Papers by Author: Miha Drofenik

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Authors: V. Dondur, Nenad Radić, Boško Grbić, Miha Drofenik
Abstract: In this paper the adsorption and oxidation of CO on nanocrystalline Au/γ-Fe2O3, Au/α- Fe2O3, γ-Fe2O3 and a series of mixed ferrite with MnxZn1-xFe2O4 composition are investigated. The catalysts were prepared by co-precipitation method and characterized using X-ray diffraction (XRPD), specific surface (BET), transition electron spectroscopy (TEM) and magnetization measurements. A temperature programmed desorption (TPD) study of the water and CO interaction with nanocrystalline adsorbents is presented. The catalytic activities towards CO oxidation increased in the following order: γ-Fe2O3 < MnxZn1-xFe2O4 < Au/γ-Fe2O3 .
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Authors: Miha Drofenik, M. Kristl, Andrej Žnidaršić, Darja Lisjak
Abstract: Nanoparticles of barium hexaferrite were prepared by controlled hydrothermal synthesis at 280oC. During the synthesis, the composition of the precursor and the suspension concentration were controlled. The as-synthesized crystalline barium hexaferrite platelets of about 50 nm in length and 5 nm in thickness exhibited a saturation magnetization of 40 emu/g.
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Authors: Darja Lisjak, Andrej Žnidaršić, Vladimir B. Bregar, Miha Drofenik
Abstract: The trend for integrating and miniaturizing electronic devices requires the co-firing of ferrites and Ag electrodes at 900°C. Here we report on compatibility studies using Z- and Y-type BaCo hexaferrites, which are interesting for microwave applications. Samples with compositions BaB3BCoB1.4BCuB0.6BFeB24BOB41 Band BaB2BCoB0.6BCuB1.4BFeB12BOB22 Bwere prepared with solid-state reactions at 1250°C and 1000°C, respectively. For compatibility tests, samples with additions of 0-25 wt.% of Ag were sintered at 900°C for 3h. The ceramics were characterized with X-ray powder diffraction and electron microscopy combined with energy-dispersive analysis. When co-sintered with Ag the hexaferrites decomposed to BaFeB12BOB19B and (Co,Cu)FeB2BOB4B or BaFeB2BOB4B. The incorporation of Ag in the spinel phase was also detected. The degree of decomposition increased with the amount of Ag and finally resulted in the complete disintegration of the samples with minimum 23 wt.% of Ag. The influence of the observed phase-composition changes on the electromagnetic properties and their dependence on frequency was evaluated.
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Authors: Irena Pibošič, Darko Makovec, Miha Drofenik
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Authors: V. Uskoković, Miha Drofenik
Abstract: Investigations of the influence of synthesis procedures and LaSr-manganite stoichiometries on the Curie point and other magnetic characteristics of the material, being the topic of this work, are attractive since they present a necessary primal step in the intended development of nano-magnetic drug carriers based on these materials. In the course of such an investigation, differences in the mechanisms of the formation of desired manganite compounds by following a classical solid-state preparation method, depending on various stoichiometries used, were noticed, with the reaction pathways thereof outlined onward.
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Authors: Aljoša Košak, Darko Makovec, Miha Drofenik
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Authors: Simona Ovtar, Darja Lisjak, Miha Drofenik
Abstract: Stable suspensions of nanosized barium hexaferrite particles were prepared with the addition of surfactants. Hydrothermally prepared particles with sizes from 5 to 20 nm and commercial particles with sizes from 10 to 160 nm were used. The films with thicknesses from 1.5 to 9.5 μm were prepared with electrophoretic deposition in an external magnetic field. The orientation of the grains in the films was due to the magneto-crystalline anisotropy of the barium hexaferrite and was determined with X-ray diffraction analysis, scanning electron microscopy and magnetic measurements. The highest degree of orientation in the films with anisotropic magnetic behaviour was 90 %.
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