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See detailDetermination of Kinetic Parameters for Heterogeneous Reaction System Employing Discrete Element Methods under HPC Platforms
Estupinan Donoso, Alvaro Antonio UL; Arenas, Monica; Borchuluun, Maitsetseg et al

Poster (2023, June 06)

The complex processes of heterogeneous reactions of granular materials such as occurring during metals-ore reduction or biomass gasification involve numerous physical phenomena. The combination of ... [more ▼]

The complex processes of heterogeneous reactions of granular materials such as occurring during metals-ore reduction or biomass gasification involve numerous physical phenomena. The combination of elevated temperature, complex flow, aggressive atmosphere and heterogeneous chemistry make it difficult to study these industrial processes. One of the most important aspects f heterogeneous reactions is to understand and quantify the evolution of the different transformations. For instance, during metal-oxides reduction processes, it is of high importance to quantify the rate at which the pure metal is formed. Nevertheless, it is almost impossible, by experimental means only, to separately observe, accurately quantify and gain insight into these mingled nonlinear physical and chemical processes. In the last decade, numerical simulation tools for particulate processes, such as the eXtended Discrete Element Method (XDEM), have become indispensable to study complex systems without the need of costly experimental practices. In the past, the XDEM has been employed to predict the reduction of tungsten trioxide (WO 3) in dry hydrogen (H2) atmospheres [1] and reduction of iron ores [2]. In the before-mentioned research works, it was employed kinetic data extracted from literature. On one hand, in these processes the kinetic data differ from each other. This is due to the fact that the experimental data in the literature is interpreted with lumped models and empirical models bonded to the specific experimental conditions. On the other hand, advanced simulation tools, such as XDEM, account for all the influencing phenomena (e.g. species and energy distribution, flow conditions, particles shape, rheological properties) constantly interacting in time and space. In these advanced simulation tools, each particle is treated and solved as individual entities and an accurate prediction of the species formation and transport in time and space is provided. Thus, in such advanced numerical tools, the reaction rate parameters representative of the kinetics alone of the involved chemical reactions must be employed. In this contribution, two XDEM simulation case studies accounting for the industrial reduction of WO 3 are presented. The first case study is employed to determine the reaction rate parameters of the four prevalent reduction steps (WO 3↔WO2.9↔WO2.72↔WO2↔W) upon the H 2 reduction of O3. Where the reaction rates are modeled following an Arrhenius law with two parameters per step i.e. pre-exponential factor and activation energy). The constituted optimization problem of minimization of error of the XDEM simulations vs experimental data, implemented and solved in a High Performance Computing (HPC) cluster, is presented and discussed. The determined parameters are later assessed by comparison to a secondly presented case study. [less ▲]

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See detailOn the angular anisotropy of the randomly averaged magnetic neutron scattering cross section of nanoparticles
Adams, Michael Philipp UL; Sinaga, Evelyn Pratami UL; Michels, Andreas UL

in IUCrJ (2023), 10(3), 261-269

The magnetic small-angle neutron scattering (SANS) cross section of dilute ensembles of uniformly magnetized and randomly oriented Stoner–Wohlfarth particles is calculated using the Landau–Lifshitz ... [more ▼]

The magnetic small-angle neutron scattering (SANS) cross section of dilute ensembles of uniformly magnetized and randomly oriented Stoner–Wohlfarth particles is calculated using the Landau–Lifshitz equation. The focus of this study is on the angular anisotropy of the magnetic SANS signal as it can be seen on a two-dimensional position-sensitive detector. Depending on the symmetry of the magnetic anisotropy of the particles (e.g. uniaxial, cubic), an anisotropic magnetic SANS pattern may result, even in the remanent state or at the coercive field. The case of inhomogeneously magnetized particles and the effects of a particle-size distribution and interparticle correlations are also discussed. [less ▲]

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See detailGeneric role of the Dzyaloshinskii–Moriya interaction in nanocrystalline ferromagnets
Erokhin, S.; Berkov, D.; Michels, Andreas UL

in New Journal of Physics (2023), 25

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See detailMagnetic neutron scattering from spherical nanoparticles with Néel surface anisotropy: atomistic simulations
Adams, Michael Philipp UL; Michels, Andreas UL; Kachkachi, Hamid

in Journal of Applied Crystallography (2022), 55(6), 1488-1499

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See detailMagnetic neutron scattering from spherical nanoparticles with Néel surface anisotropy: analytical treatment
Adams, Michael Philipp UL; Michels, Andreas UL; Kachkachi, Hamid

in Journal of Applied Crystallography (2022), 55(6), 1475-1487

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See detailUniaxial polarization analysis of bulk ferromagnets: theory and first experimental results
Malyeyev, Artem UL; Titov, Ivan UL; Dewhurst, Charles et al

in Journal of Applied Crystallography (2022), 55

Based on Brown’s static equations of micromagnetics, the uniaxial polarization of the scattered neutron beam of a bulk magnetic material is computed. The approach considers a Hamiltonian that takes into ... [more ▼]

Based on Brown’s static equations of micromagnetics, the uniaxial polarization of the scattered neutron beam of a bulk magnetic material is computed. The approach considers a Hamiltonian that takes into account the isotropic exchange interaction, the antisymmetric Dzyaloshinskii–Moriya interaction, magnetic anisotropy, the dipole–dipole interaction, as well as the effect of an applied magnetic field. In the high-field limit, the solutions for the magnetization Fourier components are used to obtain closed-form results for the spinpolarized SANS (small-angle neutron scattering) cross sections and the ensuing polarization. The theoretical expressions are compared with experimental data on a soft magnetic nanocrystalline alloy. The micromagnetic SANS theory provides a general framework for polarized real-space neutron methods, and it may open up a new avenue for magnetic neutron data analysis on magnetic microstructures. [less ▲]

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See detailOn the Reduction of Computational Costs for Tungsten Powder Bed Processes
Estupinan Donoso, Alvaro Antonio UL; Aminnia, Navid UL; Peters, Bernhard UL et al

Scientific Conference (2022, May 31)

During the Discrete Element Method (DEM) representation of powder bed processes (e.g. tungsten oxide reduction, tungsten carbide synthesis, selective laser sintering) a numerical solution for each single ... [more ▼]

During the Discrete Element Method (DEM) representation of powder bed processes (e.g. tungsten oxide reduction, tungsten carbide synthesis, selective laser sintering) a numerical solution for each single particle is impractical due to the extremely high number of particles (e.g. 10^12). However, in such processes, particles in the vicinity of each other observe low gradients concerning their thermodynamic state. This characteristic can be exploited to avoid solving repeatedly numerically equivalent equation systems. This contribution presents two numerical methods aiming to reduce the computational costs of DEM approaches for the thermochemical conversion of powder beds. In the two methods after an appropriated numerical treatment, a group of particles under similar boundary conditions is substituted by a single-effective-entity. Consequently, the entire powder space is divided into sub-domains to be solved. The methods result in considerable lower number of equations that increase computational efficiency and enable feasible time simulations. The applications of the industrial synthesis of tungsten powders and the selective laser sintering (SLS) of powder metals are presented and discussed. [less ▲]

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See detailUsing small-angle scattering to guide functional magnetic nanoparticle design
Honecker, Dirk; Bersweiler, Mathias UL; Erokhin, Sergey et al

in Nanoscale Advances (2022), 4

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See detailMuMag2022: a software tool for analyzing magnetic field dependent unpolarized small-angle neutron scattering data of bulk ferromagnets
Adams, Michael Philipp UL; Bersweiler, Mathias UL; Jefremovas, Elizabeth Martín et al

in Journal of Applied Crystallography (2022), 55

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See detailSmall-angle neutron scattering by spatially inhomogeneous ferromagnets with a nonzero average uniaxial anisotropy
Zaporozhets, V. D.; Oba, Y.; Michels, Andreas UL et al

in Journal of Applied Crystallography (2022), 55

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See detailMagnetic order and disorder environments in superantiferromagnetic NdCu2 nanoparticles
Jefremovas, E.M.; Svedlindh, P.; Damay, F. et al

in Scientific Reports (2022), 12

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See detailQuantum Skyrmion Lattices in Heisenberg Ferromagnets
Haller, Andreas UL; Groenendijk, Solofo; Habibi, Alireza et al

E-print/Working paper (2021)

Skyrmions are topological magnetic textures which can arise in non-centrosymmetric ferromagnetic materials. In most systems experimentally investigated to date, skyrmions emerge as classical objects ... [more ▼]

Skyrmions are topological magnetic textures which can arise in non-centrosymmetric ferromagnetic materials. In most systems experimentally investigated to date, skyrmions emerge as classical objects. However, the discovery of skyrmions with nanometer length scales has sparked interest in their quantum properties. Quantum corrections to the classical magnetic textures have already been considered in the semiclassical regime. Here, we go beyond this limit by investigating quantum skyrmions in the deep quantum regime. We use density matrix renormalization group techniques to study two-dimensional spin-1/2 Heisenberg ferromagnets with Dzyaloshinskii-Moriya interactions and discover a broad region in the zero temperature phase diagram which hosts quantum skyrmion lattice ground states. We argue that this novel quantum skyrmion phase can be detected experimentally in the magnetization profile via local magnetic polarization measurements as well as in the spin structure factor measurable via neutron scattering experiments. Finally, we explore the resulting quantum skyrmion state, analyze its real space polarization profile and show that it is a non-classical state featuring entanglement between quasiparticle and environment mainly localized near the boundary spins of the skyrmion. [less ▲]

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See detailRole of higher-order effects in spin-misalignment small-angle neutron scattering of high-pressure torsion nickel
Oba, Yojiro; Bersweiler, Mathias UL; Titov, Ivan et al

in Physical Review Materials (2021), 5

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