1、Interactive experimentation and thermodynamic modelingWeiping Gonga,Marcelle Gaune-Escardb,Zhanpeng JinaaState Key Lab of Powder Metallurgy,Central South University,Changsha,Hunan,P.R.China bEcole polytechnique,Mecanique Energetique,Technopole de Chateau-Gombert,Marseille,France.The CODATA conferenc
2、e,Beijing,China,2006Outline1.Introduction2.Structural behavior and thermodynamic properties of SrZrO3 3.Thermodynamic modeling and experimentation of KBr-TbBr3 system 4.SummariesIntroductionnPhase diagrams functions:blueprints or roadmap for materials design,development,processing and basic understa
3、ndingvvisual representations of the state of a material:T,P,CnThe correlation between thermodynamics and phase equilibriumvJ.W.GibbsvModern development:modeling and computer technology phase equilibrium computer calculation possibilityvCrucial thermodynamic modeling in binary systemvcan be extrapola
4、ted to multi-component systemsvQuestion:Can we believe the results of modeling?nTwo method to check the results of modelingvComparison between the calculated and measured data in literature is the most usually employed test (example one on SrZrO3)vthe best way is to couple interactive experimentatio
5、n and modeling(example two on KBr-TbBr3)nTwo example were used to illustrate theses two methodsvStructure behavior and thermodynamic properties of SrZrO3vKBr-TbBr3 Phase diagram and the decomposition of K3TbBr6Example 1:structural behavior and thermodynamic properties of SrZrO3 nTwo different review
6、s about the structure behavior of SrZrO3 existed in literature vOne review:the room temperature structure of SrZrO3 was pseudo-cubic,and this pseudo-cubic structure did not undergo any phase transformation upon heatingvSecond review:the room temperature structure of SrZrO3 was orthorhombic,and the o
7、rthorhombic perovskite SrZrO3 will transform through higher symmetries during heating,eventually to ideal cubicnA series of thermodynamic data available in literature but great difference existedvDifferent structure?vEffect of impurities,minor departures from nominal stoichiometry,or changes in synt
8、hesis temperatures?nHow to identify and resolve the inconsistency between various kinds of experimental data?vBasic tool:thermodynamic modelingvcomplementary experimentationnExperimental data evaluation and thermodynamic modelingvThermodynamic data and structural information evaluation,thus two opti
9、mization procedure were adoptedOne optimization procedure:dont consider structure transformation Thermodynamic modeling of SrZrO3:GSrZrO3=a1+b1T+c1T lnT+d1T 2+e1T 1 (1)Second optimization procedure:consider structure transformation,Thermodynamic modeling of SrZrO3:similar equation as(1)to describe o
10、rthorhombic SrZrO3 pGSrZrO3=oGSrZrO3+H1-T S1 (2)tGSrZrO3=pGSrZrO3+H2-T S2 (3)cGSrZrO3=tGSrZrO3+H3-T S3 (4)H1,S1,H2,S2,H3,S3 are the corresponding enthalpies and entropies of the transformationsThermodynamic modeling on SrZrO3nComparison between Experimental data and Thermodynamic calculationStructur
11、e transformation and the corresponding enthalpy were detected by thermodynamic modelingnPrepare the samplesvSolid reaction to prepare SrZrO3:SrCO3+ZrO2 vHeat-treated at 1150,1000,850 0CvAir quenched or furnace-coolednXRD determinationExperimentation on SrZrO3nXRD curve:sample quenched from 1150 0C a
12、nd furnace-cooled to room temperature show the cubic and orthorhombic structure,respectively.The observed patterns from SrZrO3,showing the fundamental perovskite reflections.The patterns were recorded at 850,room temperature and 1150oCnXRD curve results illustrate:negative the pseudo-cubic SrZrO3 in
13、 room temperature,confirm the structure transformation its quite difficult to obtain the tetragonal SrZrO3 due to the impurity,minor departures from nominal stoichiometryConclusionsnThermodynamic modeling and experimentation b e n e f i t t h e s t r u c t u r e b e h a v i o r a n d thermodynamic p
14、roperties investigationnThermodynamic modeling is based on the experimental information and can be used to identify and resolve the inconsistency between various kinds of experimentalExample 2:KBr-TbBr3 system nMeasured KBr-TbBr3 phase diagram by L.Rycerz et alvTwo eutectic reactionsvThree compounds
15、K3TbBr3:a solid phase transition at 691 K,melt congruently at 983 KK2TbBr5:a solid phase transition at 658 K,melt incongruently at 725 KKTb2Br7:form from K2TbBr5 and TbBr3 at 694K,melt incongruently at 741 K nMeasured thermodynamic data by L.Rycerz and M.Gaune-EscardvHeat capacity of K3TbBr6:thermal
16、 effect at about 691 and 983K vEnthalpy of mixing of liquid at 1113 K:the minimum located at about 0.3 KBr suggested the existence of TbBr6-3 Thermodynamic modeling of KBr-TbBr3 system nthermodynamic modeling of each phasevPhase without composition range:G(T)functionCompounds without thermodynamic d
17、ata:Neumann-Kopp rule K2TbBr5:A1+B1T+2/3GKBr(s)+1/3GTbBr3(s)KTb2Br7:A2+B2T+1/3GKBr(s)+2/3GTbBr3(s)K3TbBr6 with thermodynamic data and structural information two equations were used to describe two forms of K3TbBr6 lGK3TbBr6=a1+b1T+c1T lnT+d1T 2+e1T 1 hGK3TbBr6=a2+b2T+c2T lnT+d2T 2+e2T 1vThermodynami
18、c description of liquid phase:associated solution(K+)P(Br-,TbBr6-3,TbBr3)Q was introduced to describe short-range order around K3TbBr6 compositionnThermodynamic calculation and comparison(Thermo-Calc software)vCalculated phase diagramGood agreement Exception:decomposition of K3TbBr6 at 593 KvThe det
19、ected thermo effect in the heat capacity curve of K3TbBr6 at low temperatureAssessed to be structure changeKey experiments were conducted to check the existence temperature range of K3TbBr6Key experiments to check the existence temperature of K3TbBr6 nPrepare the samplesnDSC measurements between roo
20、m temperature and 650 K with a rate of 1 K/minvDSC heating and cooling curve:thermal effect at about 593KvResults:K3TbBr6 KBr+K2TbBr5 at 593 K DSC heating and cooling traces on K3TbBr6 compoundConclusions nBased on the measured data,each phase in KBr-TbBr3 system was thermodynamically modeling,KBr-T
21、bBr3 phase diagram and thermodynamic properties were preliminarily calculated.nGuided by the calculated phase diagram and thermodynamic properties,key experiments were carried out,then model of the relate phases were modified to explain the literature and the present measured experimental data.nThe
22、finally obtained thermodynamic properties and phase diagram were more reasonableSummaries nTwo examples,i.e.structure behavior of SrZrO3 and the phase diagram of KBr-TbBr3 system were provided to illustrate the i n t e r a c t i v e e x p e r i m e n t a t i o n a n d thermodynamic modelingnThermodynamic calculation is based on the experimental data and can provide important information for materials experiments,thus guide materials design,development,processing and materials understanding.Thank You!Welcome to China!
