Fe-H System Research Articles

Atomistic Study of the Effect of Hydrogen on the Tendency toward Slip Planarity in Bcc Iron.

H-enhanced slip planarity is generally explained in terms of H-reducing stacking fault energy in fcc systems. Here, we showed that H-decreasing dislocation line energies can enhance the tendency toward slip planarity in bcc Fe through systematically studying the interaction between H and 1/2 <111> {110} dislocations using the EAM potential for Fe-H systems. It was found that the binding energy of H, the excess H in the atmosphere, and the interaction energy of H increased with edge components, leading to larger decrements in the line energies of the edge and increased mixed dislocations than those of a screw dislocation. The consequence of such interaction patterns is an increment in the energy change in the system when the edge and mixed dislocations are converted to screw dislocations as compared to the H-free cases. The cross-slip in bcc Fe is thus suppressed by H, increasing the tendency toward slip planarity.

Machine learning force field for Fe-H system and investigation on role of hydrogen on the crack propagation in [formula omitted]-Fe

A machine learning force field of Fe-H is constructed to study the hydrogen embrittlement via molecular dynamics (MD) simulations. The machine learning force field (MLFF) is obtained by learning the results of the density functional theory (DFT) MD calculation for various configurations, using a neural networks (NNs) model, with decomposed atomic energies in DFT calculations. Various tests are carried out to ensure that the MLFF describes well the statistic and dynamic property of iron + hydrogen systems. Using this MLFF, MD simulations of model iron sample with a small pre-crack tip at different grain boundaries are carried out with different loadings. We found that a high concentration of H ahead the crack tip will enhance the propagation of the crack, while the degree of enhancement depends on the type of the grain boundary. We also found the formation of microvoid ahead of crack and it might also contribute to the crack propagation.

Effect of nickel on the high-pressure phases in FeH

Hydrogen-rich metal alloys and compounds have drawn interest from planetary geophysics and condensed matter physics communities because of their potential for deep hydrogen storage in planets and high-temperature superconductivity. We find that a small amount of Ni can alter the phase behavior in the FeH alloy system. Ni can stabilize the double hexagonal close-packed (dhcp) structure in FeH up to the liquidus at 33 GPa, which is in contrast with the stability of the face-centered cubic (fcc) structure in Ni-free FeH at the same conditions. Above 60 GPa, Ni suppresses the stability of the tetragonal ${\mathrm{FeH}}_{2}$ phase but stabilizes fcc FeH at higher temperatures. At the same pressure range, we find tetragonal ${\mathrm{FeH}}_{2}$ and cubic ${\mathrm{FeH}}_{3}$ to be stable at temperatures above 2500 K without Ni. Therefore, in planetary interiors, Ni will expand the stability field of dense close-packed structures in the FeH system. If the Ni content is low, then ${\mathrm{FeH}}_{2}$ and ${\mathrm{FeH}}_{3}$ can play an important role in the cores of hydrogen-rich planets. Also, our study demonstrates that a secondary alloying component can severely impact the high-pressure stability of polyhydrides.

Engaging yne-allenones in tunable catalytic silane-mediated conjugate transfer reductions.

New tunable catalytic [2+2] cycloaddition/silane-mediated conjugate transfer reductions of yne-allenones have been developed, by which substituent-diverse cyclobutarenes with generally good yields were selectively synthesized by adjusting Fe-H and Cu-H catalytic systems. Use of the Fe-H system triggers 1,6-conjugate reduction to dihydrocyclobuta[a]naphthalen-4-ols whereas the Cu-H complex enables 1,4-conjugate reduction to cyclobuta[a]naphthalen-4(2H)-ones.

Solubility of deuterium and hydrogen in fcc iron at high pressures and temperatures

An isobar $x(T)$ of deuterium solubility in iron is constructed at $P=6.3\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ and $100\ensuremath{\le}T\ensuremath{\le}800{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ based on the results of thermal desorption analysis of $\mathrm{Fe}{\mathrm{D}}_{x}$ samples produced by quenching under high ${\mathrm{D}}_{2}$ pressure to the temperature of liquid nitrogen. The experiment confirms the value of $x=0.64$ at $T=715{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ proposed previously in a neutron diffraction work [Machida et al., Nature Commun. 5, 5063 (2014)] for \ensuremath{\gamma} iron deuteride under the assumption that deuterium atoms occupy both octa- and tetrahedral interstices in its fcc metal lattice. An estimate of $\mathrm{\ensuremath{\Delta}}V/x=2.2\phantom{\rule{0.16em}{0ex}}{\AA{}}^{3}/\mathrm{atom}$ D made in that work for the deuterium-induced volume expansion $\mathrm{\ensuremath{\Delta}}V(x)$ of fcc iron is also confirmed. To prove that the absorption of protium leads to a similar volume expansion, we constructed an isotherm $x(P)$ of hydrogen solubility in fcc iron at $T=600{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ and ${\mathrm{H}}_{2}$ pressures from 4.3 to 7.4 GPa. The available $\mathrm{\ensuremath{\Delta}}V(P,T)$ data of in situ x-ray diffraction studies of iron hydrides [T. Hiroi et al., J. Alloys Compd. 404--406, 252 (2005); H. Saitoh et al., J. Alloys Compd. 706, 520 (2017)] agree with this isotherm under the assumption that $\mathrm{\ensuremath{\Delta}}V/x=2.2\phantom{\rule{0.16em}{0ex}}{\AA{}}^{3}/\mathrm{atom}$ H. The transformation between the high-temperature fcc (\ensuremath{\gamma}) and low-temperature dhcp (\ensuremath{\epsilon}\ensuremath{'}) deuterides of iron is shown to occur at 260 \ifmmode^\circ\else\textdegree\fi{}C, which is approximately 100 \ifmmode^\circ\else\textdegree\fi{}C lower than the temperature of the \ensuremath{\gamma} \ensuremath{\leftrightarrow} \ensuremath{\epsilon}\ensuremath{'} transformation in the Fe-H system at the same pressure of 6.3 GPa.

Synthesis of new nickel hydrides at high pressure

We predict two new nickel hydrides, $\mathrm{N}{\mathrm{i}}_{2}{\mathrm{H}}_{3}$ ($C2/m$) and $\mathrm{Ni}{\mathrm{H}}_{2}$ ($I4/mmm$), to be thermodynamically stable at 60 GPa by DFT calculations. The calculated structure of $\mathrm{Ni}{\mathrm{H}}_{2}$ is similar to the one observed earlier for $\mathrm{Fe}{\mathrm{H}}_{2}$. However, to the best of our knowledge, the monoclinic structure predicted for $\mathrm{N}{\mathrm{i}}_{2}{\mathrm{H}}_{3}$ was never reported in the other hydrides. We successfully synthesized the monoclinic $\mathrm{N}{\mathrm{i}}_{2}{\mathrm{H}}_{3}$ phase using a laser-heating technique in a diamond anvil cell at pressures around 60 GPa. The $\mathrm{N}{\mathrm{i}}_{2}{\mathrm{H}}_{3}$ phase can be retained down to 17 GPa, and DFT calculations predict it to be nonmagnetic and nonsuperconducting. However, we did not find in our experiments the theoretically predicted $\mathrm{Ni}{\mathrm{H}}_{2}$ phase. Higher pressures and/or different synthesis conditions might be needed to synthesize this and other polyhydrides of nickel. Our results show that the Ni-H system behaves differently in comparison to the Fe-H system: Ni extends its own chemical identity to pressures as high as 60--80 GPa. This finding may have significant implications for the high-pressure behavior of Fe-Ni alloys at the high-pressure conditions relevant for the Earth and planetary sciences.

High chemisorption abilities of hydrogen and oxygen on ultrasmall iron clusters: A first-principles study

The interactions between atoms and small metal clusters are of great significance in the exploration of novel bonding mechanism. We present the strong chemisorption abilities of ultrasmall iron clusters interacting with large numbers of hydrogen and oxygen atoms from first-principles calculations. Geometric structures show that, the maximum numbers of the sequential hydrogen (oxygen) chemisorption on Fe1 to Fe4 clusters can be 11 to 28 (only 5 to 11). Using ab initio molecular dynamics, different kinds of hydrogen diffusion behaviors are found in the FeH systems, and two main types of FeO bonds are addressed in the stable FeO systems.

Iron Superhydrides FeH5 and FeH6: Stability, Electronic Properties, and Superconductivity

Recently a big number of works devoted to search for new hydrides with record high-temperature superconductivity and at the same time the successful synthesis of potential high-TC superconducting FeH5 was reported. We present a systematic search for stable compounds in the Fe-H system using variable-composition version of the evolutionary algorithm USPEX. All known (FeH, FeH3, FeH5) and several new Fe3H5, Fe3H13 and FeH6 iron hydrides were found to be stable, resulting in a very complex phase diagram with rich structural relationships between phases. We calculate electronic properties of two potentially high-TC FeH5 and FeH6 phases in the pressure range from 150 to 300 GPa. Indeed, hydrogen-rich FeH5 and FeH6 phases were found to be superconducting within Bardeen-Cooper-Schrieffer theory, with TC values of up to 46 K.

New iron hydrides under high pressure.

The Fe-H system has been investigated by combined x-ray diffraction studies and total energy calculations at pressures up to 136 GPa. The experiments involve laser annealing of hydrogen-embedded iron in a diamond anvil cell. Two new FeHx compounds, with x∼2 and x=3, are discovered at 67 and 86 GPa, respectively. Their crystal structures are identified (unit cell and Fe positional parameters from x-ray diffraction, H positional parameters from ab initio calculations) as tetragonal with space group I4/mmm for FeH(∼2) and as simple cubic with space group Pm3m for FeH3. Large metastability regimes are observed that allowed to measure the P(V) equation of state at room temperature of FeH, FeH(∼2), and FeH3.

809 第一原理計算によるFeとFe-H系の基本物性と原子間ポテンシャルの評価(OS08.電子・原子・マルチシミュレーションに基づく材料特性評価(3))

809 第一原理計算によるFeとFe-H系の基本物性と原子間ポテンシャルの評価(OS08.電子・原子・マルチシミュレーションに基づく材料特性評価(3))

シンクロトロン放射光と超高圧下のＸ線実験 （第２回）

Recent high pressure and high temperature in situ X-ray experiments using synchrotron radiation are reviewed. Among them are the behavior of Fe-H system, the conversion of graphite into hexagonal diamond, and an in situ observation of the formation of MgSiO3 perovskite from enstatite. The latter two studies were made by the newly developed Drick-amer-type high pressure apparatus using sintered diamond anvil, which is capable up to at least 30 GPa and 1500°C. Experiments up to 210 GPa were performed using diamond anvil apparatus combined with a very thin collimator system. A design of the apparatus to be constructed in the new synchrotron facility is discussed.

Thermodynamic functions in dilute PdH solid solutions

In recent reports concerning the thermodynamic properties of H in Ni and Fe, it was shown that the non-regular solubilities of H in these metals in equilibrium with H/sub 2/-gas at constant pressure was consistent with a chemical potential for H in the solid which contains a term corresponding to a simple oscillator with negligible anharmonicity. Such a chemical potential leads to a prediction of large departures from ''regular'' solubility behavior at low temperatures. In this context the word ''regular'' means that Arrhenius plots of the H-solubility vs. reciprocal temperature are linear. Whilst accurate data for the partial molar enthalpy H /SUB i/ and excess entropy S /SUP xs/ /SUB i/ as functions of temperature are not available for the Ni-H and Fe-H systems, such data can be obtained from the large number of T-theta /SUB i/ (i.e. temperature-composition) isobars or P-theta /SUB i/ (i.e. pressure-composition) isotherms measured for the Pd-H system. The quantities H /SUB i/ and S /SUP xs/ /SUB i/ vary strongly with temperature. Data for both H /SUB i/ and S /SUP xs/ /SUB i/ taken from the same source have the same symbol. The symbol code is given in Table 1. The data refer tomore » an atomic ratio theta /SUB i/ of H to Pd of 10/sup -3/ and the points were taken at theta /SUB i/ = 7 x 10/sup -3/. All the remaining data were taken in solutions for which theta /SUB i/ <10/sup -2/. The object of this communication is to compare the temperature-dependence of H /SUB i/ and S /SUP xs/ /SUB i/ and with that predicted by the simple model given previously.« less

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