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英文原文DispersionofnanoparticlesbynovelwettypepulverizerutilizedsupersonicjetflowAbstract.WehaveexaminedthedispersionofbariumtitanatenanoparticlesBTNPsandhavediscussedtheeffectofairpressuresuppliedtothenozzleonthedispersionbyusingnovelwettypepulverizerutilizedsupersonicjetflowSSJM.Theaggregatedparticlesizewasdecreasedwithincreasingtheairpressureandthecollisiontimes.Intheoptimizedcondition,almosttheBTNPsweredispersedwiththeprimaryparticles,however,furtherexcessivecollisionhadcausedreaggregations.Thedegreeofdispersionhasbeenaffectedbytheairpressure.Theinjecteddropletshadformedalmostthesamediameterregardlessofairpressureandthevelocitywasincreasedwithincreasingoftheairpressureandreached300m/s.WehavespeculatedthattheshockwavedominatesthedispersionofBTNPs.1.IntroductionNanoparticlesarerequiredhighlyinmanyapplicationssuchasdielectricmaterialsforelectronicdevices,electrodematerialsforsecondarybatteries,etc.Thenanoparticleshavebeenfrequentlyproducedbythesocalledbuildupprocessessuchashydrothermalprocess,coprecipitationprocess,andsolgelmethod.Forexploitingsizeeffectofnanoparticles,itiscrucialtocontrolthedispersionandaggregationofthenanoparticlesinsuspension.However,nanoparticlesaggregatemoreeasilyandstronglythansubmicronsizedparticles,andaggregatednanoparticlesdonotfragmenteasily.Therefore,itisquitedifficulttodispersenanoparticlesperfectly,andthedispersionofnanoparticleshasbecomeafundamentaltechniqueforhandlingnanoparticlesinindustries.Ithasbeenreportedthathenanoparticleswerewelldispersedbyusingbeadsmill1.Beadmillingwithballsseveraltensofmicrometersindiameterhasrecentlybeendevelopedasanewmethodtodispersenanoparticlestoalmostprimaryparticlesize1.However,thecontaminationcausedbythegrindedballinbeadmillingwastentimeshigherthanthatcausedbydrygrinding2.Forprovidingnanoparticlesdispersingmethodthatcansolvetheaboveproblem,wehavedevelopednovelwettypepulverizerutilizedsupersonicjetflowhereafterreferredtoassupersonicwetjetmillSSJM.Inthisstudy,wehavereportedthedispersingresultofbariumtitanatenanoparticlesBTNPsandhavediscussedtheeffectofairpressureonthedispersionbyusingtheSSJM.2.Experimentalapparatusandprocedure2.1.ExperimentalapparatusFigure1showsschematicdiagramoftheSSJMleft.Therightpartofdescribesshowstheinternalconfigurationofthenozzlepart.Thecompressedairmaximumairpressurewas0.6MPawassuppliedatthetoppartofthenozzle.TheLavalnozzle,whichwasusedfortheSSJMasshowninFigure1,isusedtoaccelerateacompressedairpassingthroughittoasupersonicspeed,anduponexpansion,toformtheexhaustflowsothattheheatenergypropellingtheflowismaximallyconvertedintokineticenergy.Asaresult,theinjecteddropletspassingthroughthenozzlewereacceleratedtosupersonicandwerenaturallycooled.Thesuspensioninthefeedtankwassuppliedtothethroatofthenozzle,whilecontrollingthevolumeflowthroughthepumptubing.Thesuppliedsuspensionhadbeenformeddropletsbyjetflowandhadbeenacceleratedinsidethenozzle.TheaccelerateddropletshadcollidedwiththeSiCplate.Mostoftheprocessedsuspensionwascollectedatthebottomtank,andsomeoftheprocessedsuspensionwasevacuatedalongwiththejetflow,therefore,thesolventrecoverytankunitattachedtotheexhaustline.Figure1.Schematicdiagramsofsupersonicwetjetmillleftandthenozzlepartright,showingapproximateflowvelocityV,togetherwiththeeffectontemperatureTandpressureP.2.2.ExperimentalprocedureTwokindsofBTNPwereusedinthiswork.BTNPswiththeaverageparticlesizeof30nmweresynthesizedbythesolgelmethod3referredtoassolgelBT.CommerciallyavailableBTNPsBT01,SakaiChemicalIndustry,Japanwiththeaverageparticlesizeof100nmweremanufacturedbyhydrothermalmethodreferredtoashydrothermalBT.AdispersantusedinthisstudywasanammoniumsaltofpolyacrylicacidPAANH4,Mw8000,Touagousei,Japan.ThesolgelBTwasaddedtoethyleneglycolmonomethyletherin2volumereferredtoassolgelBTsuspension.PAANH4wasaddedtodistilledwaterin5wtagainstpowderweightandthenthehydrothermalBTwasaddedin20volumepercentsagainstdistilledwaterreferredtoashydrothermalBTsuspension.Eachsuspensionwasinjectedundervariousairpressuresfrom0.3to0.6MPa.AnaggregatedparticlesizewasevaluatedbydynamiclightscatteringmethodDLS,NanoZS,Malvern,UK.AshapeandmicrostructureoftheBTNPswereexaminedwithatransmissionelectronmicroscopeTEM,JEM3200EX,JEOL,JapanandafieldemissionscanningelectronmicroscopeFESEM,S4800,Hitachi,Japan.FordiscussingtheeffectofairpressureonthedispersionbyuseoftheSSJM,sizeandvelocitydistributionsofdropletsweremeasuredasfollows.Distilledwaterwasinjectedundervariousairpressuresfrom0.3to0.6MPa.Thesizeandvelocitydistributionofdropletsatadistanceof100mmawayfromthenozzleexitweremeasuredsimultaneouslybyPhaseDopplerAnemometryDantecDynamics,Denmark3.ResultanddiscussionFigure2.EffectofcollisionnumberoncumulativemeandiameterofsolgelBTsuspensionsundervariousairpressures.Figure4.FESEMimagesofhydrothermalBTNPsAandBwerebeforecollisionprocess,andCandDwereaftercollisionprocessfor3timesat0.6MPa3.1.DispersionofBTNPsFigure2showschangeofcumulativemeandiameterDA,ofwhichthevaluerepresentstheaverageaggregatedsize,withcollisionnumberundervariousairpressuresforsolgelBT.TEMimagesofBTNPscollidedundervariousconditionswereshowninFigure3.DAoftheBTNPscollidedat0.3MPawasdecreasedwithincreasingcollisionnumber.TheBTNPscollidedfor3timesat0.3MPaweredispersedwithalmosttheprimaryparticlesasshowninFigure3B,however,furtherexcessivecollisionhadcausedreaggregations.AlthoughDAcollidedat0.4and0.6MPawerealsodecreasedbythecollisionatonceortwice,DAwasincreasedimmediately.AsshowninFigure3D,solgelBTNPswerepulverizedtofinerBTNPswiththesizeunder10nmthantheinitialparticlesize,andwereformedaggregationswiththesizeover100nmconsistedofthepulverizedfinerparticles.Figure4showsFESEMimagesofthehydrothermalBTNPs.AsrecievedhydrothermalBTNPswereaggregatedwiththesizesover1μmasshowninFigure4A,andwerewidelydistributedinrangeoffrom100to200nmandunder100nmFigure4B.Afterthecollisionfor3timesat0.6MPa,BTNPswiththesizeunder100nmwereclearlyincreasedandtheaggregatedparticleswerenotexistedasfarasFESEMobservationwasconcerned.Figure5showsthehydrothermalBTparticlesizedistributionscollidedat0.3MPaand0.6MPa.LiketheFESEMobservation,theaggregatedparticlesweredecreasedandtheparticleswiththesizeunder100nmwereincreasedwithincreasingcollisionnumber.However,reaggregationswiththesizeover1μmandquitefineBTNPsunder10nmhadbeengeneratedbythecollisionfor5timesat0.6MPaasshowninFigure5.Excessivecollisionat0.6MPahadcausedreaggregations,similarlythesolgelBTNPsdispersionresult.Thedegreeofdispersionhasbeenaffectedbyairpressure.3.2.EffectofairpressureonthedispersionbySSJM.Figure6showsthesizeandthevelocitydistributionofinjecteddropletsundertheairpressuresfrom0.3to0.6MPameasuredatadistanceof100mmawayfromthenozzleexit.Theinjecteddropletsformedalmostthesamediameterregardlessofairpressureandthemediandiameterwasabout7μm.Thedropletsvelocitywasincreasedwithincreasingoftheairpressureandthevelocityinallmeasurementsreached300m/s.Incaseofdrytypejetmill,ofwhichthepulverizingprincipalissimilartotheSSJM,ithasbeenreportedthatthedrivingforceofpulverizingweretheshockwavegeneratedbythecollisionandtheinterparticlecollisioninsidethenozzle4.Figure5.ParticlesizedistributionsinhydrothermalBTsuspensionscollidedat0.3MPaleftand0.6MParight.FortheSSJM,theshockwavehasbeenoccurredmorestronglythanthatbyusingtheconventionaljetmill,ofwhichtheimpactvelocityis80m/sorless5,sincetheshockwaveisproportionaltotheimpactvelocity4.Inaddition,thecavitationandtheshearstresscanbegenerated6,andtheshearstressarisenfromthedeformationofdropletatthecollisionisalsoproportionaltotheimpactvelocity.Therefore,wehavespeculatedthattheshockwaveandtheshearstressarisesfromdeformationofdropletdominatethedispersionofBTNPs.4.ConclusionTheBTNPscollidedatoptimizedconditionweredispersedwithalmosttheprimaryparticle,however,furtherexcessivecollisionhadcausedreaggregations.TheBTNPscollidedat0.6MPa
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