首页 最新固相反应精品课件

最新固相反应精品课件

举报
开通vip

最新固相反应精品课件Chapter7SolidStateReactionXuLingling,Dr.CollegeofMaterialsScienceandEngineeringNanjingUniversityofTechnology**第一页,共89页。PopularphysicochemistryduringhightemperatureprocessofsolidsMajorprocessofmaterialsmanufactureControltheindustrialprocessNecessary**第二页,共89页。D...

最新固相反应精品课件
Chapter7SolidStateReactionXuLingling,Dr.CollegeofMaterialsScienceandEngineeringNanjingUniversityofTechnology**第一页,共89页。PopularphysicochemistryduringhightemperatureprocessofsolidsMajorprocessofmaterialsmanufactureControltheindustrialprocessNecessary**第二页,共89页。DefinitionIngeneralchemicalreactionwithsolidphaseStrictlysolid+solidsolid**第三页,共89页。Classicalsolidstatereaction:Thestartingmaterialsarefinelygrindedpressedtoapelletandheatedtoatemperature„near“themeltingtemperature.Thereactionprogressthendependsondifferentparameters1.Temperature-activationenergyofdiffusionisloweredwithincreasingtemperatureempiricalrule:Treaction>2/3Tmeltingtemp.(T[K])2.Energetics-classicalSolidStatereactionsareingeneralexothermicand„thermodynamicallycontrolled“!3.YieldProductsareformedinayieldof100%4.GrainStructurePorosity,grainsizedistributionandcontactplanesbetweenreactinggrainsareofparamountimportanceforthereactionprogress7.1SolidStateReactions:GeneralAspects**第四页,共89页。CharacteristicsHeterogeneousreactionReactioninterfacebetweenthereactingphases,suchasnucleusandmatrixorcrystalandmeltThreestepsinseriesMaterialtransporttotheinterfaceReactionatthephaseboundarySometimes,transportofreactionproductsawayfromtheinterface(4)Reactionatthephaseboundaryliberateorabsorbheat,changingtheboundarytemperatureandlimitingtherateoftheprocess**第五页,共89页。Characteristics(5)Thetemperatureofsolidstatereactiontakesplaceislowerthanthatofmeltingtemperatureofreactantsoreutectictemperatureofsystem.~obviousdiffusion——TammanTemperature(泰曼温度)/Sintering(烧结)Temperature。metal:Ts=(0.3~0.4)Tmsalt:Ts=0.57Tmsilicate:Ts=(0.8~0.9)Tm(6)Anincreaseinsolid–statereactionrateisfrequentlyobservedatapolymorphictransitiontemperature——HedvallEffect(海德华(déhuá)定律)。**第六页,共89页。TypesofsolidstatereactionAccordingtothestateofreactantsolid-solidreactionreactionwithliquidreactionwithgas**第七页,共89页。AccordingtothecharacteristicsOxidation氧化反应Deoxidation还原反应Adding加成反应Replacement置换(zhìhuàn)反应Decomposition分解反应……**第八页,共89页。diffusion-limited扩散控制reaction-limited化学反应(huàxuéfǎnyìng)速度控制nucleus-limited晶核成核速率控制sublimation-limited升华控制………Accordingtothereactionmechanism**第九页,共89页。7.2Processofsolidreaction1.Mixingofreactantparticles,contacteachother2.Newphase(withlargeamountofdefect)formedbychemicalreactionontheinterfaceStructuretendstoperfect,crystalgrowthFurtherreactioncontrolledbythediffusion(bysurface,boundary,crystalfissure)ofreactantsubstancesthroughthelayerofproduct**第十页,共89页。ABgasphasediffusionvolumediffusioninterfacediffusionsurfacediffusionPossiblereactionpathesbetweentwosolidgrainsAandB**第十一页,共89页。Modelforaclassicalsolid-solidreaction(belowmeltingpoint!):Interfacebetweentwocrystalsortwograinsofapowderpossibleproducts:smallcrystallites(“powder”),singlecrystals...MgO+Al2O3MgAl2O4(Spinell)Phase1:formationofseedsPhase2:growthofseedsMgOAl2O3MgOAl2O3dx/dt~1/xxSolid-SolidReaction**第十二页,共89页。Diffusion–reactioninasolid/liquiddiffusion–coupleSolidparticlesLiquidPenetratingLiquidInterfaceThinoxidelayerasresultofsolid–liquidreactionattheinterface**第十三页,共89页。Step5.Theproductreturnstosurroundings.Step1.Thegaseousreagentdiffusesfromthesurroundingsontothecatalystsurface.Step2.diffusesintotheporousstructure.Step3.reactsattheporewalls.Step4.Theproduct,,diffusesoutofthepores.Diffusion–ReactioninaPorousCatalyst**第十四页,共89页。7.3GeneralkineticlimitsTheoverallreactionrateisdeterminedbytheslowestofallseriessteps.Classicalchemical-reactionkinetics:homogeneousreactionsThebasisforunderstandingratephenomenaofheterogeneousreaction**第十五页,共89页。ConsideringtheoxidationofmetalAfterreactingtimet,alayerofproductMOwithwidthhasbeenformedonthesurfaceofmetalMFurtherreactioncontrolledbytheprocesses:(1)diffusionofO2tointerfaceofM-MO;(2)oxidationofmetal**第十六页,共89页。Onthebasicprincipleofchemicalreactionkinetics,theoxidationrateofmetalperunitareaontheinterfaceVR:K——constantofchemicalreactionC——concentrationofoxygenontheinterfaceD——diffusioncoefficientofoxygenintheproductlayerOxidationofmetalOnFick’sFirstlaw,thediffusionrateofoxygenVD:**第十七页,共89页。Atstablestateofoverallreaction**第十八页,共89页。(1)Rateofdiffusion>>rateofreaction——chemicalreaction-limited**第十九页,共89页。——diffusion-limited(2)Rateofdiffusion<>Chemicalreactionrate(2)Theoverallrateofprocesscontrolledbytherateofchemicalreaction**第二十四页,共89页。Where:CA、CB、CC:concentrationofreactantandproduct;K:constantofreaction:K0:constant:activationenergyHomogeneousreaction**第二十五页,共89页。ConcentrationInthecaseofanyhomogeneoussysteminwhichallreactingsubstancesmixedattheatomicorthemolecularlever,thedefinitionofconcentrationastheamountofasubstanceperunitvolumeisapplicabletotheentiresystemconsistingofinitialsubstanceandreactionproductsasawhole.Inthecaseofanyheterogeneoussystem,itisonlyrationalforcomponentsAandBwithineachofitshomogeneousparts.Ahomogeneoussysteminwhichtheconcentrationofgivensubstanceatanymomentoftimeisthesameatallpointoratleastchangescontinuouslyfrompointtopoint.Inaheterogeneoussystemtheconcentrationofcomponentsisingeneraldifferentatdifferentpoints,andatthephaseinterfacesitsvaluechangesabruptly.**第二十六页,共89页。Sphericalparticle,R0,reactiontimet,productthicknessxAquantitativecharacteristicoftherateofachemicalreactioninanyheterogeneoussystemisthechangeperunittimeofthethicknessormassofasolidlayerformed(转化率G).参与反应的一种反应物,在反应过程(guòchéng)中被反应了的体积分数(Volumefraction)**第二十七页,共89页。where:n——reactionorderK——constantofreactionrateF——surfaceareaofcontactofthereactantsKineticequationofsolidstatereaction,ingeneralform**第二十八页,共89页。FirstorderConsideringinitialconditiont=0、G=0Sphericalreactant**第二十九页,共89页。Parallel-planelayers’sthicknessisthesameovertheentiresurfaceofcontactofthereactantsConsideringinitialconditiont=0、G=0Firstorderreaction**第三十页,共89页。[Example]SolidreactionbetweenNa2CO3andSiO2at740CR0=0.036mmSmallamountofNaClassolventOverallratecontrolledbychemicalreactionrate**第三十一页,共89页。7.5Diffusion-limitedSolidreaction–masstransportInsolids,diffusionisusuallyslow——diffusion-controlledReactioninterface(plane,sphere)Jander’sEquationGenstleng'sEquation**第三十二页,共89页。7.5.1Parabolic(抛物线)ratelawSlipCasting——CeramicprocessingtechniqueSchematicrepresentationoftheformationofaslip-castlayerformedbytheextractionofwaterbycapillaryactionofaplasterofparismold**第三十三页,共89页。Therateofprocessisdeterminedbythetransportofwateroutoftheslipandintothecapillaries(毛细孔)Therate-limitingstepistheflowofwaterthroughthecompactclaylayerAsthelayerthicknessincreases,theoverallrateofmaterialtransportdecreasesbecauseoftheincreasedpermeationdistanceThefluxequationforwaterPermeationcoefficient:clayparticlesizeparticlepackingtheviscosityofwatertemperature-sensitive**第三十四页,共89页。ThewaterpressureintheslipThepressureinthemoldPm,determinedbycapillarityUntilthecapillariesbecomefilledwithwater,PisapproximatelyconstantThefluxcanberelatedtothechangeofthelayerthicknessdx/dt--densityofcaselayerk—factorforconvertingthevolumeofwaterremovedtothevolumeofclayparticlesdeposited**第三十五页,共89页。IntegrationofthisequationinthegeneralparabolicformThewallthicknessofaplanarcastingshouldincreasewiththesquarerootoftimeThisparabolicratelawiscommonlyobservedforkineticprocessesinwhichthelimitingstepismasstransportthroughareactionlayer**第三十六页,共89页。7.5.2Jander’sEquationOfparticularinteresttoceramistsisthelargenumberoftransformationswhichoccurwithgranularorpowderedrawmaterials:thedehydrationofminerals,decarbonizationofcarbonates,polymorphictransformation……….Schematicrepresentationofreaction-productlayersformingonsurfaceofparticlesinpowdermixture**第三十七页,共89页。Ifthereactioniscarriedoutisothermally,therateofformationofthereactionzonedependsontherateofdiffusion.Fortheinitialpartsofthereactiontherateofgrowthoftheinterfacelayerisgiventoagoodapproximationbytheparabolicrelationship.V——thevolumeofmaterialunreactedattimetthefractionofthevolumealreadyreacted**第三十八页,共89页。Thenformanysolid-statereactionSilicatesystemsFormationofferritesToformtitanates(钛酸盐)…………**第三十九页,共89页。Hypothesis(1)Reactant–sphericalparticlesR0;(2)ReactantA——diffusionAandBcontactwithproductreactionfromsurfacetocore(3)ConcentrationofAinproductlayerislinear,diffusionareaisconstant。**第四十页,共89页。InitialvolumeofreactantunreactedvolumethevolumeofproductJander’sequation**第四十一页,共89页。ParabolicratelawJander’sequation**第四十二页,共89页。Solidreactionbetweensilicaandbariumcarbonate(a)timedependence(b)particle-sizedependence(c)temperaturedependencelineardependencelineardependenceThetemperaturedependenceofthereaction-rateconstantfollowsanArrheniusequationAsexpectedfromthemajordependenceondiffusioncoefficient**第四十三页,共89页。ZnFe2O4formation**第四十四页,共89页。TwooversimplificationofJander’sEquationValidonlyforasmallreactionthickness,yNoconsiderationofachangeinmolarvolumebetweenthereactantsandtheproductlayerLimittheapplicabilityandtherangeoverwhichitadequatelypredictsreactionrates.**第四十五页,共89页。7.5.3Genstleng’sEquationProductlayerisnotaplaneasphericalshell**第四十六页,共89页。AdiffusionA-ABinterface,CA=C0B-ABinterface,CA=0TheoverallratecontrolledbythediffusionrateofAinproductABGenstleng’sEquation**第四十七页,共89页。dmA/dt——amountofAdiffusionfromsurfaceofspherethroughthelayerofproductABperunittimeSteady-statediffusionM(x)——constantamountofAdiffusionthroughthesphericalshellwithrperunittimeAccordingtoFick’sFirstLaw**第四十八页,共89页。——moledularweightn——moleculenumbersofAinABTheamountofAinthevolumeofproductlayer——densityofproductAB**第四十九页,共89页。Genstleng'sEquationi.e.**第五十页,共89页。SolidreactionbetweenNa2CO3andSiO2at820Ct(min)GofSiO2KK104KJ10441.549.077.099.5168.0193.0222.0263.5296.0312.0332.00.24580.26660.32800.36860.46400.49200.51960.56000.58760.60100.61561.831.831.831.831.831.831.831.831.831.831.831.811.962.002.022.102.122.142.182.202.242.25**第五十一页,共89页。[SiO2]:[Na2CO3]=1,r=0.036mm,t=820C**第五十二页,共89页。Discussion**第五十三页,共89页。low=GlowParaboliclaw=Jander’s=Genstleng’s图7-8反应产物层增厚速率(sùlǜ)与的关系Relationship=0.5minimumorDiffusionveryfastChemicalreactioncontrolled**第五十四页,共89页。Discussion**第五十五页,共89页。RelationshipG~QGlow,Q=1Jander’s=Genstleng’sDeparturelargerwithincreasingGJander’sGenstleng’sGenstleng’s~GhighJander’s~Glow**第五十六页,共89页。LimitationofGenstleng‘sEquationSteady-statediffusion——Genstleng'sEquationnotsuitableofoverallprocessofdiffusion-controlledsolidreactionNoconsideringthedifferenceofdensitybetweenreactantandproduct——noconsideringthevolumeeffect**第五十七页,共89页。Carter’sEquationZ——thevolumeofparticleformedperunitvolumeofthesphericalparticlewhichisconsumed,i.e.,theratioofequivalentvolumes**第五十八页,共89页。ReactionbetweenZnOandAl2O3toformZnAl2O4at1400°Cinair(twosphericalparticlesizes)validevento100%**第五十九页,共89页。SolidstatereactionCompositionCrystalstructurePaticlesizeHomogeneousTemperaturePressureAtmosphereMineralizer7.6Factorseffectonsolidstateeaction**第六十页,共89页。ImportantForexampleCompositionandstructureAl2O3burnedatlowtemperature(lightburned)athightemperature(deadburned)Therateofreaction~10times**第六十一页,共89页。Particlesize**第六十二页,共89页。<0.030mm,CaCO3]:[MoO3]=151—0.052mm2—0.064mm3—0.119mm4—0.13mm5—0.153mmReactionofCaCO3withMoO3at620C**第六十三页,共89页。MoO3:CaCO3=1:1,=0.036mm1—=0.13mm,T=600C2—=0.135mm,T=600C3—=0.13mm,T=580CDifferentkineticregionbyparticlesize**第六十四页,共89页。ThecommonsurfaceofreactinggrainsinfluencesstronglythereactionrateCube:1cmedgelength(=104µm)SurfaceareaS=6cm2=6x10-4m2=6x108µm2grindingTypical10medgelength10m=S‘=6x102µm2109particlesS‘total=109x6x102µm2=6x1011µm2enlargementofthesurfaceareabyafactorof103Importanceofthesurfaceareaforsolidstatereactions**第六十五页,共89页。ChemicalreactionTheeffectoftemperatureontherateofprocessestakingplaceisfrequentlygreat.ArrheniusequationQ——experimentalactivationenergydiffusion无论是扩散控制或化学反应控制的固相反应,温度的升高(shēnɡɡāo)都将提高扩散系数或反应速率常数**第六十六页,共89页。压力是影响固相反应的另一外部因素。对于纯固相反应,压力的提高可显著地改善粉料颗粒之间地接触状态,如缩短颗粒之间距离,增加接触面积并提高固相反应速率。对于有液相、气相参与的固相反应中,扩散过程主要不是通过固相粒子直接接触进行的。因此提高压力有时并不 关于同志近三年现实表现材料材料类招标技术评分表图表与交易pdf视力表打印pdf用图表说话 pdf 现出积极作用(zuòyòng),甚至会适得其反。例如粘土矿物脱水反应和伴有气相产物的热分解反应以及某些由升华控制的固相反应等等,增加压力会使反应速率下降,由表7-6所列数据可见随着水蒸气压的增高,高岭土的脱水温度和活化能明显提高,脱水速度降低。**第六十七页,共89页。水蒸汽压PH2O(Pa)温度T(C)活化能GR(kJ/mol)<0.1061318676265390–450435–475450–480470-495214352377469**第六十八页,共89页。气氛对固相反应也有重要影响。它可以通过改变固体(gùtǐ)吸附特性而影响表面反应活性。对于一系列能形成非化学计量的化合物ZnO、CuO等,气氛可直接影响晶体表面缺陷的浓度和扩散机构与速度。**第六十九页,共89页。在固相反应体系中加入少量非反应物质或由于某些可能存在于原料中的杂质,则常会对反应产生特殊的作用(这些物质常被成为矿化剂,它们在反应过程中不与反应物或反应产物起化学反应,但它们以不同的方式和程度影响着反应的某些环节)。实验表明矿化剂可以产生如下作用:(1)影响晶核的生成速率;(2)影响结晶速率及晶格结构(jiégòu);(3)降低体系共熔点,改善液相性质等。**第七十页,共89页。例如在Na2CO3和Fe2O3反应体系加入NaCl,可使反应转化率提高约0.5~0.6倍之多。当颗粒尺寸越大,这种矿化效果越明显。例如在硅砖中加入1%~3%[Fe2O3+Ca(OH)2]作为矿化剂,能使其大部分-石英不断熔解而同时不断析出-鳞石英,从而促使-石英向鳞石英的转化。关于矿化剂的一般矿化机理则是复杂多样的,可因反应体系的不同而完全不同,但可以认为(rènwéi)矿化剂总是以某种方式参与到固相反应过程中去的。**第七十一页,共89页。7.7Reactioninparticulatesystem7.7.1CalcinationCalcinationreactionsarecommonfortheproductioofmanyoxidesfromcarbonates,hydroxides,sulfates,nitrates…….Ingeneral,thereactionsproduceanoxideandavolatilereactionproduct(CO2,SO2,H2O……)Processcontrolledby:ThereactionrateatthereactionsurfaceGasdiffusionorpermeationthroughtheoxideproductlayerHeattransfer**第七十二页,共89页。CalcinationofCaCO3Standardfreeenergyofreactionasafunctionoftemperature(thedashedlinesaretheequilibriumgaspressureabovetheoxideandcarbonate/hydroxide)**第七十三页,共89页。DecompositionofasphericalparticleThereactionatthesurfaceTheflowofheatfromthefurnacetothereactionsurfaceThediffusion(permeation)oftheproductgasfromthereactionsurfacetotheambientfurnaceatmosphere**第七十四页,共89页。DecompositionofasphericalparticleTheinitialdecompositionmustbecontrolledbyatomistic(原子论的)processThereisnoreaction-productinterferenceinthetransportofheattothereactioninterfaceorgaseousproductawayfromtheinterfaceheterogeneous**第七十五页,共89页。TEMofMgOpreparedbythermaldecompositionofbasicmagnesiumcarbonatePseudomorphed(假晶)MgO(550°Ccalcine)Crystalliteapproachingcubeform(550°Ccalcine)Two-dimensionalmoire(波纹(bōwén)的)patternfromoverlappedcrystallites(550°Ccalcine)**第七十六页,共89页。DecompositionofMg(OH)2showingfirst-orderkinetics**第七十七页,共89页。RateofdecompositionofCaCO3inCO2atmosphere**第七十八页,共89页。7.7.2DecompositionofkaolinThewaterofcrystallizationisevolvedApseudomorphicstructureremainsuntil980°CThestructurecollapsesirreversiblyintocrystallinemulliteandsilicaReleaseheat**第七十九页,共89页。ThereactionkineticsiscontrolledbythediffusionofhydroxylionsinthebulkratherthantheheterogeneoussurfacedecompositionasdecompositionofCaCO3ThekineticsishomogeneouscontrolledbydiffusioninthesolidParabolicratelawParabolicplotsforthree-sizefractionsofkaoliniteat400°Cinvacuum**第八十页,共89页。[例2]BaTiO3和SrTiO3在高温下形成(BaxSr1-x)TiO3的固相反应首先用平均粒径为2m的氧化物粉料合成BaTiO3和SrTiO3,再以50wt%BaTiO3和50wt%SrTiO3高温合成两者的固溶体。在1050C、1075C、1100C和1150C,参与反应的固态粉料分别恒温若干时间,应用HT-XRD动态测定反应的结果(jiēguǒ),并作定量的相分析。在1075C时测得的动态X射线衍射图:**第八十一页,共89页。图7-13固相反应(fǎnyìng)在1075C时系统(211)衍射峰的变化S1:BaTiO3;S2:SrTiO3;S.S:(BaxSr1-x)TiO3**第八十二页,共89页。固相反应(fǎnyìng)的动力学特点:**第八十三页,共89页。将图中所示的实验数据用杨德尔模型和Carter模型分别(fēnbié)加以讨论:G0.6时,呈线性;G>0.6时,偏离线性说明(shuōmíng)了杨德尔方程的局限性。实验数据与Carter模型拟合结果良好,这表明Carter方程(fāngchéng)更适用于扩散控制的固相反应。**第八十四页,共89页。[例3]粉料尺寸不同的方镁石(含97.7wt%MgO)与刚玉(含99.2wt%Al2O3)发生固相反应形成MgAl2O4的动力学特点摩尔比为1:1的方镁石与刚玉粉料混磨后,应用筛分 方法 快递客服问题件处理详细方法山木方法pdf计算方法pdf华与华方法下载八字理论方法下载 、显微镜观察方法等把粉料按尺寸大小(dàxiǎo)分为三类:一类为1~3m,第二类为45~50m,第三类为90~105m。这三类粉料分别在高温下恒温若干时间,然后对试样进行X射线衍射分析和电子探针微区分析,以确定试样中产物的种类及数量,建立动力学模型。**第八十五页,共89页。图7-16粉料尺寸不同的方镁石与刚玉(gāngyù)在1300C时的固相反应动力学A料1~3m;B料45~53m;C料90~105m原始粉料越细,固相反应(fǎnyìng)进行得越快,而且原始粉料的尺寸不同,其固相反应(fǎnyìng)的动力学方程也有所不同。**第八十六页,共89页。[例4]外加剂Li2CO3对CaO粉料与CO2气体(qìtǐ)发生固相反应的影响CaO和CO2发生反应,在CaO的表面形成CaCO3产物层,当产物层厚度达到一定厚度时,CO2气体通过该层的扩散变得过于缓慢而阻止了反应的进一步进行。在添加(tiānjiā)Li2CO3后,改变了这一特征,使固相反应速率增大。**第八十七页,共89页。平均(píngjūn)粒径为3m的CaO粉料在不掺和掺入15wt%Li2CO3时与CO2气体发生固相反应的动力学数据如图在反应温度(wēndù)低于或接近于Li2CO3-CaCO3低共熔温度(wēndù)935K时,掺入Li2CO3的反应系统的反应速率均高于不掺Li2CO3的反应系统的反应速率,尤其当反应温度(wēndù)接近于Li2CO3-CaCO3低共熔温度(wēndù)时,前者的反应速率大大高于后者。因为当Li2CO3-CaCO3低共熔相形成时,在CaO表面的CaCO3产物层在低共熔相中溶解并重新淀析,因此反应被大大加速。在低于Li2CO3-CaCO3低共熔温度时,掺杂物Li2CO3使得所形成的多晶CaCO3产物层的粒子尺寸减小、边界(biānjiè)数量增多,为CO2气体提供了众多的扩散进入CaO的界面扩散通道,因而使反应速率增大。**第八十八页,共89页。7.8固相反应(fǎnyìng)热力学自学(zìxué)**第八十九页,共89页。
本文档为【最新固相反应精品课件】,请使用软件OFFICE或WPS软件打开。作品中的文字与图均可以修改和编辑, 图片更改请在作品中右键图片并更换,文字修改请直接点击文字进行修改,也可以新增和删除文档中的内容。
该文档来自用户分享,如有侵权行为请发邮件ishare@vip.sina.com联系网站客服,我们会及时删除。
[版权声明] 本站所有资料为用户分享产生,若发现您的权利被侵害,请联系客服邮件isharekefu@iask.cn,我们尽快处理。
本作品所展示的图片、画像、字体、音乐的版权可能需版权方额外授权,请谨慎使用。
网站提供的党政主题相关内容(国旗、国徽、党徽..)目的在于配合国家政策宣传,仅限个人学习分享使用,禁止用于任何广告和商用目的。
下载需要: 免费 已有0 人下载
最新资料
资料动态
专题动态
个人认证用户
rabbit
我是一名高中英语老师 有着丰厚的教学经验,曾经担任过学校教学教研组组长,撰写过很多论文和期刊
格式:ppt
大小:6MB
软件:PowerPoint
页数:89
分类:
上传时间:2021-12-02
浏览量:2