Diffusion Constant Of Hydrogen Research Articles

Study on Impurity Diffusion in Glow-Discharged Amorphous Silicon

The diffusion of impurities in glow-discharged hydrogenated amorphous silicon (a-Si: H) films with various hydrogen contents is studied experimentally taking boron and antimony as examples of impurities. Similar impurity diffusion in hydro-fluorinated amorphous silicon (a-Si: F: H) films is also studied for comparison. It is found that the diffusion constant of impurities in a-Si: H depends only weakly on the impurity itself and is equal to the diffusion constant of hydrogen, and that the impurity diffusion is suppressed in a-Si: F: H film.

Mechanism of impurity diffusion in a-Si:H and diffusion blocking by fluorine inclusion

Diffusion of impurities such as boron or antimony in both the glow-discharged a-Si:H and a-Si:F:H is studied by the nuclear reaction technique and the Rutherford back-scattering technique. Diffusion constant and its activation energy are evaluated and are compared with those of hydrogen in a-Si:H. It is found that diffusion constant of impurity in a-Si:H depends only weakly on impurity itself but is equal to diffusion constant of hydrogen. That is, impurity diffusion is controlled by movement of hydrogen. It is also found that impurity diffusion is apparently blocked in the film containing fluorine, a-Si:F:H.

Measurements of the diffusion of hydrogen atoms in magnesium and Mg 2Ni by neutron scattering

Mg 2Ni and the mixed system Mg-Mg 2Ni are used as hydrogen storage media for industrial applications. The mechanism of hydrogen charge and discharge in Mg-Mg 2Ni is not yet completely understood particularly because the kinetics of hydrogen exchange in magnesium are strongly influenced by the Mg 2Ni phase. In order to investigate hydrogen exchange in Mg-Mg 2Ni the diffusion constants of hydrogen in both systems have been investigated separately using a quasi-elastic neutron scattering technique with a high resolution backscattering spectrometer. The results show that the diffusion of hydrogen in the α phase of Mg 2Ni occurs more slowly than in the α phase of magnesium, so that the fast kinetics of hydrogen exchange in the combined system Mg-Mg 2Ni are probably influenced by surface effects. The diffusion rate in the β phase of magnesium is smaller by three orders of magnitude than that in the α phase.

Influence of the wall temperature on hydrogen recycling phenomena in an SS simulation apparatus

Hydrogen recycling phenomena have been investigated as a function of wall temperature T w in an SS 304 simulation apparatus. The walls of the vessel were exposed to a flux of hydrogen species from an RG-discharge (glow-discharge) and the associated pressure variation (Langmuir effect) was measured and analyzed. The curves can be fitted very well to a theoretical equation based on the simple recycling model, published previously. The fitting parameter is the recycling constant D/2σk r (D = hydrogen diffusion constant, 2σk r = surface recombination rate constant) which is determined as a function of T w. It follows an Arrhenius relation with an activation energy of −3.5 kcal/mole. Conclusions for the operation of fusion devices are discussed.

Hydrogen diffusion in β-phase titanium iron hydride

NMR pulse techniques have been used to measure proton relaxation times in high purity β-TiFeH 1.03 between 94K and 413K. Recent crystal structure parameters from neutron diffraction studies of orthorhombic β-TiFeD x have been explicitly included in the analysis of the T 2 relaxation times to obtain more accurate hydrogen diffusion parameters than were possible from previous NMR studies of β-TiFeH x. The room temperature (300K) hydrogen diffusion constant in β-TiFeH x is verified to be about 1.2 ± 0.8 × 10 −12cm 2/s, which is 10 −4–10 −5times smaller than in many other metal hydrides such as PdH x or LaNi 5H x.

Investigation of the anomalous temperature dependence of the self-diffusion constant of hydrogen in niobium by quasielastic neutron scattering

The diffusion constant of hydrogen in niobium was investigated by quasielastic neutron scattering in the temperature region 65 to 300K. By macroscopic methods, a transition from a high-temperature activation energy of 106 MeV to a low-temperature activation energy of 68 MeV was observed in this region. The value of the low-temperature activation energy was confirmed by the neutron scattering experiments. The possibility that the activation energy at low temperature is related to thermally activated tunnelling processes is discussed.

Measurement of the mutual diffusion constant of hydrogen in methane by means of spontaneous light scattering

Measurement of the mutual diffusion constant of hydrogen in methane by means of spontaneous light scattering

Molecular motion of hydrogen in liquid argon and neon

The liquid systems H2 in argon and H2 in neon have been investigated by neutron scattering. Quasi-elastic and inelastic spectra have been clearly observed, the inelastic spectra being more intense than in pure argon or neon. A diffusion constant and a frequency of vibration for each case have been extracted and compared with a calculation by Sears. The experimental and calculated vibrational spectra are in fair but not close agreement. However, the diffusion constant for hydrogen in argon is greater than that for pure argon while for hydrogen in neon it is probably smaller than for pure neon.

Meteoritic Tritium and Diffusion in α- and γ-Iron

SEVERAL points urgently require clarification following my recent exchange of communications with Mr. Tamers1,2. First and most important, the limited available evidence does indeed suggest that a difference of several orders of magnitude exists between γ- and α-phase of iron for diffusion constants of hydrogen at room temperature. It is, of course, the room-temperature behaviour which is relevant for the problem of loss on Earth. Mr. Tamers quotes the paper of Sykes, Burton and Gegg3 as showing that these two diffusion constants differ by only a factor of 10 at 650° C. The identical equations and numbers from this paper demonstrate a difference of a factor of one million at room temperature (20° C).