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)