Long-range Diffusion Of Hydrogen Research Articles

Composition-dependent hydrogen motion in a random alloy, VxNb1-xH0.2: From localized motion at V atoms to long-range hydrogen diffusion.

Proton spin-lattice relaxation times (${T}_{1}$) measured for the first time across a random transition-metal alloy system, ${\mathrm{V}}_{\mathrm{x}}$${\mathrm{Nb}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{H}}_{0.2}$, from 100 to 700 K reveal (a) a suppression of hydride phase precipitation at low temperatures accompanied by enhanced retention of hydrogen in the solid-solution (\ensuremath{\alpha}) phase compared to pure V or Nb, (b) hydrogen motion in the \ensuremath{\alpha} phase at intermediate compositions governed by a distribution of activation energies, and (c) a transition to short, almost temperature-independent, ${T}_{1}$ behavior in \ensuremath{\alpha}-${\mathrm{V}}_{0.1}$${\mathrm{Nb}}_{0.9}$${\mathrm{N}}_{0.2}$ consistent with localized hydrogen motion around attracting V atoms.

Hydrogen site occupancy and hydrogen diffusion inLaNi4BH1.5

The ${\mathrm{CeCo}}_{4}$B-type ternary compound ${\mathrm{LaNi}}_{4}$B reacts with hydrogen gas at room temperature to form the hydride ${\mathrm{LaNi}}_{4}$${\mathrm{BH}}_{1.5}$ in the pressure range 1-100 atm. Rigid-lattice proton second moments indicate that hydrogen only occupies sites within the La-Ni basal planes in this hydride. The La-B planes, which do not accommodate hydrogen, appear to act as barriers to long-range hydrogen diffusion along the [001] direction. We have studied the diffusion behavior of hydrogen in ${\mathrm{LaNi}}_{4}$${\mathrm{BH}}_{1.4}$ by NMR measurements of the proton relaxation times ${T}_{1}$ and ${T}_{1\ensuremath{\rho}}$ and find evidence for at least two activated-jump processes. The long-range diffusion process is characterized by lower mobilities and larger activation energies than observed in ${\mathrm{LaNi}}_{5}$${\mathrm{H}}_{6}$; comparison of the results with those previously obtained for ${\mathrm{LaNi}}_{4}$${\mathrm{AlH}}_{4.3}$ suggests that the activated step for diffusion in these hydrides is passage of hydrogen through the $12o$ sites, or through saddle points joining these sites to other sites occupied by hydrogen. Evidence for a low-activation-energy process is also observed; this process is interpreted as a localized hopping within clusters of $3f\ensuremath{-}12n$ sites that does not result in hydrogen transport. These observations are consistent with the five-site model [$\frac{P6}{\mathrm{mmm}} ({D}_{6h}^{1})$ space group] for hydrogen site occupancy in ${\mathrm{LaNi}}_{5}$${\mathrm{H}}_{6}$, but they are less easily related to site occupancies for the $P31m ({C}_{3v}^{2})$ model. Additionally, the presence of several anomalies in the ${\mathrm{LaNi}}_{4}$B x-ray powder pattern prompted us to conduct single-crystal investigations which indicate that the ${\mathrm{CeCo}}_{4}$B structure represents only a subcell in a larger hexagonal antiphase domain structure extending along the directions of the basal-plane axes.

Gorsky relaxation and hydrogen diffusion in the metallic glassPd80Si20

A Gorsky relaxation associated with the long-range diffusion of hydrogen has been observed for the first time in a metallic glass. The diffusion parameters for amorphous ${\mathrm{Pd}}_{80}$${\mathrm{Si}}_{20}$ are ${Q}_{D}=0.25$ eV and ${D}_{0}=0.003$ ${\mathrm{cm}}^{2}$/sec. From the characteristics of a complementary reorientation relaxation, it is concluded that the interstitial sites occupied by hydrogen possess a distinctly asymmetric character.

Anelastic measurements of long range diffusion of hydrogen in a Pd 77/Ag 23 alloy

Anelastic measurements of long range diffusion of hydrogen in a Pd 77/Ag 23 alloy

The effect of loading mode on hydrogen embrittlement

Hydrogen embrittlement is shown to occur very easily in notched-round bars under opening modeI (tension) but not under antiplane shear modeIII (torsion). The stress tensor invariants under modeI,II, andIII loadings and how these affect interstitial diffusion are discussed. It is suggested that long range diffusion of hydrogen down orthogonal trajectories to the vicinity of the crack tip, which can occur under modeI but not modeIII, is a key part of any hydrogen embrittlement mechanism. This premise was evaluated with AISI 4340 steel heat treated to ultrahigh strength levels. It was found that an initial modeI stress intensity level of 17,000 psi-in.1/2 produced failure in several minutes. ModeIII stress intensity levels three times this produced no crack initiation in 300 min. Further analysis of the time-dependent hydrogen concentrating effect utilized a stress wave emission technique. This produced plausible critical hydrogen concentrations even though the present elastic analysis is a first order approximation of the stress field.

Internal friction due to long-range diffusion of hydrogen and deuterium in vanadium

The long-range diffusion (Gorsky effect) of hydrogen and deuterium in vanadium is invesitgated by internal friction measurements in the temperature range from 110 to 930°K; the vibration frequencies are included between 8 and 68 Hz. The diffusion coefficient of hydrogen and deuterium obeys an exponential law in a wide temperature range, the preexponential factors and the activation energies being: D OH = (4.4 ± 1.5) × 10 −4 cm 2 sec , D OD = (3.1 ± 0.8) × 10 −4 cm 2 sec , W H = (0.059 ± 0.007) eV, W D = (0.073 ± 0.006) eV .

Relaxation Process Due to Long-Range Diffusion of Hydrogen and Deuterium in Niobium

We have applied a new method for the determination of diffusion coefficients to hydrogen and deuterium in niobium. The activation energies for both isotopes are comparatively small and differ by about 20%, whereas ${D}_{0}$ is the same within experimental error. The activation energy for hydrogen diffusion is equal to the energy difference $\ensuremath{\hbar}{\ensuremath{\omega}}_{\mathrm{H}}=114\ifmmode\pm\else\textpm\fi{}6$ meV between the ground state and the first excited state of the hydrogen atom in solution.