Influence of Mechanical Activation on Synthesis of Compounds in the B/C - Mg/Al/Ca System

The possibility of mechanochemical synthesis and influence of mechanical activation on thermal synthesis of borides and boron carbides of mass-low metals is investigated. The opportunity of mechanochemical synthesis in the mill AGO-2 of such compounds as AlB2 and CaC2B2 is established. Influence of mechanical activation in the mill SPEX 8000 on synthesis of such compound as Mg0.5Al0.5B2 is shown. Mechanical activation also influences on the process of thermal synthesis: compound Mg0.5Al0.5B2 is obtained in the conditions inaccessible to traditional thermal synthesis; formation of compound Mg1-xAlxB2 in literature up to x = 0.4 was established on shifts of reflexes (002) and (110) pure MgB2 aside the large corners; in our case x = 0.5 and as it was necessary to expect shifts of these reflexes exceeds shifts measured in literature only for x ≤ 0.4. Features of synthesis in systems containing metal magnesium are considered. The opportunity of application of crystalline boron for mechanochemical synthesis of borides and boron carbides of mass-low metals is established, that it was not represented probable to make in its ceramic synthesis. We revealed also that thermal analysis in conditions of helium results in crystallization almost all activated samples, and the analysis of received X-ray reflexes unambiguously allows to assert that mechanical activation accelerates synthesis of reaction products in the investigated systems in comparison with the traditional methods of its synthesis

Tribochemistry, Mechanical Alloying, Mechanochemistry: What is in a Name?

Over the decades, the application of mechanical force to influence chemical reactions has been called by various names: mechanochemistry, tribochemistry, mechanical alloying, to name but a few. The evolution of these terms has largely mirrored the understanding of the field. But what is meant by these terms, why have they evolved, and does it really matter how a process is called? Which parameters should be defined to describe unambiguously the experimental conditions such that others can reproduce the results, or to allow a meaningful comparison between processes explored under different conditions? Can the information on the process be encoded in a clear, concise, and self-explanatory way? We address these questions in this Opinion contribution, which we hope will spark timely and constructive discussion across the international mechanochemical community

Stability, Electronic, and Optical Properties of Two-Dimensional Phosphoborane

The structure and properties of two-dimensional phosphoborane sheets were computationally investigated using Density Functional Theory calculations. The calculated phonon spectrum and band structure point to dynamic stability and allowed characterization of the predicted two-dimensional material as a direct-gap semiconductor with a band gap of ~1.5 eV. The calculation of the optical properties showed that the two-dimensional material has a relatively small absorptivity coefficient. The parameters of the mechanical properties characterize the two-dimensional phosphoborane as a relatively soft material, similar to the monolayer of MoS2. Assessment of thermal stability by the method of molecular dynamics indicates sufficient stability of the predicted material, which makes it possible to observe it experimentally

Tribochemistry, mechanical alloying, mechanochemistry:what is in a name?

Over the decades, the application of mechanical force to influence chemical reactions has been called by various names: mechanochemistry, tribochemistry, mechanical alloying, to name but a few. The evolution of these terms has largely mirrored the understanding of the field. But what is meant by these terms, why have they evolved, and does it really matter how a process is called? Which parameters should be defined to describe unambiguously the experimental conditions such that others can reproduce the results, or to allow a meaningful comparison between processes explored under different conditions? Can the information on the process be encoded in a clear, concise, and self-explanatory way? We address these questions in this Opinion contribution, which we ho

Superoctahedral Two-Dimensional Metallic Boron with Peculiar Magnetic Properties

Among the diversity of new materials, two-dimensional crystal structures have been attracting significant attention from the broad scientific community due to their promising applications in nanoscience. In this study we predict a novel two-dimensional ferromagnetic boron material, which has been exhaustively studied with DFT methods. The relaxed structure of the 2D-B6 monolayer consists of slightly flattened octahedral units connected with 2c-2e B–B σ-bonds. The calculated phonon spectrum and ab initio molecular dynamics simulations reveal the thermal and dynamical stability of the designed material. The calculation of the mechanical properties indicate a relatively high Young\u27s modulus of 149 N m−1. Moreover, the electronic structure indicates the metallic nature of the 2D-B6 sheets, whereas the magnetic moment per unit cell is found to be 1.59 μB. The magnetism in the 2D-B6 monolayer can be described by the presence of two unpaired delocalized bonding elements inside every distorted octahedron. Interestingly, the nature of the magnetism does not lie in the presence of half-occupied atomic orbitals, as was shown for previously studied magnetic materials based on boron. We hope that our predictions will provide promising new ideas for the further fabrication of boron-based two-dimensional magnetic materials

Supertetrahedral Aluminum – A New Allotropic Ultralight Crystalline Form of Aluminum

A new metastable ultralight crystalline form of aluminum has been computationally designed using density functional calculations with imposing periodic boundary conditions. The geometric and electronic structures of the predicted new allotrope were calculated on the basis of a diamond lattice in which all carbon atoms are replaced by aluminum Al₄ tetrahedra. The new form of crystalline aluminum has an extremely low density of 0.61 g/cm³ and would float in water. The new aluminum form is a semimetal and shows high plasticity