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
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
Institute for Applied Materials (IAM-WPT)3
Standard melt spraying process
Established at Schott AG, MainzReasonable pebble qualityLong time experienceModerate yieldEasy 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 & SiO2 as raw materialsPlatinum crucible @ 1450 °CSpraying with an air jet in horizontal directionInitial composition: Li4SiO4 + Li6Si2O7
After heat treatment: Li4SiO4 + Li2SiO3 (MSi)
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 & SiO2 as raw materialsPlatinum crucible @ 1300 - 1450 °CSelf-decay of thin melt jetGathering of the pebbles in liquid nitrogenDropping distance can be adjustedGas pressure to control melt flow velocity
Institute for Applied Materials (IAM-WPT)5
Development of Process Modifications
Nozzle design improvementsCoping with impuritiesEnhancing the melt jet stabilityIncreasing the output
Verification of pebble purityNegligible increase of the platinum contentIncrease 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)
Referencematerial
22.824.1
46
KALOS
22.5 0.224.6 0.1
50 6
Relativechanges
-1 %+2 %
+9 %
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
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 distance 1400 cm dropping distance
Short dropping distances favor large dendritic grains
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 distance 1400 cm dropping distance
The dropping distance changes the fraction “shiny”/”opaque”
Mean crush load of shiny pebbles: 3.7 NMean crush load of opaque pebbles: 13.5 N
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 TiO2
Formation of lithium meta-titanate (MTi) as a second or third phaseUnknown phase equilibria
► Decrease of melting temperature
► Change in viscosity► Fine grained dendritic
microstructure ?
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% Li2TiO3 15 mol% Li2TiO3 20 mol% Li2TiO3
The grain size is reduced with increasing lithium titanate fraction
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-received 1 week at 950 °C 3 weeks at 950 °C
Grain growth of lithium titanate in lithium orthosilicate is comparably slow
20 mol% MTi
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 mapping Si mapping
EDX-Mapping
M.H.H. Kolb, R. Knitter - BA Workshop Meeting on Tritium and Blanket Technologies, Sept. 2011
15 mol% MTi
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 mapping Si mapping
EDX-Mapping
M.H.H. Kolb, R. Knitter - BA Workshop Meeting on Tritium and Blanket Technologies, Sept. 2011
15 mol% MTi
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 LiTiO2 (Ti+III) is formed rather than Li2TiO3 (Ti+IV)
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 to increase of dropping height
300 cm (15 mol% MTi)
Increase of crush load due to additions of TiO2
Institute for Applied Materials (IAM-WPT)16
Summary and Conclusion
Modification of Schott process to control droplet generationLow porosityControl of the microstructureNarrow pebble size distribution
Addition of titania for strengtheningVery little information in the interesting composition rangeFine grained dendritic microstructureVery limited grain coarsening of titanate phaseHeat treatment necessary to achieve monoclinic Li2TiO3
M.H.H. Kolb, R. Knitter - BA Workshop Meeting on Tritium and Blanket Technologies, Sept. 2011
Institute for Applied Materials (IAM-WPT)17 M.H.H. Kolb, R. Knitter – Workshop on Ceramic Breeder Blanket Interactions, Sept. 2011
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