多孔尖晶石耐火材料外文文獻(xiàn)

多孔尖晶石耐火材料外文文獻(xiàn) Perspectives inScience (xx)8,2224Available onlineat .sciencedirect.ScienceDirectj ourna lhomepage:.elsevier./piscIntroduction toporous spinelfor refractory(high temp)material?Kumar Saurav?,Manas RanjanMajhi,Vinay KumarSinghDepartment ofCeramic Engineering,Indian Instituteof Technology(BHU),IndiaReceived24Decemberxx;aepted26JanuaryxxAvailable online5FebruaryxxKEYWORDSCeramics;Mechanicalproperties;MicrostructureSummary Thepaper examinesthermal properties of materials.The transient pulse methodwas used forspecif ic heat,thermal diffusivityand thermal conductivity determination.PorousMgO wassynthesis byheating pelletsat1100?C for1h.The resultantporous MgOwas thenimmersedin10mol/L aluminum nitrate solution,dried,and reheated at1300?C for2h toconvertit tospinel.The evaluationwas performedwith thehelp ofmathematical apparatusused for study of fractal structures properties.The methodresults fromgeneralized relationsthatwere designedfor studyof physicalpropertiesoffractalstructures.As it is showntheserelations arein agood agreementwith theequations used for thedescription oftime responsesoftemperature forthe pulseinput ofsupplied heat.?xxPublished byElsevier GmbH.This isan openaess articleunder theCC BY-NC-ND license(creativemons/licenses/by-nc-nd/4.0/).IntroductionAmong thesuitable materials for energysaving purpose,porous ceramicsare outstandingbecause theybineintrinsic ceramicproperties,such aschemical inertnessandrefractoriness,with lowthermal conductivity.Besides sav-ing energy,the diminishedheat lossto theenvironmentalso improvesworking conditionsminimizing theemployeesstress as a resultof theirexposure tohigh temperatures.?This articlebelongs to the specialissue onEngineering andMaterialSciences.?Corresponding author.Tel.:+919621199305;fax:+919621199305.E-mail address:ksaurav.coolgmail.(K.Saurav).Porous ceramic products coverwide rangeof advancedceramicmaterials,which can be oxides ceramics:alu-mina,zirconia,or non-oxidesceramics:carbides,borides,nitrides,silicides.The propertiesof porousceramicprod-uct dependon threemain factors:the propertiesof theceramicmaterial ofwhich the product ismade;the topol-ogy(connectivity)and shapeof the pores;and therelativedensity of theproduct(Salvini etal.,2000;Colombo,xx;Lyckfeldt andFerreira,1998;Park etal.,1997;Sarkar etal.,1999;Studart etal.,xx).Meanwhile,pore formersandother starting materialsforporous ceramicsused inthe con-ventional methodswere first preparedseparately and thenmixed.Among thetechniques usedto producethese mate-rials(such asthe additionof foamingagents andorganiompounds),theporegeneration viaphase transforma-tion presentskey aspects,such aseasy processingand theabsenceof toxicvolatiles.dx.doi/10.1016/j.pisc.xx.01.0072213-0209/?xxPublished byElsevier GmbH.This isan openaess articleunder theCC BY-NC-ND license(creativemons/licenses/by-nc-nd/4.0/).Introduction toporous spinelfor refractorymaterial23Figure1Pore sizedistribution ofporous MgOwith fi fth solu-tion treatmentssample contains(48%)porosity.ExperimentalFine magnesiumoxide(Thomas baker,India,0.10mm indiameterand98%pure)wasusedas asintering additive.Ex potatostarch(.50mm,Loba Chemie)and PVAwere alsoaddedto thestartingmaterialsasapore former.All pow-ders usedas pore-formers werepreviously dried at100?Cfor24h.After thisstep,their densityand surfaceareawere measuredin AuPyc1330helium pyometerandBET equipment(Micrometrics,USA),respectively.Lightlycalcined(f ine powder)magnesia andEx potatostarchC6H10O5n(Loba Chemie,Mumbai)was mixedand thenpolyvinyl alcohol(f ine powder)are mixed.The batcheswereprised ofporous MgO(60:30:10MgO:Starch:PVA)wereattrition milledfor3h andthen driedat100?C for24h.The powderswere shapedin pellet(piece ofsmall shot)form usinghydraulic pressingmachine(uniform pressing)with appliedload of15ton.The sampleswere fired attemperatures1100?C.The heatingrate wasmaintained at3?C/min andsoaking periodwas2h.The sinteredsamplewas immersedinto thealuminum nitratesolution for1hunder vacuum,removed,andthendriedatroom tempera-ture for24h.The resultantsample wasreheatedat1300?Cfor2h inair.This solutionimmersion andreheating treat-ment was performed upto five times.After eachsolutiontreatments arecharacterized byXRD,SEM.The micrographinFig.1reveals ahomogeneous pore size ofless than2?mand variationin poreshape andsize.At leasttwo differ-ent characteristicpore sizescan beidentif i ed.The mercuryporosimetrymeasurements confi rmthat thesamples exhibitbimodalporesizedistributions,constituted bymesoporeswith diameterless than1?m andby macroporeswith diam-eter above1?m.Results anddiscussionSpinel formationTheformation of the porousspinel fromporous MgOand alu-minumnitratesolution afterfi fth solution treatmentswasFigure2XRD ofporous MgOwith solution treatments.studied.Fig.2shows diffractionpattern ofporous MgOwithnumber of aluminum nitratesolution treatments.Initiallyafter first solutiontreatment asmall peaksof spinel aredetected,which indicatedthat theMgO reactswith aluminaandforms spinel.As canbe seen,no aluminawas detectedinany sample,which indicatesthat theinitially precipitatedaluminapletely reactedwith MgOto formspinel dur-ing processing.After five solution treatments hugeamountof spinelare formed.The ratioof spinelconversion iscal-culated byweight gainformula aordingto thechemicalreaction.Actually morethan35%spinelareformed afterthefi fthsolutiontreatments.Fig.3shows anSEM micrographof aporous MgOsam-ple with fifthsolutiontreatments,a largeamount ofwhiteball aredeveloped whichindicate hugeamount ofspinel areformed.This suggeststhat thealumina plateletswere fullycoveredwith theprecipitated spinel.Thermal behaviorThetransientpulsemethod wasusedforspecif ic heat,thermal diffusivityand thermalconductivity determination.The evaluationwasperformedwith thehelp ofmath-ematical apparatususedforstudyoffractal structuresproperties.Incorporation ofporosity intoa monolithicmate-rial decreasesthe effectivethermalconductivity.Fig.4represents thetypical timeresponses oftemperature forthestep wiseof inputpower.The coeffi cientf a(fractal dimen-sion Drespectively)of the fractal heat source foreverypoint ofthe experimentaldependence(measured temper-ature dependedon time)was calculated.The fractal heatsource characterizesthe distributionofthetemperature inthespecimen inspecif ic time.From Fig.4itisevident thatforvery shorttime thereis thevalue ofthefractaldimensionD2and therefore,the planeheatsourceis formed.Figure3SEM ofporous MgOwithfifthsolutiontreatments.24K.Saurav etal.Figure4Typical timeresponses oftemperature forthe stepwiseof inputpower whenD=2.ConclusionPorous ceramicsfor applicationssuch asto reduceenergycosts,high-temperature insulationcanbeproduced bythedeposition ofEX potatoknown asstarch solu-ble(C6H10O5)n.In thisarticle,the