Growth Control of Li 2+x TiO 3+y for an Advanced Tritium Breeding Material The University of Tokyo School of Engineering, Department of Nuclear Engineering and Management Keisuke Mukai (Ph.D. student), Kazuya. Sasaki, Takayuki Terai, Akihiro Suzuki, Tsuyoshi. Hoshino 1

Contents 8 1 Background 2 Objective 3 Synthesizing Li 2+x TiO 3+y 4 Crystal structure 5 Microstructure 6 Summary 2

Contents 8 1 Background 2 Objective 3 Synthesizing Li 2+x TiO 3+y 4 Crystal structure 5 Microstructure 6 Summary 3

Li 2 TiO 3 (Lithium Meta-titanate) ○High chemical stability & Good Tritium release property ☓ Lower Li density than other candidates (ex. Li 2 O, Li 4 SiO 4 ) Li 2+x TiO 3+y ( Lithium meta-titanate with excess Li ） is expected as an advanced breeding material due to its higher Li density Background 8 4

β -Li 2 TiO 3 (Monoclinic) phase maintains its phase 1.88 ≦ Li/Ti ≦ 2.25 [1] Non-stoichiometric lithium titanate whose Li/Ti ratio is more than 2.0 Li 2+x TiO 3+y β-Li 2 TiO 3 +Li 4 TiO 4 β-Li 2 TiO 3 +Li 5 Ti 4 O 12 51% Li 2 O-TiO 2 Phase diagram [1] H. Kleykamp, Fusion Engineering and Design 61/62 (2002) 361/366 Li 2 TiO 3 Li 2+x TiO 3+y 8 What is Li 2+x TiO 3+y ? 1155 ℃ 5

Li 2 TiO 3 10μm Li-rich higher density bigger crystal grain Li 2+x TiO 3+y had SEM images on the cross sections of the sintered pellets at 1200 ℃ for 1h. but, why ?? 6 8 Previous study than Li 2 TiO 3

H 2 added sweep gas （ 1 ） diffusion in grain （ 2 ） desorption at grain boundary （ 3 ） diffusion along grain boundary （ 4 ） desorption from particle surface and etc. Li 2+x TiO 3+y pebble After T Production, T Behaviors in a blanket are HTO etc. T In a blanket with H 2 added sweep gas, process(1) is considered as on of a rate determining process [2] (4) (1) (2) (3) 8 Tritium residence in the pebbles [2] M. Nishikawa, A. Baba, Y. Kawamura, Journal of Nuclear Materials 246 (1997) 1-8 7

H 2 added sweep gas Li 2+x TiO 3+y pebble After T Production, T Behaviors in a blanket are Li 2+x TiO 3+y pebbles with smaller grains are needed to decrease tritium inventory in the pebbles. (4) (1) (2) (3) d : Grain size [m] D T : The effective diffusivity of tritium in grain (m 2 /s) θ D = d 2 /60D T （ 1 ） diffusion in grain （ 2 ） desorption at grain boundary （ 3 ） diffusion along grain boundary （ 4 ） desorption from particle surface and etc. HTO etc. T [2] [2] M. Nishikawa, A. Baba, Y. Kawamura, Journal of Nuclear Materials 246 (1997) Tritium residence in the pebbles Average residence time under diffusion of T in the crystal grain [s] is 8

Objective 8 Objective ●Crystallization Powder X-ray Diffraction (PXRD) Rietan FP (simulation) ●Microstructure Scanning electron microscope (SEM) Sample: Li 2 TiO 3 & Li 2.1 TiO 3+y To understand the detail of the sintering process of Li 2+x TiO 3+y for the fabrication of the pebbles with smaller grain 9

Contents 8 1 Background 2 Objective 3 Synthesizing Li 2+x TiO 3+y 4 Crystal structure 5 Microstructure 6 Summary 10

Neutralization method Calcined at 500 ℃ Gelled sample LiOH ・ H 2 O H 2 TiO 3 Spin-mixing for 24h Sintered at 700 ～ 1200 ℃ in Ar 2LiOH ・ H 2 O + H 2 TiO 3 → Li 2 TiO 3 + 4H 2 O SEM (coated with Osmium) XRD, TG Powder Pellet milled Pellet Powder Dummy pellet Alumina plate 11 8 Synthesis

Intensity/ a.u. 2θ/ ° Intensity/ a.u. 2θ/ ° α-Li 2 TiO 3 cubic (low temp. structure) β-Li 2 TiO 3 (monoclinic) (Below 1155 ℃ []) a= a= b= c= β= XRD peaks of α-Li 2 TiO 3 and β-Li 2 TiO 3 were calculated by Rietan-FP 002 peak of β-Li 2 TiO 3 is the diffraction from cation layer along c axis a b c a b c 8 XRD peak simulation 12

α-Li 2 TiO 3 (Cubic) β-Li 2 TiO 3 (Monoclinic) 500 ℃ 700 ℃ 800 ℃ Intensity/ a.u. Powder XRD patterns of the specimens Li 2.1 TiO 3+y sintered at ℃ All XRD pattern of 500 ℃ was attributed to α-Li 2 TiO 3. Above 700 ℃, β-Li 2 TiO 3 (Monoclinic) started to formed 8 Crystal structure Li 2.1 TiO 3+y 13

RT XRD patterns of Li 2.1 TiO 3+y were measured after sinterig at 700 ～ 1200 ℃ Intensity ratio of two peaks were calculated to roughly estimate the existing ratio of α and β phase 002(β) -133(β) 200(α) 8 Crystal structure Li 2.1 TiO 3+y 14

I 002 /I -133 was calculated from XRD patterns Sintering temperature ℃ - β-Li 2 TiO 3 phase mostly formed above 1000 ℃ (Li 2 TiO 3 ) and above 900 ℃ (Li 2.1 TiO 3+y ) - I 002 peak of Li 2.1 TiO 3+y sintered above 1100 ℃ became broadened. → This is considered to be due to the stacking fault of α and β phases along c axis. 8 I 002 /I -133 of Li 2 TiO 3 and Li 2.1 TiO 3+y 15

- β-Li 2 TiO 3 phase fully formed above 1000 ℃ (Li 2 TiO 3 ) and above 900 ℃ (Li 2.1 TiO 3+y ) I 002 /I -133 was calculated from XRD patterns Sintering temperature ℃ - I 002 peak of Li 2.1 TiO 3+y sintered above 1100 ℃ became broadened. → This is considered to be due to the stacking fault of α and β phases along c axis. 8 I 002 /I -133 of Li 2 TiO 3 and Li 2.1 TiO 3+y 16

Contents 8 1 Background 2 Objective 3 Synthesizing Li 2+x TiO 3+y 4 Crystal structure 5 Microstructure 6 Summary 17

SEM images ( ☓ 2500) on the cross sections of the sintered pellets at 1100 ～ 1200 ℃ for 1h. 8 SEM of Li 2 TiO 3 and Li 2.1 TiO 3+y 18

 Significant growth in Li 2.1 TiO →1150 → 1200 ℃  Gradual growth in Li 2 TiO 3 Li 2 TiO 3 Li 2.1 TiO 3+y 8 Grain size of Li 2 TiO 3 & Li 2.1 TiO 3+y 8 SEM of Li 2 TiO 3 and Li 2.1 TiO 3+y 19

 Significant growth in Li 2.1 TiO →1150 → 1200 ℃  Gradual growth in Li 2 TiO 3 8 Grain size of Li 2 TiO 3 & Li 2.1 TiO 3+y Li 2.1 TiO 3+y with small-homogeneous crystal grain at 1100 ℃ Monoclinic ⇔ Cubic transformation might be related to this phenomena 8 SEM of Li 2 TiO 3 and Li 2.1 TiO 3+y Li 2 TiO 3 Li 2.1 TiO 3+y 20

8 Summary The sintering process of Li 2 TiO 3 and Li 2.1 TiO 3+y were observed by investigating crystal growth and crystal strucuture.  Li 2.1 TiO 3+y specimens sintered above 1100℃ had the larger grain growth than Li 2 TiO 3. From the view point of tritium inventory in ceramic breeder, sintering temperature is needed to be less than 1100℃. High temperature XRD and Rietveld analysis are planed to understand the existing ratio of cubic & monocloinic and transformation temperature.  Ordered monoclinic β-phase was obtained above 1000℃ (Li 2 TiO 3 ) and 900℃ (Li 2.1 TiO 3+y ). Above 1100℃, peak broadening were found in Li 2.1 TiO 3+y specimens. → considered to be Cubic + Monoclinic disordering. 21

Thank you for your attention Portland 22

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Quotation 24 A. Lauman, K. Thomas Felh, et al. Z. Kristallogr 226(2011)53-61

25 Li 2 MnO 3 A. Boulineau, L. Croguennec, et al. Solid State Ionics 180(2010) Quotation

Introduction 8 Terai-Suzuki Lab. ・ Liquid Li purification ・ H 2 permeation barrier ・ Ceramic breeder ・ HLW reprocessing. etc. Chemical and Thermal property of ceramic breeder (lithium titanate) are mainly investigated under BA 26