用超临界流体化学沉积法制备陶瓷材料外文文献

用超临界流体化学沉积法制备陶瓷材料外文文献用超临界流体化学沉积法制备陶瓷材料外文文献 Contents listsavailable atScienceDirectThe Journalof Supercritical Fluidsjournal homepage elsevier locate supf l uPreparation ofceramic materialsusing supercritical f l uid chemicaldepositionLucileHenry a J r me Rogera Yann Le Petitcorps a Cyril Aymonierb Laurence Maill a a University of Bordeaux RS Safran CEA LCTS Laboratoire des CompositesThermoStructuraux UMR5801 F 33600Pessac Franceb RS Universityof Bordeaux ICMCB UPR9048 F 33600Pessac FranceG R A PH IC AL A B S T RA CTA RT IC LE IN FOKeyword SiCCarbonSupercritical f l uidchemical deposition SFCD Supercritical f l uidchemical inf i ltration SFCIn Chemical vaporinf i ltration CVI ABSTRAC TThispaper relatesan unconventionaltechnique based on thesupercritical f l uidtechnology formanufacturingdense ceramicmatrix posites which isknown as the Supercritical Fluid Chemical Deposition process SFCD By usinga conventionalprecursor in a solventabove itscritical coordinates it ispossible tofaster thedeposition rate of a SiC based matrixon f i brouspreforms in parison to the Chemical Vapor Depositiontechniquefor whicha lowpressure 1 50kPa is remendedfor asimilar rangeof temperatures800 1000 C mixture N2 tetramethylsilane99 2 0 8vol The microstructureof thecoating ormatrix ischaracterized byopticalmicroscopy Spectroscopy ElectronMicroscopy andElectron DispersiveX ray spectroscopy The inf lu ence of the mainexperimental parameters temperature pressure residence time is studiedon the chemicalposition of the ceramicdeposits The opportunityto tuhe C SiC molarratio opensthe door towardsmultilayered interfacesexhibiting multifunctional properties 1 IntroductionNon oxide ceramics generally C and SiC based ones demonstratehigh thermomechanicalproperties andlow density That iswhyceramic matrix posites CMCs are used for aerospaceand aero nautic applicationsin replacementof metalsand alloys 1 Especially SiC based positesdisplay chemicaland thermalstabilitybined with the ability to avoidfracture under extremeconditions Indeed due tohighest mechanicalproperties under hightemperature high stressand forlong utilizationtime incorrosive oroxidativeatmospheres they areused asengine ponentsfor aero propulsion systems As example for nearlystoichiometric and pure SiCf i berand matrix CMCs withstandthousands ofhours upto1600 Cwith zerostress conditions Once theyare submittedto stress time dependent deformationstarts at around1100 C 2 For ensuringsucha highperformance level the CMCsfabrication routeshould beper fectly controlledand optimizedto achieve a near dense pure and stoichiometric SiCmatrix Several conventionaltechniques aredeveloped at the industrialscalefor producingseveral tons year of CMCs Chemical Inf i ltrations doi 10 1016 j supf lu xx 11 012Received5Octoberxx Received inrevised form14Novemberxx Aepted15Novemberxx Corresponding author at LCTS 3all edela bo tie 33600Pessac France E mail address maille lcts u bordeaux fr L Maill The Journalof Supercritical Fluids xxx xxxx xxx xxx0896 8446 xxElsevier B V All rightsreserved Please citethis articleas Henry L The Journalof SupercriticalFluids xx s doi 10 1016 j supflu xx 11 012techniques arewidely employedto densify3D porous substrates Thetwo mostwell known routesare usingeither a gaseous precursor ChemicalVaporInf i ltration CVI 3 oraliquid metal Melt Inf i ltrationMIor ReactiveMelt Inf i ltrationRMI 4 For CVI the densif i cation ofthe substrate is achievedthrough thecracking of the gasin the porosityof the substrate under vacuumand at a temperaturebetween800and1000 C Whereas forMI the densif i cationof the substrateiscarried outbyinf i ltration ofmelt silicon 1400 C andunder vacuum In thecaseof CVI the densif i cation kiics areslow about1 m h asthe tem perature conditions are moderate However theporosity of the f i nalproducts islow 10 15 In thecase ofRMI high temperatures arenecessary toobtain moltenSi Hence the liquidfurther reactswith theC containing preformto giverise to a SiCdeposit Si l C s SiC s Due tohigher temperatures this techniqueallows fasterkiics However such temperature conditionsaredetrimental for the me chanical and chemical propertiesof the preform Besides the as ela borated SiCmatrix containsfree Si atoms On theother hand thedensif i cation rateis high showing a lower residualporosity of5 10 so theMI matricesshow highdensity but thecreep resistanceof theCMC is aff ectedby theimpurity level rate of free Siatoms 2 Inopposition the CVImatrices exhibitreliable structuralproperties buttheirmanufacturing costsare raisedby along depositiontime duringthe densif i cation process To overethe issuesof thesetwo conventionaldensif i cationtechniques 5 the deposition and inf i ltration of carbon materials wereinvestigatedunder supercriticalconditions Indeed the formation ofpyrocarbons from methane under high temperature and pressurecon ditions wasrecently reportedby Maill et al 6 The authorssuc ceeded totailor themorphology the anisotropyand thecrystallinity ofthe as deposited pyrocarbons Besides one majorbenef it isthat thedeposition rates ofC at a pressure of5 10MPa and a temperature of950 1050 C are ohousand timesfaster thanthe onesrecordedbelow0 1MPa in thesame temperaturerange i e aording toCVItechnique 7 10 In this paper SiC based matricesare generatedby aninnovativeprocess basedon theSupercriticalFluid ChemicalDeposition SFCD technique Indeed SFCD is a well known approachfor controllingthef inalpropertiesof inorganicdeposit inplaying withseveral operatingparameters 11 15 For instance crystalline thin anddense coatingofoxide could be preparedvia theSFCD routein a cold wall reactor 16 17 Moreover this technique of f ers agreen alternativefor surfacemodif i cation 18 So far SFCD hasnot beeninvestigated for CMCsdensif i cation Thereby this paperintroduces anew concept the pos sibility toachieveaceramic densif icationby runningthe inf i ltrationanddeposition stepsin adense media This newprocess can be namedSupercriticalFluidChemicalInf i ltration SFCIn The useof thesupercritical technologypaves theway forenhancedtunability of thechemicalposition purity andmicrostructure ofSiC based matrices Conventional techniquesare utilizingorganosilicon speciesas SiCprecursor As example tetramethylsilane TMS diethylsilane andtriphenylsi lane 19 lead to the formation of SiC materials withCpollution due to thecracking of the as released methane A solutiontoprevent thecracking of methane is to mixthe precursorwith dihy drogen tolower kiics 20 22 and ortoreact withfree Cto formmethane 23 Another optionistouse methylsilane 24 with theadvantageof notreleasing methaneupon cracking and tobe halogenfree contrarily to the classicalSiC precursors In theconsidered method the reactivemedium isconstituted ofnitrogenand alow content of TMSas precursor Only theoptimizationof the pressure andtemperature conditionswas carried out tobothprevent the C depositionfrommethanecrackingandlower the C SiCmolar ratio of thecoating 2 Experimental section2 1 ReactorA newtype ofcold wallreactor hasbeen designed The experi mental set up ismade ofdif f erent unitsallowing theheating of a gra phite support and orthe porous preformattached underhighpres sure and high temperatureconditions Fig 1 The dif f erentunits are A high pressure andhigh temperaturereactor made ofInconel with acapacity of0 5L Two electrodesto heatup the graphite supportby Jouleef f ect Two clampsto maintain a goodcontact betweenthe electrodes andthe graphite support A thermocouple K type localized inside the graphite support fromwhichthe temperature of the process is set A regulatedpower supplythat delivers a currentthrough theelec trodesand thegraphite support An inletto removeoxygenated moleculesthanks tothe vacuumpump because carbonmaterials are extremely sensitiveto oxygen and toinject the liquid orgas precursors An outletconnected tothe pressuresensor and tothebursting disk First the preformis mountedon thegraphite support Then thewhole element preform andgraphite support is maintainedin thereactorwith twoclamps The thermocoupleis theninserted insidethegraphite support After the reactor isclosed the vacuumpump isturnedon for15min Once thepump isturned off a leaktest isrun underpressurewith aninert gas nitrogen If thetest isconclusive the inertgasis f l ushed out thereactor Then the temperature issetand theprecursoris injecteduntil the working pressureis reached The contactbetweenthepreformand the precursors iskept allalong the treatmentperiod The temperaturevariation iscontrolled byplaying with thepower supply At theend of thetreatment the powersupply isstoppedand thereactor cooleddown toroom temperaturebefore releasingthepressure Before opening thereactoris putone lasttime undervacuum 2 2 MaterialsDif ferent kindsof carbonsupports wereinvestigated inthis study First to studythe depositionof SiC a tubulargraphite supportwas usedas a heatingpart length of6cm outer diameter of0 6cm andinnerFig 1 Scheme of the coldwallreactorused forthe productionof SiCmaterials L Henry etal The Journalof SupercriticalFluids xxx xxxx xxx xxx2diameter of0 3cm Secondly to studythe densif ication and inf i ltrationcapacityof themedia a porous carbon preformwas f i xedon thegra phitesupport length of2cm outer diameterof1 5cm andinner dia meterof0 6cm with an openporosityof about77 2 3 PrecursorThe tetramethylsilane TMS precursor was bought fromSigma Aldrich andits purityexceeds99 For allthe experiments nitrogenwas usedas solventto reachtheworkingpressure inwhich4mL of TMSwas injected Nitrogen gaswasboughtfrom Airliquid with a purityof99 99 The injectedquantity ofTMS is in largeexcess inparisonwith thesize of the support Hence it is considered that the criticalcoordinates of themixture N2 TMS 99 2 0 8vol areextremelycloseto theones ofN2 Tc 147 C Pc 3 4MPa 2 4 Experimental dataToassess the feasibility ofdepositing SiC or C based materialsfromTMS underdif ferent temperature and pressure conditions in acoldwallreactor two dif ferentsupports were used Firstly a graphitesupport samples1 2 3 4and5 underwent asingle step infi ltrationwith acontact time of10min a temperatureranging from650to1000 C andaninitial pressure of1or4MPa Table1 Secondly theporoussub strate sample6 was densifi edby fi vesuessive runsof infi ltrationwith a contacttime of10and5min at750and800 C respectively with aninitial pressureof4MPa For allthe runs the initialquantity ofTMS isinexcess 4mL and isprocessed intothe N2fl uid 2 5 Characterization techniquesAfterall experiments the sampleswere insertedinto anepoxy resincuredat roomtemperature for48h Then the sampleswere cutandtheir surfacefi nely polished The polarizedlight microscopy PLM ME600L fromNikon wasused totake photographyat themicron scaleofpolished surfaces The microstructurewas studiedby scanningelectronmicroscopy SEM Quanta400from FEI in thesecondary orback scattered electronsdetection modes The aelerationvoltage of5kV leadstoaspatial resolutionof about2nm The chemicalanalyseswere performedby electrondispersive X ray spectroscopy EDS Thecrystalline phaseswere assessedby X Ray Diff raction XRD D8Advance fromBruker in Bragg Brentano geometryand witha CuK radiation pointsource The XRDpatterns wererecorded overthe range20 90 a stepsize of0 01 and acounting timeof0 3s perstep 2 6 Thermodynamic studyIn the nextsection the evolution of ourreactive systemunderex perimental conditionsis assessed The temperatureranges from800to1000 C and the pressurevaries between0 1 10MPa To investigatethe reactivityofTMSunderhighpressure andtem peratureconditions theoretical calculationswere performedusing theThermocalcsoftware 25 This softwarewas runto predictthe equi librium stateofa def ined systemby minimizingits Gibbsenergy on thebasis of the NASAdatabase 26 All calculationsof ThermoCalcaim fortheminimization of the Gibbsenergy of the systemand theyare basedon thermodynamic datawhich issupplied in a database The databasesareproduced byexperts throughcritical assessmentand systematicevaluationof experimentaland theoreticaldata As norelevant super critical thermodynamicdata beingavailable forthe presentsystem atveryhigh pressures gaseous datawereusedsimplistically fortheputations bytaking into aount theentropic ef fect of the pressure A fi rstguess of the infl uence of theoperating parametersis thenex pected from the so obtained results So the amountsof thedif ferentphases SupercriticalFluidand solidcarbon or SiC orSi are estimatedatthe equilibriumstate in orderto quantifythe carbonor siliconcarbondeposition yield i e the number of carbonorSiCmoles pared tothe initialnumber ofTMS moles Firstly the criticalcoordinatesofTMS are Tc 175 6 C andPc 2 8MPa So the TMSisassociated toagas phase below2 8MPawhereas over it isreferred as a fl uidphase Then the reactionsthatcould ourin our system are Si CH3 4 l SiC s 3CH4 g 1 1 CH4 g C s 2H2 g 1 2 During deposition solid phases such asC Si and SiC anda fl uidphase containinglow molecularweight hydrocarbonscould begener ated inour system The stability of allthe phasesunder peculiarde position conditionswas studiedwith theThemocalc software Indeed itenabled usto studythe position of the system atits equilibriumstate An initialpressureof4MPa and1mol ofTMS areset in the soft ware The thermodynamic calculations arerun for3temperatures 800 850and900 C to followthe molar position of the systemfrom0 1Table1Experimental parametersusedforthe study of the densification L Henry etal The Journalof SupercriticalFluids xxx xxxx xxx xxx3to10MPa Fig 2a b andc showsthe molar position of the system of the gasphase of thesolid species C andSiC at equilibrium as afunctionof thepressure at varioustemperatures It isnoticed that the molarnumberofdeposited Cincreases with thetemperature anddecreases whenthepressuredecreases whereasthemolar numberof SiCstays constantwith thesetwo parameters Fig 2 So theoretically C andSiC solidscan beproduced overthetem peratureand pressure rangesthat arestudied inthispaper Althoughdif ferent C SiC molarratios of the final product areavailable it doesnotseem thatpure C andpureSiCmaterialscan beobtained whenpro cessing TMS However it isexpected toplay withthe Ccontentof thef inalproduct i e onthestability ofas release methane by varying thetemperature and pressure conditions Fig 2 d showsthe evolutionofthe molarposition ofthe gasphase at800 C We cansee thatCH4and H2are the majority phasesinthe system The otherphases produced C2H6 C2H4 C3H8and C3H6 are negligible As aconclusion this thermodynamic study highlightssome trendsregardingthe thermodynamicevolutionof oursystemunder peculiarconditions It appearspossible toform SiC orC rich ceramics however thestudyexhibits severalrestrictions i the kiicsare nottaken intoaount ii intermediate speciesare notrevealed and iii the fl uidphaseisconsideredasahighpressure andhigh temperature gasphase Hence it isnecessary toperform experimentsto checkif theevolutionof thesystems corroboratesthe thermodynamicstudy 2 7 Supercritical fl uidchemical deposition SFCD ona graphite supportFirst the infl uence of temperatureandpressureonthechemicalreactivity ofthesystemis detailedin thenext sections The depositionofceramics wasperformed onagraphitesupport 2 8 Inf luence of temperature at4MPaAs it canbe seen onthe SEM micrographs below Fig 3a brightnodules embeddedin afibrillar foamstructure wereobtained at1000 C and4MPa Chemical analysisrevealed thepresence ofbothcarbon foamandSiC nodules atthe surface of sample1 Fig 3 The averagepositionofthe SiCnodules ispresented inTable2 The analysisshows that33 ofthe carbon atomsare involvedin aSibond whereas66 refers tocarbon withtraces ofoxygen atoms The temperaturewas thenlowered to900 C for preventing Cde position From Fig 3b it isobserved thatby decreasingthe tempera ture the formation of carbon foam decreasestoo Hence the majorpartof the sample consistsin SiCnodules For thethird sample at atemperatureof750 C thesampledis played athick homogeneous anddense SiC coating It isclearly visiblethatcarbonfoamwas producedbut ina limitedquantity In betweenthesetwo phases homogeneous nucleationourred andgave risetoFig 2 Scheme ofmolarpositionofthesystem atequilibriumasa functionof pressure at a 800 C b 850 C andc 900 C d Evolution ofthemolarpositionofthegasphase at800 C L Henry etal The Journalof SupercriticalFluids xxx xxxx xxx xxx4carbon blacksdepending onthe temperatureandpressureconditions 24 The formationof carbonblacks resultedfrom twomain steps i the growthof primarymolecular speciesinto largepolycondensedspecies in thegasphase and ii the aggregationofCnuclei toformnano sized and then micro sized sphericalparticles The calculateddepositionratewas800 m h at750 C and4MPawhen theatmosphere involvesa N2 MTS mixture 99 2 0 8vol From literature depositionrateat900 C reaches2 m h at0 04MPawhen workingwith CH3SiHCl2in H2 10 90vol 27 and isabout100 m h at0 1MPa whenworking ina mixtureof CH3SiHCl2 H2 30 70vol 28 Hence it appearsan increase of kiicswithpressure whichcould beexplained bythe factthat thedensity oftheprecursor increasesalso withpressure This newtechniqueoffersthepossibility toplay withkiics ofthe SiCgrowth whichallows usanextremely finecontrol ofthedensificationtime The as deposited coatingwas recoveredfromthe surface ofthegraphite supportand then milled toperform X Ray Diff raction XRD analysis onpowder Aording tothe XRDpattern Fig 4 the coatingisposed ofcubic crystalsof SiC andgraphite A denseSiC coatingisadherent tothe surfaceofthegraphitesupport Fig 3c Hence it isassumed that tracesofthegraphitesupporthave beenadded tothe SiCFig 3 SEM micrographsofthe deposit embeddedinapolymer matrixanalyzed bybackscattered electronsand produceda at1000 C sample1 and b 900 C and4MPa sample2 andc Optical imageofthecoating obtained at750 C and4MPa sample3 Table2Carbon oxygen andsilicon atomicpercentage ofdifferent nodulesby EDS Atomic position12345AverageC at 817272706472 5O at 443534 1S i at 152425253324 6Fig 4 X ray diff ractionpattern ofthe milledcoating obtainedat750 C and4MPa Fig 5 SEMmicrographofthedeposit producedat