1. KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association M.H.H. Kolb, R. Knitter INSTITUTE FOR APPLIED MATERIALS - MATERIAL PROCESS TECHNOLOGY / DEPARTMENT CERAMICS www.kit.edu Enhanced melt-spraying process for tritium breeder pebbles

2. Institute for Applied Materials (IAM-WPT) 2 Outline Introduction to pebble fabrication by melt spraying Process parameters and microstructure Pebble quality M.H.H. Kolb, R. Knitter - BA Workshop Meeting on Tritium and Blanket Technologies, Sept. 2011

3. Institute for Applied Materials (IAM-WPT) 3 Standard melt spraying process Established at Schott AG, Mainz Reasonable pebble quality Long time experience Moderate yield Easy and quick reprocessing M.H.H. Kolb, R. Knitter – Workshop on Ceramic Breeder Blanket Interactions, Sept. 2011 Lithium orthosilicate with 2.5 wt.% excess of silica LiOH & SiO 2 as raw materials Platinum crucible @ 1450 °C Spraying with an air jet in horizontal direction Initial composition: Li 4 SiO 4 + Li 6 Si 2 O 7 After heat treatment: Li 4 SiO 4 + Li 2 SiO 3 (MSi)

4. Institute for Applied Materials (IAM-WPT) 4 Development of Process Modifications Modified melt-based process ►controlled droplet generation ►higher yield ►lower porosity ►improved process control M.H.H. Kolb, R. Knitter - BA Workshop Meeting on Tritium and Blanket Technologies, Sept. 2011 Lithium orthosilicate with 2.5 wt.% excess of silica or other compositions LiOH & SiO 2 as raw materials Platinum crucible @ 1300 - 1450 °C Self-decay of thin melt jet Gathering of the pebbles in liquid nitrogen Dropping distance can be adjusted Gas pressure to control melt flow velocity

5. Institute for Applied Materials (IAM-WPT) 5 Development of Process Modifications Nozzle design improvements Coping with impurities Enhancing the melt jet stability Increasing the output Verification of pebble purity Negligible increase of the platinum content Increase of alkali and alkaline elements due to handling M.H.H. Kolb, R. Knitter – Workshop on Ceramic Breeder Blanket Interactions, Sept. 2011 Element Li (wt.%) Si (wt.%) Pt (µg/g) Element Li (wt.%) Si (wt.%) Pt (µg/g) Reference material 22.8 24.1 46 Reference material 22.8 24.1 46 KALOS 22.5  0.2 24.6  0.1 50  6 KALOS 22.5  0.2 24.6  0.1 50  6 Relative changes -1 % +2 % +9 % Relative changes -1 % +2 % +9 %

6. Institute for Applied Materials (IAM-WPT) 6 Pebble size distribution M.H.H. Kolb, R. Knitter – Workshop on Ceramic Breeder Blanket Interactions, Sept. 2011 The achievable pebbles size distribution is very narrow ► Improvement of the yield

7. Institute for Applied Materials (IAM-WPT) 7 Effect of the dropping distance M.H.H. Kolb, R. Knitter – Workshop on Ceramic Breeder Blanket Interactions, Sept. 2011 140 cm dropping distance1400 cm dropping distance Short dropping distances favor large dendritic grains

8. Institute for Applied Materials (IAM-WPT) 8 Effect of dropping distance M.H.H. Kolb, R. Knitter – Workshop on Ceramic Breeder Blanket Interactions, Sept. 2011 140 cm dropping distance1400 cm dropping distance The dropping distance changes the fraction “shiny”/”opaque” Mean crush load of shiny pebbles: 3.7 N Mean crush load of opaque pebbles: 13.5 N

9. Institute for Applied Materials (IAM-WPT) 9 Variations in the Chemical Composition M.H.H. Kolb, R. Knitter – Workshop on Ceramic Breeder Blanket Interactions, Sept. 2011 F. A. Hummel, T. Y. Tien, K. H. Kim, Journal of The American Ceramic Society Vol. 43, No. 4, pp. 192, 1960 Change in the chemical composition Strengthening by additions of TiO 2 Formation of lithium meta- titanate (MTi) as a second or third phase Unknown phase equilibria ►Decrease of melting temperature ►Change in viscosity ►Fine grained dendritic microstructure ?

10. Institute for Applied Materials (IAM-WPT) 10 Effect of titania on pebble microstructure M.H.H. Kolb, R. Knitter – Workshop on Ceramic Breeder Blanket Interactions, Sept. 2011 10 mol% Li 2 TiO 3 15 mol% Li 2 TiO 3 20 mol% Li 2 TiO 3 The grain size is reduced with increasing lithium titanate fraction

11. Institute for Applied Materials (IAM-WPT) 11 Effect of heat treatment on the microstructure M.H.H. Kolb, R. Knitter – Workshop on Ceramic Breeder Blanket Interactions, Sept. 2011 As-received1 week at 950 °C3 weeks at 950 °C Grain growth of lithium titanate in lithium orthosilicate is comparably slow 20 mol% MTi

12. Institute for Applied Materials (IAM-WPT) 12 Element mapping of as-received material Lithium titanate is located at the grain boundaries of lithium orthosilicate SE image SEM Ti mappingSi mapping EDX-Mapping M.H.H. Kolb, R. Knitter - BA Workshop Meeting on Tritium and Blanket Technologies, Sept. 2011 15 mol% MTi

13. Institute for Applied Materials (IAM-WPT) 13 Element mapping of heat treated material Lithium titanate is located at the grain boundaries of lithium orthosilicate SE image SEM Ti mappingSi mapping EDX-Mapping M.H.H. Kolb, R. Knitter - BA Workshop Meeting on Tritium and Blanket Technologies, Sept. 2011 15 mol% MTi

14. Institute for Applied Materials (IAM-WPT) 14 Composition of phases M.H.H. Kolb, R. Knitter – Workshop on Ceramic Breeder Blanket Interactions, Sept. 2011 Initially LiTiO 2 (Ti +III ) is formed rather than Li 2 TiO 3 (Ti +IV )

15. Institute for Applied Materials (IAM-WPT) 15 Mechanical strength of 500 µm pebbles M.H.H. Kolb, R. Knitter – Workshop on Ceramic Breeder Blanket Interactions, Sept. 2011 Increase of crush load due toincrease of dropping height 300 cm (15 mol% MTi) Increase of crush load due to additions of TiO 2

16. Institute for Applied Materials (IAM-WPT) 16 Summary and Conclusion Modification of Schott process to control droplet generation Low porosity Control of the microstructure Narrow pebble size distribution Addition of titania for strengthening Very little information in the interesting composition range Fine grained dendritic microstructure Very limited grain coarsening of titanate phase Heat treatment necessary to achieve monoclinic Li 2 TiO 3 M.H.H. Kolb, R. Knitter - BA Workshop Meeting on Tritium and Blanket Technologies, Sept. 2011

17. Institute for Applied Materials (IAM-WPT) 17 M.H.H. Kolb, R. Knitter – Workshop on Ceramic Breeder Blanket Interactions, Sept. 2011 Thank you for listening