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简介：TherearemanyprocessestoproduceCr2O3fromchrome-ores,DifferentparticlesizerangesofCr2O3powder,finepinmentgradegreenCr2O3andcoarsemetallurgygradeblackCr2O3,aremadebydifferentprocessesinChina,GreenCr2O3assuperfineandadditionandmetallurgygradeblackCr2O3usedtosynthesizeCr2O3graincanbeappliedtorefractories.ItisverydifficultforhighpurityCr2O3tosintertodensificationandTiO2additioniscontributedtodensificationofCr2O3sinteredathightemperature,Cr2O3grainswithrelativedensityof91%-95%aregainedbysinteringCr2O3withTiO2additionandelectrofusingCr2O3rawmaterials.

简介：Thehydrationoftricalciumaluminate(C3A)hasasignificanteffectontheeffectivenessofcement-basedsystems.Inaddition,thecarbonationofhydrationproductsofC3Aisparticularlyimportantinrespectofdurabilityperformance.ThepresentworkinvestigatesthehydrationandcarbonationreactionsofC3AandthechangesinducedbythepresenceoftheheavymetalionssuchasZn2+,Pb2+,Cu2+andCr3+byX-raydiffractometry(XRD).DuringhydrationofC3A,gehlenitehydrate,hydrogarnet,calciummonoaluminate(C4AHx)andcalciumcarboaluminateweredetectedinC3ApastesexcepttheZn2+dopedpaste,wherehydrogarnetdidnotform.Theexaminationsrevealedthatheavymetalscoexistedwithgehlenitehydrate,calciummonoaluminate(C4AHx)andcalciumcarboaluminate,inhibitingtheformationofhydrogarnet.HydratingC3Awasliabletobecarbonatedonexposuretoairandcarbondioxide,especiallyinthepresenceofheavymetals,resultingintheformationofcarboaluminateand/orcalciumcarbonate.Thepresenceofheavymetalsin-fluencedthepolymorphismofcalciumcarbonate,ndicatingthatheavymetalscouldco-precipitatewithcalciumtoformacarbonatesolidsolution.

简介：ThemagnesiabasedcurablespecimenswithdifferentSi3N4contentswerecastedusingsinteredmagnesite(w(MgO)=95%)asstartingmaterial,SiO2micro-powderasbinder,0.3%,4%and5%β-Si3N4powderreplacingtheequaladditionofmagnesiapowderrespectively.Theslagresistancetestwascarriedoutat1550℃for3husingBaosteeltundishslagandstaticcruciblemethod.Theresultindicatesthat:introducingSi3N4couldobviouslyimprovetheslagresistanceofMgObasedcastable,whichincreasedwithincreasingSi3N4.DenseSiO2sinteredlayerformedonthesurfaceofmagnesiabasedcastablebecauseoftheoxidationofSi3N4addition,whichcanpreventthefurtherslagpenetration.Inthedeepinnerofcastable,thepartial-pressureofoxygenwasverylow,soSi3N4canexiststably.Meanwhileinreducingatmosphere,Si3N4washardtobesintered,whichresultedinthelooseinteriorstructureofMgObasedcastable.

简介：Si3N4powderandhot-pressedSi3N4ceramicsaddedwithAl2O3areusedforinvestigatetheiroxidationbehviorinairandnitrogenatmosphere(withoxygenpartialpressurePO2=1-10Pa),TheoxidationproductsofSi3N4areexaminedbychemicalanalysi,X-raydiffraction(XRD)andXPSmethod,Also,thermodynamiccalculationismadetoanalyzeoxidationbehaviorofSi3N4.TheresultsshowthatonlypassiveoxidationwilloccurwhenSi3N4isoxidizedinairathightemperature,whereasinN2athightemperature,theactiveoxidationisdominantinspiteoftheexistenceofalittlepassiveoxidation.

简介：ThemechanicalpropertiesofpressurelesssinteringFe-Si3N4bondedSiCandSi3N4bondedSiCwithsamemanufactureprocesshavebeencomparedinthispaper.TheoxidizingmechanismofFe-Si3N4bondedSiCceramicmatrixcompositehasbeeninvestigatedespeciallythroughTG-DSC(thermogravimetricanalysis-differentialscanningcalorimeter)experiment.DuringoxidationprocedurethemainreactionistheoxidationofSiCandSi3N4,SiO2whichformprotectingfilmtopreventfurtheroxidizing.AndresidualironinthesamplesbecomeFe2O3andFe3O4,theoxidationkineticsat1100～1300℃ofre-Si3N4bondedSiChasbeenstudiedespecially.Theweightgainperunitareaatinitialstagechangesaccordingtobeelinerule,inthemiddleaccordingtoconic,andinthelastoxidationperiodfollowsparabolarule.

简介：DenseSi3N4BNcompositeceramicswerefabricatedbysparkplasmasinteringat1500,1600and1650℃under50MPafor5minusingSi3N4andBNpowdersasstartingmaterialsand2mass%Al2O3and6mass%Y2O3assinteringadditives.ThevolumefractionofBNinSi3N4BNcompositepowderswaschosenas10%,20%,and30%,respectively.TheresultsofXRDandSEMshowthatα-Si3N4completelyturnsintoβ-Si3N4whenthecompositeceramicsaresinteredat1650℃;theadditionofBNhindersthegrowthofSi3N4grains,refiningthestructure;VickershardnessandfracturetoughnessofthecompositeceramicsdecreasewiththeincreaseofBNcontent.

简介：Inthispaper,theinflucnceofchiefprocessparametersontheontinuousproductionofSi3N4powderbyrenitridationhasbeenstudied,Thesutiableprocessparametershavebeenfound,andhighqualitySi3N4powderhasbeendeveloped.

简介：Thespecimenswerepreparedbymoldingthemixtureofsilicafume(w(SiO2)=94.5%;averageparticlesize:0.08μm)andsiliconnitride(≤0.074mm)withamassratioof11,carbonembeddedfiringat1300℃,1450℃,1500℃,1550℃and1600℃for3hinair,andthenwater-cooling,respectively.Themicrostructureandphasecompositionofthespecimenswereanalyzed.Theresultsshowthat:(1)silicafumereactsobviouslywithSi3N4formingSi2N2Oabove1550℃.TheedgesandcornersofSi3N4grainsbecomesmoothandtheSi3N4grainsdistributeinthecontinuouscementationphaseofSi2N2OformingthedensestructureofSi2N2OpackedSi3N4;(2)below1500℃,theedgesandcornersofSi3N4grainsareclear,Si2N2Odoesn'tform,andonlySiO2crystallizesfromsilicafumewhichhappensobviouslyat1300℃.

简介：TheeffectoftheadmixturesofAlandSimetalsandB4CandMgAlONcompoundsontheoxidationofMgO/Si3N4compositerefractoryhasbeenstudied,whichisapromisingcarbonfreerefractoryforsteel-makingapplicatlon.Thefourkindsofadmixturescanbeusedasanti-oxidantsforSi3N4,butthemixtureofAlandSiachievedthebestresult.Themixturecannotonlyplaytheroleasantioxidant,butalsoassistthesinteringprocessandhelpformdensesinteringlayer,improvingthepropertyofthecomposite.

简介：Cr2O3canbesinteredwellat1500℃incarbon-embeddedconditionorH2atmosphere.Butthehighchromebearingrefractoriescannotreachdensificationwhensinteredat1700℃for10hinweakreducingatmosphereformedbythecombustionoffuel,anditsapparentporosityisabout18%.Thehighchromebearingrefractoriesaremainlyusedincoalgasifiers.Thetemperatureinthefurnaceisabout1500℃andtheproductsareH2andCO,whicharejustthesinteringconditionsofthedensechromerefractorieswithapparentporositylessthan10%.Thehighchromebearingrefractoriesusedincoalgasifiersmaybesinteredagainandthenshrink,destroyingthegasifierlining.Thethermodynamiccalculationshowsthatitissafeaboutthehighchromebearingrefractoriesusedingasifiers.Itisalsoexplainedthatthehighchromebearingrefractoriescan’tbesintereddenselyinweakreducingatmosphereformedbythecombustionoffuel.Thenewsinteringtechnologiescanbeusedtoimprovethebulkdensityofthehighchromebearingrefractories.

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简介：Reactionsintereddensezirconia-mullitecompositeswerepreparedbyisostaticallypressingfromzirconflourandreactivealuminawithdifferentproportionsofTiO2andCr2O3additives.Thepressedcompactsweresinteredatdifferentelevatedtemperatureswithvariablesoakingtimes.Microstructuresandphasedevelopmentinthesinteredcompactswereanalysedtoassesstheinfluenceoftheadditivesonthepropertiesofthezirconiamullitecomposite.