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The Influence of Preparation Methods on Magnetic Properties of Fe/SiO₂ Soft Magnetic Composites

100%
Füzerová J., Füzer J., Kollár P., Kabátová M., Dudrová E.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
816-818
EN
An analysis of several variants of the Fe/polymer/SiO₂ composites in terms of the impact of iron powder particle shape (irregular, spherical), of the content (0.4-2.0 wt%), of the polymer type (shellac, thermoset SL450) and the method of its application as well as the effect of the preparation procedure of the composites (mixing and/or vacuum-pressure impregnation) on properties of electrical insulating layer (thickness and coherence), electrical resistivity and magnetic properties was carried out. It was found that the main governing factor of the microstructure formation is the shape, surface microgeometry of the iron particles and the insulator layer. These determine not only the uniformity of thickness and cohesion of the insulating layer of the applied polymer or its hybrid modification (polymer+SiO₂ nanoparticles), but also the most suitable method of preparation in terms of the achieved values of electrical and magnetic properties of the composites.
2
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Preparation and Characterization of Fe/SiO_{2} Powder Composites Using Impregnation Method

100%
Kabátová M., Füzer J., Füzerová J., Dudrová E., Kollár P.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
134-135
EN
Fe/SiO_{2} powder composite materials based on irregularly and/or spherically shaped iron powder particles with an addition of SiO_{2} nanopowder were prepared in two ways, (i) by mixing the Fe/SiO_{2} powder with 1.0 wt.% of Shellac dissolved in ethanol and (ii) by vacuum/pressure impregnation of low-temperature sintered Fe/SiO_{2} components with shellac dissolved in ethanol and with thermoplast SL450. SiO_{2} was implemented either as nanopowder or by sol-gel coating. Vacuum/pressure impregnation (VPI) of pre-sintered samples was performed in a steel container. The influence of iron particle shape and processing conditions on the electro-insulating layer was microscopically evaluated and correlated with the values of the electrical resistivity and coercivity. It has been found that the continuity, distribution and thickness of insulating phase is strongly controlled by the shape of iron particles. Using the VPI procedure, the irregular surface of iron particles may cause discontinuities of insulating layer, while the spherical iron particles are well covered with continuous evenly distributed insulating layer.
3
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Microdeformation Processes in Soft Magnetic Compounds

86%
Bidulský R., Bidulská J., Petroušek P., Fedoriková A., Dudrová E., Actis Grande M.
Acta Physica Polonica A
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2017
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vol. 131
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issue 5
1367-1370
EN
Porosity can be defined in different ways. The most frequently used definition is the total porosity, which is the total volume fraction of empty space in the specimen. The presence of pores strongly affects the fracture mode. Besides the evaluation of geometry and quality of connections, fractographic analysis enables a quantification of the important microstructural characteristics of the plane porosity. This quantity allows to quantify the existing relations between microstructure and properties. The fractographic evaluation of the distribution of microdeformation processes in the volume of experimental material demonstrates the influence of porosity on the concentration of deformation flows into the microvolume of connections. Plain porosity contributes to the recognition of critical microstructural defects and therefore, to enable evaluating the relationship between the processing parameters, microstructural constituents, and pores. In the fractography evaluation, the analysis of the quality of interparticle bonding using determination of elementary types of fracture facets allows to interpret the mechanical and plastic properties of investigated materials.
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