Exact Crystal Structure of the Zirconium Hydride Determined
by Neutron Powder Diffraction
T. Maimaitiyili1, J. Blomqvist1, A. Steuwer2, O. Zanellato3 , C. Bjerken1, M. Hölzel4
1Malmö University, Malmö, Sweden, 2ESS AB, Lund, Sweden and 3IRSN DPAM/SEMCA/LEC, France, 4FRM II, Germany.
Objective
• Develop a method for in-situ preparation of γ-ZrH/D • Determine and verify the reported structures
• Identify the stability of various hydride phases and the transition temperatures between them.
Deuteration
• High purity zirconium powder (99.2% purity) is used.
• All powder handling done inside glove box under argon environment.
• Sample baked three days at 300 °C prior to deuteration.
• The high temperature, gas loading setup is used (Fig.2).
• Charged at 300 °C.
• The final atomic ratio of Zr to D was approximately 1:1.
Background
Zirconium alloys have a strong affinity for hydrogen which leads to hydrogen pick up when exposed to water (Fig.1a). Since the hydride phase is very brittle it leads to significant degradation of the material strength and ductility [1,3].
At least three hydride phases are presumed to exist at ambient temperature depending on hydrogen concentration and quenching rate (Fig.1b). However, some controversy exists regarding the exact nature, structure and stability of the γ-hydride phase, which is closely related to the δ-hydride phase through ordering of the hydrogen on tetrahedral sites on alternating 110 planes [1,3].
Fig.1: a) The illustration of nuclear fuel cladding and hydrogen related degradation. b) The H-Zr phase diagram [2].
Experimental procedure
Fig.2: The photographic image of high temperature, gas loading set up.
Deuterium
filling steps Pressure before absorption [mbr] Pressure after absorption [mbr] Step 1 1896 69 Step 2 1902 120 Step 3 1902 96 Step 4 1936 195 Step 5 2100 11
Table1: The deuterium loading steps.
Fig.3: Schema of SPODI. In-situ experiments
• The SPODI beam line (Fig.3) at FRM2 is used for investigation. • The neutron wave length kept
constant (λ=1.54821 Å).
• The measurements were
conducted for sample
temperatures ranging from 25 to 286 °C.
Results
Phase Structure Space group a(Å) c(Å)
α(Zr) HCP P63/mmc 3.23446 5.15031
δ(𝑍𝑍𝑍𝑍𝑍𝑍1.66) FCC Fm-3m 4.77265 4.77265
ε(𝑍𝑍𝑍𝑍𝑍𝑍2) FCT I4/mmm 3.52050 4.45050
Table 2: The refined crystal structure parameters of powder at room temperatures.
Acknowledgements: FRM2 is gratefully acknowledged for the provision of beam time. We also thankful for Swedish research foundation (VR) for financial support.
a
b
Reference
[1] A. Steuwer, J. R. Santisteban, M. Preuss, M. J. Peel, T. Buslaps and M. Harada “Evidence of stress-induced hydrogen ordering in zirconium hydrides” Acta Mat. Vol 57, Iss 1, p145-152, 2009.
[2] E. Zuzek, J. P. Abriata, A. San-Martin, and F. D. Manchester, Bulletin of Alloy Phase Diagrams (American Society for Metals, Metals Park, Ohio, 1990), Vol. 11, No. 4.
[3] L. Lanzani and M. Ruch, "Comments on the stability of zirconium hydride phases in Zircaloy," Journal of Nuclear Materials, vol. 324, no. 2, pp. 165-176, 2004.
Corresponding author: tuerdi.maimaitiyili@mah.se
Fig.4: The diffraction patteren of Zr-powder at different temperetures.
Conclusions
• The present study has demonstrated the potential use of neutron diffraction on in situ measurement of phase transformation and identifications of Zr-H system.
• The high temperature gas loading procedure is an effective way to produce deuterated samples for investigation of the deuteride
structures.
• The preparation route which we implement does not produce a
γ-hydride phase, instead it gives a δ- and ε-phases at room temperature. • The cooling from 286 °C with cooling rate of 10 °C /min, will not
produce any γ-hydride phase, instead δ-hydrides precipitate.
• After cooling there are shoulder/gradients observed next to the α-Zr peaks.
• The hydrogen rich ε-phase irreversibly transforms to δ-phase as temperature increases.
• The crystal structure of both α- and δ-phases showed isotropic thermal expansion. However, the hydrogen rich ε-phase showed anisotropic thermal expansion.
Fig.5: a) The Rietveld fit of the deuterated Zr powders at room temperature (25 °C), b) after annealing at room temperature.
