Effect of Co-Mo catalyst preparation and CH4/H2 flow on carbon nanotube synthesis

Supported Co-Mo catalysts with a given ratio of metals were prepared from polyoxomolybdate Mo12O28(μ2-OH)12{Со(H2O)3}4 using impregnation and combustion methods. Effects of the type of catalyst and the ratio and flow of methane and hydrogen gases on the structure of carbon nanotubes (CNTs) synthesized by catalytic chemical vapor deposition (CCVD) method were studied using transmission electron microscopy and Raman spectroscopy. The catalyst prepared by combustion method yielded mainly individualized CNTs, while the CNTs were highly entangled or bundled when impregnation method was used. In both cases, addition of hydrogen to methane led to reduction of the CNT yield. The samples synthesized using two different catalysts and the same CH4/H2 ratio and flow of gases were tested in electrochemical capacitors. A higher specific surface area of the CNTs grown over impregnation-prepared catalyst caused a better performance at scan rates from 2 to 1000 mV/s

Hydrothermal Activation of Porous Nitrogen-Doped Carbon Materials for Electrochemical Capacitors and Sodium-Ion Batteries

Highly porous nitrogen-doped carbon nanomaterials have distinct advantages in energy storage and conversion technologies. In the present work, hydrothermal treatments in water or ammonia solution were used for modification of mesoporous nitrogen-doped graphitic carbon, synthesized by deposition of acetonitrile vapors on the pyrolysis products of calcium tartrate. Morphology, composition, and textural characteristics of the original and activated materials were studied by transmission electron microscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, infrared spectroscopy, and nitrogen gas adsorption method. Both treatments resulted in a slight increase in specific surface area and volume of micropores and small mesopores due to the etching of carbon surface. Compared to the solely aqueous medium, activation with ammonia led to stronger destruction of the graphitic shells, the formation of larger micropores (1.4 nm vs. 0.6 nm), a higher concentration of carbonyl groups, and the addition of nitrogen-containing groups. The tests of nitrogen-doped carbon materials as electrodes in 1M H2SO4 electrolyte and sodium-ion batteries showed improvement of electrochemical performance after hydrothermal treatments especially when ammonia was used. The activation method developed in this work is hopeful to open up a new route of designing porous nitrogen-doped carbon materials for electrochemical applications

Effect of ultrasound pretreatment on bromination of double-walled carbon nanotubes

Bromination of double-walled carbon nanotubes (DWCNTs) was carried out using a saturated vapor of Br2 at room temperature with or without a pretreatment in bromine water. X-ray photoelectron spectroscopy revealed that ultrasound pretreatment modified the chemical state of bromine in the product. The binding energies of the Br 3d electrons in the pre-sonicated DWCNT sample were between those characteristic of the covalent C–Br bonds and the negatively charged Br2 molecules, observed when the pretreatment was not performed. Raman spectroscopy, however, clearly evidenced Br–Br vibrations in both brominated samples. Calculations of CNT–Br2 models within density functional theory were used to propose that the electronic state of a Br2 molecule depends on the adsorption site. The bromine molecules prefer to be located near edge hydroxyl groups, which acept the electron density from Br2. This increases the binding energy of Br 3d levels as compared to that for Br2 molecules in other adsorption sites

ЗАСТОСУВАННЯ МЕТОДУ СКІНЧЕННИХ ЕЛЕМЕНТІВ ДЛЯ ВИЗНАЧЕННЯ НАПРУЖЕНО-ДЕФОРМАНОГО СТАНУ ЕЛЕМЕНТІВ ЗАЛІЗНИЧНОЇ КОЛІЇ

The main principles of the construction and operation of the software complex for estimating the stress-strain state of structural elements of the upper structure of the track under the influence of spatial forces from the rolling stock are determined. The proposed software package is based on a step-by-step definition of the spatial forces of interaction between the dynamic system "crew way" and subsequent evaluation by the finite element method. As a computer implementation of the finite element method, the program "Lira" was adopted. Design models of rails, elements of intermediate rail fasteners, sleepers and ballast are developed. The modeling is based on the modular principle, which allows, depending on the nature of the task, to calculate the section of the railway track, practically of any length. The structural and physical non-linearity of their work, the presence of frictional forces and one-way connections between individual nodes and details were taken into account when modeling railway track elements.Определены основные принципы построения и работы программного комплекса для оценки напряженно-деформированного состояния конструктивных элементов верхнего строения пути под действием пространственных сил от подвижного состава. В основу предложенного программного комплекса заложено поэтапное определение пространственных сил взаимодействия динамической системы «экипаж-путь» с последующей оценкой по методу конечных элементов. Разработаны расчетные модели рельсов, элементов промежуточных рельсовых скреплений, шпал и балласта. При моделировании элементов железнодорожного пути учитывались конструктивная и физическая нелинейность их работы, наличие сил трения и односторонних связей между отдельными узлами и деталями.Визначено основні принципи побудови і роботи програмного комплексу для оцінки напружено-деформованого стану конструктивних елементів верхньої будови колії під дією просторових сил від рухомого складу. В основу запропонованого програмного комплексу закладено поетапне визначення просторових сил взаємодії динамічної системи «екіпаж-колія» із подальшою оцінкою за методом скінченних елементів. Розроблено розрахункові моделі рейок, елементів проміжних рейкових скріплень, шпал і баласту. При моделюванні елементів колії враховувалися конструктивна і фізична нелінійність їх роботи, наявність сил тертя і односторонніх зв'язків між окремими вузлами і деталями

Simulation of performance of circular CFST columns under short-time and long-time load

The method of calculation of concrete-filled steel tubular (CFST) columns with consideration of physical nonlinearity of materials, geometric nonlinearity of the confinement and the effect of the gain in strength of the core is considered. The method uses a step iteration algorithm, which involves analytical dependencies and the ultimate element simulation method. Allowance for creep of concrete is based on using the generalized kinetic long-term deformation curve and phenomenological deformation development equations. Creep of concrete is controlled through new structural factors that determine the structure of cement rock layers between sand and mortar grains between chip grains. The method is validated by comparing experimental results and theoretical data. The suggested method allowed to study the stress-strain and limit state of circular concrete-filled steel tubular columns, as well as to evaluate their effectiveness with account for the time factor

МОДЕЛЮВАННЯ РОБОТИ ТРУБОБЕТОННИХ ЕЛЕМЕНТІВ ПРИ КОРОТКОЧАСНОМУ ТА ТРИВАЛОМУ НАВАНТАЖЕННІ

The method of calculation of concrete pipe elements with consideration of physical nonlinearity of materials, geometric nonlinearity of the confinement and the effect of the gain in strength of the core is considered. The method uses a step iteration algorithm which involves analytical dependencies and the ultimate element simulation method. Allowance for creep of concrete is based on using the generalized kinetic long-term deformation curve and phenomenological deformation development equations. Creep of concrete is controlled through new structural factors that determine the structure of cement rock layers between sand and mortar grains between chip grains. The method is validated by comparing experimental findings and theoretical data. The suggested method allowed to study the stress-strain and limit state of concrete pipe elements, as well as to evaluate their effectiveness with account for the time factor.  Рассмотрен подход расчета трубобетонных элементов с учетом физической нелинейности материалов, геометрической нелинейности обоймы и эффекта увеличения прочности ядра. Методика использует шагово-итерационный алгоритм с участием аналитических зависимостей и конечно-элементного моделирования. Учет ползучести бетона основан на использовании обобщенной кинетической кривой длительного деформирования. Адекватность методики обеспечивается сопоставлением экспериментальных и теоретических данных. Предложенная методика позволила исследовать напряженно-деформированное и предельное состояние трубобетонных элементов, а также оценить их эффективность с учетом фактора времени.Розглянуто підхід розрахунку трубобетонних елементів з урахуванням фізичної нелінійності матеріалів, геометричної нелінійності обойми та ефекту збільшення міцності ядра. Методика використовує кроково-ітераційний алгоритм за участю аналітичних залежностей і скінченно-елементного моделювання. Облік повзучості бетону побудованийна використанні узагальненої кінетичної кривої деформування. Адекватність методики забезпечується порівнянням експериментальних і теоретичних даних. Запропонована методика дала змогу дослідити напружено-деформований та граничний стан трубобетонних елементів, а також оцінити їх ефективність з урахуванням фактора час

SIMULATION OF PERFORMANCE OF CIRCULAR CFST COLUMNS UNDER SHORT-TIME AND LONG-TIME LOAD

The method of calculation of concrete-filled steel tubular (CFST) columns with consideration of physical nonlinearity of materials, geometric nonlinearity of the confinement and the effect of the gain in strength of the core is considered. The method uses a step iteration algorithm, which involves analytical dependencies and the ultimate element simulation method. Allowance for creep of concrete is based on using the generalized kinetic long-term deformation curve and phenomenological deformation development equations. Creep of concrete is controlled through new structural factors that determine the structure of cement rock layers between sand and mortar grains between chip grains. The method is validated by comparing experimental results and theoretical data. The suggested method allowed to study the stress-strain and limit state of circular concrete-filled steel tubular columns, as well as to evaluate their effectiveness with account for the time factor

Modelling of motorway bridge spans under modernization with consideration of rheological properties of the materials

The paper presents a computer modelling technique for modernization of bridgework operations by building-up a mounted reinforced concrete slab. It implements the technique of the evolutionary transformation of a model in one calculation cycle with redistribution of forces between the elements of the built-up section, and consideration of the impact of elastoplastic and rheological properties of the materials. Consideration of the concrete creep implies the application of the generalized kinetic curve of prolonged deformation and phenomenological deformation development equations based on the colloid-chemical concept of the prolonged concrete deformation mechanism. The creep control was implemented through new structural coefficients which determined the structure of matrix interlayers between the sand grains, and mortar between the crushed stone grains. The technique proposed was realized in the program complex “LIRA-SAPR” based on the building information modelling (BIM) and the finite element method (FEM). The multistage modelling technique was shown by an example of calculation of a motorway bridge slab span within the transport structures under modernization along the Lev Landau Avenue in Kharkiv (Ukraine)

Modelling of motorway bridge spans under modernization with consideration of rheological properties of the materials

The paper presents a computer modelling technique for modernization of bridgework operations by building-up a mounted reinforced concrete slab. It implements the technique of the evolutionary transformation of a model in one calculation cycle with redistribution of forces between the elements of the built-up section, and consideration of the impact of elastoplastic and rheological properties of the materials. Consideration of the concrete creep implies the application of the generalized kinetic curve of prolonged deformation and phenomenological deformation development equations based on the colloid-chemical concept of the prolonged concrete deformation mechanism. The creep control was implemented through new structural coefficients which determined the structure of matrix interlayers between the sand grains, and mortar between the crushed stone grains. The technique proposed was realized in the program complex “LIRA-SAPR” based on the building information modelling (BIM) and the finite element method (FEM). The multistage modelling technique was shown by an example of calculation of a motorway bridge slab span within the transport structures under modernization along the Lev Landau Avenue in Kharkiv (Ukraine)