1. Surface Analysis Surface interface controls many aspects of chemistry
Catalysts
Corrosion
Thin films
Surfaces
Methods

2. Surface Boundary between solid and other phase Gas, vacuum, liquid
Surface differs from solid bulk
Decarburised surface layer on the seal rim. Preferential grain boundary oxidation evident

3. Spectroscopic Surface Methods
Incident beam and secondary beam
Photons, electrons
Incident particle not same as secondary

4. X-ray photoelectron spectroscopy
Examination of surface with x-rays and measurement of electrons
Evaluation of elements on surface by x-rays and Auger
A+g->A+*+e-
Electron energy (Ek) is measured
Eb=g-Ek-w
w is work function

5. XPS
The momentum p of the outgoing electron is determined from the kinetic energy

6. XPS spectra Chemical shifts can be observed
Variation with oxidation state
Substituant groups

7. Auger Electron Spectroscopy
A+e1-->A+*+e1-’+eA-
Relaxation can occur in two ways
A+* => A++ + eA-
eA- = Auger electron
A+* => A+ + gf
Auger emission types
KLL
LMM
MNN
Removal, transition to removed state, ejection of electron
favored by low atomic number elements
hnf => fluorescence photon

8. Auger Electron Spectroscopy

9. Similar to other procedures for fuel preparation
Ceramic Synthesis
Dried at 90°C
Calcination, Reduction, Sintering
Final Product
Precipitate-acetone mix from Zr, Th, U salts with NH4OH
≈5 g total salt
Similar to other procedures for fuel preparation

10. Ceramic Synthesis Parameters
Use of H2 and reduction step examined
Calcination
Performed in air at 750 oC for one hour
Reduction
One hour at 600 oC under Ar/4% H2
Powders placed in 5 mm die and cold pressed at 55 MPa for 1-2 minutes
Low pressure, higher surface area
Not to standard fuel surface areas
Sintering
Performed in air or Ar/4% H2(g) at 1500 oC for 4 hours

11. Ceramic Characterization
EDX (Energy Dispersive X-ray) (e-)
Emission of characteristic X-rays
XRD (X-ray diffraction) (g)
EELS (Electron Energy Loss Spectroscopy) (e-)
Loss of energy by monoenergetic e-
Can be used to determine oxidation state
3d3/2 -> 5f5/2 (M4) and 3d5/2 -> 5f7/2 (M5) ratio
Based on lanthanides
XANES/EXAFS (g)
Oxidation state and near neighbor chemistry

12. Element bright in EDX mapping
EDX Results
0.5m
TEM Picture Th Zr U Mg
Element bright in EDX mapping
Two phases found
Low mutual solubility of Zr and Th
Zr rich and Th rich phase
Little solubility of Th in Zr
U and Mg distributed throughout the ceramic

13. XRD Results: Standards
U3O8
ThO2
UO2

14. Influence of synthesis conditions
Zr6Th3UO20
Calcined in air/No reduction
Calcined in air/Reduction
No effect on the inclusion of reduction step: U as U(IV)

15. XRD Results U is reduced to the tetravalent state in Zr-Th-U ceramic
Th and Zr stabilize tetravalent U
Calcine in air, no reduction step, sinter under Ar/4% H2
Zr-U ceramic requires reduction step
Calcination performed under reducing conditions
more U incorporated into the ZrO2 lattice structure
Unit Cell Measured for Th3UO8 Å

16. Th-U solid solution cell parameters
Black points from Hubert et al (2001)

17. EELS Spectra
ZrTh3UO10

18. EELS analysis Evaluation of U oxidation state
Multiple analysis of samples
Evaluation of M4/M5 ratio for U
UO2: 0.41±0.03
U3O8: 0.48±0.04
Th3UO8: 0.40±0.03
ZrTh3UO10: 0.40±0.03
Tetravalent U for above samples
U oxidation with higher Zr is noted in some samples
Air ingress into furnace

19. X-ray Absorption Spectroscopy
Utilizes x-rays from synchrotron source to probe local structure
High intensity, broad spectral range
Spectra can be separated into regions containing different information
Global technique
yields average structure of sample

20. XAS setup

21. XAS spectrum

22. XANES Spectroscopy X-Ray Absorption Near Edge Structure
Region between absorption edge and start of EXAFS oscillations, up to 40 eV above edge
Absolute position of edge contains information on oxidation state
Also contains information on vacant orbitals, electronic configuration, and site symmetry

23. EXAFS Spectroscopy X-ray Absorption Fine Structure
Above absorption edge, photoelectrons created by absorption of x-ray
Backscattering photoelectrons effect x-ray absorption
Oscillations in absorption above edge
Oscillations used to determine
atomic number
Distance
coordination number of nearest neighbors

24. XAS Procedure Scanned U, Th, and Zr separately Th L 3 edge to k = 13
U L 3 edge to k = 14
Zr K edge to k = 14
U L 2 edge also scanned
Th EXAFS interference in U spectra due to proximity of edges

25. Th and U Edges

26. Uranium XANES Tetravalent U for Zr=0 or 1
U oxidation evident with higher Zr
Agrees with EELS

27. Th3UO8 EXAFS

28. EXAFS Analysis EXAFS equation
Phase(k) and Amp(k) calculated from theory
Fit data to determine: N
coordination number R
bond length s
Debye-Waller term

29. EXAFS Zr and U interchangeability limited Mg affects U solubility
Increase in Mg decrease in U solubility
ThO2 structure
U and Th completely interchangeable in lattice
Th-Th(U): Å
Th-O: Å

30. Th-Th(U) and Th-O distance

31. Characterization Results
Two phases
Th rich and Zr rich
Tetravalent U in ZrTh3UO10 and Th3UO8
Identified by EELS and XANES
Unit Cell Parameter and Th interatomic distances agree with other work
Solubility Experiments
pH 4, 7, and 10 under Ar, pH 4, 5.25, 6.5 under Ar/10% CO2
Collect samples up to 5 months