Deuterium Permeation Mechanism in Erbium Oxide Coatings

Transcription

1 3rd China-Japan Workshop on the Tritium and Breeding Blanket Technology June 21, 2010, Kunming, China Deuterium Permeation Mechanism in Erbium Oxide Coatings (Univ. Tokyo, Japan) Takumi Chikada, Akihiro Suzuki, Takayuki Terai (RIKEN, Japan) Tomohiro Kobayashi (NIFS, Japan) Teruya Tanaka, Takeo Muroga (MP-IPP, Germany) Christoph Adelhelm, Hans Maier

2 Outline 1. Background 2. Experimental equipment Coating methods Analysis Deuterium permeation measurement 3. Results and discussion PVD coatings MOD coatings 4. Summary / Plan 2/17

3 ΔG [kj/mol] Background Tritium permeation through structural materials at a blanket section Crucial loss of fuel Tritium Permeation Barrier (TPB) Coating material: Erbium Oxide (Er 2 O 3 ) Originally selected as an insulating coating High thermodynamic stability Compatibility with liquid lithium Lower crystallization temperature (< Al 2 O 3 ) R&D needs: Obtain a high permeation reduction factor (PRF, >10 3 ) Clarify the hydrogen permeation mechanism in the coating Objectives of this work Cooling system Wall Tritium recovery system HT/T 2 Na 2 O Cr 2 O 3 Al 2 O 3 Li 2 O Er 2 O Gibbs free energy of oxides ( ) 3/17

4 Coating Methods (1) Vacuum arc deposition Good adhesion on substrates Low impurity Compatibility with liquid lithium (~700 ) Substrate: SS316, SS430, JLF-1, F82H Substrate temperature: room temp. (R.T.), 700 Coating thickness: mm Vacuum arc deposition device (IPP-Garching) (2) Metal organic decomposition (MOD) Ability to coat on complex-shape substrates Potential to apply plant-scale fabrication Substrate: JLF-1, F82H Heat-treatment temperature: atmosphere: Ar, H %H 2 O Coating thickness : mm solvent coating substrate holder Precursor : Er-03 Er 2 O 3 content : 3% rpm MOD method (spin-coating) 4/17

5 Characterization (1) Surface observation Examine holes/cracks in the coatings Method: Laser microscopy / SEM (2) Cross-section observation Examine coating-substrate interface Method: SEM / TEM (3) Microstructure analysis Obtain crystal-structure information and grain size of the coating Method: X-ray diffraction (XRD) / TEM (4) Deuterium permeation measurement Upstream Downstream Gauge 1 Gauge 3 Sample Gauge 2 QMS D 2 J P p d n J : permeation flux [mol/(m 2 sec)] P : permeability [mol/(m s Pa 0.5 )] p : D 2 pressure of upstream [Pa] d : thickness of sample [m] TMP 1 RP 1 Furnace TMP 2 RP 2 Calibration Volume Deuterium permeation apparatus 5/17

6 Analysis -PVD coating- Substrate temperature SS316 JLF-1 Er 2 O 3 coating 700 Peeling / rough surface Oxide layer Substrate 300nm SS316 JLF-1 Columnar structure Room temperature Polishing flaw Smooth 100mm Intermediate layer Substrate 100nm Peeling is considered to be caused by the brittle oxide layer of the substrates Intermediate layer is thought to help good adhesion of the coating

7 Analysis -MOD coating- Atmosphere min (20K/min) F82H min (30K/min) F82H Ar Rough surface min (30K/min) F82H coat once min (30K/min) F82H coat 3 times H %H 2 O Smooth, crystallized 50mm Heat-treated in Ar: a relatively thick Fe-Cr-O layer was generated in H 2 +H 2 O: the Fe-Cr-O layer was thin (~50 nm) Surface condition of the coating depends on the thickness of the Fe-Cr-O layer

8 Intensity Intensity Analysis X-ray diffraction- PVD R.T h Cubic MOD H %H 2 O Coat 3 times R.T. Monoclinic Er 2 O Cubic+oxides Ar (degree) The rough surface of the sample is caused by oxide layer on the substrate By optimizing fabrication parameter, crystallization of Er 2 O 3 and reducing oxidation can be achieved (Fe,Cr) 2 O (degree)

9 Permeation Behaviors -PVD coating (1)- Temporal change of deuterium permeation flux of the coating deposited at R.T. Permeation flux decreased to 25 % during the measurements at 500 At 600, the flux decreased again to 60 % Because of a crystal-structure change of the coating? 9/17

10 Permeation Behaviors -PVD coating (1)- Crystal grain has grown after permeation measurements As deposited After permeation measurements at 500 = Average grain size = as deposited : 20 nm after meas. at 500 : 90 nm 600 :250 nm 700 :280 nm Grain growth Enhance TPB efficiency After permeation measurements at 600 After permeation measurements at 700 Deuterium permeation through the coating is dominated by grain boundary diffusion rather than lattice diffusion 10/17

11 Permeability (mol/m/s/pa 0.5 ) Permeation Behaviors -PVD coating (2) D 2 flux T [K] /T (1/K) One side F82H 1.3 mm one side 2.6 mm one side 1.3/1.3 mm both sides 2.0/2.0 mm both sides No energy barrier Both sides Permeabilities of both sides coated samples are one order of magnitude lower than those of one side coated samples with the same total thickness PRFs: No degradation during measurements Activation energies of the permeation one side: kj/mol both sides: kj/mol = dissociation & recombination behaviors on the coating surfaces Not only thickness (permeation path) but also surface behaviors are important to obtain high PRFs 11/17

12 Permeability (mol/m/s/pa 0.5 ) Permeation Behaviors -PVD coating (2) T [K] F82H low D 2 pressure side high D 2 pressure side /T (1/K) Different permeabilities are observed on the coatings facing to high or low deuterium pressure sides Difference of absorption/dissociation and recombination/desorption? A possibility of different crystal structure during grain growth The PRF value of the coating deposited on both sides can be expressed not as an addition but as a multiplication of those of each side. 1/ /500 1/40 D 2 D 2 = 12/17

13 Permeation Behaviors -MOD coating- Heat-treated in Ar min 20 K/min min 20 K/min min 30 K/min Smooth surface High PRF Degraded as repeating the measurement The thick Fe-Cr-O layer caused the defect of the coatings 13/17

14 Permeation Behaviors -MOD coating- When heat-treated in H 2 with moisture, the sample showed about a PRF value of 10 2, and was not degraded Heat treatment in lower oxygen potential is effective to reduce oxidation of the RAFM substrate By repeating coating procedure simply 3 times, a PRF value of about 10 3 was obtained (e) Coated once (f) Coated 3 times Higher PRF is obtainedby thickening of the coating A 0.3 mm-thick coating showed a comparable PRF to the 1 mm-thick coating deposited by PVD method 14/17

15 Summary PVD coatings An oxide layer of the substrate peeling An intermediate layer prevention of peeling Small substrate-dependence / D 2 dissociates in the coating A grain growth has occurred at 500 and 600 Hydrogen permeation is dominated by grain boundary diffusion Coatings deposited on both sides shows a PRF of 10 5 The highest PRF results from high energy barriers of dissociation and recombination processes MOD coatings Control of an Fe-Cr-O layer generation is important to obtain uniform coatings Heat treatments under milder oxidizing condition (H 2 with moisture) is effective to prevent generation of the oxide layer A compatible PRF to PVD method is obtained by a 0.3 mm-thick coating 15/17

16 Future Investigations Permeation measurements Discussion of solution/desorption behaviors T-trace measurement with ionization chamber Plant-scale fabrication Coating on tube materials Permeation measurement under blanket environment simulation Permeation behavior through the material-liquid breeders Permeation from PbLi under flowing conditions Irradiation effect 16/17

17 Thank you for your kind attention!

18 Permeation Behaviors -PVD coating (1)- 500 Small substrate-dependence Deuterium permeation was controlled only by the coating Permeation regime of the coating J = P p n /d n = 0.45~0.61 Deuterium dissociated in the coating Appendix 1

19 Appendix different crystal structures 27down 27up 26down The crystal structure of the samples after permeation measurements is different A possibility of strong orientation during grain growth under high D 2 partial pressure Further characterizations are needed 26up up down (degree) D 2 XRD spectra of the samples after permeation measurements Appendix 2