Dissertation > Excellent graduate degree dissertation topics show

Study on the Preparation of Nanosized-ZnO and Skin-colored Products Through Immediate Precipitation-Microwave Calcining

Author: CaoJun
Tutor: ZhouJiCheng
School: Xiangtan University
Course: Chemical Engineering
Keywords: Zinc   precursor   basic zinc carbonate   direct precipitation method   Microwave   roasting time   roasting   Nano   microwave field   precipitation reaction
CLC: TQ133
Type: Master's thesis
Year: 2004
Downloads: 0
Quote: 0
Read: Download Dissertation

Abstract


SummaryStudyonthepreparationofnanosized-ZnOthroughimmediateprecipitation–microwavecalcining1.1Theimmediateprecipitationmethodbelongstothereactiveprecipitationinanhydrousmethods.Atpresent,theenhydrousmethodsareseldomusedinindustrialproductionofnanosized-ZnO,buttheimmediateprecipitationmethodhassamplecraftsandcostsless.TheZnOnanoparticlespreparedbythismethodareverysmallinsizeandevenlydistributed,andskin-coloredproductscanbegainedthroughtreatingforerunnerwithammonia.Incontrastwiththemethodsofadvancedtechniqueandhighcostabroad,theimmediateprecipitationmethodismoresuitabletoourcountry’srealconditions.Asotherreactiveprecipitationmethods,ithasthesameproblemsasfollowed:(1)Becauseofthesmallsizeandstrongsurfacetension,theyareeasilyagglomeratedwhennanoparticlesareprepared.Theagglomerationcanbedividedintotwotypes:oneissoft-agglomeration,andtheotherishard-agglomeration.Thesoft-agglomerationcanberemovedmostlybychemicalormechanicalprocess,whilethehard-agglomerationisreallyhardlyeliminatedbythem.So,thehard-agglomerationmakesthesmallparticleshardtodisperse.(2)Routinecalciningisinefficient.Ifcalciningtemperatureistoolow,theforerunnerwillbenotdecomposedcompletely,iftoohigh,thecrystalparticleswillgrowupandbesintered.1.2Inordertosolvethoseproblemsabove,webringforwardaimprovedcraft.Ithasthosefollowingadvantagesandspecialtiescomparedtothatreported:(1)Advantages:a.ThenewcraftusescheapheptahydratedzincsulfateandAmmoniumhydrogencarbonateasmaterials.wecangetwelldispersedparticlesbywashingitonetimewithethanolaftertheforerunnerwaspreparedandwashed,anditreducedtheagglomeration;b.Thenewmicrowave-calciningtechniquewasusedinthisexperiment.Itmadethesystembeevenlyheatedandthetemperaturerisedsorapidlythattheforerunnerwereswiftlydecomposed.Sowecanrestrainthegrowingandsinteringofcrystalparticlesandpromotethecalciningefficiency.(2)Specialties:Theagglomerationofparticlescanbechangedthroughtreatingforerunnerwithammonia.AsbasicZinccarbonateasconcerned,itisnotseriouslyagglomeratedinliquidevenifwithoutthedisposingbyammonia.Butwiththeaddingofammonia,thefinalproductsareskin-colored.1.3Processofpreparation:TheimmediateprecipitationreactionoccurredwhentheAmmoniumhydrogencarbonatesolutionwasaddedintothezincsulfatesolution.Wecangetforerunnerfromtheprecipitationafterfiltrating,washing,anddrying.Thentheforerunnerwassetintomicrowaveovenandcalcined.Afteritdecomposedcompletely,nanosized-ZnOwasgained.UsingammoniatoadjustthepHvalueoftheliquidaftertheprecipitationreaction,wecangetskin-coloredproductsatlast.1.4Craftsofpreparationofnanosized-ZnOthroughimmediateprecipitationµwave-calciningwasstudiedthroughexperiments,theresultsasfollowed:(1)Theforerunnerwillbeagglomeratedandbeyellowincolor,iftapwaterwithimpuritieswaschosenasreactiveliquid.Distilledwaterwillreducethisdisadvantageousphenomenon.Addingethanolintotheliquidafterimmediateprecipitation,wecanchangetheagglomerationofforerunner.Ifthevolumeratioofethanolinliquidisunder40%(including0%),theagglomerationislight,above60%,thenheavy.Beingwashedwithethanolonceatlasttime,light-agglomeratedforerunnerwasgottenfinally,anditiseasilydispersed.(2)Theagglomerationcanbechangedbyusingammoniatoadjusttheliquid’spHvalueaftertheprecipitationreaction.BetweenpH=7.8~8.1,hard-agglomerationcomesintobeing.Soagglomerationislightevenifnoammoniawasbeenaddingintotheliquidafterthereaction.Skin-coloredproductscanbegainedultimatelyifwetreatsforerunnerwithammonia,andmoreammoniaisbeenadding,deeperthecoloris.WhenthepHisabove8.5,itisdistinctlyskin-colored,buttheforerunnerislargelydissolved.(3)Calcinedbymicrowaveat900W&2450MHz,theforerunnerwasswiftlyandcompletelydecomposed.Itisefficient.Thetimeofcalciningisinterrelatedwiththechangeofrateofweightlessnessofforerunnerandintensityofelectricfield、distributingofradiationofmicrowave、accumulatingofparticles、contentofcombo-waterinforerunnerandetc.1.5Throughanalysisofproduct’sAFM,TEMimagesandXRDspectrum,itshowsthatnanosized-ZnOpreparedbyimmediateprecipitation-microwavecalciningispurifiedhexagonalstructuredandapproximatlyspherical,under100nmoreven10~20nminsize,evenlydistributed,welldispersedandsoft-agglomerated.2.mechanismofmicrowave-calciningandcomparewithroutinecalciningBasedonthestudyoncraftsofprepatrationofnanosized-ZnOthroughimmediateprecipitation-microwavecalcining,westudiedthemechanismofmicrowave-calciningandcomparewithroutinecalciningthroughexperimentsandtheoreticaldeduction.2.1Experimentalmeasures:Setthedriedforerunnerintothemicrowaveoventocalcine,at900Wandhighfire.Controlthecalciningtimeandpayattentiontothechangeofweightoftheforerunner.Useaccurateelectronicbalancetomeasureits’weight.AnnexathermocoupletothemicrowaveoveninordertomeasuretherisingtemperatureofZnOunderthemicrowaveradiation.2.2Theoryofmicrowave-heating:Microwave-heatingchangesmicrowave-electromagneticenergyintoheatenergy.Theenergytransmitsaselectromagneticwavethroughspaceandintermedium,whathasaimportantrelationtotheheatingprocessofsubstanceandpolarizationofinnermoleculesofsubstance.Theheatingofsubstanceinmicrowavefielddependsontwotypesofpolarization:polarizationofdipolaronandinterface.Thepolarizationofsubstanceappearsasullageofdensityofcurrentinelectricfield.Ullageofconductanceofsubstancepossessedcharactersofsemi-conductordevotesmuchtotheefficientullage.Dipolarpoisecausedbylacunasinthecrystalparticlesplaysalargeroleinthehighullageofsubstance.Besides,becauseofthelacunasinboundaryfloorofsubstance,Maxwell-Wangerpoiseoccurstorespondtothepolarization,anditmakesthetemperatureofsystemsharplyraisedtoo.Correspondingtothevelocityofrisingoftemperatureinmicrowavefield:(T-To)/t=C·ε”eff·f·E2/Cp·ρ(Cisaconstant,ρisthedensityofsubstance,Cpisthespecificheat,fisthefrequencyofmicrowave,Eistheintensityofelectricfield)thepowerconsumedbyelectricfieldistheenergyabsorbedbythesubstance,anditwasincreasedasthetimeofradiationraised,sodidthetemperatureofthesystem.2.3Conclusionsandresultsofexperimentsasfollowed:(1)ThetemperatureofforerunnerbasicZinccarbonateinthemicrowavefieldisnotsharplyrising,onthecontrary,risinggently.ButtheZnOhasasharprisingoftemperatureinthemicrowavefieldasitcanreach600℃in10sseconds.(2)Underthemicrowaveradiation,theforerunner’stemperaturerisesgradually,thenitwasdecomposed.ThetemperatureisexplosivlyrisingwhenZnOisgenerated,ifdidn’tputitundercontrol,thetemperaturerisedtoohightoburntheproducts.Sobeforethathappened,wemustcontrolthetimeofcalcining,interrupttheradiationandchurnuptheforerunnertolettheheatgetputinordertoavoidtheparticles’beingsintered.Infact,microwave-calciningisaintermittentprocess,andthetemperatureisfluctuatingaroundacertainvalue.Thetimeofcalciningiscorrelativetothecharactersofthesubstance,sizeofcrystalparticles,fillingvolumeanddensity,andintensityofelectricfieldandetc.Itistoocomplextoexplain.(3)TheMicrowave-calciningofbasicZinccarbonateconsistsofthreeparts:Losingofcombo-water,warming-upofforerunner-risingoftemperatureofforerunner-decomposingofforerunner.Intheprocessofcalcinging,thesubstanceintenselyabsorbedtheenergyofmicrowaveandchangeditintoheatenergy.Theforerunnerwasrapidlydecomposedandsmallparticleswasgeneratedeasilyundertheconditionofevenheating-upandtemperature’ssharprising.3.Studyonpreparationofskin-coloredflake-shapedZnOandmechanismofpigmentationSomesampleswastreatedwithammoniaaftertheforerunnerwaspreparedbyimmediateprecipitationreaction,sosomeproductsappearedasskin-colored.Itshewusanewmethodtoprepareskin-colorednanosizedZnO.Atthesametime,thecollectingratedescendedastheconcentrationofammoniaisraised.Becausetheforerunnerisamphotericandcanbeeasilydissolvedbyammonia,apartofZincionsreturnedtotheliquidandflewawaywiththefiltrate.IflettingoffthewastewithZincions,itwillwastethematerialsandpollutetheenvironment.Sotakingthisintoaccount,wereclaimedthepartofZincionsfromthefiltratebyvaporizingandre-crystaling,andgotskin-coloredflake-shapedZnOatlast.3.1Experimentalmeasures:afterthepHvalueoftheliquidwasadjustedto8.5byammonia,apartoftheforerunnerwasdissolved.Thefiltrateandtheprecipitationwerecollectedrespectivelyafterfiltrating,andthetreatmentsofthemisasfollowing:(1)Washingtheprecipitationwithdiluentammoniaandethanolbeforesetttingitintotheovenunder80℃,andcalciningitinamicrowaveovenafteritwasdried,thentheskin-colorednanosized-ZnOwasgotten.(2)Filtratingthefiltrateseveraltimestillclearliquidwasgained.Vaporizingtheclearliquidinthemicrowaveoventillitturnsintodope.Then,washingandfiltratingthedopewithdistilledwaterandethanol.Dryingthesub-forerunnerinovenunder80℃andcalciningit,thentheflake-shapedskin-coloredproductswasgottenfinally.ObservetheappearanceofthecrystalwithX-650ScanElectronicMicroscopeandPicoscanAtomicForceMicroscoperespectively,analysethestructureoftheproductswithD/max-3cX-radiationdiffracter.3.2Theoryofexperiment:BecausetheforerunnerbasicZinccarbonate:ZnCO3?2Zn(OH)2?H2Oisamphoteric,soitcanbedissolvedbyammoniaandtheZincionsreturnstothefiltrate.Byvaporizingthefiltrate,theZincionswasprecipitatedassub-forerunnerZn(OH)2.Then,beingcalcined,theZn(OH)2wasdecomposedintoZnO.3.3Tokenofskin-coloredZnO:(1)TheSEMimagesofflake-shapedandskin-coloredZnOpreparedbyfiltrate-vaporizingandcalciningisirregularflake-shapedstructure.Thosesmallandbigfragmentspilesuptogetherorlapsover.Thosefragmentsareseveraltenstoseveralhundredsmicronsinsize.TheXRDspectrumshowsthatafewmaindiffractiveapicesarethediagnosticdiffractiveapicesofhexagonalZnOcrystal.Itprovedthattheflake-shapedproductiscomposedbynumeroushexagonalZnOcrystals.Butseveralsecondarydiffractiveapicesemergingneartothemainonesindicatedthattheflake-shapedstructureisdevotedtothispeculiarXRDspectrum.(2)TheXRDspectrumoftheskin-colorednanosizedZnOshowedthattheparticlesispurifiedhexagonalZnOcrystals.TheAFMimagesindicatedthatthesizeoftheparticlesisunder100nm,andseveralparticlespilesuptogether.3.4Studyonmechanismofpigmentation:calcinethesub-forerunnerpreparedbyfiltrate-vaporizingunderdifferenttemperaturetoseeaboutthetemperatureinfluenceonskin-coloredproductscanbegainedthroughtreatingforerunnerwithammonia.ThecoloroftheZnOiscausedbythedissolvingofnitrogenatomsintothesolidphaseofZnO.Above350~400℃,thenitrogenatomscancompletelypenetratetheZnOcrystallatticeandmakestheproductshowskincolor.4.conclusionsandexpectationsNanosized-ZnOcanbepreparedthroughimmediateprecipitation–microwavecalciningandskin-coloredproductscanbegainedthroughtreatingforerunnerwithammonia.Vaporizeingthefiltrateafterfiltratinganddisposingitproperly,wecangetflake-shapedskin-coloredZnOultimately.Buttherearelotsofworkscanbedoneontheinfluenceofammoniaontheparticles,thepigmentationofZnOandthemicrowave-calciningoftheforerunnerandsoon.……

Related Dissertations

  1. Process Optimization and Degradation Kinetics for Microwave Vacuum Drying of Different Traditional Chinese Medicine Extract,TQ461
  2. Research on Geological Features of Yinchanggou-Qiluogou Lead-Zinc Ore Deposit, Ningnan County, Sichuan Province,P618.4
  3. ( Hydroxy) Iron Oxide and the removal of arsenic in drinking water,O614.811
  4. Synthesis and Seperation of 1,1’-binaphthol,O625.3
  5. Copper slag roasting modified experimental study,X758
  6. Study of Microwave Assisted Incineration of Asphalt Flue Gas,X701
  7. Situ synthesis of mullite stone whisker toughening microwave metallurgical corundum - mullite Refractories,TQ175.6
  8. Experiments on Microwave Radiation Activation YunNan Unburned Coal-gangue Concrete,TU528
  9. Silica fume wet purified preparation of spherical nano-silica,TB383.1
  10. The Study of Anode Catalyst Pd/C for Direct Formic Acid Fuel Cell,O643.36
  11. Study on the Synthesis of the Polypyrrole-Cobalt Oxides and Their Catalytic Behavior for the Electroreduction of H2O2,O643.32
  12. Study on Technics & Performance of Nano Electroless Composite Plating on 20~# Steel,TQ153
  13. Curing Mechanism and Properties of Fluorenyl Epoxy Resin,TQ323.5
  14. Anti-corrosion Property of Flake Zinc Epoxy Coating Doped with Rare Earth in SRB,TQ630.1
  15. Effects of Nano-Packing on Preservation Quality of Flammulina Velutipes and Agaricus Bisporus,TS219
  16. Modification for PVA-Based Composite Packaging Material with Nano-SiO2 and Its Influence on Fresh Preservation Effect of Salted Duck Eggs,TS253.46
  17. Study on Drying Processing and Sterilization on Spinach,TS255.52
  18. Study on Chitosan-Based Composiate Nano-Coating Dope and Its Effect of Fresh-Keeping for Coated Egg,TS253.2
  19. Effects of Different Applying Methods of Copper and Zinc and AM Fungi under Different P-Applied Levels on Growth and Tanshinones of Salviae Miltiorrhizae Bunge,S567.53
  20. Effects of Different Gas Composition and Packaging Materials on Postharvest Quality and Active Oxygen Metabolism of Flammulina Velutipes,S646.15
  21. Preparation of Essence and Residues Powder from Flammulina Velutipes and Evaluation of Their Physical-Chemical Properties,S646.15

CLC: > Industrial Technology > Chemical Industry > Inorganic compounds, the chemical industry of the metal elements > Section III group metal elements of inorganic compounds
© 2012 www.DissertationTopic.Net  Mobile