Gl Glass ass, , cr crysta ystall lliza ization tion an and d ph phase ase sep separ aration tion Sophie SCHULLER, Elise RÉGNIER, Judith FOURNIER-RENAUD, Hélène PABLO, *Stéphane GOSSÉ, *Alain CARTALADE DE2D/SEVT/- CEA Marcoule - *CEA Saclay Joint ICTP-IAEA Workshop “Fundamentals of Vitrification and Vitreous Materials for Nuclear Waste Immobilization” November 6-10 2017 | PAGE 1/35
Nuclear glasses Nuclear wastes o Fission products o Actinides Glass precursors o Corrosion Loading rate products o Borosilicate Phosphate Eu Gd Sm Se o Aluminate Nd Rb Th Pr HLW (UOx, MOx, UMo), Fe U Sr Zr MLW (actinides, plant Ce Np rinsing before Zn Y P decommissioning) Pu La F Li P Nb Nuclear Am Ba Ca Glass S Mo Mg Cm Cs Na Cl Tc Al Fe Al I Ru Ni B Te Si Cr Rh Sb Pd Sn Ag Cd Containment properties S. Gin, P. Jollivet, M. Tribet, S. Peuget, S. Schuller Radiochimica Acta | PAGE 2/35 “Radionuclides containment in nuclear glasses: an overview” 2017
Finding the best matrices Find the best compromise Glass and melt Glass feasibility homogeneity Calcine Formation Redox Chemical reactivity between precursor Nuclear glass Thermal waste form Crystallization conductivity Phase separation Electrical conductivity Electromagnetism Viscosity Hydrodynamic (stirring, Thermal air bubbling) homogeneity (T, gradient zone) Long term behavior Vitrification process Academic research | PAGE 3/35
Crystallization Phase separation Glass surface: Zone 1 Liquid: Zone 2 How to control vitrification, crystallization and phase separation processes ? LSF : Zone 3 During glass synthesis Glass: Zone 4 Zone 4 Zone 1 Zone 2 Zone 3 T Surpercooled liquid Glass Homogenous Liquid Glass surface Cooling Glass stability Chemical reactions 1100°C - 1200°C T g Time
Crystallization Phase separation Supercooled ...But depending on the: liquid Composition Structure T ga Temperature Time … Crystallization and phase separation are difficult to be predict P. G. Debenedetti , 2001 | PAGE 5/35
Three main approaches Thermodynamic Kinetic Structural aspect Niraj S., Lynne S. Taylor CrystEngComm , 2012 Models (Zachariasen, Dietzel, Sun Thermodynamic stability Crystallization rate, Warren& Pincus, Block and Levin, (free enthalpies, entropies, morphology and diffusion McGahay, Tomozawa ,…) temperature) Theories and the experimental work | PAGE 6/35
Phase separation
Phase separation mechanism Nucleation and growth Separated phases are spherical with low connectivity 80% of B Simulation coupled Cahn-Hilliard and Navier-Stokes equations – Alain Cartalade CEA Saclay | PAGE 8/35
Phase separation mechanism Spinodal decomposition Separated phases are not spherical and connected Cahn-Hilliard coupled to Navier-Stokes equations – Simulation result Alain Cartalade CEA Saclay | PAGE 9/35
Like in solutions, phase separation depends on the mixing enthalpy and the energy bonds between A and B Δ H m : Mixing enthalpy Δ H m < 0 → Any combination of components leads to a reduction of ΔG m Δ G m < 0 ΔH m > 0 Regular solution ( ΔVm , ΔHm ≠ 0) Bond AB weaker than AA and BB →Immiscibility ΔG m depends on entropy | PAGE 10/35
Immiscibility field ΔG m = ΔH m -T ΔS m ΔH m > 0 : Competition between entropy and temperature High temperature : ΔS ↑, free enthalpy is minimum → Miscibility region Temperature decrease : ΔS ↓, the system is divided into 2 phases to minimize ΔG m Critical or consolute temperature The immiscibility field is limited by a binodal curve
Free enthalpy of excess ΔG m = Gliq ref + Gliq ideal + Gliq excess 0 G A + x B 0 G B + RT(x A lnx A + x B lnx B x B ) + x A x B L AB ΔG m = x A x = molar fraction, L AB = Interaction parameter attractive or repulsive between A and B L AB = Interaction parameter : determines the positive or negative sign of the free enthalpy of excess Repulsive Attractive CALPHAD calculation - Stéphane Gossé CEA Saclay L ZN [ E 1 / 2 ( E E )] A AB AA BB AB
Link to the structure of glass Type ype of of l liqui iquidus dus cur curves es is is cor correla elated ted z/r z/r to to In the alkali and alkali earth silica glasses, cation field strength has an impact on the liquidus curves Cation Ionic Cation field Type of radius, r (Å) strength curve z/r 0,61 Cs 1,64 Straight 0,67 Rb 1,49 line 0,75 K 1,33 1,02 Na 0,98 1,28 Li 0,78 S-shaped 1,40 Ba 1,43 1,57 Sr 1,27 Plateau Ca 1,06 1,89 near the 2,56 Mg 0,78 monotectic Type of liquidus curve depending on cation field strength Kracek, F.C., Journal of American Chemical Society 1930. 52 (4) | PAGE 13/35
Increasing of immiscibility field in alkali borosilicate glasses with cation field strength z/r z/r Im Immiscibility miscibility fie field ld incr increase ease Porai-Koshits, E.A., Phase separation in glass , ed. E.A.P.-K. O.V Mazurin. 1984, Amsterdam, New York ; North-Holland | PAGE 14/35
Molybdenum silica glass : SiO 2 -MoO 3 Cation field strength Mo-O ( z/r) = 10,2 L MoO3-SiO2 = + 70 KJ/mol Interaction between SiO 2 and MoO 3 is repulsive Consolute temperature > 1800°C 2 liquids CALPHAD calculation - Stéphane Gossé CEA Saclay Large immiscibility field in the liquid. | PAGE 15/35
Tendency towards phase separation is limited by the addition of sodium oxide Immiscibility field in SiO 2 -Na 2 O-MoO 3 M. Stemprok (1974) “Geological significance of immiscibility in fused silicate systems containing tungsten and molybdenum” Internat. Geology Rev.,17 (11), 1306-1310. Nuclear waste glasses domain S. Gossé, C. Guéneau, S. Bordier, S. Schuller, A. Laplace, J.Rogez (2014) “A Thermodynamic Approach to predict the Metallic and OxidePhases Precipitations in Nuclear Waste Glass Melts” Summer School Sumglass, Procedia Materials Science. | PAGE 16/35
Immiscibility temperature decrease in alkali and alkali earth borosilicate SiO 2 -B 2 O 3 -Na 2 O-MO-MoO 3 SiO 2 -B 2 O 3 -Na 2 O-CaO-MoO 3 SiO 2 -20B 2 O 3 -Na 2 O-CaO-MoO 3 3000 SiO 2 -B 2 O 3 -Na 2 O-Cs 2 O-MoO 3 SiO 2 -B 2 O 3 -Na 2 O-MoO 3 2800 CALPHAD calculation SiO 2 -MoO 3 Silicate glass 2600 CALPHAD calculation 2400 Temperature (°C) 2200 2000 1800 1600 1400 Borosilicate glasses Experimental data obtained by 1200 viscosity measurements 1000 800 S. Schuller, O. Pinet, B. Penelon (2011) “Liquid - 600 liquid phase separation process in borosilicate liquids enriched in molybdenum and phosphorus 0 1 2 3 4 5 6 7 8 9 10 11 12 13 oxides.” J. Am. Ceram. Soc., 94, 447 -454. Glass or SiO 2 molar % MoO 3 Liquidus curves are lower in borosilicate glasses than in silicate glasses | PAGE 17/35
Structural explanation Stabilization of molybdate units by sodium that compensated molybdate and modified the silica network borosilicate glass network Schematic silicate glass network 2- unit Structural stabilization of MoO 4 D. Caurant, O. Majerus, E. Fadel, A. Quintas, C. Gervais, T. Charpentier, D. in sodium silicate glass Neuville (2010) “Structural investigation of boroslicate glasses containing MoO 3 by NMR and Raman spectroscopies.” Journal of Nuclear Materials, 396, 94 -101. Favorable effect of rare earths (Nd, Gd) to stabilized Mo 6+ in borosilicate glass Rare earths increase the charge close to the molybdates, and modified the silica network | PAGE 18/35
Mechanism of phase separation and the kinetic Nucleation-type mechanism : separated phases are spherical with low connectivity Spinodal-type mechanism : separated phases are not spherical and have high connectivity Haller et al : data thermodynamic interpretation J. Am. Ceram. Soc. 57 (3), 120-126 (1974) Nucleation and growth Spinodal decomposition 1 µm 1 µm Kukizaki, M., Journal of Membrane Science 2010. 360 (1-2)
It depends on the composition and temperature Field II Field I G’(E 1 ) > G(E 1 ) G’(E 2 ) < G(E 2 ) G’’> 0 : in the convex G’’< 0 : in the concave portion portion of the ΔG curve Zone iI of the Δ G curve Nucleation and growth Spinodal decomposition Zone I → the system is stable → A small variation of for a small variation composition causes an of composition instability I II I | PAGE 20/35
Nucleation and growth Spinodal decomposition Up Hill diffusion Down-Hill diffusion Small fluctuation of composition gradually grows Fixed compositions with sharp over a period of time via Up-Hill diffusion interfaces Time increase E.P. Favras, A.C.M., What is spinodal decomposition , in lecture note , E.s.a.T. review, Editor. 2008. p. 25-27. | PAGE 21/35
Example of sodium borosilicate glass enriched in MoO3 Morphology ? SiO 2 -B 2 O 3 -Na 2 O-MoO 3 Glass Immiscibility temperature 1150 1 liquid 1 liqu id Na-M1 810°C Na-M1,5 980 °C 1100 Na-M1,8 1010°C 1050 Na-M2,5 1090°C Temperature (°C) Na-M3 1130°C 1000 950 2 liquids 2 liqu ids 900 850 800 750 725°C 700 1 2 3 4 5 % MoO 3 Molar % MoO 3 % SiO 2 -B 2 O 3 -Na 2 O
1.8 % molar. MoO 3 725°C 1 % molar. MoO 3 725°C 725°C 3 % molar. MoO 3 ESEM images in-situ in temperature acquired at 725°C 10 µm 10 µm
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