Features of hydrogen accumulation in metals during saturation in plasma, electrolyte, and hydrogen under pressure

Features of the temperature spectra of thermally stimulated gas evolution are investigated to determine features of the incorporation of hydrogen into titanium, palladium, and steel of 12Kh12M1BFR grade (metals substantially different with regard to hydrogen solubility) from media of various aggregate states. The conclusions are drawn with regard to the order of filling of high-temperature and low-temperature traps in dependence on the metal and method of saturation.     

Thermal expansion and the heat capacity of nanocrystalline and coarse-crystalline silver sulfide Ag2S

The thermal expansion and the heat capacity of coarse-crystalline and nanocrystalline silver sulfide Ag₂S were studied by dilatometry and differential scanning calorimentry for the first time in the temperature range 290–970 K. It is found that the thermal expansion coefficient and the heat capacity of nanocrystalline silver sulfide in this temperature range are higher than those in the case of the coarse-crystalline sulfide. It is revealed that the transformation of α-Ag₂S acanthite to β-Ag₂S argentite and β-Ag₂S argentite to γ-Ag₂S phase are the first-order phase transitions; the temperatures and the enthalpies of these transformations have been determined.

     

Pionic hydrogen and deuterium

The ground-state level shifts and broadenings of the hydrogen isotopes caused by the strong interaction have been redetermined by using a high-resolution crystal spectrometer. An additional measurement of muonic hydrogen reveals properties of the de-excitation cascade of such electrically neutral exotic atoms, in particular Coulomb de-excitation, the understanding of which is essential for the analysis of the hadronic-atom data.     

Features of excitation of the hydrogen (deuterium)-metal system by an electron bunch

We report on the results of mass-spectroscopic analysis of the hydrogen yield from metals saturated with hydrogen under the action of accelerated electrons (with an energy of up to 100 keV and a current density from 3 to 30 μA). It is found that the desorption rate is determined not only by parameters of the electron bunch, but also by the structure of the oxide film. It is discovered that the electronic subsystem of hydrogen-enriched metals enhances their ability to absorb the energy of the external electromagnetic action and to preserve it for a longer time as compared to a pure metal. This facilitates nonequilibrium migration and yield of hydrogen under the action of radiation in the subthreshold range. A theoretical model is proposed and analytic dependences are derived for the intensity of hydrogen yield from metals exposed to an electron bunch. The results of this study can be used for the removal of hydrogen from metals and for obtaining submicrocrystalline materials (e.g., titanium).     

Heavy-ion-induced desorption of deuterium from titanium

A titanium-layer of approximately 90 nm thickness has been homogeneously loaded with deuterium by implantation and diffusion. Desorption was studied by use of²⁸Si ions of up to 20 MeV energy (and other ions). The spectrum of the elastic-recoil-detection method serves as indication of the released and retained amount of deuterium. The retained deuterium is recorded as a function of the employed ion dose and is converted into a desorption rate as a function of the retained deuterium concentration. — A one-dimensional theory considering transitions from vacuum to surface and surface to Ti volume (and back) leads to a system of equations, the solutions of which allow adaptation to the experiment and therefore an evaluation with respect to certain characteristic parameters. — Some of the results might be influenced by the high concentration of C and O impurities.     

Effect of a magnetic field on the radiation emitted by a nonequilibrium hydrogen and deuterium plasma

Radiative transfer in a nonequilibrium plasma in an external electric field is considered. The system of kinetic equations determining the populations of atomic levels is written taking into account the combination of collision and radiative processes and is solved together with the kinetic equation for photon of various frequencies, which are emitted and absorbed in the radiative transitions from the states of the continuous and discrete spectra. The shape of spectral lines is determined from the solution of the quantum-mechanical problem on the emission of an atom in the electric field of the plasma and an external magnetic field, taking the Doppler effect into consideration. The developed approach is used in the model calculation of radiative transfer under the conditions corresponding to the edge plasma in a tokamak, which is simulated by a homogeneous plane layer of a deuterium plasma. It is shown that the joint action of the external magnetic field and the electric plasma fields considerably affects the spectral and integrated characteristics of the radiation.     

Thermal expansion of nanocrystalline and coarse-crystalline silver sulfide Ag<Subscript>2</Subscript>S

In situ studies of the thermal expansion of polymorphic phases of coarse-crystalline and nanocrystalline silver sulfide, namely, monoclinic acanthite α-Ag₂S and cubic argentite β-Ag₂S, have been performed for the first time by high-temperature X-ray diffraction. The temperature dependences of the unit cell parameters of acanthite and argentite have been measured from temperatures in the range of 300–623 K, and the thermal expansion coefficients of acanthite and argentite have been determined. The observed difference between the thermal expansion coefficients of nano- and coarse-crystalline acanthite is shown to be due to a small size of nanocrystalline silver sulfide particles, which leads to an increase in the anharmonicity of atomic vibrations.     

The effect of a nitrogen-rich surface layer on the sub-surface deuterium (hydrogen) concentration distribution in titanium

Deuterium and nitrogen depth profiles in Ti with modified surfaces have been measured with Auger electron spectroscopy, secondary ion mass spectroscopy, and D(³He,p)⁴He nuclear reaction analysis. Nitrogen-rich surfaces layers of varying thicknesses were created on Ti by exposure to N₂ gas at 650°C. Deuterium loading was performed by exposure to 1 Torr of D₂ gas at 500°C. The deuterium distribution was influenced by nitrogen in the near-surface regions of all samples. Specifically, deuterium solubility was suppressed in surface regions of high (greater than 1%) nitrogen concentration. The deuterium solubility also remained low within the first few microns, well beyond the region of high nitrogen concentration. This effect is attributed to internal elastic stresses imposed by the non-deuterium absorbing nitrogen-rich layer on the Ti. These stresses prohibit the volume expansion associated with deuterium absorption. We estimate stresses on the order of 3–4 GPa are required to suppress the deuterium solubility to the values observed. The deuterium absorption kinetics were observed to depend systematically on the thickness of the nitrogen-rich layer. This is consistent with limited solubility near the surface or a surface poisoning effect influencing the overall deuterium diffusion from the gas phase into the Ti bulk.     

Heavy-ion induced desorption of deuterium from titanium

The model used in the first part of this investigation is enlarged to take account of the experimentally found inhibition of desorption by gases from the rest-gas atmosphere of the target chamber. The main parameters that can be found by adaptation of a model set of equations are the rate ratios for transfer of chemisorbed atoms in the surface and back, and of the maximal desorption current densities from the surface into the vacuum for deuterium and foreign gases. The desorption cross sections are discussed in relation to the electronic stopping power of the fast ions.     

Low-temperature plasticity in nanocrystalline titanium and copper

The stress-strain compressive curves, temperature dependences of the yield stress, and small-inelastic-strain rate spectra of coarse-grained and ultrafine-grained (produced by equal-channel angular pressing) titanium and copper are compared in the temperature range 4.2–300 K. As the temperature decreases, copper undergoes mainly strain hardening and titanium undergoes thermal hardening. The temperature dependences of the yield stress of titanium and copper have specific features which correlate with the behavior of their small-inelastic-strain rate spectra. Under the same loading conditions, the rate of microplastic deformation of ultrafine-grained titanium is lower than that of coarse-grained titanium and the rate peaks shift toward high temperatures. The deformation activation volumes of titanium samples differing in terms of their grain size are (10–35)b ³, where b is the Burgers vector magnitude. The dependences of the yield stress on the grain size at various temperatures are satisfactorily described by the Hall-Petch relation.     

Light scattering from hydrogen and deuterium halides

Light scattering measurements along the coexistence line show that reorientation in liquid HCl, DCl, and HBr is strongly hindered at low temperature and collision limited on approaching the critical point. Discrepancies with NMR data are observed.     

Formic acid in deuterium and hydrogen matrices

ABSTRACT

Formic acid (HCOOH, FA) was studied experimentally, by infrared spectroscopy, in H₂ and D₂ matrices, with focus on the preparation and characterisation in these matrix media of structures containing the higher-energy (cis) conformer. The cis-FA monomer and the cis-FA^?…?N₂ complex were successfully produced by selective vibrational excitation of corresponding trans-FA based species, and vibrationally characterised. The tunneling-induced conversion of the cis-FA^?…?N₂ complex in the studied matrices into the corresponding trans-FA complex was also investigated, and the found tunnelling properties discussed, in particular in comparison with those observed for the spontaneous conversion of cis-FA monomer into trans-FA. This article constitutes the first report on the infrared spectrum of FA conformers and stability of cis-FA monomer in a D₂ matrix, and on the structure, spectroscopy and stability of the cis-FA^?…?N₂ complex in both H₂ and D₂ matrices. Different attempts to prepare the cis-FA^?…?H₂O complex in the two investigated matrices are also described in detail, both from previously in situ generated cis-FA monomer followed by thermal mobilisation and by direct selective vibrational excitation of the trans-FA-H₂O complex.     

Plasma electrolytic saturation of titanium and its alloys with light elements

This review is devoted to analyzing the results of the thermochemical treatment of titanium-alloy surfaces under plasma action in electrolytes. Plasma electrolytic saturation (PES) with light elements is found to have advantages over alternative methods. Electrolyte compositions by means of which titanium is rapidly saturated with nitrogen, carbon, boron, and oxygen are presented. The treatment modes and characteristics of the modified layers, such as the phase and elemental composition, surface roughness and microhardness, friction coefficient, wear rate, and corrosion resistance, are discussed. Attention is paid to the thermophysical and electrochemical aspects of PES, in particular, to the specifics of titanium heating and its anodic dissolution and oxidation.     

Precision measurement of antiprotonic hydrogen and deuterium X-rays

X-rays from antiprotonic hydrogen and deuterium have been measured at low pressures. Using the cyclotron trap, a 105 MeV/c antiproton beam from LEAR was stopped with an efficiency of 86% in 30 mbar hydrogen gas in a volume of only 100 cm³. The X-rays were measured with Si(Li) detectors and a Xe-CH₄ drift chamber. The strong interaction shift and broadening of the Lyman transition and the spin-averaged 2p width in antiprotonic hydrogen was measured with unprecedented accuracy. The triplet component of the ground state in antiprotonic hydrogen was determined for the first time.The authors would like to thank the LEAR staff for their efforts in providing the antiproton beam. The help of P. Gauss from the CERN cryogenic group and of P. Zettwoch from the PS workshop is gratefully acknowledged. We wish to thank K.-P. Wieder for his help with the drawings. This work is part of the Ph.D. thesis of one of us (K.H., University of Karlsruhe, 1990).     

Phonons and librons in solid hydrogen and deuterium

The coupled system of phonons and librons is treated in the Random Phase Approximation. The short range correlations are taken into account by an effective Hamiltonian. Dispersion curves and spectra are calculated for both the fcc and hcp phases. All calculations are performed a) with quadrupole-quadrupole forces only b) including the other anisotropic forces.     

Inversion degree and saturation magnetization of different nanocrystalline cobalt ferrites

The inversion degree of a series of nanocrystalline samples of CoFe₂O₄ ferrites has been evaluated by a combined study, which exploits the saturation magnetization at 4.2 K and ⁵⁷Fe Mössbauer spectroscopy. The samples, prepared by sol-gel autocombustion, have different thermal history and particle size. The differences observed in the saturation magnetization of these samples are explained in terms of different inversion degrees, as confirmed by the analysis of the components in the Mössbauer spectra. It is notable that the inversion degrees of the samples investigated are set among the highest values reported in the literature.     

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 H₂ and D₂, 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 - atm² - 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.