ofalcohol-watermixture.[16]

Additiveconcentration/wt.%

Ethanol-watermixture1-propanol-watermixture10-4.0-2.330-14.0-8.3Inourpreviouswork[17],thelong-rangeorderedlamellararchitecturecanbeclearlyobservedfromthesinteredporousAl2O3ceramicwithoutanyalcoholadditives.However,withtheaddition135140145150155160165

of30wt.%alcohols,theceramicwallssurroundingporechannelsarealmostfullydenseforbothtypesofalcoholadditives.Thedifferencesinmicrostructuresmaybecausedbytheequilibriumamongthediffusionrateofalcohols,icecrystalgrowthrateandthealuminaparticleexpellingrate.Ontheotherhand,highviscosityoftheslurryalsoinhibitedtheexpellingofaluminaparticlesfromthegrowingicecrystalsonacertainextent[14].Duetothehigherviscosityofthesuspensionspreparedby30wt.%concentrationofbothtypesofalcohols,thefreezingfrontexperiencedhigherresistanceinthefreeze-castprocessandobtainedarelativelydensestructure,asshowninFig.2(C)andFig.3(B).Aftertheunidirectionalprocess,sublimationoftheicebondsbetweenceramicparticleswouldresultinmanysmallporestructuresintheceramicwallwhichwerenoteliminatedbythefollowingsinteringprocess.Moreover,theadditionofalcoholschangedthehydrogenbondingofwater.Itisknownthatintheethanol-watermixturesand1-propanol-watermixtures,boththehydroxylhydrogenandoxygenplaytherolesofprotondonorandacceptorintheformationofhydrogenbonds,respectively.Furthermore,thehydrogenbondsbetweenthehydroxylhydrogenandoxygenbecomestrongwiththeincreaseofalcoholsconcentration,resultinginthestronghydrogen-bondinginteractionsbetweenalcoholsandwatermolecules[13],whichmaydisruptthecrystallizationoficeandresultinthedifferencesinthemicrostructureofporousaluminaceramic[4].Inaddition,asshowninTable1,theadditionofethanolor1-propanolhaddifferenteffectonthefreezingpointsofalcohol-watermixtureswhichmayberesultindifferentmicrostructuresofsinteredporousaluminaceramics.2.3PorosityandthecompressivestrengthFig.4showstheeffectsofdifferentconcentrationsofbothtypesofalcoholspreparedfrom10vol.%solidsloadingslurriesonthecompressivestrengthandporositiesofporousAl2O3ceramics.Withtheadditionofethanolrangingfromnoneto30wt.%,theporositydecreasedfrom74.35%to68.52%andthecorrespondingcompressivestrengthincreasedfrom13.4MPato18.2MPa.Theporositydecreasedfromto74.35%to73.72%andthecorrespondingcompressivestrengthincreasedfrom13.4MPato15.0MPapreparedbythe1-propanoladditive.Theadditionofethanolresultedinlowerporositythanthatofthe1-propanolsamplesforalltheconcentrationsof10vol.%solidsloading.Forthecompressivestrength,thetrendwasreversed.Thecompressivestrengthoftheporousceramicspreparedbytheethanolwerearound1.1timeshigherthanthoseoftheceramicspreparedbythe1-propanoladditiveatthesameconcentrationasshowninFig.4.Theincreaseofcompressivestrengthmaybeattributedtothevaryingoftheconnectionbetweenceramiclamellae,exhibitingagreatpotentialintheloadingbiologicalapplication.[18]-5-

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30Concentration,%Fig.4.PorosityandcompressivestrengthoftheporousAl2O3ceramicasfunctionoftheconcentrationofbothtypesofthealcohols.170175180185190195200205

3ConclusionsTheeffectsoftheadditionofethanolor1-propanolontheviscosity,microstructure,porosityandcompressivestrengthoftheporousaluminabyfreezecastingtheaqueousaluminaslurrieswith10wt.%solidloadingwereinvestigated.Withtheincreaseofalcoholconcentrationsrangingfromnoneto30wt.%theviscositiesoftheslurriesandporositiesofsinteredbodiesdecreased.Duetoagoodconnectivitybetweenlamellaewiththeadditionofbothtypesofalcohols,thecompressivestrengthsofthesinteredporousaluminaceramicswereimproved.Withtheadditionof30wt.%ethanoland1-propanol,thelowestporositiesof68.52%and73.72%andhighestcompressivestrengthsof18.2MPaand15.0MPawereobtained,respectively.AcknowledgementsTheauthorsaregratefultotheSpecializedResearchFundfortheDoctoralProgramofHigherEducation(Nos.20210162130003and20210162110044),theNationalNaturalScienceFoundationofChina(Nos.51172288and51072235)References[1]DEVILLES,SAIZE,TOMSIAAP.Ice-templatedporousaluminastructures[J].ActaMaterialia,2007,55:1965-1974.[2]MORITZT,RICHTERHJ.Ice-mouldfreezecastingofporousceramiccomponents[J].JournaloftheEuropeanCeramicSociety,2007,27(16):4595-4601.[3]OHST,CHANGSY,SUKMJ.MicrostructureofporousCufabricatedbyfreeze-dryingprocessofCuO/campheneslurry[J].TransactionsofNonferrousMetalsSocietyofChina,2021,22:s688-s691.[4]SOFIESW,DOGANF.Freezecastingofaqueousaluminaslurrieswithglycerol[J].JournaloftheAmericanCeramicSociety,2001,84(2):1459-1464.[5]BARGS,SOLTMANNC,ANDRADEM,KOCHD,GRATHWOHLG.CellularCeramicsbyDirectFoamingofEmulsifiedCeramicPowderSuspensions[J].JournaloftheAmericanCeramicSociety,2021,91(9):2823-2829.[6]FUQ,RAHAMANMN,BALBS,BROWNRF,DAYDE.Mechanicalandinvitroperformanceof13-93bioactiveglassscaffoldspreparedbyapolymerfoamreplicationtechnique[J].ActaBiomater,2021,4(6):1854-1864.[7]DEVILLES,SAIZE,NALLARK,TOMSIAAP.Freezingasapathtobuildcomplexcomposites[J].Science,2006,311(5760):515-518.[8]HONGCQ,DUJC,LIANGJ,ZHANGXH,HANJ.Functionallygradedporousceramicswithdensesurfacelayerproducedbyfreeze-casting[J].CeramicsInternational,2021,37(8):3717-3722.[9]DEVILLES.Freeze-CastingofPorousCeramics:AReviewofCurrentAchievementsandIssues[J].AdvancedEngineeringMaterials,2021,10(3):155-169.[10]KOHYH,LeeEJ,YOOHBH,SONGJH,KIMHE,KIMHW.EffectofP