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Speciation of 14C in Irradiated Graphite
Mary Lou Dunzik-GougarIdaho State University and Idaho
National Laboratory
INGSM-14, Seattle, WA, USASeptember 2013
Due recognition of student researchers, consultants and startup funding
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
3
The Objective is to . . .
. . . determine the chemical nature of 14C on irradiated graphite surfaces
Characterize unirradiated and irradiated graphite surfaces with respect to 14C
Thermally treat irradiated graphite for removal of surface 14C
The graphite irradiation
Graphite Liquid N2 exposed pre-irradiation
Facility
Time Neutron Flux(n/cm2/s)
NBG-18✓ MURR 120 d 1013PocoFoam
®
NBG-25 ATR <400 d 1014
Characterize pre- and post-irradiated graphite
Focus on 14C and precursor 14N XPS, Raman – Bond Information ToF-SIMS – Speciation SEM/EDS – Morphological Features,
Chemical Environment
The characterization
6
Surface Analyses CompletedType XPS ToF-SIMS Raman SEM EDS
NBG-25Unirradiated X X X X X
Irradiated X X X X X
Thermally Treated
X X X X X
NBG-18Unirradiated X X X X X
LN2 immersed X X X X X
Irradiated X X X X X
Thermally Treated
X X X X X
POCOFoam®
Unirradiated X X X X X
LN2 Immersed X X X X X
Irradiated X X X X X
Thermally Treated
X X X X X
CHARACTERIZATION
SEM and EDS
SEM
Irradiated NBG-18 (LN2
immersed before
irradiation)
Irradiated POCOFoam®
(LN2 immersed before
irradiation)
Irradiated NBG-25
N cluste
r
N cluste
r
SEM Nitrogen Nucleation
Nitrogen clusters preferentially nucleate at edges and activation sites
Poco 1500 x
NBG-18 35000 x
Poco 50000 x
Energy Dispersive X-Ray
Carbon (red), oxygen (blue) and nitrogen (green) on
surface of irradiated graphite
11
SEM: Nitrogen Clusters in Irradiated NBG-25
Irradiated NBG-25 (3500x)
Irradiated NBG-25(65000x)
(FIB surface)
CHARACTERIZATION
X-ray Photoelectron and Raman Spectroscopy
XPS Survey Scans: POCOFoam
200 250 300 350 400 450 500 550 600
Thermally Treated
Irradiated
LN2 Immersed
Binding Energy (eV)
Unirradiated
POCOFoam: XPS Results
C1s
C1s
C1s
C1s
N1s O1s
O1s
O1sUnirradiated
LN2 immersed
Irradiated
Thermally Treated
XPS Survey Scans: NBG-18
200 250 300 350 400 450 500 550 600
O 1s
O 1s
O 1s
N 1s
C 1s
C 1s
C 1s
Binding Energy (eV)
Unirradiated
LN2 Immersed
Irradiated
Thermally Treated
NBG-18: XPS Results
C 1s
O 1s
Thermally Treated
Irradiated
LN2 immersed
Unirradiated
C1s
C1s
C1s
C1s
N1s O1s
O1s
O1s
O1s
15
200 250 300 350 400 450 500 550 600
O 1s
O 1s
O 1s
C 1s
C 1s
C 1s
LN2 Immersed
Thermally Treated
Irradiated
O 1s
Binding Energy (eV)
C 1s
Unirradiated
XPS Results: NBG-25
XPS Survey Scans: NBG-25
16
XPS: NBG-25 Surface Scans
Binding Energy (eV)
N(E)
Min: 0 Max: 49743
600 564.6 529.2 493.8 458.4 423 387.6 352.2 316.8 281.4 246
N 1sO 1s Ca 2p
C 1sAtomic ConcentrationN 1s0.6 %O 1s2.1 %Ca 2p 1.1 %C 1s96.2 %
Binding Energy (eV)
N(E)
Min: 0 Max: 30157
600 565.2 530.4 495.6 460.8 426 391.2 356.4 321.6 286.8 252
N 1s
C 1s
Ca 2p
O 1s
Atomic ConcentrationC 1s92.2 %Ca 2p 0.7 %O 1s7.1 %
IRRADIATED
UNIRRADIATED
Trace amounts of nitrogen presentin unirradiated samples
Some bound oxygen (~2%) to graphite surfaces
No discernible presence of nitrogenin irradiated samples
Amount of bound oxygen increases(to ~7%) due to irradiation
17
Binding Energy (eV)
N(E)
Min: 3 Max: 9217
1200 1080 960 840 720 600 480 360 240 120 0
Atomic ConcentrationO 1s23.2 %N 1s36.8 %C 1s40.1 %
Binding Energy (eV)
N(E)
Min: 3 Max: 9407
600 540 480 420 360 300 240 180 120 60 0
C 1s48.0 %
N 1s38.0 %
O 1s14.0 %
Atomic ConcentrationC 1s48.0 %N 1s38.0 %O 1s14.0 %
XPS: Irradiated NBG-18 & POCOFoam® Surface Scans
Significant increase in the amount of surface nitrogen and oxygen present
Attributed to exposure to air and excess LN2 during irradiation
NBG-18
POCOFoam®
18
XPS: NBG-25 C 1s Peak Deconvolution
C 1s peak for Unirradiated NBG-25
C 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
282 283 284 285 286 287 288 289 290
C-aC
O=C-OHC=O
C-O(-H)
C-C(sp3)
C-C(sp2)
NBG-25: Surface(unirradiated)
Rel
ativ
e In
tens
ity (a
rb. u
nits
)
Binding Energy (eV)
282 283 284 285 286 287 288 289 290
C-C(sp3)
C-O(-C) / C=O
O=C-O
C-O(-H)
O=C-OH
Rel
ativ
e In
tens
ity (a
rb. u
nits
)
Binding Energy (eV)
C-C(sp2)
NBG-25: Surface(irradiated)
C-aC
19
XPS: C 1s Peak for All Irradiated Graphites
282 283 284 285 286 287 288 289 290
C-C(sp3)
C-O(-C) / C=O
O=C-O
C-O(-H)
O=C-OH
Re
lativ
e I
nte
nsi
ty (
arb
. u
nits
)
Binding Energy (eV)
C-C(sp2)
NBG-25: Surface(irradiated)
C-aC
283 284 285 286 287 288 289 290 291 292 293 294 295
O=C-OO
O=C-OH
O=C-O
C=O
C-O
C-N
C-C(sp3)
C-C(sp2)
NBG-18 Surface(irradiated)
Rela
tive Inte
nsi
ty (
arb
. units
)
Binding Energy (eV)
CF/CF2/ ?
283 284 285 286 287 288 289 290 291 292 293 294 295 296
O=C-OO
CF/CF2
complexes?
O=C-OH
O=C-O
C=O
C-NRela
tive Inte
nsity (
arb
. units)
Binding Energy (eV)
POCOFoam(R) Surface(irradiated)
C-C(sp2)
Significant amounts of oxides are observed on the surfaces of all graphites and are directly attributed to neutron irradiation.
20
1000 1100 1200 1300 1400 1500 1600 1700 1800
1410R
ela
tive
In
ten
sity (
arb
. u
nits)
Raman Shift (cm-1)
NBG-25 Unirradiated
NBG-25 Irradiated
1330
1580 1610Unirradiated Peak Values:1330=C-C sp3
1410=OH, C-C, O=C-O1580=C-C sp2
1610=C-C(-C=O,-H)
Raman: Unirradiated vs. Irradiated NBG-25
D (sp3) peak G (sp2) peak
CHARACTERIZATION
Secondary Ion Mass Spectroscopy (SIMS)
22
ToF-SIMS: Species of Interestm/z value Possible 14C-Bearing Species
14 14C (N)
15 14CH (NH)
16 14CH2 (NH2)
26 14CC (CN)
28 14CN (N2), 14CCH2 (CH2N)
29 14CNH (HN2)
30 14CO (NO), 14CNH2 (N2H2)
42 14C-CO (CNO), 14C-14C-14C (N3)
46 14CO2 (NO2)
23
ToF-SIMS: Surface Concentration of 14C (NBG-25)
13.96 13.98 14.00 14.02 14.040
20
40
60
80
100
To
tal C
ou
nts
Integral: 4730 Centroid: 14.0147 MassRes: 911.49 C-NBG-25 NEG UNSPUTTERED.TDC - Ions 65µm 393704 cts Ga 15 kev neg ion unbunched unsputtered
14.0175
13.96 13.98 14.00 14.02 14.040
5
10
15
20
Tot
al C
ount
s
Integral: 173 Centroid: 14.0119 C-NBG-25 NEG 15 MIN SPUTTER.TDC - Ions 65µm 111562 cts Ga 15 kev neg ion unbunched 15 min sputter
14.0064
14C, N
14C, N
Surface
5 nm
Sputtering of surface layers removes substantial amount (~90%) of suspected 14C
Indicates that 14C is concentrated on graphite surface
24
ToF-SIMS: Positive Ion Spectra
m/z Amount Remaining Post-Sputter (%)
Possible Species
NBG-25 NBG-18POCOFoam
®
14 11.6 23.3 0.0 14C (N)
15 34.0 8.0 0.0 14CH (NH)
16 0.0 11.7 34.6 14CH2 (NH2)
26 N/A N/A N/A 14CC (CN)
2879.0N/A
N/A14.3
N/A52.1
14CN (N2)14CCH2 (CH2N)
29 113.3 N/A N/A 14CNH (HN2)
300.00.0
11.7N/A
0.0N/A
14CO (NO)14CNH2 (N2H2)
4294.80.0
~1800N/A
N/AN/A
14C-CO (CNO)14C-14C-14C (N3)
46 N/A 0.0 N/A 14CO2 (NO2)
25
ToF-SIMS: Negative Ion Spectram/z Amount Remaining Post-Sputter
(%)Possible Species
NBG-25 NBG-18POCOFoam
®
14 8.6 N/A N/A 14C (N)
15 0.0 3.2 13.4 14CH (NH)
16 N/A N/A N/A 14CH2 (NH2)
26 265.9 245.4 581.0 14CC (CN)
28N/AN/A
248.0N/A
1009.0N/A
14CN (N2)14CCH2 (CH2N)
29 N/A N/A N/A 14CNH (HN2)
300.0N/A
13.423.7
38.4N/A
14CO (NO)14CNH2 (N2H2)
42N/AN/A
30.7N/A
105.7N/A
14C-CO (CNO)14C-14C-14C (N3)
46 N/A 166.0 183.3 14CO2 (NO2)
26
ToF-SIMS: m/z = 26 (CN-) Conundrum
25.8 25.9 26.0 26.10
10
20
30
40
50
To
tal C
ou
nts
(0
.00
03
am
u b
in)
Integral: 2765 Centroid: 26.0075 MassRes: 1171.59 C-NBG-25 NEG UNSPUTTERED.TDC - Ions 65µm 393704 cts Ga 15 kev neg ion unbunched unsputtered
26.0030
25.8 25.9 26.0 26.10
20
40
60
80
To
tal C
ou
nts
(0
.00
03
am
u b
in)
Integral: 4401 Centroid: 26.0055 MassRes: 1421.12 C-NBG-25 NEG 15 MIN SPUTTER.TDC - Ions 65µm 111562 cts Ga 15 kev neg ion unbunched 15 min sputter
26.0024
Surface
5 nm
Lack of substantial surface (and sub-surface) presence of N in irradiated NBG-25 suggests m/z=26 signal is predominantly 14CC (some CN possible)Strength of sub-surface signal further suggests that 14C
is bound within the graphite lattice
Possible correlation between 14CC and elevated sp3 bonding just below surface
27
XPS: C 1s Analysis for All Irradiated Graphites
282 283 284 285 286 287 288 289 290
C-C(sp3)
C-O(-C) / C=O
O=C-O
C-O(-H)
O=C-OH
Re
lativ
e I
nte
nsi
ty (
arb
. u
nits
)
Binding Energy (eV)
C-C(sp2)
NBG-25: Surface(irradiated)
C-aC
283 284 285 286 287 288 289 290 291 292 293 294 295
O=C-OO
O=C-OH
O=C-O
C=O
C-O
C-N
C-C(sp3)
C-C(sp2)
NBG-18 Surface(irradiated)
Rela
tive Inte
nsi
ty (
arb
. units
)
Binding Energy (eV)
CF/CF2/ ?
283 284 285 286 287 288 289 290 291 292 293 294 295 296
O=C-OO
CF/CF2
complexes?
O=C-OH
O=C-O
C=O
C-NRela
tive Inte
nsity (
arb
. units)
Binding Energy (eV)
POCOFoam(R) Surface(irradiated)
C-C(sp2)
Surface species dominated by oxides for irradiated NBG-18 & POCOFoam®
Significant amount of surface oxides for irradiated NBG-25
28
XPS: C 1s Analysis for All Thermally Treated Graphites
282 283 284 285 286 287 288 289 290 291 292
O=C-OH
C=O
C-O(-H)
C-C(sp3)
C-C(sp2)
Rela
tive Inte
nsi
ty (
arb
. units
)
Binding Energy (eV)
NBG-25 Surface(thermally treated irradiated)
282 283 284 285 286 287 288 289 290
C=O
C-O
C-C / C-N
Rela
tive Inte
nsi
ty (
arb
. units
)
Binding Energy (eV)
NBG-18 Surface(thermally treated irradiated)
C-C(sp2)
282 283 284 285 286 287 288 289 290
C=O
C-O
C-C / C-N
C-C(sp2)
Re
lativ
e I
nte
nsi
ty (
arb
. u
nits
)
Binding Energy (eV)
POCOFoam(R) Surface(thermally treated irradiated)
Removal of 14C?
Removal of significant portions of surface oxides and sp3 bonding for all irradiated graphite
29
ToF-SIMS: Removal of 14C via Thermal Treatment of NBG-25
Amount of 14C on the surface of irradiated NBG-25 is reduced by 85-90% due to thermal treatment
Pre-Thermal Treatment
Post-Thermal Treatment
13.90 13.95 14.00 14.050
20
40
60
80
100
To
tal C
ou
nts
(0
.00
02
am
u b
in)
Integral: 1089 Centroid: 14.0152 MassRes: 2281.16 SAMPLE C PI 07058 NEG UNSPUTTERED.TDC - Ions 65µm 111075 cts Sample C pi 07058 neg unsputtered
14.0177
13.90 13.95 14.00 14.050
20
40
60
80
100
To
tal C
ou
nts
(0
.00
02
am
u b
in)
Integral: 4715 Centroid: 14.0147 MassRes: 911.49 C-NBG-25 NEG UNSPUTTERED.TDC - Ions 65µm 393704 cts Ga 15 kev neg ion unbunched unsputtered
14.0175
14C, N
14C, N
Pre-Thermal Treatment
30
13.90 13.95 14.00 14.050
100
200
300
400
To
tal C
ou
nts
(0
.00
02
am
u b
in)
Integral: 6920 Centroid: 14.0132 MassRes: 3059.46 ACTIVE_NBG18_+GA_A.TDC + Ions 50µm 716089 cts Active Sample, Not Sputtered
14.0127
13.90 13.95 14.00 14.050
5
10
15
20
25
30
To
tal C
ou
nts
(0
.00
02
am
u b
in)
Integral: 1047 Centroid: 14.0166 MassRes: 11813.13 SAMPLE 8-25 SURFACE.TDC + Ions 140µm 60183 cts 8-25 surface
14.0245
Pre-Thermal Treatment
Post-Thermal Treatment
14C, N
14C, N
Amount of 14C removed via thermal treatment:-NBG-18: ~95%
ToF-SIMS: Removal of 14C via Thermal Treatment of NBG-18
31
Pathways of Release for 14C 14CO and 14CO2 are the main desorption species
released during thermal treatment
Dependent on surface chemistry (C-O functional groups) 14CO2 – dominant at lower (< 600 oC) temperatures 14CO – dominant at higher (> 600 oC) 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: 14CO2 – aldehydes, carboxylics, lactones 14CO – ethers, ketones, quinones
32
Temperature Dependency of 14C Removal
CO is removed at higher temperatures (> 600 oC)
CO2 is prominently removed at lower temperatures (with limited desorptionat higher temperatures)
150-400 oC
350-650 oC
600-950 oC
600-700 oC
~700 oC
700-950 oC
Figueiredo, 1999
33
Conclusions Presence of 14C is confirmed on surfaces of
irradiated graphite Species containing 14C (or 14N) were identified using SIMS XPS and Raman analysis eliminates substantial presence
of 14N Relative concentration of 14C 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
Thank You!
SEM of NBG-25
Unirradiated (1000x) Thermally Treated (1000x)Irradiated (2000x)
(1/2)
36
SEM: Surface Morphology
Unirradiated NBG-25 (500x)
Irradiated NBG-25
(500x)
Thermally Treated NBG-25
(500x)