A Study of Hydrogen Diffusion in Titanium Hydride using Nuclear Magnetic Resonance Techniques*

Bustard, L.D.; Cotts, R. M.; Seymour, E F W

doi:10.1524/zpch.1979.115.2.247

Cited by 16 publications

(6 citation statements)

References 11 publications

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“…The absolute values, however, are 10%-15% lower than the results obtained in the modelindependent PFG measurements. This is consistent with previous reports [14,18] [19]. The increase in H a with decreasing x is in accordance with the present and with previous NMR studies but, as pointed out by the authors [19], the QNS result for x 2.50 can only be considered as a gross approximation as the corresponding linewidth broadening is almost 2 orders of magnitude smaller than the instrument resolution.…”

supporting

confidence: 94%

Model-Independent Measurements of Hydrogen Diffusivity in the Lanthanum Dihydride-Trihydride System

Majer¹,

Kaess²,

Barnes

1999

Phys. Rev. Lett.

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First model-independent measurements of the hydrogen diffusivity D in lanthanum trihydrides LaH x ͑2.00 # x # 3.0͒ have been performed by PFG-NMR. At a fixed concentration x # 2.92, D͑T ͒ shows single Arrhenius behavior over wide temperature ranges. The activation enthalpy decreases with increasing x from 0.55 ͑x 2.00͒ to 0.17 eV ͑x 2.92͒, resulting in a strong increase in D. The formation of a hydrogen superstructure associated with the semiconductor-to-metal transition results in a strong reduction in D. It was also observed for the first time that in the stoichiometric limit D depends on the thermal history of the sample. 76.60.Lz Recent experiments demonstrating the switchable optical properties of yttrium, lanthanum, and other rare-earth hydride films have again focused interest on these unusual systems [1][2][3]. An important factor underlying the switching speed is the diffusivity of hydrogen in the hydride. But in spite of intensive investigations over the years [4], the mechanisms of hydrogen diffusion in these systems are not yet understood.Lanthanum forms nonstoichiometric homogeneous hydrides LaH x with the fluorite structure in the concentration range from x ഠ 1.9 to x 3.0. The hydrogen atoms occupy predominantly the tetrahedral ͑T ͒ interstitial sites at low concentrations, and with increasing concentration, the octahedral ͑O͒ sites are also filled.Nuclear magnetic resonance (NMR) offers unique capabilities to measure the diffusion on both macroscopic and microscopic scales [5,6]. The pulsed-field-gradient technique (PFG-NMR) permits model-independent measurement of the long-range diffusivity D. We report here the first PFG measurements of hydrogen diffusivity in lanthanum hydrides, LaH x ͑2.0 # x # 3.0͒, over a wide range of temperatures, 235 # T # 800 K, as well as the discovery of unusual hysteresis effects accompanying an order-disorder transition in stoichiometric LaH 3 .The six samples of the present work with 2.0 # x # 2.92 are those used in previous NMR studies [7-9]. They were prepared from the highest-purity Ames Laboratory lanthanum available, having a total magnetic rare-earth impurity content, determined by mass spectroscopy, below 4.5 ppm. The LaH 3 sample has a higher magnetic rare-earth impurity content of 25 ppm. The uncertainties in the hydrogen concentrations x are about 1% of the quoted values.The PFG measurements were performed by using the stimulated-echo sequence [10]. Typical operating parameters were gradient pulse length d 1 ms and diffusion time D 10 ms. Within D the hydrogen atoms diffuse over a distance of the order of 1 mm. The diffusivities were determined from the variation of the echo attenuation with the amplitude of the gradient pulses up to 25 Tm 21 .

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supporting

confidence: 94%

Model-Independent Measurements of Hydrogen Diffusivity in the Lanthanum Dihydride-Trihydride System

Majer¹,

Kaess²,

Barnes

1999

Phys. Rev. Lett.

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“…Further calculations may be summarized by estimating an averaged energy barrier of 0.5 and 0.75 eV at the surface and in bulk, respectively. This compares well with the experimental values of the bulk hydrogen diffusion in TiH 2 : Bustard et al report energy barriers of 0.53 eV in TiH ≃1.7 . This corroborates the relatively high mobility of hydrogen in Ti; the numbers may be compared to hydrogen diffusion in V (Δ E diff = 0.045 eV), Ni (Δ E diff = 0.40 eV), and in Mg (Δ E diff = 0.24 eV) and MgH 2 (Δ E diff ≃1 eV) .…”

Section: Discussionsupporting

confidence: 86%

“…This compares well with the experimental values of the bulk hydrogen diffusion in TiH 2 : Bustard et al report energy barriers of 0.53 eV in TiH ≃1.7 . 62 This corroborates the relatively high mobility of hydrogen in Ti; the numbers may be compared to hydrogen diffusion in V (ΔE diff = 0.045 eV), 63 Ni (ΔE diff = 0.40 eV), 63 and in Mg (ΔE diff = 0.24 eV) 64 and MgH 2 (ΔE diff ≃1 eV). 65 The case of Mg is particularly illustrative, as hydrogen diffusion in Mg is relatively fast, while long-range diffusion in MgH 2 can be considered as nonexistent.…”

Section: Methods To Determine Surface Hydrogen Content By Reflecting ...supporting

confidence: 69%

Surface Properties of the Hydrogen–Titanium System

2021

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Titanium is an excellent getter material, catalyzes gas−solid reactions such as hydrogen absorption in lightweight metal hydrides and complex metal hydrides and has recently been shown as a potential ammonia synthesis catalyst. However, knowledge of the surface properties of this metal is limited when it absorbs large quantities of hydrogen at operation conditions. Both the conceptual description of such a surface as well as the experimental determination of surface hydrogen concentration on hydride-forming metals is challenging due to the dynamic bulk properties and the incompatibility of traditional surface science methods with the hydrogen pressure needed to form the metal hydride, respectively. In this paper, the surface pressure-composition isotherms of the titanium−hydrogen system are measured by operando reflecting electron energy loss spectroscopy (REELS). The titanium thin films were deposited on and hydrogenated through a palladium membrane, which provides an atomic hydrogen source under ultrahigh vacuum conditions. The measurements are supported by density functional theory calculations providing a complete picture of the hydrogen-deficient surface of TiH 2 being the basis of its high catalytic activity.

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“…The values from Eq. (23)(24)(25) (also listed in Table I) are shown by the three square marks for tb, t~, and tL, respectively; whereas, the hydrogen concentration was estimated from the associated time value and the current, assuming 100% coulombic efficiency.…”

Section: Methodsmentioning

confidence: 99%

Electrochemical Studies of Kinetic Properties of Titanium‐ and Vanadium‐Hydrogen Systems at Intermediate Temperatures Using Molten Salt Techniques

Liaw

Deublein

Huggins

1995

J. Electrochem. Soc.

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A novel molten salt technique for studying hydrogen transport in Ti and V metals is described. The molten-salt electrolytes were euteetic mixtures of alkali halides dissolved with excess LiH, operating in temperature ranges typically above 300~ to which electrochemical techniques were difficult to apply conventionally. We used the molten salt technique to investigate the thermodynamic properties of the Ti-H system previously. In this work, we determined composition-dependent diffusion and permeation data of hydrogen in Ti and in binary hydride phases using a galvanostatie intermittent titration technique (GITT). The results are in accordance with the best values reported by others using different techniques. We also reported some preliminary results regarding the kinetic properties of hydrogen in V and its hydride measured by more conventional time-lag and steady-state permeation techniques. The successful application of this molten salt technique in the metal hydrogen systems opened a new arena for potential applications in energy conversion and storage.

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A Study of Hydrogen Diffusion in Titanium Hydride using Nuclear Magnetic Resonance Techniques*

Cited by 16 publications

References 11 publications

Model-Independent Measurements of Hydrogen Diffusivity in the Lanthanum Dihydride-Trihydride System

Model-Independent Measurements of Hydrogen Diffusivity in the Lanthanum Dihydride-Trihydride System

Surface Properties of the Hydrogen–Titanium System

Electrochemical Studies of Kinetic Properties of Titanium‐ and Vanadium‐Hydrogen Systems at Intermediate Temperatures Using Molten Salt Techniques

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