Electronic structure and stability of nonstoichiometric titanium monoxide TiOy with structural vacancies in one of the sublattices

The electronic structure of nonstoichiometric titanium monoxide TiOy with different compositions y, which contains structural vacancies either in the metallic sublattice or in the nonmetallic sublattice, has been investigated using the supercell method within the DFT-GGA approximation with pseudopotentials. The cases of ordered and disordered arrangements of vacancies have been considered. It has been found that the complete removal of vacancies from the sublattice is energetically unfavorable, and the ordering of oxygen vacancies according to the type of the Ti6O5□1 superstructure, as well as titanium vacancies according to the Ti5black small square1O6 type, does not lead to the stabilization of the B1 basic structure of titanium monoxide. © 2013 Pleiades Publishing, Ltd

Internal energy and parameters of the order-disorder phase transition in titanium monoxide TiO y

Quantum-mechanical ab initio calculations are used to simulate the free energy functions for titanium monoxide TiO y . The effect of the long-range order of the Ti5O5 type superstructure on the internal energy of the compound is studied by the supercell method. The dependences of the configuration entropy and free energy on the long-range order parameter are determined. It is found that the order-disorder phase transition in titanium monoxide must occur in accordance with the mechanism of the first-order phase transition with a critical value of the long-range order parameter of 0.971. The calculated parameters of the phase transition are compared with the experimental data and the results obtained using the model of point charges and by calculating the Madelung energy. It is concluded that the short-range order and the phonon entropy must be taken into account in calculating the equilibrium phase diagrams for strongly nonstoichiometric compounds. © 2013 Pleiades Publishing, Ltd

Ice Lens Formation, Frost Heave, Thin Films, and the Importance of the Polar H2O Reservoir at High Obliquity

Several lines of evidence indicate that the volume of shallow ground ice in the martian high latitudes exceeds the pore volume of the host regolith. Boynton et al. found an optimal fit to the Mars Odyssey Gamma Ray Spectrometer (GRS) data at the Phoenix landing site by modeling a buried layer of 50-75% ice by mass (up to 90% ice by volume). Thermal and optical observations of recent impact craters in the northern hemisphere have revealed nearly pure ice. Ice deposits containing only 1-2% soil by volume were excavaged by Phoenix. One hypothesis for the origin of this excess ice is that it developed in situ by a mechanism analogous to the formation of terrestrial ice lenses and needle ice. Problematically, terrestrial soil-ice segregation is driven by freeze/thaw cycling and the movement of bulk water, neither of which are expected to have occurred in the geologically recent past on Mars. If however ice lens formation is possible at temperatures less than 273 K, there are possible implications for the habitability of Mars permafrost, since the same thin films of unfrozen water that lead to ice segregation are used by terrestrial psychrophiles to metaboluze and grow down to temperatures of at least 258 K

Character of Mg(ClO4)2 Brines Under Mars Regolith Conditions

Elsewhere, we report on our investigation of the initiation and growth of ice lenses under Mars like conditions. In that work, we assume that the soil-water-ice system is gas and solute free. We conclude that initiation of lens initiation - the unloading of particle-particle contacts by thermomolecular forces at a given soil horizon - may be a common process in the shallow Martian regolith, and that the dominant property controlling the rate of lens growth is the freezing point depression (Delta-T(sub f)) associated with the interfacial forces of the soil. Lens growth is thus favored in clay-sized soils over silt soils due to the greater Delta-T(sub f), but segregated ice was observed at the Phoenix site, where soils were predominantly siltsized.. Perchlorate salts were also observed at the Phoenix site, and will strongly affect some of the properties associated with potential ice lens growth, over and above increases to Delta-T(sub f),. Here, we investigate the nature of Mg(ClO4)2 brines under Mars-like conditions, with particular emphasis on those aspects that might influence the in situ segregation of residual liquids during phase change, potentially leading to the formation of subsurface excess ice. We also discuss cyclic variations in the water activity (a(sub w)) that might affect the habitability of solutions in the shallow regolith

Vacancies in ordered and disordered titanium monoxide: Mechanism of B1 structure stabilization

The electronic structure and stability of three phases of titanium monoxide TiOy with B1 type of the basic structure have been studied. Cubic phase without structural vacancies, TiO, and two phases with structural vacancies, monoclinic Ti5O5 and cubic disordered TiO 1.0, was treated by means of first-principles calculations within the density functional theory with pseudo-potential approach based on the plane wave's basis. The ordered monoclinic phase Ti5O5 was found to be the most stable and the cubic TiO without vacancies the less stable one. The role of structural vacancies in the titanium sublattice is to decrease the Fermi energy, the role of vacancies in the oxygen sublattice is to contribute to the appearance of Ti-Ti bonding interactions through these vacancies and to reinforce the Ti-Ti interactions close to them. Listed effects are significantly pronounced if the vacancies in the titanium and oxygen sublattices are associated in the so called "vacancy channels" which determine the formation of vacancy ordered structure of monoclinic Ti5O 5-type. © 2013 Elsevier Inc

Simulation of the short-range order in disordered cubic titanium monoxide TiO1.0

A model of the atomic structure with the short-range order in the vacancy distribution for the disordered cubic phase of titanium monoxide TiO1.0 has been proposed. The effect of the short-range order on the electronic structure and the stability of the compound has been studied by the supercell method within the DFT-GGA approximation with the use of pseudopotentials. It has been established that the appearance of the short-range order considerably decreases the total energy. The decrease in the energy is comparable with the energy gain during the ordering of the vacancies according to the type of monoclinic superstructure Ti5O5 to the long-range order parameter η = 0.7. It has been shown that the discrepancies between the theoretical and experimental electronic spectra of titanium monoxide can be explained by allowance for the short range order. © 2013 Pleiades Publishing, Ltd

Hybrid nanoparticles based on sulfides, oxides, and carbides

The methods for synthesis of hybrid nanoparticles based on sulfides, oxides, and carbides of heavy and transition metals were considered. The problem of the influence of the method of synthesis of the hybrid nanoparticles on their atomic structure, morphology of the nanomaterials, and functional properties was analyzed. The areas of practical use of the hybrid nanoparticles were proposed. © 2013 Springer Science+Business Media New York

Transition to chaos in a reduced-order model of a shear layer

The present work studies the non-linear dynamics of a shear layer, driven by a body force and confined between parallel walls, a simplified setting to study transitional and turbulent shear layers. It was introduced by Nogueira \& Cavalieri (J. Fluid Mech. 907, A32, 2021), and is here studied using a reduced-order model based on a Galerkin projection of the Navier-Stokes system. By considering a confined shear layer with free-slip boundary conditions on the walls, periodic boundary conditions in streamwise and spanwise directions may be used, simplifying the system and enabling the use of methods of dynamical systems theory. A basis of eight modes is used in the Galerkin projection, representing the mean flow, Kelvin-Helmholtz vortices, rolls, streaks and oblique waves, structures observed in the cited work, and also present in shear layers and jets. A dynamical system is obtained, and its transition to chaos is studied. Increasing Reynolds number $Re$ leads to pitchfork and Hopf bifurcations, and the latter leads to a limit cycle with amplitude modulation of vortices, as in the DNS by Nogueira \& Cavalieri. Further increase of $Re$ leads to the appearance of a chaotic saddle, followed by the emergence of quasi-periodic and chaotic attractors. The chaotic attractors suffer a merging crisis for higher $Re$, leading to chaotic dynamics with amplitude modulation and phase jumps of vortices. This is reminiscent of observations of coherent structures in turbulent jets, suggesting that the model represents dynamics consistent with features of shear layers and jets.Comment: 28 pages, 18 figure

Role of structural vacancies in the stabilization of the basic B1 structure in nonstoichiometric titanium monoxide TiO y

The electron structures and formation enthalpies of vacancy-free cubic TiO, vacancy-ordered monoclinic Ti5O5, and vacancy-disordered cubic TiO y have been investigated using DFT+GGA calculations. Ti5O5 was found to be the stablest phase and TiO was found to be the least stable. The reason for the stability of the titanium and oxygen vacancies in the basic B1 structures of Ti5O5 and TiO y has been deduced. The titanium vacancies lead to a decrease in the Fermi energy. Oxygen vacancies cause strengthening in covalent Ti-Ti bonding. © 2013 Allerton Press, Inc

MgCl2 and KCl Recovery from Brine Wastewater

This project’s aim was to design an improved brine wastewater treatment system for desalination facilities. While a multitude of methods exist to do so, General Electric (GE)’s brine concentrator is leading the market by providing a method that not only treats the brine waste, but also recovers anywhere from 60- 94% of the water from the feed. However, their brine concentrator is relatively inefficient from both a financial and energetic perspective; our goal was to develop a system to match their results, while limiting costs and energy usage as best possible. We subsequently designed a system (referred to from here on out as the ‘MgCl2 Separation Unit’) to accomplish the aforementioned objectives. In addition to recovering pure water from concentrated brine, our process also recovers high purity MgCl2 and KCl crystals that are later sold to alleviate the overall process costs. The MgCl2 Separation Unit saw an increased ROI by 22.53% as compared to the GE Brine Concentrator, as well as a surge in NPV of $20,749,200. Additionally, we estimate an aggregate equipment cost of roughly$6,960,000, significantly less than GE’s $8,980,000, and utilities costs of$1,590,000 relative to their $6,920,000. The GE process deals with vapor phase water and thus relies on compressors for pressure changes, which are costly in terms of energy consumption and capital costs, whereas our proposed MgCl2 Separator Unit is limited to liquid/aqueous streams, eliminating the need for costly compressors (from both an energy and economic standpoint). Finally, while both systems are fit to treat 1- 2mgd, the MgCl2 Separation Unit was optimized to recover roughly 84% of feed water, positioning itself in the upper limit of GE’s possible water recovery spectrum