Theoretical fundamentals of mechanochemical reactions in the solid phase

This article presents the research results on a dry mechanochemical synthesis of barium titanate at a low temperature in which the reaction model and kinetics were determined during the activation of a powder mixture of titanium dioxide and barium oxide. The solid-state reaction achieved high degree of conversion (0.99). Successive analyses were conducted throughout the reaction, revealing the presence of both the starting powders and newly formed intermediate compounds. Phase transformations were monitored via X-ray diffraction, allowing the dynamics of the synthesis to be characterized. It was established that, for the given system, 440 min of mechanical activation in a high-energy vibration mill was required to complete the neutralization reaction and produce barium titanate. The reaction mixture composition was tracked by sampling at five intervals, confirming the presence of intermediate compounds and mapping the reaction pathway from the initial barium and titanium oxides to the final BaTiO3 product.

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Barium titanate was prepared by the advanced procedure of mechanochemical synthesis from barium and titanium oxides after 50 hours of milling. The X-ray examination of the milled powders showed the phase evolution during synthesis and the perovskite phase was initiated after 5 hours and was completed after 50 hours. Sintered samples from these nanopowders show different dielectric properties for fine and coarse grained ceramics. Samples with an average grain size of 2 ?m showed the highest dielectric constant of 5800 at room temperature. A sharp maximum of the dielectric constant with values of about 16000 was recorded at the Curie temperature.

Reactive single-solute liquid chromatography in fully porous fixed-bed columns involves complex transport and chemical reaction processes occurring simultaneously in both the liquid and solid phases. This work presents a comprehensive analytical-numerical framework based on a linear general rate model that incorporates key transport mechanisms including axial dispersion, external film diffusion, intraparticle pore diffusion, and interfacial mass transfer coupled with first-order homogeneous reactions in the liquid phase and heterogeneous reactions on the solid adsorbent. A key novelty of this study is to investigate how homogeneous and heterogeneous reactions influence concentration fronts during linear chromatographic processes and the hybrid analytical numerical framework that solves the coupled transport-reaction equations in the Laplace domain, followed by a numerical inversion to capture time-resolved concentration profiles. Analysis of elution curves under varying kinetic and transport conditions shows that increasing both homogeneous and heterogeneous reaction rates enhances separation efficiency and reactor performance. The model’s predictions are validated against a high-resolution finite-volume scheme and benchmarked with existing models, demonstrating superior accuracy and reliability. These results highlight the proposed methodology as a valuable tool for optimizing the design and operation of reactive chromatographic systems.

Barium titanate precursor gel was successfully obtained by a sol-gel process with the use of barium acetate and titanium isopropoxide as starting materials. The calcination process of the barium titanate gel was characterized by FTIRPAS, TG-DTA, XRD and acid extraction method. These analyses indicate that barium acetate was distributed uuiformly in the gel matrix formed by hydrolysis and polymerization of titanium isopropoxide. The barium titanate was formed rapidly at higher temperatures than 823-873K resulted from the reaction between titanium oxide and barium carbonate or barium oxide.

Polyvinyl chloride (PVC) is the third most commonly produced polymer and is important because of its mechanical characteristics. The most common method of PVC manufacturing is the process of suspension. Although, there are several benefits associated with suspension, this study will focus on the bulk polymerization of vinyl chloride; highlight the physical and chemical properties of PVC, which can be changed through an estimation of the optimum ratio that exists between the hydrophilic and hydrophobic parts of the polymer’s surface, and propose a new mathematical model which will be helpful for the conversion of PVC into a useful form. The result will be the proposal of a new dynamic mathematical model for the three-phase structure model. All particles have been taken into account in the proposed model, which helped contribute to the reaction in gel, solid, and liquid phases, emphasizing the use of mercury (Hg) as a catalyst. The proposed mathematical model considers the heat and mass transfer between the liquid, gel, and solid phases with chemical reactions that occur between the liquid and solid phases, and between the gel and solid phases. The effect of the catalyst and volumetric flow rates of vinyl chloride monomer (VCM) on the system have been evaluated through the proposed mathematical model. Furthermore, the study’s experimental data have been compared with the findings of the suggested model in the context of concentration and temperature reaction. Obtained results show good agreement between the proposed mathematical model and the actual plant data.

Particle image and tracking velocimetry of solid-liquid turbulence in a horizontal channel flow

Organic composition and multiphase stable isotope analysis of active, degrading and restored blanket bog

The effect of grain refinement of titanium on its mechanical performance and cell response

Supramolecular coordination: self-assembly of finite two- and three-dimensional ensembles.

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We present the porousGasificationFoam solver and libraries, developed in the open-source C++ code OpenFOAM, for the comprehensive simulation of the thermochemical conversion in porous media.The code porousGasificationFoam integrates gas flow through a porous media with the models of heterogeneous (drying, gasification, pyrolysis, solid combustion, precipitation) and homogeneous (gas combustion) chemical reactions. Inside porous media transport equations are formulated applying the spatial averaging methodology. The mass and enthalpy transfer between solid and gas phases is suitable for systems out of the thermal equilibrium. The convection and radiation modes of the heat transfer are included for gas and solid phases, and the immersed boundary technique is applied for the porous media inside the computational domain.We validate the elements of the model against a set of experimental and theoretical results. Amongst them, Thermogravimetric Analysis experiments of thermal conversions of two wooden particles: one of millimeter size the other of centimeter size. Simulations feature reaction schemes and physical parameters established in the literature. We show the influence of the porous media size on the gasification process. The millimeter particle remains uniform, while for the centimeter setup, the pyrolysis front is reproduced. The spatial patterns in physical conditions modify the course of chemical reactions and influence media composition and structure evolution. Another important example is a gasifier where we obtain a self-sustaining front propagation because of an exothermic heterogeneous reaction. Program summaryProgram Title: porousGasificationFoamCPC Library link to program files:https://doi.org/10.17632/s6sj9kgp69.1Developer's repository link:https://github.com/pjzuk/porousGasificationFoam (foam-extend-4.1); https://github.com/btuznik/porousGasificationFoam (OpenFOAM 8)Licensing provisions: GNU General Public Licence version 3Programming language: C++External routines/libraries: OpenFOAM 8, foam-extend-4.1Nature of problem: The developed software is a solver and a set of libraries for simulating the thermal conversion in porous media, including drying, pyrolysis, gasification, and combustion. The model includes the flow of the reactive gas mixture and the transfer of mass and enthalpy between the gas and solid phases. The porous medium can change during the process. The model is transient and enables three-dimensional simulations.Solution method:: The finite-volume method is used in the code for equation discretization. A set of governing equations is solved for the gas and solid phases, including mass conservation of gas species and solid components, momentum conservation in the gas phase, and equations of enthalpy conservation in both phases. The porous media region inside the whole computational domain is defined using the immersed boundary approach.

Self-assembled stoichiometric barium titanate thin films grown by molecular beam epitaxy

Нитевидные кристаллы имеют важное практическое применение в машиностроении позволяя улучшать прочностные, эксплуатационные и физические характеристики конструкционных материалов при создании композитов армированных усами. Модель роста усов кремния, контролируемого химической реакцией на границе жидкостьгаз, дополнена учетом давления насыщенного пара кремния в расплаве на вершине кристалла. Для кристаллов достаточно малых размеров давление насыщенного пара кристаллизующегося вещества становится столь значительным, что рост кристалла прекращается. Модель предполагает диффузионную доставку исходных веществ и отвод продуктов реакции в тонкий приповерхностный слой газа у поверхности раздела жидкость-газ, где концентрации реагентов остаются постоянными. Концентрации реагентов в этом слое определяют скорость химической реакции выделения кристаллизующегося вещества.Учтён поток, возникающий за счет давления насыщенного пара кремния над расплавом,при условии, что испаряющиеся атомы практически полностью вступают во взаимодействие с реагентами в газовой фазе. Баланс диффузионных, химических потоков и потоков испарения позволяет найти скорость роста нитевидного кристалла в зависимости от его радиуса и технологических параметров процесса. Зависимость скорости роста нитевидного кристалла от его радиуса имеет максимум, а при достаточно малых поперечных размерах кристалла обращается в нуль. Получено выражение для радиуса кристалла, при котором скорость роста обращается в нуль. Рост кристалла прекращается при достаточно больших радиусах. Получено выражение, определяющее максимальный радиус кристалла, при котором рост становится невозможным. Результаты работы будут полезны при анализе роста нитевидных кристаллов различных веществ, который сопровождается химической реакцией. Модель, предложенная в работе, будет востребована для разработки технологических процессов массового производства кристаллов с целью получения композиционных материалов. ЛИТЕРАТУРА1. Вагнер Р. Монокристальные волокна и армированные ими материалы / Под ред. А. Т. Туманова.М.: Мир, 1973, 64 с.2. Гиваргизов Е. И. Рост нитевидных и пластинчатых кристаллов из пара. М.: Наука, 1977, 304 с.3. Небольсин А. А., Щетинин А. А. Рост нитевидных кристаллов. Воронеж: ВГТУ, 2003, 620 с.4. Дубровский В. Г., Цырлин Г. Э., Устинов В. М. Полупроводниковые нитевидные нанокристаллы:синтез, свойства, применения // ФТП, 2009, т. 43(12), с. 1585–1628.5. Антипов С. А., Дрожжин А. И., Рощупкин А. М. Релаксационные явления в нитевидных кристаллахполупроводников. Воронеж: ВГУ, 1987, 192 с.6. Дрожжин А. И. Преобразователи на нитевидных кристаллах Р–Si<111>. Воронеж: ВГПИ, 1984, 241 с.7. Spinelli P., Verschuuren M. A., Polman A. Broadband omnidirectional antirefl ection coating based onsubwavelength surface Mie resonators // Nat. Commun., 2012, v. 3(1), p. 692. DOI: https://doi.org/10.1038/ncomms16918. Zhang R., Zhang Y., Zhang Q., Xie H., Qian W., Wei F. Growth of half-meter long carbon nanotubesbased on schulz-fl ory distribution // ACS Nano, 2013, v. 7 (7), pp. 6156–6161. DOI: https://doi.org/10.1021/nn401995z9. Козенков О. Д. Модель роста нитевидного кристалла, лимитируемого гетерогенной химической реакцией // Неорганические материалы, 2014, т. 50 (11), с. 1238. DOI: https://doi.org/10.7868/S0002337X1411010410. Козенков О. Д. Зависимость скорости роста нитевидного кристалла, лимитируемого гетерогенной химической реакцией, от состава жидкой фазы // Конденсированные среды и межфазные границы, 2016. т. 18(3), с. 338–344. Режим доступа: https://journals.vsu.ru/kcmf/article/view/141/99 (датаобращения: 02.12.2019)11. Shchetinin A. A., Bubnov L. I., Kozenkov O. D., Tatarenkov A. F. Infl uence of various impurities on theaxial growth rate of silicon whiskers. Известия Академии наук СССР. Неорганические материалы, 1987,т. 23(10), с. 1589–1592.12. Козенков О. Д., Горбунов В. В. Модель теплового баланса бесконечно длинного нитевидногокристалла // Неорганические материалы, 2015, т. 51(5), с. 576–580. DOI: https://doi.org/10.7868/S0002337X1505007313. Козенков О. Д., Щетинин А. А., Горбунов В. В., Сычев И. В. Зависимость скорости роста нитевидного кристалла, лимитируемого гетерогенной химической реакцией, от состава газовой фазы при больших концентрациях тетрахлорида кремния //Вестник ВГТУ, 2016, т. 13(4), с. 78–184.14. Козенков О. Д., Косырева Л. Г. Зависимость скорости роста нитевидного кристалла, лимитируемого гетерогенной химической реакцией, от состава газовой фазы // Неорганические материалы,2015, т. 51(11), с. 1255–1259. DOI: https://doi.org/10.7868/S0002337X1510009715. Даринский Б. М., Козенков О. Д., Щетинин А. А. О зависимости скорости роста нитевидных кристаллов от их диаметра // Известия вузов. Физика, 1986, т. 32(12), с. 18–22.16. Щетинин А. А., Козенков О. Д., Небольсин В. А. О зонах питания нитевидных кристаллов кремния растущих из газовой фазы // Известия вузов, Физика, 1989, т. 32(6), с. 115–116.17. Щетинин А. А., Дунаев А. И., Козенков О. Д. О травлении монокристаллов кремния через жидкуюфазу и образовании систем обычных и «отрицательных» нитевидных кристаллов. Воронеж: ВГПИ, 1981, 9 с.18. Козенков О. Д., Козьяков А. Б., Щетинин А. А. О конусности нитевидных кристаллов кремния //Известия вузов, Физика, 1986, т. 29(9), с. 115–117.19. Козенков О. Д. Конусность нитевидного кристалла, обусловленная гетерогенной химической реакцией // Неорганические материалы, 2016, т . 52 (3), с. 279–284. DOI: https://doi.org/110.7868/S0002337X16030064

Transport phenomena