Current Status of Lithium Ceramic Pebble Manufacturing in Korea

Current Status of Lithium Ceramic Pebble Manufacturing in Korea Yi-Hyun Park1, In-Keun Yu1, Mu-Young Ahn1, Seungyon Cho1, Duck Young Ku1, and Sang-Jin Lee2 1 National Fusion Research Institute, Daejeon, Korea 2 Mokpo National University, Jeonnam, Korea

Ⅰ Ⅱ Ⅲ Ⅳ Contents Background R&D Status-1 : Synthesis of Li4SiO4 Powder • R&D Status-2 : Fabrication of Li4SiO4 Pebble • Compression Molding Method • Slurry Droplet Drying Method • Slurry Droplet Wetting Method Summary and Future Works

Background Korea Helium Cooled Solid Breeder TBM (KO HCSB TBM) • Reduced Activation Ferritic/Martensitic steel as structural material • Li4SiO4(LS) or Li2TiO3(LT) pebble as breeder • Be pebble as multiplier • Graphite pebble as reflector • SiC coating is necessary to avoid air/water contact, to enhance pebble strength, and to handle easily.

Required Properties for Li-ceramic

Synthesis Process of Li4SiO4 powder • Synthesis Process for Li4SiO4 powder by PVA Solution Route • Lithium Nitrate (LiNO3) • Silica sol (SiO2) PVA D.I. water D.I. water 5 wt.% PVA solution Mixing (entrapment) Drying (Li4SiO4 ceramic precursor) Calcination & Crystallization

Thermal Analysis of Li4SiO4 Precursor • Thermo Gravimetry (TG) / Differential Thermal Analyzer (DTA) The calcination process was finished below about 800 oC. Crystallization Process : >800 oC

Synthesized Li4SiO4 Powders • Effects of Crystallization Temperature 800oC 900oC 1000oC Primary Particle Size : about 200 nm

Synthesized Li4SiO4 Powders • Effects of PVA Type Low Mw High Mw High Mw Low Mw • Effects of PVA Content 5 wt.% 10 wt.% 10 wt.% 5 wt.%

Fabrication of Pebble : Compression Molding Method • Fabrication Process of Compression Molding Method Li4SiO4 powder PVA solution Mixing Dia. : about 0.3mm PVA cont.: 5~10wt.% Granulation Li4SiO4 Granules Punch Spherical Green Body Pressing using Compression Mold Sintering Compression Mold for Pebble

Strength Properties Upper anvil Pebble Lower anvil • Equipment : Micro-force Material Tester • Cross-head Speed : 0.5 mm/min • Test Temperature : R.T.

Fabrication of Pebble : Slurry Droplet Drying Method • Fabrication Process of Droplet Drying Methodby using Hydrophobic Cloth Li4SiO4 powder D.I. water Mixing (1:2 wt.%) Dropping on Hydrophobic Cloth Drying (24h) Rolling Sintering

Photographs of Green Bodies as-dried green body slurry droplets rolled green body rolling (3h, 100 rpm) Average diameter of rolled green body was about 1 mm. It could be easily controlled by changing of rolling conditions.

Fabrication of Pebble : Slurry Droplet Wetting Method • Fabrication Process of Dropping Wetting Methodby using Hydrogen Peroxide Solution PVA D.I. water Li4SiO4 powder 10wt.% PVA solution Li4SiO4 Powder PVA solution Mixing slurry Dropping into 34%-H2O2 solution syringe needle Drying (R.T., 12h) H2O2 solution gel-sphere Sintering

Photographs of Gel-spheres • Dropped and Floating Gel-spheres gel-sphere after 30 seconds gel-sphere Decomposition Reaction of H2O2 : 2 H2O2 (aq)  2 H2O (l) + O2(g) After about 30 seconds settling at the bottom, Li4SiO4gel-spheres came up to the surface of the H2O2. bubble Flat surface was not observed at the gel-sphere.

Photographs of Green Body and Pebble • Spherical Green Bodies and Sintered Li4SiO4 Pebbles sintering (1000oC, 4h, in air) spherical green bodies sintered Li4SiO4 pebbles average diameter : 2.5 mm average diameter : 1.5 mm

XRD Patterns of Powder and Sintered Pebble Intensity (counts) pebble powder 2θ (o) • Li2Si2O5 and SiO2 included in starting powder were reacted and removed by sintering process.

Crush Load and Microstructure Diameter : about 1.5 mm 0.5 mm/min Room Temp. 50μm Compressive Load (N) 10μm Displacement (mm) • Crush Load : 15 N ~ 35 N • Particle Size < 10 μm

Summary and Future Works • Pure and stable Li4SiO4powder was successfully synthesized by polymer solution route employing PVA as an organic carrier. • Li4SiO4pebbles with relatively high sphericity, high strength and fine grain size could be successfully fabricated by a compression molding method, a slurry droplet drying method, and a slurry droplet wetting method. • It is expected that these methods are easily-controllable and high-yield process for solid breeder pebbles. • These methods should be constantly improved for high performance of Li-ceramic pebbles such as high-temperature properties, irradiation properties, and recycling process.

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PVA amount of polymer controls the particle size distribution O : cation ion ~ : polymer chain (a) Excess or not enough polymer results in large particle size distributions. (b) the optimal amount should give a more uniform distribution. PVA type and mixing amount PVA content The proportions of the PVA to cation sources in the solution were adjusted in such a way that there were 0.5~1 times more positively charged valences from the cations than from the potentially negatively charged –(OH) functional groups of the polymers. Two types of PVA  High degree of polymerized PVA :D.P. value = 1625 (monomers/polymer) molecular weight = 153,000  Low degree of polymerized PVA : D.P. value = 428(monomers/polymer) molecular weight = 40,000

Current Status of Lithium Ceramic Pebble Manufacturing in Korea