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Emilie Boulay , Céline Ragoen , Stéphane Godet

Influence of amorphous phase separation on the crystallization behavior of glass-ceramics in the BaO-TiO 2 -SiO 2 system. Emilie Boulay , Céline Ragoen , Stéphane Godet ULB, 4MAT Department, CP194/3, 87 Av. Buyl , 1050 Brussels, Belgium. Crystallization 2012 Goslar, Germany

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Emilie Boulay , Céline Ragoen , Stéphane Godet

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  1. Influence of amorphous phase separation on the crystallization behavior of glass-ceramics in the BaO-TiO2-SiO2 system Emilie Boulay, Céline Ragoen, Stéphane Godet ULB, 4MAT Department, CP194/3, 87 Av. Buyl, 1050 Brussels, Belgium • Crystallization 2012 Goslar, Germany • 25th September 2012

  2. Outline • Influence of phase separation on crystallization • Motivations • The BaO-TiO2-SiO2 system • Results & Discussion • Conclusions • Perspectives Crystallization 2012 - Goslar 2

  3. APS role Amorphous phase separation (APS) • Wellknown in glasssystems • APS = matrix + droplets due to liquidimmiscibility Crystallization 2012 - Goslar 3

  4. APS role Amorphous phase separation (APS) • Wellknown in glasssystems • APS = matrix + droplets due to liquidimmiscibility  Shift in composition + creation of interfaces Interfaces In the droplets Shift In the matrix I. Gutzow, J. Schmelzer, “The vitrous state: thermodynamics, structures, rheology and crystallization, Springer, 1995 Crystallization 2012 - Goslar 4

  5. APS role Possible effects of APS on crystallization [1] Scherrer, G W et Uhlmann, D R. , 1976 [8] ] Harper, H et McMillan, P W. , 1972 [2] Hammel, J J. , 1966 [9] Bhattacharyya, S, et al., 2009 [3] Boulay, 2011 [10] Tomozawa, M, et al., 1990 [4] K. Nakagawa, T. Izumitani, 1969 [11] Hijiya, H et al., 2008 [5] James, P F et Ramsden, A H. , 1984 [12] Li Z., 1985 [6] Katsumata, K, et al., 2004 [7] Jiazhi, L et Chih-yao, F. , 1986 Crystallization 2012 - Goslar 5

  6. APS role Possible effects of APS on crystallization • Systematic study of prior amorphous phase separation effect on crystallization in the BaO-TiO2-SiO2 system: • Interfaces: debated in literature • Photoluminescence properties Crystallization 2012 - Goslar 5

  7. BaO-TiO2-SiO2 The BaO-TiO2-SiO2 system • This glass system exhibitsAPS by the presence of a large miscibility gap in the silica corner • The exact miscibility gap location isunknown • Crystal phase nearimmiscibility: fresnoite(2BaO.TiO2.2SiO2) ? * Hijiya et al., “Effect of phase separation on crystallization of glasses in the BaO-TiO2-SiO2 system”, 2009 Crystallization 2012 - Goslar 6

  8. BaO-TiO2-SiO2 Technical interests of fresnoite • Fresnoite exhibits blue/white photoluminescence (PL) under ultraviolet excitation • PL effect can be optimized by heat treatments on the stoichiometric composition Excitation at 254 nm Response at 470 nm Photoluminescence T. Komatsu, “Effect of heat treatment temperature on the optical properties of Ba2TiSi2O8nanocrystallized glasses”, 2005 Crystallization 2012 - Goslar 7

  9. BaO-TiO2-SiO2 Possible enhancement of optical properties • No stoichiometric compositions show also PL effect (=254 nm) • Hijiya (2008) suggested phase separation may have an influence on crystallization and PL effect Stoich. Non stoich. SiO2↑ APS [211] intensityvs [002]: orientation PL effect Hijiyaet al., “Effect of phase separation on crystallization of glasses in the BaO-TiO2-SiO2 system”, 2009 8

  10. Results& Discussions Materialinvestigated – Fresnoite-SiO2 line Mixingpowder + melting (1500-1560°C, 3H) Air quenched + annealed(600C, 10H) Quenched after melting FRES: stoichiometric composition NoAPS: non stoichiometric composition outside the miscibility gap FRES NoAPS APS Quenchedaftermelting APS: non stoichiometric composition inside the miscibility gap Quenchedaftermelting Water-quenchedaftermelting Crystallization 2012 - Goslar 9

  11. Results& Discussions • Crystallizationmechanism by DSC • Effect of quenching rate • Effect of composition • Microstructure by SEM • Morphologies atearly and final stages of crystallization • Morphological orientation: • Large scale: XRD • Small scale: EBSD (FEG– SEM) and ACOM (TEM) Crystallization 2012 - Goslar 10

  12. Results& Discussions APSair-quenched versus APS water-quenched No priorAPS (APS) Prior APS (APS) Crystallization 2012 - Goslar 11

  13. Results& Discussions Cristallization mechanism – Effect of composition APS FRES 10°C/min G>850µm 200<G<850µm 112<G<200µm 25<G<112µm 25<G<112µm 112<G<200µm 200<G<850µm G>850µm 25<G<112µm 40K/min 30K/min 20K/min 10K/min 5K/min 5K/min 20K/min 10K/min 30K/min 40K/min Crystallization 2012 - Goslar 12

  14. Results& Discussions Cristallization mechanism – Effect of composition APS NoAPS 10°C/min 25<G<112µm 112<G<200µm 200<G<850µm G>850µm 25<G<112µm 112<G<200µm 200<G<850µm G>850µm 25<G<112µm 40K/min 30K/min 20K/min 10K/min 5K/min 5K/min 20K/min 10K/min 30K/min 40K/min Crystallization 2012 - Goslar 13

  15. Results& Discussions Determination of Avrami parameters • n (Ozawa’smethod) x= crystallized fraction n= Avrami’sparameter (growth dimension) m= Avrami’sparameter (growth direction) Crystallization 2012 - Goslar 14

  16. Results& Discussions Activation energy = heating rate [K/min] n= Avrami’sparameter (growth dimension) Tp=Max crystallisationpeak Eact=activation energy [kJ/mol] m= Avrami’sparameter (growth direction) R= gas constant • Eact(Matusita’smethod) Crystallization 2012 - Goslar 15

  17. Results& Discussions Activation energy = heating rate [K/min] n= Avrami’sparameter (growth dimension) Tp=Max crystallisationpeak Eact=activation energy [kJ/mol] m= Avrami’sparameter (growth direction) R= gas constant • Eact(Matusita’smethod) Hijiyaet al., “Effect of phase separation on crystallization of glasses in the BaO-TiO2-SiO2 system”, 2009 Crystallization 2012 - Goslar 15

  18. Results& Discussions • Crystallizationmechanism by DSC • Effect of quenching rate • Effect of composition • Microstructure by SEM • Morphologies atearly and final stages of crystallization • Morphological orientation: • Large scale: XRD • Small scale: EBSD (FEG– SEM) and ACOM (TEM) Crystallization 2012 - Goslar 10

  19. Results& Discussions Crystal morphologies – Final stage • It changes and becomesfiner • Finer crystallization should mean PL enhancement … 1000°C 72H FRES NoAPS 5 µm 5 µm SiO2  + APS APS 5 µm Crystallization 2012 - Goslar 16

  20. Results& Discussions Crystal morphologies – Final stage • It changes and becomesfiner • Finer crystallization should mean PL enhancement … 1000°C 72H FRES NoAPS 5 µm 5 µm SiO2  + APS APS More study on early and finalstages 5 µm Crystallization 2012 - Goslar 16

  21. Results& Discussions APScrystal morphologies – Final stage • Longs treatments: fine microstructure withsometime the disappearance of APS • Role of APS if same final microstructure ??? Surface: 950°C 24h Surface: 950°C 72h [HIJ] – 1200°C 24H Crystallization 2012 - Goslar 17

  22. Results& Discussions APScrystal morphologies – Early stage • Complexcrystallizationmicrostructures withsurfacecrystallization • Role of APS as nucleation site? a/a interfacialenergytoolow… • Conditions to becomehomogeneously fine : dendrite fragmentation? • Energie interface Crystallization 2012 - Goslar 18

  23. Results& Discussions • Crystallizationmechanism by DSC • Effect of quenching rate • Effect of composition • Microstructure by SEM • Morphologies atearly and final stages of crystallization • Morphological orientation: • Large scale: XRD • Small scale: EBSD* (FEG– SEM) and ACOM** (TEM) *Electron BackScattered Diffraction ** Automated Crystallographic Orientation Mapping Crystallization 2012 - Goslar 10

  24. Results& Discussions Orientation - XRD 002 001 211 002 211 001 APS: case 1 FRES APS: case 2 NoAPS Crystallization 2012 - Goslar 19

  25. Results& Discussions Crystallographic orientation – EBSD and ACOM 15° FRES - ACOM NoAPS – EBSD APS - ACOM Crystallization 2012 - Goslar 20

  26. Conclusions • Mechanism: surface crystallization for APS and NoAPS • Microstructures: evidence of surface crystallization for APS and NoAPS • NoAPS: dendrites • APS • Short treatments: complex microstructures, no clearcrystallizationfrom interfaces • Long treatments: single microstructure, sometimeswithout APS ! • Morphological and crystallographic orientation • Often[002] orientedgrowth for APS • Amorphousdroplets do not seem to have any influence  This systematicstudy shows that APS does not influence the crystallizationmechanism • Possible explainations: • Amorphous/amorphousinterfacialenergytoolow to promotecrystallization • Effect of viscositythrough composition Crystallization 2012 - Goslar 21

  27. Perspectives • Clarify APS’s role on morphology … • By using compositions closer to the miscibilty gap boundary – avoid the « composition effect » • By developing EBSD measurements on early and final crystallization for APS • By finding mid-treatment to clarify the transformation into fine crystallization • Why amorphous phase separation disappears with fresnoite dendrites ? Crystallization 2012 - Goslar 22

  28. Thank you for your attention Any questions? We acknowledge the financial support of FRIA. Crystallization 2012 - Goslar

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