Electromigration Of Hydrogen Research Articles

Direct Concentration Measurement of Hydrogen Electromigration Using Nuclear Reaction Analysis

AbstractLateral concentration profiles of hydrogen (1H) have been measured using nuclear recoil analysis on electrolytically charged metal (V, Nb, Ta) foils subjected to current densities of order 103 amps/cm2 for various times in order to study the electromigration of hydrogen. Initially uniformly loaded foils exhibited a dramatic redistribution of the hydrogen. Numerical analysis of these data using the conventional solution of the electromigration equation is used to extract the hydrogen effective charge (Z*) from the steady state data and the diffusion coefficient from the time-dependent data. The nuclear technique permits rapid and accurate direct concentration measurements capable of distinguishing surface and subsurface transport.

Electromigration of hydrogen and deuterium in tantalum: Isotope effect

Electromigration experiments at steady-state were conducted to determine the effective valence of hydrogen isotopes in tantalum specimens at room temperature (25 °C). Varying solute concentrations were obtained by gas-phase and electrolytic charging of the specimens. The transient concentration profiles of several specimens were monitored by a resistance technique allowing a controlled current through the samples. Steady-state concentration profiles were obtained by direct hot-vacuum extraction measurements. The results indicate a strong concentration dependence for the effective valence and evidence of a possible reversal in the direction of solute migration. While the reversal in the case of deuterium migration is not certain, an isotope effect on the effective valence as a whole is substantial. Deuterium has a 30 pct higher effective valence. The hypothesis that solute segregation at lattice defects and differing electronic structure of the defects and the perfect lattice are responsible for the concentration dependence of effective valence is found invalid as both cold-worked and annealed specimens did not indicate any microstructure effect on Z*. The concentration dependence of diffusion coefficient does not justify the strong dependence of Z* on concentration observed experimentally.

Electromigration of hydrogen in tantalum

Electromigration of hydrogen in tantalum

Electromigration of Hydrogen and Deuterium in Titanium

Electromigration of Hydrogen and Deuterium in Titanium

Electromigration of hydrogen and deuterium in vanadium and niobium by a resistance method

The electric mobility of hydrogen and deuterium has been measured at 30°C in niobium (Cb) and vanadium by a resistance method. The electric mobility was found to be 5.7 × 10−4 cm2/V-s for hydrogen and 2.8 × 10−4 for deuterium in niobium. In vanadium the electric mobilities were 2.3 × 10−3 and 1.3 × 10−3 cm2/V-s for hydrogen and deuterium respectively. The effective charges calculated using reported diffusion coefficients are positive and are slightly greater for deuterium than for hydrogen in both vanadium and niobium. The resistivity increase due to the hydrogen isotopes in vanadium and niobium was also measured. Hydrogen was found to contribute 0.65 μ ohm-cm/at, pct and deuter-ium 0.58 μ ohm−cm/at, pct to the resistivity of niobium. In vanadium, the solute resistivi-ties were found to be 0.98 μ. ohm-cm/at, pct and 0.90 μ ohm−cm/at, pct for hydrogen and deuterium respectively.

Electromigration and permeation of hydrogen and deuterium in silver

A steady state flow technique was used to measure the effective charge number ( Z*) and permeability ( N) of hydrogen and deuterium in silver. Over the range of temperature (485–720°C) and pressure (220–750 torr) the effective charge number is a constant. The interstitial impurity migrates in the direction of the electron wind with Z H * = −6·8 and Z D * = − 18. The values of Z* are of the same order as self-electromigration but the size of the isotope effect is surprising. The quantum theories used to explain the isotope effect for hydrogen electromigration in Fe and Ni appear to fail here. In order to determine the effective charge number is was necessary to measure the permeability. For both H 2 and D 2, the permeability in silver follows the equation N = N O exp(− Q/RT) where N 0D = 2·39 ± 0·40, Q D = 14400 ± 300, N OH = 2·86 ± 0·70 and Q H = 14200 ± 500. Here Q is in units of cal/mol and N is in units of cc(ntp)/(sec - atm 2 - cm) The isotope effect ratio N H / N D = 1·25 was smaller than the classically expected value of (2) 1/2, but could be explained by the theory of Ebisuzaki, Kass and O'Keeffe.