Influence of Microstructure on the Absorption of Tritium into Gold-Plated 316 Stainless Steel Values <1 indicate reduced absorption in gold-plated samples 200 nm Vendor #1 Vendor #1 NL Vendor #1 Vendor #1 Vendor #2 (hard Au) Vendor #2 (hot Au) Relative inventory 200 nm 0 5 10 15 20 25 Sample number M. Sharpe, C Fagan, and W. T. Shmayda Tritium Focus Group-Sandia University of Rochester Albuquerque, NM Laboratory for Laser Energetics 22–25 October 2018 1 Summary High-integrity gold layers reduce tritium absorption into 316 stainless steel (SS316) • High-integrity gold layers on SS316 are challenging to obtain commercially – vendors follow MIL-DTL-45204 • Greater than 25% reduction in tritium inventory is not observed for gold-plated SS316 E27914 2 Gold layers on national lab samples contain deep valleys that may reach the substrate ) m 9 – 10 120 # ( 80 4.5 ) 40 m 3.0 n axis z 0 5 1.5 4 3 2 1 0 x axis ( y axis ( nm) Au thickness ~ 100 nm Fe Au Fe Cr Cr Ni Ni 1.6 3.2 4.8 6.4 X-ray energy (keV) 4 5 6 7 8 9 200 nm X-ray energy (keV) E27917 3 Samples from Vendor #1 have smooth surfaces with sporadic pinholes Gold-plating specification MIL-DTL-45204C Type I ($99.7% Au) # ) 2 Grade A (HK 90 kgf mm ) 1 nm 10 nm E27915 4 Samples from Vendor #1 have porous gold layers 200 nm Ni Au Au (0.8 nm) Ni (6 nm) 1 nm 0.8 1.6 2.4 3.2 4.0 4.8 Substrate X-ray energy (keV) E27916 5 Samples from Vendor #2 show complete gold layers with different roughness “Hard” gold “Hot” gold MIL-DTL-45204 MIL-DTL-45204 $ ) 2 # ) 2 Grade D (HK 201 kgf mm ) Grade A (HK 90 kgf mm ) Type II (99.0% Au) Types I and III ($99.7% Au) 200 nm 200 nm E27918 6 High-resolution STEM of “hot” gold reveals high-porosity gold layers 1 nm SS316 Ni Au (~1.5 nm) 500 nm 100 nm E28054 STEM: scanning transmission electron microscopy 7 SEM cross section of “hard” gold reveals large grains in both gold and nickel layers Au Ni 200 nm SS316 E28088 8 XPS analysis confirms thick, pure gold layers for “hard” and “hot” gold 18,000 16,000 14,000 ) 12,000 O 1s 10,000 C 1s • Lack of O 1s 8,000 post-sputter Intensity indicates 6,000 arbitrary units ( no hydroxide 4,000 or metal oxide 2,000 0 1200 1000 800 600 400 200 0 Binding energy (eV) No evidence of SS316 lines indicate a Au layer > 10 nm. E27919 XPS: x-ray photoelectron spectroscopy 9 Surface activity was measured by immersing the coupon in either ZnCl2, water, or 15% surfactant “Hot” gold sample in • ZnCl used for water 2 non-plated SS316 – solution liberates adsorbed tritium* • Surfactant or water used H+ ZnCl2 mechanism H+ H+ for Au-plated samples – – Cl Cl– Cl– Cl– Cl– Cl– Cl– surfactant mixture Zn2+ Cl– mildly etches SS316 Zn2+ Zn Zn Zn OH OH OH OH OH OH O O O O O O Surface oxide film Surface oxide film Substrate Substrate E27921 * M. D. Sharpe et al., Fusion Eng. Des. 130, 76 (2018). 10 The total tritium inventory was influenced by the integrity of the gold layer Source Observation Values <1 indicate reduced absorption National Rough layers in gold-plated samples lab (NL) Valleys reach substrate Porous layers Vendor #1 Vendor #1 Sporadic large pinholes Vendor #1 Porous layers Vendor #2 NL Vendor #1 Different roughness Vendor #1 Vendor #2 (hard Au) Vendor #2 Mean relative Relative inventory Gold type (hot Au) inventory “Hard” 0.97!0.22 “Hot” 0.75!0.17 0 5 10 15 20 25 Sample number E27923 11 Surface inventory appears to be influenced by roughness for “hard” and “hot” gold 3.5 Hard Au • Surfactant removes more (surfactant) activity than water 3.0 ) – etching? ) ) mCi 2.5 ( hard Au surfactant ^ h = 18. 2.0 hot Au surfactant Non-plated Hard Au ^ h surfactant RF - 10 shots Hot Au ( Hot Au ( SS316 (ZnCl2) (water) hard Au water 1.5 ^ h = 19. hot Au water ^ h 1.0 Hot Au (water) Surface activity 0.5 0.0 1 2 3 4 5 6 7 8 9 10 11 Sample number E27986 RF: radio frequency 12 Summary/Conclusions High-integrity gold layers reduce tritium absorption into 316 stainless steel (SS316) • High-integrity gold layers on SS316 are challenging to obtain commercially – vendors follow MIL-DTL-45204 • Greater than 25% reduction in tritium inventory is not observed for gold-plated SS316 E27914 13 Supplemental material 14 The void fraction in gold layers from General Plating was estimated to be 0.01% • Volume etched ~ 69 nm3 Mean!v = 451!14 nm # voids = 80 • Void volume ~ 0.01% of surface • Assuming 1 atm of T2 gas Counts present in all voids – activity = 0.43 nCi 20 30 40 50 60 70 80 90 Void diameter (nm) 200 nm E27926 15.