docSupercooling Study of Hydrogen on Template Materials
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Supercooling Study of Hydrogen on Template Materials
Lawrence Livermore National Laboratory Supercooling Study of Hydrogen on Template Materials to Deterministically Seed Ignition Quality Solid Fuel Layers Swanee J. Shin, Luis Zepeda-Ruiz, Jonathan R. I. Lee, Salmaan H. Baxamusa, Rebecca Dylla-Spears, Bernard Kozioziemski, Tayyab Suratwala Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551 This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 LLNL-PRES-671878 DT (Deuterium-Tritium) fuel Layering process centers around an attempt to isolate a single seed of the proper phase Lawrence Livermore National Laboratory 2 DT (Deuterium-Tritium) fuel Layering process centers around an attempt to isolate a single seed of the proper phase Filltube fully melted H Liquid DT Lawrence Livermore National Laboratory 3 DT (Deuterium-Tritium) fuel Layering process centers around an attempt to isolate a single seed of the proper phase crystallites Solid DT Filltube fully melted H Liquid DT T frozen plug Lawrence Livermore National Laboratory hh 4 DT (Deuterium-Tritium) fuel Layering process centers around an attempt to isolate a single seed of the proper phase crystallites Solid DT Filltube fully melted H Liquid DT T frozen plug Lawrence Livermore National Laboratory h 5 DT (Deuterium-Tritium) fuel Layering process centers around an attempt to isolate a single seed of the proper phase single seed crystal crystallites Solid DT Filltube fully melted H Liquid DT T frozen plug Lawrence Livermore National Laboratory h h/H = fractional melt h 6 DT (Deuterium-Tritium) fuel Layering process centers around an attempt to isolate a single seed of the proper phase single seed crystal crystallites Solid DT Filltube fully melted H Liquid DT T frozen plug h/H = fractional melt h h Ignition quality single crystal solid DT layer Lawrence Livermore National Laboratory 7 Current seeding process has several failure modes 1. Multiple seeds Polycrystalline DT layer Restart seeding process ICF fuel layer formation has unique challenges: 2. Lost seed • No initial seed Restart seeding process Lawrence Livermore National Laboratory • • • • Cryogenic Anisotropic growth Self heating due to β-decay Radial temperature profile 8 Supercooling is the difference between melting and freezing temperature Freezing occurs ∆T below the melting temperature: “nucleation” process ∆T depends on materials and environment Temperature Tm fully melted Liquid Cooling ∆T : Supercooling Solid Seed Tm- ∆T Liquid Nucleation Time Lawrence Livermore National Laboratory 9 Templating goal is to identify material that produces solid seeds at low supercooling of hydrogen Identify material that nucleates HCP (vs. FCC) D-T solid with supercooling < 10 mK Currently, supercooling is 20-80 mK with hydrogen solid in fill-tube • Result in poor quality layer (polycrystalline) Took the approach of trying materials without special surface processing/cleaning etc. so that they can be practically fielded in production targets • Surfaces are not pristine, may have oxide, water, or organic contamination • Started with materials that are stable in air Lawrence Livermore National Laboratory 10 A planar cryostat is developed for studying nucleation on different substrates Identify materials for promoting HCP growth at low supercooling Liquid droplet on substrate Cell wall Liquid H2/D2 droplet H2/D2 condensation is confined to the cold finger area (polished Cu post) Supercooling (∆T) is measured for several cooling-heating cycles Testing Template Material Cold Finger Temperature 5 mm Substrate material selection, relevant physical parameters guided by MD simulations Lawrence Livermore National Laboratory 11 Early MD simulations showed best results expected with lattice matched, prismatic HCP material surfaces Growth on HCP prismatic II (1120), ∆T set to 1 K Red = HCP, Green = FCC Yellow = Template template fcc -∆ε 15% compression bcc 10% bcc hcp 5% hcp 0 strain (ε) hcp dislocations 5% no nucleation 10% 15% +∆ε tension Template-to-hydrogen lattice spacing mismatch impacts nucleation/crystallization ZnS (1120) would be a good candidate Lawrence Livermore National Laboratory 12 Hydrogen on (1120) plane of ZnS result did not match expectation • Strain between H2 and ZnS is only -0.8% and -5% between D2 and ZnS Expected low supercooling (Goal is <10 mK) MD simulation: HCP template with (1120)-plane Mixed HCP/FCC Red = HCP, Green = FCC Purple = BCC Yellow = Template HCP growth Expected for H2 Expected for D2 template Compression -4 % -2 % Lattice mismatch +2 % Tension • Observed supercoolings were high: 145 mK for H2 and 120 mK for D2 MD did not match expectation Lawrence Livermore National Laboratory Explored other materials and variables 13 Metals and insulators tended to result in undesirable supercoolings 300 Supercooling (∆T, mK) 250 High supercooling (>100 mK) for most tested samples Cu post GDP H2 D2 CVD diamond ZnO Si 200 Si (back)Fused Quartz DCPD Cu ZnS 150 Pt/Si CH3/ Au/Si np-Au Au/Si Ge Ni 100 50 0 Lawrence Livermore National Laboratory Goal: <10 mK 14 We do not observe a clear correlation with lattice constant of the template Supercooling (∆T, mK) 200 ZnO Mismatch with H2, FCC H2, HCP It is NOT straightforward to compare these due to: Si 150 ZnS Pt Cu Au Ge 100 Ni Surface oxide Surface impurities Moisture (H2O) Hydrocarbon Poly-, Single-crystal, Amorphous 50 <10 mK 0 -30 -20 -10 0 10 20 30 Lattice mismatch (%) Lawrence Livermore National Laboratory 15 Lower supercooling have been found with “van der Waals solids” Inert gas substrate: cleaner surface (no oxide, surface contamination) Expanded to solid materials bounded by vdW bonding: Layered materials Desirably lower supercooling! (< 100 mK) 120 CNT sheet Vertically Aligned Teflon CNT H2 D2 Supercooling (∆T, mK) 100 Graphene Aerogel 80 MoS2 H2O 60 Xe Ne N2 Ar 40 HOPG Kr 20 0 Lawrence Livermore National Laboratory <10 mK 16 Templates with low supercooling can produce good quality layer Kr islands grown on the cold finger is used as a template H2 : 3 mK supercooling vs D2 : 25 mK supercooling H2 Cold finger (Cu post) Lawrence Livermore National Laboratory Kr islands D2 17 No real correlation observed between vdW solids lattice mismatch and supercooling 40 Xe Supercooling (∆T, mK) 30 Ne Xe Ar N2 Ne Kr Ar 20 N2 Mismatc with H2 D2 10 Kr 0 -20 -15 -10 -5 0 5 10 15 20 Lattice mismatch (%) Lawrence Livermore National Laboratory 18 No real correlation observed between vdW solids lattice mismatch and supercooling 40 Xe Supercooling (∆T, mK) 30 Ne Xe Ar N2 Ne Kr Ar 20 N2 Mismatc with H2 D2 10 Kr 0 -20 -15 -10 -5 0 5 10 15 20 Lattice mismatch (%) What about template-hydrogen interaction? Lawrence Livermore National Laboratory 19 Recent MD results suggest template-hydrogen interaction could play important role H2 nucleates better on Kr than on Ar Agree with experiment (Kr: 3 mK, Ar: 20 mK) H2-H2 Ar-H2 Kr-H2 H2-H2 potential (eV) 0.005 0.000 -0.005 Ar Kr 3 4 5 6 7 r(Å) Kr-H2 more favorable for H2 nucleation Lawrence Livermore National Laboratory 20 Recent MD results suggest template-hydrogen interaction could play important role D2 nucleates better on Ar than on Kr Do not agree with experiment (Kr: 25 mK, Ar: 30 mK) D-D Ar-D Kr-D D2-D2 potential (eV) 0.005 0.000 -0.005 Ar Kr 3 4 5 6 7 r (Å) Ar-D2 more favorable for D2 nucleation Lawrence Livermore National Laboratory 21 HOPG is one of the most practical materials so far for templating HOPG: Highly Ordered Pyrolytic Graphite Low supercooling: H2: ~15 mK, D2: ~25 mK Key Questions: - Are the supercooling values consistent? - Which feature (e.g. size, morphology) is important? Lawrence Livermore National Laboratory 22 Supercooling varied: HOPG size was more important than surface morphology 60 Supercooling (mK) 50 40 #5: ~400 µm sample #4: ~600 µm sample #2:#1 cleaved surfaces & #3 backside 30 #6: #2 O2 plasma etched 20 #3: scratched 10 #1: as-cut (starting piece) 0 Lawrence Livermore National Laboratory 23 23 We tested HOPG in a mock capsule: HOPG effect on supercooling is not observed Courtesy of N. Teslich HOPG Fill-tube D2 5 µm NIF fill-tube Same behavior as capsules without HOPG FCC solid grows from filltube-side at ~20 mK below FCC D2 triple point, then transform to more stable HCP at lower T Lawrence Livermore National Laboratory 24 We tested Zn with LLE, Schaefer: Size effect was observed 100 11:45 D. Harding, LLE 12:05 T. Bernat, Schafer <150µm - Etched bead - Melted bead - Deposited films - Laser transferred dots Zn bead Zn powder Supercooling (mK) 80 ~200 µm - Etched Powder 60 ~800 µm - Powder 40 ~200 µm - Etched bead 20 > 1mm - Beads 0 200 400 Lawrence Livermore National Laboratory 600 800 1000 Lateral size (µm) 25 We tested Zn with LLE, Schaefer: Morphology effect was observed 11:45 D. Harding, LLE 12:05 T. Bernat, Schafer ~800µm Zn powder 100 Supercooling (mK) 80 60 40 No treatment Etched+Air exposed 20 Etched+10c Al2O3 ALD Etched 0 Lawrence Livermore National Laboratory 26 Summary More desirable supercooling values (< 100 mK) were measrued for vdW solids than for metals/insulators (> 100 mK) We have explored and will continue to explore important parameters: - Lattice mismatch - Interaction potential - Sample size, morphology HOPG and Zn are the most promising materials so far. Need better understanding Supercooling (∆T, mK) 250 200 Cu post 120 GDP H2 D2 CVD diamond ZnO Si Si (back)Fused Quartz DCPD Cu ZnS 150 100 Pt/Si CH3/ Au/Si np-Au Au/Si Ge Ni CNT sheet Vertically Aligned Teflon CNT H2 D2 100 Supercooling (∆T, mK) 300 Graphene Aerogel 80 H2O 60 Xe Ne N2 Ar 40 50 20 0 0 Lawrence Livermore National Laboratory MoS2 HOPG Kr 27
