Isotope effects in metal-hydrogen systems

Sicking, G.

doi:10.1016/0022-5088(84)90093-6

Cited by 51 publications

(35 citation statements)

References 49 publications

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“…Above 500 K the lighter isotope diffuses fastest, while at lower temperatures a reverse isotope effect is observed. These results are in good agreement with diffusion measurements reported by Vö lkl and Alefeld (Sicking, 1984;Wicke and Brodowsky, 1978). In order to understand this transition from a reverse isotope effect at low temperatures to the more expected behaviors at high temperatures we look at the differences in the isotopes.…”

Section: Diffusivitysupporting

confidence: 95%

“…The vibrational frequencies and the ZPE of H at the TS are higher than those at the O site resulting in the difference in energy between these sites to decrease as the isotope mass increases (Wicke and Brodowsky, 1978). The outcome of this situation is that quantum corrected energy barrier at lower temperatures decreases (Jost, 1960;Sicking, 1984). This means that at low temperatures the effects of the first term in Eq.…”

Section: Diffusivitymentioning

confidence: 93%

“…There is good agreement between the experimental results and our calculated values. By comparing the ZPE between the atomic and the molecular state of each isotope to H, it can be observed that heavier isotopes have a deeper zero point level in the gas state than in the interstitial state (Fukai, 2005;Sicking, 1984;Wicke and Brodowsky, 1978). This effect means that the isotopic solubility is ordered as T < D < H. This can also be seen from our calculated binding energies in the Pd O site; for H, D, T our calculations give E b,H = À0.176 eV, E b,D = À0.166 eV, and E b,T = À0.161 eV respectively.…”

Section: Dft Calculations For Interstitial Atomsmentioning

confidence: 96%

“…This effect means that the isotopic solubility is ordered as T < D < H. This can also be seen from our calculated binding energies in the Pd O site; for H, D, T our calculations give E b,H = À0.176 eV, E b,D = À0.166 eV, and E b,T = À0.161 eV respectively. This ordering is known as a reverse isotope effect (Alefeld and Vö lkl, 1978;Sicking, 1984).…”

Section: Dft Calculations For Interstitial Atomsmentioning

confidence: 97%

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Predictions of H isotope separation using crystalline and amorphous metal membranes: A computational approach

Semidey-Flecha

Hao

Sholl

2009

Journal of the Taiwan Institute of Chemical Engineers

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Section: Diffusivitysupporting

confidence: 95%

Section: Diffusivitymentioning

confidence: 93%

Section: Dft Calculations For Interstitial Atomsmentioning

confidence: 96%

Section: Dft Calculations For Interstitial Atomsmentioning

confidence: 97%

See 2 more Smart Citations

Predictions of H isotope separation using crystalline and amorphous metal membranes: A computational approach

Semidey-Flecha

Hao

Sholl

2009

Journal of the Taiwan Institute of Chemical Engineers

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“…However, for most systems of interest, exchange rates are limited not by diffusion but by surface reactions; only for large Pd particles at low temperatures does the former limit the exchange [13][14][15]. Many researchers have examined specific aspects of the exchange process [16][17][18][19][20][21][22][23], and still others have proposed mathematical models [24][25][26][27][28][29], but significant uncertainties remain with regard to the physics and chemistry that must be included to yield a predictive model.…”

Section: Introductionmentioning

confidence: 99%

Isotope exchange kinetics in metal hydrides I : TPLUG model.

Larson¹,

James²,

Nilson³

2011

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A one-dimensional isobaric reactor model is used to simulate hydrogen isotope exchange processes taking place during flow through a powdered palladium bed. This simple model is designed to serve primarily as a platform for the initial development of detailed chemical mechanisms that can then be refined with the aid of more complex reactor descriptions. The onedimensional model is based on the Sandia in-house code TPLUG, which solves a transient set of governing equations including an overall mass balance for the gas phase, material balances for all of the gas-phase and surface species, and an ideal gas equation of state. An energy equation can also be solved if thermodynamic properties for all of the species involved are known. The code is coupled with the Chemkin package to facilitate the incorporation of arbitrary multistep reaction mechanisms into the simulations. This capability is used here to test and optimize a basic mechanism describing the surface chemistry at or near the interface between the gas phase and a palladium particle. The mechanism includes reversible dissociative adsorptions of the three gas-phase species on the particle surface as well as atomic migrations between the surface and the bulk. The migration steps are more general than those used previously in that they do not require simultaneous movement of two atoms in opposite directions; this makes possible the creation and destruction of bulk vacancies and thus allows the model to account for variations in the bulk stoichiometry with isotopic composition. The optimization code APPSPACK is used to adjust the mass-action rate constants so as to achieve the best possible fit to a given set of experimental data, subject to a set of rigorous thermodynamic constraints. When data for nearly isothermal and isobaric deuterium-to-hydrogen (D→H) and hydrogen-to-deuterium (H→D) exchanges are fitted simultaneously, results for the former are excellent, while those for the latter show pronounced deviations at long times. These discrepancies can be overcome by postulating the presence of a surface poison such as carbon monoxide, but this explanation is highly speculative. When the method is applied to D→H exchanges intentionally poisoned by known amounts of CO, the fitting results are noticeably degraded from those for the nominally CO-free system but are still tolerable. When TPLUG is used to simulate a blowdown-type experiment, which is characterized by large and rapid changes in both pressure and temperature, discrepancies are even more apparent. Thus, it can be concluded that the best use of TPLUG is not in simulating realistic exchange scenarios, but in extracting preliminary estimates for the kinetic parameters from experiments in which variations in temperature and pressure are intentionally minimized.5

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Depth Profiling of Hydrogen Isotopes in Metals by Elastic Recoil Detection and Nuclear Reaction Techniques under In‐Situ Conditions

Albers¹,

Sicking²,

Earwaker

et al. 1987

Ber Bunsenges Phys Chem

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The application of the ERD‐technique with 2.8 MeV and 25 MeV α‐particles respectively and of the specific nuclear reaction D(d,p)T for the determination of hydrogen isotopes in metals is described in detail. — The methods were applied to hydrided and/or deuterated elements (Ti, Zr, Pd), alloys (Pd0.92Y0.08, Fecralloy, steels), intermetallic compounds (TiMn‐ and ZrMn‐Laves phases) and a Ti/Cu‐target containing all the three hydrogen isotopes. — Images are obtained about the hydrogen depth distribution in near surface regions of the materials (roughly 400 nm in case of 2.8 MeV ERD, 200 um in case of 25 MeV ERD, and 500 nm in case of D(d,p)T). By aid of standardization the hydrogen content of a number of samples was determined. Information was obtained about the presence of impurities in the specimens. Prominent results of the investigations are: Laves‐phase systems (Ti0.4Mn0.6, Zr0.33Mn0.67) are activated for hydrogen absorption by segregation processes, whereby overlayers of Ti(Zr)‐hydride are formed. These overlayers are separated from the bulk‐hydride by a hydrogen depletion zone. Cold‐rolled specimens (Pd, Pd0.92Y0.08) trap hydrogen in near surface states. Surface oxidation of Fecralloy leads to an effective barrier for hydrogen‐uptake, due to the formation of Al‐oxide overlayers.

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Isotope effects in metal-hydrogen systems

Cited by 51 publications

References 49 publications

Predictions of H isotope separation using crystalline and amorphous metal membranes: A computational approach

Predictions of H isotope separation using crystalline and amorphous metal membranes: A computational approach

Isotope exchange kinetics in metal hydrides I : TPLUG model.

Depth Profiling of Hydrogen Isotopes in Metals by Elastic Recoil Detection and Nuclear Reaction Techniques under In‐Situ Conditions

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