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19 ThethicknesdataforNGPspreparedinExamples1-3are summarizedinFIG.1,indicatingtheefectivenesofasur factantinpromotingexfoliation. EXAMPLE 4 SupercriticalFluidIntercalationandExfoliationof GraphiteFibersandMCMBs Continuousgraphitefiberyams(MagnamitefromHer10 cules)werecutintosegmentsof5mmlongandthenball milledfor24hours. MCMB2528microbeadsweresuppliedbyAluminaTrad ing,whichistheU.S.distributorforthesuplier,OsakaGas 15 ChemicalCompanyofJapan.Thismaterialhasadensityof about2.24g/cm;aparticlesizemaximumforatleast95%by weightoftheparticlesof37microns;mediansizeofabout 22.5micronsandaninter-planardistanceofabout0.336mm. Approximately5gramsofgraphitefibersand5grams MCMBswereseparatelyplacedinahighpressurevesel, whichwasSuppliedwithCOgasthroughpipemeansasin Example 1. The pressure at approximately 8.5 MPa was maintained while the vessel was heated to about 70° C. to achieveasupercriticalconditionofcarbondioxide.This25 intercalationprocesswasproceededforabout1hour,fol lowedbyasuddendepresurizationtotheambientpresure. Theresultingexpanded/exfoliatedstructureaftertheinitial cyclefortheMCMBsandgraphitefibersareshowninFIG. 2(A)andFIG.3(A),respectively.Foreachsample,theinter30 calationandexfoliationstepswererepeatedforanothercycle. RepresentativeTEMimagesoftheresultingNGPsareshown inFIG.2(B)andFIG.3(B),respectively.TheNGPsobtained fromgraphitefiberswerefoundtohavealength-to-width ratiogreaterthan10andanaveragethicknessof7.6run.The35 NGPsfromMCMBswerefoundtohaveanaveragethicknes of2.3nm. EXAMPLE 5 SupercriticalFluidIntercalationandExfoliationof GraphiteOxide(GO) 20 agentwith100partsofepoxyresinandcuredat60°C.for24 hourstoobtainanNGPnanocomposite. EXAMPLE 6 IntercalationandExfoliationofGraphitewitha SupercriticalFluidContainingSO SO vaporwasgeneratedbyaddingandheating10gof fumingsulfuricacidintoareactor.TheSOvaporwaspassed throughacolumninwhich10gofMCMBswaspackedfor receivingSO.AfterexposureofMCMBstoSO forone hour,thetreatedMCMBsamplewasplacedinapressure vesel.TheveselwassuppliedwithCO gasthroughpipe meansasinExample1.Thepressureatapproximately8.5 MPa was maintainedwhilethevesselwas heatedtoabout70° C.toachieveasupercriticalconditionofcarbondioxide. PresumablySOwasdissolvedinsupercriticalCO.This CO/SOintercalationprocesswasallowedtoproceedfor about3hours,followedbyasuddendepresurizationtothe ambientpresure. Uponcompletionoftheprocedure,theveselcontaining NGPswasslightlyheatedatabout60°C.forabout15min utestoremoveexcessiveamountofSO condensedonthe surfaceoftheNGPs,andtheseparatedSOwasrecovered andabsorbedintothesulfuricacidinthereactor.SO-treated NGPs were washed with water and filtered. Surprisingly, SO-treatedNGPswerefoundtobereadilydispersiblein waterwhiletheNGPSobtainedfromthesameMCMBswith outSO werenotdispersibleinwater.ItappearsthatSO has slightly oxidized or sufonated NGPs, imparting desirable functionalgroupsthereto. ItisofsignificancetonotethatSOO (oZone)andO.are butafewexamplesofreactivespeciesthatcanbeincludedin aSupercriticalfluidforexfoliatingand,esentialyconcur rently,functionalizingNGPs. InSummary,thepresentlyinventedprocessisSuperiorto manypriorartprocessesinseveralaspects: 2)Inanothercommonlyusedpriorartapproach,thegraph iteoxidedispersedinanaqueoussolutionwasreduced withhydrazine,inthepresenceofapolymer,Suchas poly(sodium4-styrenesulfonate).Thisprocessledto theformationofastableaqueousdispersionofpolymer coated graphene platelets. In some aplications of NGPs,however,apolymercoatingmaybeundesirable. Furthermore,thecommonlyusedreducingagent,hydra Zine,isatoxicSubstance. US 8,696,938B2 40 Graphite oxide was prepared by oxidation of graphite flakeswithSulfuricacid,Sodiumnitrate,andpotassiumper manganateataratioof4:1:0.05at30°C.for24hours, accordingtothemethodofHummers U.S.Pat.No.2,798, 878, Jul. 9, 1957. Upon completion of the reaction, the mixturewaspouredintodeionizedwaterandfiltered.The samplewasthenwashedwith5% HClsolutiontoremove mostofthesulfateionsandresidualsaltandthenrepeatedly rinsedwithdeionizedwateruntilthepHofthefiltratewas approximately7.Theintentwastoremovealsulfuricand nitricacidresidueoutofgraphiteinterstices.Theslurywas spray-driedandstoredinavacuumovenat60°C.for24 hours.Theinterlayerspacingoftheresultinglaminargraphite oxidewasdeterminedbytheDebey-ScherrerX-raytech niquetobeaproximately0.73nm(7.3A),indicatingthat extremelytedious.Suchalongprocessisnotamenable graphitehasbeenconvertedintographiteoxide. tothemassproductionofconductivenanographene 45 50 55 A curingagent,aliphaticamine(EPIKURE3223),was 60 platelets. mixedwiththeGOpowderata1:1weightratio.Themixture 4)Thepresentlyinventedprocessiscapableofproducing wasthenplacedinapressureveselandSubjectedtoCO. NGPswithnoorlitleimpurity. Supercriticalfluidintercalationandexfoliationtreatments Theprocesscanobviatetheneedforwashingandrinsing undercomparableconditionsdescribedinExample1.After depresurization,theNGPswerenaturalycoatedwiththe65 curingagent.Epoxyresin(EPON828)wasthenmixedwith thecuringagent-coatedNGPSataratioof12partsofcuring theplatelets(whichwasrequiredinthepriorartsolution approachtotheexfoliationofGOand/orsubsequentchemi calreduction).Thepresentlyinventedprocessisfastand environmentallybenign. 1)Priorartprocessesbasedongraphiteintercalation/oxi dationandhigh-temperatureexfoliationdidnotallow foragoodcontrolovertheoxygencontentoftheresult ingGOorNGPplatelets.Thepresentlyinventedprocess iscapableofproducingpristineNGPsthathavenever beenexposedtooxidation. 3)ConventionalprocessesofpreparingGO nanoshets that included chemical exfoliation typicaly werePDF Image | SCO2 Producing Nanographine Platelets
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