Technological Schemes for Preparation and Deep Beneficiation of Technogenic Waste Containing Fine Slimes Environmental Component

This article evaluates a new procedure for choosing special methods of disintegration for technogenic rock materials with fines and slimes. The article describe different examples of beneficiation technology for chromium-containing slime tails of the Donskoy beneficiation plant (Republic of Kazakhstan), hematite tails of Magnitogorskiy Metallurgical Plant, and tin waste with fines particles. Keywords: fine slimes, environmental component, technological schemes, Preparation technogenic wast

Screw dislocation in zirconium: An ab initio study

Plasticity in zirconium is controlled by 1/3 screw dislocations gliding in the prism planes of the hexagonal close-packed structure. This prismatic and not basal glide is observed for a given set of transition metals like zirconium and is known to be related to the number of valence electrons in the d band. We use ab initio calculations based on the density functional theory to study the core structure of screw dislocations in zirconium. Dislocations are found to dissociate in the prism plane in two partial dislocations, each with a pure screw character. Ab initio calculations also show that the dissociation in the basal plane is unstable. We calculate then the Peierls barrier for a screw dislocation gliding in the prism plane and obtain a small barrier. The Peierls stress deduced from this barrier is lower than 21 MPa, which is in agreement with experimental data. The ability of an empirical potential relying on the embedded atom method (EAM) to model dislocations in zirconium is also tested against these ab initio calculations

Hydrogen-enhanced local plasticity in aluminum: an ab initio study

Dislocation core properties of Al with and without H impurities are studied using the Peierls-Nabarro model with parameters determined by ab initio calculations. We find that H not only facilitates dislocation emission from the crack tip but also enhances dislocation mobility dramatically, leading to macroscopically softening and thinning of the material ahead of the crack tip. We observe strong binding between H and dislocation cores, with the binding energy depending on dislocation character. This dependence can directly affect the mechanical properties of Al by inhibiting dislocation cross-slip and developing slip planarity.Comment: 4 pages, 3 figure

ADULT ACGUIRED FLATFOOT DEFORMITY (REVIEW)

Flatfoot deformity represents a complex pathology often observed in active adult population. Conservative treatment does not  always yield the intended outcome.  Various  surgical  methods  addressing  mentioned pathology  were actively developing  during  past decades. However,  despite  diversity  of procedures there  are many contradictions in respect  of necessity  and efficiency of a certain  procedure especially in grades II and IV of the disease. The paper presents  clinical, roentgenological and biomechanical  features of acquired flatfoot deformity. The authors  analyzed literature publications dedicated to different correction methods  adopted  in world orthopaedics

Mesoscopic Analysis of Structure and Strength of Dislocation Junctions in FCC Metals

We develop a finite element based dislocation dynamics model to simulate the structure and strength of dislocation junctions in FCC crystals. The model is based on anisotropic elasticity theory supplemented by the explicit inclusion of the separation of perfect dislocations into partial dislocations bounding a stacking fault. We demonstrate that the model reproduces in precise detail the structure of the Lomer-Cottrell lock already obtained from atomistic simulations. In light of this success, we also examine the strength of junctions culminating in a stress-strength diagram which is the locus of points in stress space corresponding to dissolution of the junction.Comment: 9 Pages + 4 Figure

Исследование физических явлений в барботажной зоне плавильного агрегата «Победа» методом холодного моделирования Сообщение 3. Гидрогазодинамика комбинированной продувки жидкости газом с помощью донной и боковой фурм

Hydro-gas regularities of liquid combined blowing by gas were studied using cold modeling method at Archimedes criterion for lateral Arl = 12÷120 and bottom blowing Arb = 5÷60 simulating Pobeda bubbling unit. The blowing was performed simultaneously by bottom lance vertically fixed in centre of reactor and by the lateral lance which was attached at an angle 5° to the horizontal axis. The quantitative estimation of instantaneous and average circulation velocities (Vav) of liquid flow elements in different bath areas, depending on the location of blowing zone and Archimedes criterion, was performed. The liquid motion trajectory was determined. A vortex zone was revealed near the liquid surface and the reactor shell, where instantaneous velocity of the liquid flow elements changes from 69.9 to 181.1 mm/s and Vav = 123.8 mm/s. The circulation flows fade in the bulk of liquid and Vav decreases from 123.8 to 47.0 and 54.1 mm/s. It was shown that, in general, circulation velocity depends on the blowing intensity and appears to be higher for the zone of overlapping of lateral and bottom streams. The dynamic blowing conditions, which ensure the direct contact of lateral and bottom jets leading to their interflow and increased spatter formation, were identified. The characteristics of 3 types of surface oscillations for interface phases “pure liquid- gas-liquid layer”, as well as the estimation of the lateral and bottom blowing impact on the type of oscillation were provided. It has been noted that the introduction of the bottom blowing (Arb = 5) causes the wave-like motion of liquid (the 2nd type) along with the transverse oscillations of the 1st type, and at higher values of Arb = 25 the angular oscillations of the 3rd type develop. It has been shown that the presence of a lateral jet at the combined blowing decreases angles of bath swinging to 8–12° to horizontal axis. For the estimation of oscillation intensity, Δhl = (hl )max – (hl )min value, which means the difference between maximum (hl )max and minimum (hl )min height of liquid for the full-wave oscillations (τ), was introduced. The height of liquid (hl ) was plotted as a function of τ, Arl , Arb, Δhl was determined on the basis of obtained graph values, which varied upon modeling over the range of 7.7–69.5 mm. The relation between the liquid circulation velocity and the oscillation value (Δhl ) was established for different bath zones and dynamic conditions of the blowing. The impact of all oscillations types on potential erosive lining wear of Pobeda bubbling unit and the completeness of adoption of charging material nearby the bath surface was investigated.Методом холодного моделирования в интервалах величин критерия Архимеда для бокового (Arб = 12÷120) и донного (Arд = 5÷60) дутья применительно к условиям работы барботажного плавильного агрегата «Победа» (ПАП) исследованы гидрогазодинамические закономерности комбинированной продувки жидкости газом. Продувку осуществляли одновременно донной фурмой, установленной вертикально по центру реактора, и боковой, расположенной под углом 5° к горизонтальной оси. Проведена количественная оценка мгновенной и средней (Vср) скоростей циркуляции элементов потока жидкости на разных участках ванны в зависимости от местонахождения зоны продувки и критериев Архимеда. Определена траектория движения жидкости. Вблизи поверхности жидкости и корпуса реактора обнаружена вихревая зона, где мгновенная скорость движения элемента потока жидкости изменяется от 69,9 до 183,1 мм/с и Vср = 123,8 мм/с. В объеме жидкости циркуляционные потоки затухают, и Vср уменьшается от 123,8 до 47,0 и 54,1 мм/с. Показано, что в общем случае скорость циркуляции зависит от интенсивности продувки на фурмах и становится выше для области наложения боковой и донной струй. Определены динамические условия продувки, обеспечивающие непосредственный контакт бокового и донного факелов, приводящий к слиянию потоков и повышенному брызгообразованию. Приведена характеристика 3 видов колебаний поверхности раздела фаз «чистая жидкость – газожидкостный слой» и дана оценка влияния бокового и донного дутья на разновидность возникающих колебаний. Отмечено, что ввод донного дутья (Arд = 5) приводит, наряду с поперечными колебаниями 1-го типа, к появлению волнообразного движения жидкости (2-й тип), а при более высоких значениях Arд = 25 – к угловым колебаниям (3-й тип). Показано, что при комбинированной продувке наличие бокового факела уменьшает углы раскачивания ванны к горизонту до 8–12°. Для оценки интенсивности колебаний введена величина Δhж = (hж)max – (hж)min, т.е. разность между максимальной (hж)max и минимальной (hж)min высотой жидкости за полный цикл колебаний (τ). Построены зависимости высоты жидкости (hж) от τ, Arб и Arд, на основании которых определены величины Δhж, варьируемые при моделировании в интервале 7,7–69,5 мм. Для различных областей ванны и динамических условий продувки установлена взаимосвязь между скоростью циркуляции жидкости и величиной колебаний (Δhж). Рассмотрено влияние всех видов колебаний на возможный эрозивный износ футеровки ПАП и полноту усвоения шихтовых материалов вблизи поверхности ванны

Fingering Instability of Dislocations and Related Defects

We identify a fundamental morphological instability of mobile dislocations in crystals and related line defects. A positive gradient in the local driving force along the direction of defect motion destabilizes long-wavelength vibrational modes, producing a ``fingering'' pattern. The minimum unstable wavelength scales as the inverse square root of the force gradient. We demonstrate the instability's onset in simulations of a screw dislocation in Al (via molecular dynamics) and of a vortex in a 3-d XY ``rotator'' model.Comment: 4 pages, 3 figure

Temperature effects on dislocation core energies in silicon and germanium

Temperature effects on the energetics of the 90-degree partial dislocation in silicon and germanium are investigated, using non-equilibrium methods to estimate free energies, coupled with Monte Carlo simulations. Atomic interactions are described by Tersoff and EDIP interatomic potentials. Our results indicate that the vibrational entropy has the effect of increasing the difference in free energy between the two possible reconstructions of the 90-degree partial, namely, the single-period and the double-period geometries. This effect further increases the energetic stability of the double-period reconstruction at high temperatures. The results also indicate that anharmonic effects may play an important role in determining the structural properties of these defects in the high-temperature regime.Comment: 8 pages in two-column physical-review format with six figure

Plastic Flow in Two-Dimensional Solids

A time-dependent Ginzburg-Landau model of plastic deformation in two-dimensional solids is presented. The fundamental dynamic variables are the displacement field \bi u and the lattice velocity {\bi v}=\p {\bi u}/\p t. Damping is assumed to arise from the shear viscosity in the momentum equation. The elastic energy density is a periodic function of the shear and tetragonal strains, which enables formation of slips at large strains. In this work we neglect defects such as vacancies, interstitials, or grain boundaries. The simplest slip consists of two edge dislocations with opposite Burgers vectors. The formation energy of a slip is minimized if its orientation is parallel or perpendicular to the flow in simple shear deformation and if it makes angles of $\pm \pi/4$ with respect to the stretched direction in uniaxial stretching. High-density dislocations produced in plastic flow do not disappear even if the flow is stopped. Thus large applied strains give rise to metastable, structurally disordered states. We divide the elastic energy into an elastic part due to affine deformation and a defect part. The latter represents degree of disorder and is nearly constant in plastic flow under cyclic straining.Comment: 16pages, Figures can be obtained at http://stat.scphys.kyoto-u.ac.jp/index-e.htm

Ab initio and finite-temperature molecular dynamics studies of lattice resistance in tantalum

This manuscript explores the apparent discrepancy between experimental data and theoretical calculations of the lattice resistance of bcc tantalum. We present the first results for the temperature dependence of the Peierls stress in this system and the first ab initio calculation of the zero-temperature Peierls stress to employ periodic boundary conditions, which are those best suited to the study of metallic systems at the electron-structure level. Our ab initio value for the Peierls stress is over five times larger than current extrapolations of experimental lattice resistance to zero-temperature. Although we do find that the common techniques for such extrapolation indeed tend to underestimate the zero-temperature limit, the amount of the underestimation which we observe is only 10-20%, leaving open the possibility that mechanisms other than the simple Peierls stress are important in controlling the process of low temperature slip.Comment: 12 pages and 9 figure