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

 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

... 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

 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

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

SEM and EDS

Irradiated NBG-18 (LN 2 immersed before irradiation) Irradiated POCOFoam® (LN 2 immersed before irradiation) Irradiated NBG-25 N cluster

 Nitrogen clusters preferentially nucleate at edges and activation sites Poco 1500 x NBG x Poco x

Carbon (red), oxygen (blue) and nitrogen (green) on surface of irradiated graphite

11 Irradiated NBG-25 (3500x) Irradiated NBG-25 (65000x) (FIB surface)

X-ray Photoelectron and Raman Spectroscopy

C1s N1sO1s Unirradiated LN 2 immersed Irradiated Thermally Treated

Irradiated LN 2 immersed Unirradiated C1s N1sO1s

15

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

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®

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

19 Significant amounts of oxides are observed on the surfaces of all graphites and are directly attributed to neutron irradiation.

20 D (sp 3 ) peakG (sp 2 ) peak

Secondary Ion Mass Spectroscopy (SIMS)

m/z value Possible 14 C-Bearing Species C (N) CH (NH) CH 2 (NH 2 ) CC (CN) CN (N 2 ), 14 CCH 2 (CH 2 N) CNH (HN 2 ) CO (NO), 14 CNH 2 (N 2 H 2 ) C-CO (CNO), 14 C- 14 C- 14 C (N 3 ) CO 2 (NO 2 ) 22

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

m/zAmount Remaining Post-Sputter (%)Possible Species NBG-25NBG-18POCOFoam® C (N) CH (NH) CH 2 (NH 2 ) 26N/A 14 CC (CN) N/A 14.3 N/A CN (N 2 ) 14 CCH 2 (CH 2 N) N/A 14 CNH (HN 2 ) N/A 0.0 N/A 14 CO (NO) 14 CNH 2 (N 2 H 2 ) ~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

m/zAmount Remaining Post-Sputter (%)Possible Species NBG-25NBG-18POCOFoam® 148.6N/A 14 C (N) CH (NH) 16N/A 14 CH 2 (NH 2 ) CC (CN) 28 N/A N/A N/A 14 CN (N 2 ) 14 CCH 2 (CH 2 N) 29N/A 14 CNH (HN 2 ) N/A N/A 14 CO (NO) 14 CNH 2 (N 2 H 2 ) 42 N/A 30.7 N/A N/A 14 C-CO (CNO) 14 C- 14 C- 14 C (N 3 ) 46N/A CO 2 (NO 2 ) 25

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

27 Surface species dominated by oxides for irradiated NBG-18 & POCOFoam® Significant amount of surface oxides for irradiated NBG-25

28 Removal of 14 C? Removal of significant portions of surface oxides and sp 3 bonding for all irradiated graphite

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

30 Pre-Thermal Treatment Post-Thermal Treatment 14 C, N Amount of 14 C removed via thermal treatment: -NBG-18: ~95%

 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

32 CO is removed at higher temperatures (> 600 o C) CO 2 is prominently removed at lower temperatures (with limited desorption at higher temperatures) o C o C o C o C ~700 o C o C Figueiredo, 1999

 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

Unirradiated (1000x)Thermally Treated (1000x) Irradiated (2000x) (1/2)

36 Unirradiated NBG-25 (500x) Irradiated NBG-25 (500x) Thermally Treated NBG-25 (500x)