Hydrogen In Aluminum Research Articles

Hydrogen and deuterium solubility in aluminum with voids

Hydrogen and deuterium concentrations in aluminum were measured at 600°C in the pressure range from 0.2 to 1.0 atm, by means of a desorption technique which was an outgassing study from thermally gas-charged cylindrical samples with various amounts of voids. The relation between the pressure of hydrogen or deuterium and the equilibrium concentration in a void-free sample was observed to follow Sieverts' law. In the sample with voids, an apparent hydrogen or deuterium concentration was given by the sum of the gas solved in the lattice and that held in the voids in the molecular state thermally equilibrated with the gas pressure of the atmosphere. In the as-cast sample with blowing hydrogen gas through the melt, the average hydrogen pressure in the voids was calculated to be about 7.3 atm at room temperature (about 23 atm at 660°C), and the apparent hydrogen diffusion coefficient decreased with increasing amount of voids.

Possible uses of sensors in the aluminium industry

AbstractThere is a requirement for on-line monitoring of elements in molten aluminium and one possible approach is to use electrochemical sensors which produce a voltage that is related to the concentration of an element in the melt. The principle of electrochemical sensors is outlined and examples given for hydrogen, lithium, and sodium determination in molten aluminium using sensors based upon calcium hydride, lithium silicate–phosphate, and sodium β-alumina, respectively: sensors could also be used to control the Hall–Heroult cell and possible examples are the measurement of the NaF/AlF3 ratio in the cryolite bath, the evolved CO/CO2 ratio from the anode, as well as the concentration of sodium and lithium in the aluminium tapped from the cell.MST/571

The diffusivity of hydrogen in aluminum

Using an electrolytic method employing a viscous electrolyte, the diffusivity of hydrogen in aluminum has been measured in the temperature range 285–328 K. The results show that H diffuses by a single-stage process from 285 K up to the melting temperature and no departures from Arrhenius behavior due to trapping effects involving lattice vacancies are observed.

アルミニウム中の水素の定量下限改善に関する研究

The purpose of this experiment was to improve the limit of determination of hydrogen in aluminum. As variation of surface gases on samples affected the limit of determination in an usual analytical method (a method of determing internal hydrogen by correcting surface hydrogen), a way of removing surface gases by discharge cleaning prior to analysis was studied in the present work. The results were as follows;1) Aluminum surface gases consisted of mainly H2, H2O, CO, and CO2.In those gases, H2 and CO were remarkably detected.2) Those surface gases could be removed by He discharge cleaning.CO as surface gas was 1×10-5torr.l (3.5×1013molec./cm2) after discharge cleaning, and was about 1×10-3 torr.l(3.5×1015molec./cm2) with no discharge cleaning.3) Analyzing aluminum sample which contained internal hydrogen of 0.11cc/100g Al after discharge cleaning, all internal hydrogen measured by an usual analytical method.Improvement of the limit of determination of internal hydrogen by discharge cleaning is considered to be possible.

Time-resolved measurement of acoustic pulses generated by MeV protons stopping in aluminum.

A wide-band capacitive detector has been constructed to make time-resolved measurements of acoustic pulses generated in aluminum and in other solids by ns pulses of MeV protons. The near-field signal observed traveling in the beam direction is a measure of the initial pressure distribution along the path of the stopping protons. The measured amplitudes and shapes of such signals are consistent with the thermoelastic model of sound generation. From the signal rise time (<2 ns), it can be concluded that the conversion into heat of the energy loss of a slowing proton is localized within a radius of several micrometers. For the data presented, the fraction of beam-pulse energy absorbed from acoustic radiation by the detector is about 5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}14}$. Acoustic signals which generate ${10}^{\mathrm{\ensuremath{-}}2}$ eV of electrical energy in the detector (\ensuremath{\sim}4 \ensuremath{\mu}V into 50 \ensuremath{\Omega} for 5 ns) are easily discernible after signal averaging. Acoustic signals were used to probe the formation of microbubbles in hydrogen-implanted aluminum. From bubble growths inferred from acoustic measurements, the diffusivity of hydrogen in aluminum is estimated at a temperature where the diffusivity is 8 orders of magnitude smaller than in previous measurements.

Heat of Solution of Hydrogen in Aluminum

AbstractThe heat of solution of hydrogen in aluminum is investigated accounting for both, the lattice dilation and its relaxation. The lattice contribution is evaluated using a linearly screened local model potential for the ions. The non‐linear screening in the density functional formalism along with the exchange and correlation corrections in the jellium model is used to evaluate the proton contribution. The dilation enhances the lattice contribution by about 12% and decreases the protonic contribution by about 5%. The relaxation energy is reduced by about 40% for the dilated lattice. Adding all the contributions, the heat of solution is found to be 20% larger for the dilated lattice than that for the undilated lattice. The calculated heat of solution is found in good agreement with the experimental value. Comparing the results with the calculations of Perrot and Rasolt, the spherical solid model correction is estimated and it is found that it further improves the results.

Lattice relaxation around interstitial hydrogen in aluminium

Lattice relaxation around interstitial hydrogen in aluminium

Hydrogen diffusion in aluminum

Although the diffusivity of hydrogen in aluminum has been measured by several different authors, there is essentially no mutual agreement and the sets of data are separated by orders of magnitude. There is little doubt these mass-flow determinations of the H-diffusivity are subject to great uncertainties connected with the presence of the surface oxide layer, as has been discussed recently in general by Volkl and Alefeld and more specifically for the Fe-H system by Kiuchi and McLellan. However, recent discussions of the thermodynamic behavior of H in the noble metals have pointed out the possibility of H-vacancy interactions being reflected in the observed solubility and diffusivity of H in these metals; the H-Al system is a prime candidate in which the manifestation of such H-vacancy interactions would be expected. This possibility has been made more probable by the recent measurements of Hashimoto and Kino of the diffusivity of H through Al foils. These authors used a permeation technique in which the H-permeation rate through Al foils was measured by the change in H/sup +//sub 2/ ion current detected by a quadrupole mass spectrometer. The samples were lightly abraded before mounting in the UHV (2.6 x 10/sup -8/ Pa) measuring system.more » Diffusivities measured in the range 573-673 K using foils of differing thickness indicated that surface effects had been obviated. This note discusses findings on the H-Al system in terms of the kinetic behavior predicted for solutions of H in metals where there is a high concentration of vacancies in thermal equilibrium.« less

Lattice relaxation around interstitial hydrogen in aluminium

The lattice deformation in a simple metal host due to an interstitial hydrogen-like impurity is studied by extending the jellium density approximation of Popovic et al. (1976) to calculate displacing forces and the method of lattice statics to find equilibrium. The validity of the approach is discussed in the framework of the perturbed electron liquid formalism. It is shown, in particular, that the method is incomplete for the long-wavelength components of the strain field, a generalisation of the earlier result concerning the special case of linear screening. In determining the volume dilatation, the 'slope theorem' connecting density distribution with the derivative of the impurity energy in jellium, recently derived by Stott and Zaremba (1980), proves to be essential. The energy of lattice relaxation around a tetrahedral interstitial is found to be -0.18 eV, the heat of solution is 0.71 eV, near to the experimental value (0.66 eV). The energy minimum is at the tetrahedral site, but the barrier is extremely low so that the energetics seem to allow an almost free motion of the proton along the cubic diagonal. The individual displacements of near neighbours are in reasonable agreement with the available experimental data.

Hydrogen diffusion in aluminium at high temperatures

The diffusion of hydrogen in aluminium has been measured by the permeation method using a quadrupole mass spectrometer. Hydrogen was introduced by gas phase charging in the temperature range of 300-400 degrees C, and by electrochemical charging at room temperature. It was found that the diffusivity of hydrogen depends on the relative concentration of vacancies to the dissolved hydrogen concentration. The activation energy for the diffusion of hydrogen was found to be 0.61-0.62 eV at high temperatures where the concentration of vacancies was much higher than that of dissolved hydrogen. The value is near the migration energy of a vacancy in aluminium. On the other hand, at room temperature where the hydrogen showed a diffusivity considerably larger than that extrapolated from high temperatures. These facts suggest that hydrogen in aluminium migrates together with a vacancy at high temperatures due to a large binding energy between them.

The computation of the vibrational spectrum of hydrogen in aluminium by the recursion method

The vibrational density of states of hydrogen in aluminium was calculated by the recursion method using central pair potentials determined from pseudopotential theory. The coupling between hydrogen and aluminium atoms is fairly weak, and the low-frequency resonance appears in the spectral density due to weak transverse coupling.

The electronic structure of a hydrogen impurity in aluminium III. The energy and the metal‐impurity interaction

AbstractA theoretical approach to the study of both, the energy of a hydrogen impurity in a metal and the metal‐hydrogen impurity interaction is described. The analysis involves the virial and Hellmann Feynman theorems and the Kohn‐Sham formalism. Detailed calculations are performed for the case of hydrogen in aluminium. It is found that the non‐spherical component of the hydrogen induced electronic structure greatly modifies the hydrogen‐aluminium interaction, and the aluminium lattice expands about both, octahedrally and tetrahedrally sited impurities. These results, and the determination of the electric field gradient, compare favourably with those obtained from muon spin rotation experiments on such systems.

The nature of the bound state induced by an interstitial hydrogen in aluminium

Previous calculations have indicated the formation of a bound state due to the interstitial hydrogen below the bottom of the metal conduction band, particularly in aluminium and palladium metals. We investigated the nature of this bound state by performing a supercell calculation of the electronic structure of the interstitial hydrogen in the octahedral position in aluminium. We found that the metal states are perturbed by the hydrogen potential and that the lowest band is split off resulting in a gap between the lowest state and the rest of the bands. The lowest state is thus a metal-hydrogen bonding state and not a bound state since no additional state is formed as would be the case for a bound state.

Electron transfer of hydrogen in aluminum at 20 and 800�C

Electron transfer of hydrogen in aluminum at 20 and 800�C

Evidence for Dislocation Transport of Hydrogen in Aluminum

The use of concurrent plastic straining during cathodic charging of equiaxed-grain, high purity 7075 aluminum has provided evidence that dislocations can transport large amounts of hydrogen deep into the interior of the alloy; as a direct consequence of this, highly brittle intergranular fracture ensues. This effect is most pronounced for heat treatments that produce a microstructure which allows for planar dislocation arrays and long slip lengths. The implications of these findings to the occurrence of hydrogen embrittlement in other alloy systems have been assessed.

Diffusion of hydrogen in pure large grain aluminum

The solubility of hydrogen at 600°C and the diffusion rate at a given temperature were both found to be lower than reported previously. The activation energy for diffusion was nearly the same as in several earlier reports indicating that diffusion was the rate controlling step in all cases. Hydrogen diffusion in large grained high purity aluminum followed the expression: D = 1.01 × 10 −5 (m 2/sec) exp − 47.7 kJ/RT.

Energetics of hydrogen in aluminum

A detailed account of the results obtained for the energetics of a proton in aluminum is reported. The central model used in the calculations is the so-called ''spherical solid model'' in which the part of the ionic potential which is spherically symmetric around the impurity is treated to all orders. Various additional effects, such as the contributions of the nonspherical potential and lattice relaxation are investigated. The variation of the heat of solution of H in Al with position is calculated, and the zero-point vibration energy estimated.

Diffusion of hydrogen in high purity aluminium

Diffusion of hydrogen in high purity aluminium

Heat of solution of hydrogen in aluminum

The interaction of a proton with an aluminum host is treated within the spherical model of a solid. Our results give for the heat of solution and activation energy of H in Al 0.593 and 0.5 eV, respectively, compared with the experimental values of 0.66 and 0.52 eV. The previously untreated nonspherical corrections are also estimated and shown to be small.

アルミニウム中の水素の拡散係数と溶解度におよぼすボイドの影響

アルミニウム中の水素の拡散係数と溶解度におよぼすボイドの影響