Molecular Dynamics Study of Interaction of Carbon, Nitrogen, and Oxygen Impurity Atoms with Self-Interstitial Atoms in Nickel, Silver and Aluminum

The interaction of impurity atoms of carbon, nitrogen, and oxygen with self-interstitial atoms in FCC metals like nickel, silver, and aluminum is studied using the molecular dynamics method. It is found that the self-interstitial atom migration in the crystal lattice follows two mechanisms: dumbbell and crowdion. In this case, the first mechanism that includes one interatomic distance displacement and the rotation of the <001> dumbbell is characterized by broken paths of atomic migration. The second mechanism is described by straight paths along the close-packed directions <011> in the crystal. The binding energies between impurity atoms and selfinterstitial atoms in Ni, Ag, and Al are calculated in the paper. It is shown that impurity atoms are effective “traps” for interstitial atoms that migrate relatively quickly in a crystal. During the interaction of an interstitial and an impurity atom, the interstitial atom forms a dumbbell configuration with an axis along the <001> direction, and the impurity atom is located in the nearest octahedral pore. It is found that the mobility of interstitial atoms is significantly reduced due to the presence of impurities in the metal. The introduction of 10 % impurity atoms leads to a severalfold increase in the migration energy of interstitial atoms. At the same time, the contribution of the crowdion mechanism is noticeably reduced while the dumbbell mechanism contribution is increased.

Ab Initio Study of Helium in Tantalum: Interaction, Migration, and Clustering with Helium and Vacancies

Ab initio calculations based on the Density Function Theory (DFT) have been performed to study the interaction between helium and helium, helium and vacancy, migration of helium, and the stability of small helium-vacancy clusters in tantalum. The following results are found: (I) The tetrahedral interstitial helium atoms have weak interactions in tantalum, suggesting that no stable covalent bond is formed between this two helium atoms; (II) The stability of small helium-vacancy clusters is investigated. The interstitial helium atom and vacancy to the clusters are found to be positive in almost all case, i.e., all interactions are attractive; (III) The activation energies for a substitutional helium atom migration by the dissociation or vacancy mechanisms are estimated under the irradiation condition.

Theoretical studies on the initial reaction kinetics and mechanisms of p-, m- and o-nitrotoluene

Direct bond dissociations of C–NO2 are dominant at high temperatures for p- and m-nitrotolune, while O transfer are predominant at low to intermediate temperatures. For o-nitrotoluene, the H atom migration and C–NO2 bond dissociation are important.

The facilitated magnesium atom adsorption and surface diffusion kinetics via artificial bismuth-based interphases

Robust bismuth-based interphases, composing of bismuth and bismuth oxides, were developed by galvanic replacement reaction. The facilitated Mg atoms adsorption and distinct interfacial Mg atom migration were demonstrated, greatly lowering...

Strong-field ionization of polyatomic molecules: Ultrafast H atom migration and bond formation in photodissociation of CH3OH

Strong-field ionization induces various complex phenomena like bond breaking, intramolecular hydrogen migration, and bond association in polyatomic molecules. The H-atom migration and bond formation in CH3OH induced by intense femtosecond...

Facilitating hydrogen atom migration via a dense phase on palladium islands to a surrounding silver surface

The migration of species across interfaces can crucially affect the performance of heterogeneous catalysts. A key concept in using bimetallic catalysts for hydrogenation is that the active metal supplies hydrogen atoms to the host metal, where selective hydrogenation can then occur. Herein, we demonstrate that, following dihydrogen dissociation on palladium islands, hydrogen atoms migrate from palladium to silver, to which they are generally less strongly bound. This migration is driven by the population of weakly bound states on the palladium at high hydrogen atom coverages which are nearly isoenergetic with binding sites on the silver. The rate of hydrogen atom migration depends on the palladium−silver interface length, with smaller palladium islands more efficiently supplying hydrogen atoms to the silver. This study demonstrates that hydrogen atoms can migrate from a more strongly binding metal to a more weakly binding surface under special conditions, such as high dihydrogen pressure.