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Speciation of 14 C in Irradiated Graphite Mary Lou Dunzik-Gougar Idaho State University and Idaho National Laboratory INGSM-14, Seattle, WA, USA September 2013
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Students James Cleaver, MS Dec 2011 Shilo McCrory, MS Dec 2011 Tara Smith, MS Dec 2012 Dan LaBrier, PhD 2013 Kathy Nelson, MS 2014 Ted Pollock, MS 2014 Consultants Johannes Fachinger, FNAG Will Windes, INL Abbie Jones, U of Manchester Tony Wickham, Nuclear Technology Consultancy
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... determine the chemical nature of 14 C on irradiated graphite surfaces Characterize unirradiated and irradiated graphite surfaces with respect to 14 C Thermally treat irradiated graphite for removal of surface 14 C 3
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Characterize pre- and post-irradiated graphite Focus on 14 C and precursor 14 N XPS, Raman – Bond Information ToF-SIMS – Speciation SEM/EDS – Morphological Features, Chemical Environment The characterization
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TypeXPSToF-SIMSRamanSEMEDS NBG-25 UnirradiatedXXXXX IrradiatedXXXXX Thermally TreatedXXXXX NBG-18 UnirradiatedXXXXX LN 2 immersedXXXXX IrradiatedXXXXX Thermally TreatedXXXXX POCOFoam ® UnirradiatedXXXXX LN 2 ImmersedXXXXX IrradiatedXXXXX Thermally TreatedXXXXX 6
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SEM and EDS
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Irradiated NBG-18 (LN 2 immersed before irradiation) Irradiated POCOFoam® (LN 2 immersed before irradiation) Irradiated NBG-25 N cluster
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Nitrogen clusters preferentially nucleate at edges and activation sites Poco 1500 x NBG-18 35000 x Poco 50000 x
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Carbon (red), oxygen (blue) and nitrogen (green) on surface of irradiated graphite
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11 Irradiated NBG-25 (3500x) Irradiated NBG-25 (65000x) (FIB surface)
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X-ray Photoelectron and Raman Spectroscopy
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C1s N1sO1s Unirradiated LN 2 immersed Irradiated Thermally Treated
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Irradiated LN 2 immersed Unirradiated C1s N1sO1s
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16 IRRADIATED UNIRRADIATED Trace amounts of nitrogen present in unirradiated samples Some bound oxygen (~2%) to graphite surfaces No discernible presence of nitrogen in irradiated samples Amount of bound oxygen increases (to ~7%) due to irradiation
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17 Significant increase in the amount of surface nitrogen and oxygen present Attributed to exposure to air and excess LN 2 during irradiation NBG-18 POCOFoam®
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C 1s peak for Unirradiated NBG-25C 1s peak for Irradiated NBG-25 Broadening of C 1s peak in irradiated NBG-25 (along with increased oxygen presence) suggests the formation of additional surface oxides 18
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19 Significant amounts of oxides are observed on the surfaces of all graphites and are directly attributed to neutron irradiation.
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20 D (sp 3 ) peakG (sp 2 ) peak
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Secondary Ion Mass Spectroscopy (SIMS)
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m/z value Possible 14 C-Bearing Species 14 14 C (N) 15 14 CH (NH) 16 14 CH 2 (NH 2 ) 26 14 CC (CN) 28 14 CN (N 2 ), 14 CCH 2 (CH 2 N) 29 14 CNH (HN 2 ) 30 14 CO (NO), 14 CNH 2 (N 2 H 2 ) 42 14 C-CO (CNO), 14 C- 14 C- 14 C (N 3 ) 46 14 CO 2 (NO 2 ) 22
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23 14 C, N Surface 5 nm Sputtering of surface layers removes substantial amount (~90%) of suspected 14 C Indicates that 14 C is concentrated on graphite surface
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m/zAmount Remaining Post-Sputter (%)Possible Species NBG-25NBG-18POCOFoam® 1411.623.30.0 14 C (N) 1534.08.00.0 14 CH (NH) 160.011.734.6 14 CH 2 (NH 2 ) 26N/A 14 CC (CN) 28 79.0 N/A 14.3 N/A 52.1 14 CN (N 2 ) 14 CCH 2 (CH 2 N) 29113.3N/A 14 CNH (HN 2 ) 30 0.0 11.7 N/A 0.0 N/A 14 CO (NO) 14 CNH 2 (N 2 H 2 ) 42 94.8 0.0 ~1800 N/A 14 C-CO (CNO) 14 C- 14 C- 14 C (N 3 ) 46N/A0.0N/A 14 CO 2 (NO 2 ) 24
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m/zAmount Remaining Post-Sputter (%)Possible Species NBG-25NBG-18POCOFoam® 148.6N/A 14 C (N) 150.03.213.4 14 CH (NH) 16N/A 14 CH 2 (NH 2 ) 26265.9245.4581.0 14 CC (CN) 28 N/A 248.0 N/A 1009.0 N/A 14 CN (N 2 ) 14 CCH 2 (CH 2 N) 29N/A 14 CNH (HN 2 ) 30 0.0 N/A 13.4 23.7 38.4 N/A 14 CO (NO) 14 CNH 2 (N 2 H 2 ) 42 N/A 30.7 N/A 105.7 N/A 14 C-CO (CNO) 14 C- 14 C- 14 C (N 3 ) 46N/A166.0183.3 14 CO 2 (NO 2 ) 25
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26 Surface 5 nm Lack of substantial surface (and sub-surface) presence of N in irradiated NBG-25 suggests m/z=26 signal is predominantly 14 CC (some CN possible) Strength of sub-surface signal further suggests that 14 C is bound within the graphite lattice Possible correlation between 14 CC and elevated sp 3 bonding just below surface
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27 Surface species dominated by oxides for irradiated NBG-18 & POCOFoam® Significant amount of surface oxides for irradiated NBG-25
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28 Removal of 14 C? Removal of significant portions of surface oxides and sp 3 bonding for all irradiated graphite
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29 Amount of 14 C on the surface of irradiated NBG-25 is reduced by 85-90% due to thermal treatment Pre-Thermal Treatment Post-Thermal Treatment 14 C, N Pre-Thermal Treatment
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30 Pre-Thermal Treatment Post-Thermal Treatment 14 C, N Amount of 14 C removed via thermal treatment: -NBG-18: ~95%
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14 CO and 14 CO 2 are the main desorption species released during thermal treatment Dependent on surface chemistry (C-O functional groups) 14 CO 2 – dominant at lower (< 600 o C) temperatures 14 CO – dominant at higher (> 600 o C) temperatures Complexity of species formed on surface will be affected by duration of irradiation, coolant, gamma radiation Based on XPS results, most likely surface functional groups: 14 CO 2 – aldehydes, carboxylics, lactones 14 CO – ethers, ketones, quinones 31
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32 CO is removed at higher temperatures (> 600 o C) CO 2 is prominently removed at lower temperatures (with limited desorption at higher temperatures) 150-400 o C 350-650 o C 600-950 o C 600-700 o C ~700 o C 700-950 o C Figueiredo, 1999
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Presence of 14 C is confirmed on surfaces of irradiated graphite Species containing 14 C (or 14 N) were identified using SIMS XPS and Raman analysis eliminates substantial presence of 14 N Relative concentration of 14 C is ~10 times higher on graphite surfaces than below (< 10 nm) the surface Carbon-oxygen functional groups identified on irradiated graphite surfaces Bond information surmised using XPS; confirmed by Raman Chemical species identified using SIMS Temperature dependency based on thermal treatment data 33
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Unirradiated (1000x)Thermally Treated (1000x) Irradiated (2000x) (1/2)
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36 Unirradiated NBG-25 (500x) Irradiated NBG-25 (500x) Thermally Treated NBG-25 (500x)
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