硅灰粉煤灰对水泥石膏微观结构的影响的AFMSEM研究毕业论文外文翻译.docx
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硅灰粉煤灰对水泥石膏微观结构的影响的AFMSEM研究毕业论文外文翻译.docx
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硅灰粉煤灰对水泥石膏微观结构的影响的AFMSEM研究毕业论文外文翻译
外文资料
AnAFM-SEMinvestigationoftheeffectofsilicafumeandflyashoncementpastemicrostructure
Atomicforcemicroscopy(AFM)wasusedtoobserveparticleshapeandsurfacetexturedetailsofnormalportlandcementandsupplementarycementingmaterials(silicafume,low-calciumflyash,andhigh-calciumflyash).Thelattermaerialsmixedwithcementwereexaminedafterprolongedhydration.Significantinnovativeinformationonparticleshapeandhydratedpastemicrostucturewasobtained.Conventionalmicroscopytechniques,suchasscanningelectronmicroscopy(SEM),cannotprovidesuchdetailedimagesandsurfacetexturecharacteristicsofthefinematerials(especiallysilicafume)andoftheproductmicrostructure.AFMshowed,forthefirsttime,thatsilicafumeparticlesareprimarilycomposedoftwocomplimentaryparts(hemispheresorsemicylinders).Nano-sizeparticleswerefoundinallmaterials.Arelativelysmoothproductsurfacewasobservedinthehydratedcementpaste.Thehydratedsurfaceoftheaddition-cementpastespresentedsmallspheroidbulges,givinganadditionalroughnessaswasmeasuredbyAFM.Asufficientcorrelationofthismicroscopicalquantitativeinformationwithmacroscopicalengineeringanddurabilitypropertiesofcementproductsisalsopresented.
1.Introduction
Fortechnicalandeconomicreasons,newmaterialswithpozzolanicandcementitiouspropertieshavebeenmixedwithcementduringthelastyears.Amongthesematerialsareindustrialby-productssuchasflyashfromcoal-burningelectricpowerplants,slagsfrommetallurgicalfurnaces,silicafume(ormicrosilica)fromelectricarcfurnacesproducingsiliconandferrosiliconalloys,andsomenaturallyactivematerialssuchasvolcanictuffs.TheiractivityismainlyduetotereactionoftheiractiveconstituentswithCa(OH)2producedfromcementhydration(pozzolanicactivity)andtheformationofhydratedproductswithbindingproperties.Theexactstuctureandchemicalformulaoftheseproductsarestillunknown.
Thedetailedknowledgeofcementpastemicrostructureisofgreatimportancefortheunderstandingandpredictionofcementapplications’performance.Visualexamination,opticalmicroscopy,andscanningelectronmicroscopy(SEM)havebeenextensivelyusedinmicrostuctureresearchofhardenedcementpasteandconcrete,providingadditionalunderstandingofmacroscopicalproperties.Electronmicroprobeanalysisstudiesofhardenedcementpasteshavecontributedtothecompositionalcharacterizationofhydrationproductsandspatialinformation.Transmissionenergymicroscopy(TEM)enablestheidentificationandanalysisoffeaturesonasignificantlysubmicrometrescale.However,thesetechniquesmostcommonlyinvestiatespecimensunderhighvacuum,andthusalterationofdamageonmicrostructuremorpologymayoccur.Furthermore,someofthesematerials,suchassilicafume,withagrainsizedistributioninthe0.02to0.3umrange,aretoosmalltobeobservedindetailbySEM.Techniqueswithstrongermagnificationcapabilitieswouldbeveryusefulinthesecases,aswellinthebetterconceptionofthepurecementpastemicrostructure.
Byatomicforcemicroscopy(AFM),asharptipisscanningoverasamplesurfaceandthreedimensionalimageshaveingresolutionatnanometerlevelareobtainedatatmosphericconditions(roomtemperature,humidity,andambientpressure).AFMhasbeenusedtoproduceatomicresolutionimagesofbothconductorsandnonconductors.Inthepresentdecade,AFMhasalsobeenusedinthestudyofcementsurfacemicrostucture,especiallybecausesurfacescanbeimagedunderaqueoussolutionsatnormalconditions.AFMhasbeenappliedtoinvestigatethesurfaceofalitealoneandofalitecoveredwithanorganicadmixtureandhasshownthatthesurfaceroughnessofthealitedecreasedmarkedlyafterreactionwiththeorganicadmixture.AFMwasalsousedtoinvestigatetheearlyperiodofportlandcementhydration,andamembrane/osmosismodelwasproposed.Acombinationofnuclearmagneticresonance(NMR)andAFMshowedthatthehydrationrateishighlycorrelatedwiththeroughnessofthegelsurface.Forflyashparticles,AFMshowedtwotypesofspheres,dark,largeones(approximately100um)withnumerouscratersontheirsurfaceandclear,smallones(approximately10um)withsmoothsurface.
Inthepresentwork,AFMwasusedtoobserveparticleshapeandsurfacetexturedetailsofcementsilicafume,flyashes,andhydratedmixtures.Distinctmicrographsof1um×1umweretaken,providinginformationontheparticleshapeoftheadditionsandmicrostructureofthehydratedmixtures.ThesamematerialswereexaminedunderSEMtoobtainageneraloverview,andthecomparativeuseofthesetwomethods(SEM-AFM)isdiscussed.Finally,thecorrelationbetweenthemicrostructureandthemacroscopicalengineeringanddurabilitypropertiesofcementproductsisdiscussed.
2.Experimentalprocedure
2.1.Materialsandsamplepreparation
Threetypicalcementitiousand/orpozzolanicadditionswereexamined;asilicafume,alow-calciumflyash,andahigh-calciumflyash.Thesilicafume(SF)originatedfromNorway(ElkemMaterialsA/S,Kristiansand)andisatypicalhighlypozzolanicmaterial.Thelow-Caflyash(FL)wasproducedisDenmark(distributedbyDanaskeI/S,Aalborg)andiscategorizedasnormalpozzolanicmaterial.Thehigh–Caflyash(FH)wasproducedinGreece(PublicPowerCorporation,Ptolemais)andisacementitiousmineraladmixture.Thus,thechoiceofthesematerialscoversalmostalltherangeofcementitious-pozzolanicby-productsusedinconcrete.SFandFLwereusedastheyweredeliveredfromtheproducers,whereasFHwaspulverizedpriortouse,tomeettheFLmeanparticlesize.Anormalportlandcement(350m2/gBlaine’sfineness)wasused.
Themainphysicalpropertiesandchemicalanalysesofthematerials,determinedbyX-raysedimentationtechnique,showedthatthemeanparticlediameterofflyasheswas13um,similartothecementparticles.SFparticles,asreportedintheliterature,areabout100timessmallerinsize(0.1umaveragediameter).
Fourpastespecimenswerecastinsmallplasticcontainers.Thepastesweremadeofnormalportlandcement(control),cementplus10%silicafume,cementplus20%low-calciumflyash,andcementplus20%high-calciumflyash.Awater-to-cementratio(W/C)of0.5wasretainedforallpastes.First,thecementamount(10g)wasaddedandthenthecorrespondingamountoftheadditive.Thesematerialsweremixedbyhandfortwomin;thenthecorrespondingamount(5g)ofthewaterwasaddedandthefreshpastewasfurthermixedfor2min.Onedayafterthecasting,1mlofwaterwasaddedtoallspecimens.Thecontainerswerehermeticallysealedandplacedat20℃constanttemperature.Microscopyanalyseswereperformedaftersixmonths.
2.2.Atomicforcemicroscopy
Materialparticlesandpastesampleswereexaminedbyatomicforcemicroscope(RasterscopeTM4000,DanishMicroEngieeringA/S)runninginnoncontactmode(0.1nNforce).Theparticlesinthecement,silicafume,andflyashesweredispersedbyultrasonictreatment;thesilicafumeindistilledwaterandtheothercomponentsinacetoneinordertoavoidhydartion.Thespecimenswerepreparedbyleavingonedropofthesuspensiontodryatroomconditionsonablockofhighlyorientedpyrolyticgraphite(HOPG).Thesamplesfromtepasteswereremovedbyhammerstrokefromthepastespecimens,oven-driedat105℃for24h.SmallpiecesofmaterialwerethengludeontoAFMsampleholdersandslightlypolishedindrycondition.Allspecimenswereexaminedatroomconditions(~20℃,1atmand40-60%relativehumidity).
2.3.Scanningelectronmicroscopy
Alloftheaboveparticlesandpasteswerealsoexaminedbymeansofscanningelectronmicroscope(LEO435VP).Surfacemicrographsof8,000magnificationsizewereobtainedandcanbeusedasageneraloverviewofthematerials.
3.Resultsanddiscussion
3.1.Cement,silicafume,andflyashparticles
TypicalSEMmicrographsinFigs2-5.
AsobservedbySEM(Fig.1a),cementparticleshaveandirregularpolygonalshape.Particlesizesrangefrom15tolessthan0.5um.FromAFM(Fig.2),someparticlesofsize1to0.5umndiameterarerounded,withaglobularsurface,whereasothersarepolygonal.However,someirregularparticlesofsizelessthan0.1umindiameterwereobserved(Fig.2,right).
SilicafumeparticlesaretoosmallinsizetobeimagedindetailbySEM(Fig.1b).FromAFM(Fig.3),thesilicafumeinvestigatedhasparticlediametersofabout0.1um,inagreementwithpreviousreporteddimensions.Twoparticleshapesarepresent,onespheroidandonecylindrical.Itisverycharacteristicofthematerialthatallparticlesarecomposedoftwocomplimentaryparts(hemispheresorsemi-cylinders).Thisfeaturecanbeexplainedfromtheproductionofsilicafume,wherethereductionofquartztosiliconatabout2000℃producesagaseousSiO,whichistransportedtolowertemperatrues,whereitisoxidizedandcondensed.ThisparticularshapecanhelpinSFidentificationincementpasteduringthehydrationprocess.
Ingeneral,flyashesconsistofglassyspheresofvarioussizes.Duetothelowerproportionofsurfacedepositsconsistingofalkalisulphatecrystals,FLtendstoshowacleanerappearanceinSEM(Fig.1c).FortheFH,manyoftheparticlesareplerospherescontainingnumeroussmallerparticles,butaftergrinding,smallersizeparticlesareproducedhavinganirregularshapelikethecementparticles(Fig.1d).UsingAFMtechnique,itisobserved(Fig.4)thattheFLconsistsprimarilyoflargespheroidparticles(approximately3um)withasmoothsurface,likefoundpreviously,andofsmaller(inonedimension).Thesenano-sizeparticlesmaybecorrelatedwiththeearlypozzolanicactivityoftheflyashes.
3.2.Pastemicrostructure
SEMmicrographsforallmaturepastesaresummarized
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