Diffusion of hydrogen and deuterium in Nb and Ta at high concentrations

Bauer, Hubert; Völkl, J.; Tretkowski, J.; Alefeld, G.

doi:10.1007/bf01354833

Cited by 78 publications

(35 citation statements)

References 19 publications

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“…[14][15][16] These results are in consistent with the past findings that the hydrogen diffusion coefficient for pure niobium decreases with increasing the hydrogen concentration. 17) Surprisingly, the hydrogen diffusion during the hydrogen permeation is found to be faster in Pd-26 mol%Ag alloy with fcc crystal structure than that in bcc niobium at 773 K. It is also interesting that the addition of Ru or W into niobium increases the hydrogen diffusion coefficient during the hydrogen permeation. From the results of PCT measurements shown in Figs.…”

Section: Hydrogen Diffusion Coefficient During Hydrogenmentioning

confidence: 97%

Alloy Design of Nb-Based Hydrogen Permeable Membrane with Strong Resistance to Hydrogen Embrittlement

et al. 2008

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The alloying effects of Ru and W on the hydrogen solubility, the resistance to hydrogen embrittlement and hydrogen permeability are investigated quantitatively for Nb-based hydrogen permeable alloys. It is found that the hydrogen solubility decreases by the addition of alloying element into niobium or by increasing the temperature. As a result, the resistance to hydrogen embrittlement is improved by reducing the hydrogen concentration. On the other hand, the hydrogen flux, J, through the alloy membrane increases linearly with increasing difference of hydrogen concentration, ÁC, between both sides of the membrane. It is shown that the Nb-5 mol%X (X = Ru and W) alloys possess excellent hydrogen permeability without showing any hydrogen embrittlement when used under appropriate permeation conditions, i.e. temperature and hydrogen pressures. Also, the hydrogen diffusion coefficients during the practical hydrogen permeation at high temperature are evaluated from the linear relationship between the hydrogen flux and the hydrogen concentration difference. It is found that the hydrogen diffusion coefficient of pure Nb is much lower than the reported values measured for dilute hydrogen solid solutions. Surprisingly, the hydrogen diffusion is found to be faster in Pd-26 mol%Ag alloy with fcc crystal structure than in pure niobium with bcc structure at 773 K during the hydrogen permeation. It is also interesting that the addition of Ru or W into niobium enhances the hydrogen diffusion of the practical hydrogen permeation at high temperature.

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Section: Hydrogen Diffusion Coefficient During Hydrogenmentioning

confidence: 97%

Alloy Design of Nb-Based Hydrogen Permeable Membrane with Strong Resistance to Hydrogen Embrittlement

et al. 2008

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“…At temperatures below room temperature the hydrogen plus binding-site pair and the strain field are considered to be fully coupled, and at temperatures below 244 K phonon-assisted tunneling dominates hydrogen diffusion [76]. The strain field also correlates with hydrogen concentration, as demonstrated by nuclear magnetic resonance [77] and Gorsky effect [78] studies, which display increasing activation energies for hydrogen diffusion in the α and α' phases with increasing hydrogen concentration. Our calculations support these observations because we find an increase in strain energy with increasing concentration, and we also find an increase in the self-trapping energy per hydrogen atom.…”

Section: Application To Niobium Superconducting Radio Frequency Cavitiesmentioning

confidence: 99%

First-principles calculations of niobium hydride formation in superconducting radio-frequency cavities

Ford

Cooley

Seidman

2013

Supercond. Sci. Technol.

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Abstract. Niobium hydride is suspected to be a major contributor to degradation of the quality factor of niobium superconducting radio-frequency (SRF) cavities. In this study, we connect the fundamental properties of hydrogen in niobium to SRF cavity performance and processing. We modeled several of the niobium hydride phases relevant to SRF cavities and present their thermodynamic, electronic, and geometric properties determined from calculations based on density-functional theory. We find that the absorption of hydrogen from the gas phase into niobium is exothermic and hydrogen becomes somewhat anionic. The absorption of hydrogen by niobium lattice vacancies is strongly preferred over absorption into interstitial sites. A single vacancy can accommodate six hydrogen atoms in the symmetrically equivalent lowest-energy sites and additional hydrogen in the nearby interstitial sites affected by the strain field: this indicates that a vacancy can serve as a nucleation center for hydride phase formation. Small hydride precipitates may then occur near lattice vacancies upon cooling. Vacancy clusters and extended defects should also be enriched in hydrogen, potentially resulting in extended hydride phase regions upon cooling. We also assess the phase changes in the niobium-hydrogen system based on charge transfer between niobium and hydrogen, the strain field associated with interstitial hydrogen, and the geometry of the hydride phases. The results of this study stress the importance of not only the hydrogen content in niobium, but also the recovery state of niobium for the performance of SRF cavities.

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“…6, in which lines are guides to the eye: Dash-dotted lines are for protium, dotted line for deuterium and solid line for tritium. The data for protium have been measured by Fukai et al, 7) Mauger et al (NMR) 6) and Bauer et al 5) The data for deuterium have been measured by Bauer et al 5) While there are differences among the values of the reported data for protium, the increase in E a of tritium was the smallest among that of all three isotopes. It was found through these comparisons that there was the isotope effect on the concentration dependence of the tracer diffusion coefficient of hydrogen isotopes.…”

Section: Resultsmentioning

confidence: 99%

“…The values of D Ã have been often obtained from the Gorsky effect measurement, in which both D t and F can be calculated. The chemical diffusion coefficients D Ã of protium and deuterium were reported in the systems of -VH x , 2,3) -NbH x , [4][5][6][7] -NbD x , 6) -TaH x 3,6) and -TaD x 6) up to 0.4 atomic fraction, while that of tritium was obtained only at a dilute tritium concentration (less than 0.014 atomic fraction) by Qi et al 8) This lack of experimental data for tritium may be attributed to the practical difficulties in such measurements because of its radioactivity. In the absence of data for tritium, the D t values for protium or deuterium are often substituted for that of tritium, or a certain kind of extrapolation from the data for protium and deuterium is carried out.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen Concentration Dependence of Tritium Tracer Diffusion Coefficient in Alpha Phase of Niobium

Sakamoto¹,

Hashizume

Sugisaki

2006

J. Nucl. Sci. Technol.

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In order to examine influences of coexistent hydrogen isotopes on diffusion behavior of tritium in niobium, tracer diffusion coefficients D t of tritium in alpha phase of hydrogenated and deuterized niobium (-NbH x T y and -NbD x T y ðx<0:8; y(xÞ) have been measured at 473 K, 493 K and 553 K. The data on D t show typical hydrogen concentration dependence: D t of tritium for both -NbH x T y and -NbD x T y decreases with hydrogen concentration under all experimental conditions. The obtained concentration dependence of D t of tritium differs from that of D t of protium inNbH x or of deuterium in -NbD x . On the other hand, no appreciable differences in the concentration dependence of D t of tritium between -NbH x T y and -NbD x T y are observed: there are no definite isotope effects due to the coexisting hydrogen isotopes. This result suggests that D t of tritium for a tritiated niobium (-NbT x ) is not very different from that for -NbH x T y and -NbD x T y . The chemical diffusion coefficient D Ã of tritium is also evaluated on the basis of the obtained D t of tritium and of a literature value of a thermodynamic factor F for Nb-H and Nb-D systems.

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Diffusion of hydrogen and deuterium in Nb and Ta at high concentrations

Cited by 78 publications

References 19 publications

Alloy Design of Nb-Based Hydrogen Permeable Membrane with Strong Resistance to Hydrogen Embrittlement

Alloy Design of Nb-Based Hydrogen Permeable Membrane with Strong Resistance to Hydrogen Embrittlement

First-principles calculations of niobium hydride formation in superconducting radio-frequency cavities

Hydrogen Concentration Dependence of Tritium Tracer Diffusion Coefficient in Alpha Phase of Niobium

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