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The magnetic and colloidal properties of $CoFe_2O_4$ nanoparticles synthesized by co-precipitation
Sašo Gyergyek, Mihael Drofenik, Darko Makovec, 2014, original scientific article

Abstract: Magnetic $CoFe_2O_4$ nanoparticles were synthesized by co-precipitation at 80 °C. This co-precipitation was achieved by the rapid addition of a strong base to an aqueous solution of cations. The investigation of the samples that were quenched at different times after the addition of the base, using transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDXS) and X-ray powder diffractometry, revealed the formation of a Co-deficient amorphous phase and $Co(OH)_2$, which rapidly reacted to form small $CoFe_2O_4$ nanoparticles. The nanoparticles grew with the time of aging at elevated temperature. The colloidal suspensions of the nanoparticles were prepared in both an aqueous medium and in a non-polar organic medium, with the adsorption of citric acid and ricinoleic acid on the nanoparticles, respectively. The measurements of the room-temperature magnetization revealed the ferrimagnetic state of the $CoFe_2O_4$ nanoparticles, while their suspensions displayed superparamagnetic behaviour.
Keywords: cobalt ferrite, nanoparticles, co-precipitation, colloidal suspensions, magnetic properties
Published: 30.08.2017; Views: 1876; Downloads: 58
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Sensing heavy metals using mesoporous-based optical chemical sensors
Špela Korent Urek, Nina Frančič, Matejka Turel, Aleksandra Lobnik, 2013, review article

Abstract: Heavymetal pollution is one of the more serious environmental problems; therefore, there is a constant demand for the development of new analytical tools for its monitoring. An optical chemical sensor represents a good alternative to classical instrumental methods.The mesoporous materials used in optical chemical sensorsʼ fabrications have properties such as high porosity, exceptional adsorption capacity, tuneable 3D shape, geometry, and morphology, which enable improved limit of detection, response time, and selectivity properties of optical sensors. In this review, we firstly present the properties of mesoporous materials, provide a brief description of sensing mechanisms, and briefly discuss the importance of continuous monitoring. Recent advances in those mesoporous silica-based optical sensors used for heavy metal detection have been reported and their advantages and limitations also discussed. This review covers publications that have appeared since 2008.
Keywords: heavy metals, magnetic properties, structural properties, heavy metal pollution
Published: 14.06.2017; Views: 1204; Downloads: 261
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A facile route to the synthesis of coated maghemite nanocomposites for hyperthermia applications
Gregor Ferk, Irena Ban, Janja Stergar, Darko Makovec, Anton Hamler, Zvonko Jagličić, Mihael Drofenik, 2012, original scientific article

Abstract: CM-dextran-covered maghemite particles for applications in magnetic hyperthermia treatments were synthesized and their physical, magnetic and morphological properties were examined. Magnetic fluids were prepared and their heating proper ies in an alternating magnetic field were studied. The results reveal that the particle size and the thickness of the carboxy-methyl-dextran (CM-dextran) coatings have a decisive influence on the heating properties: specific absorption rate (SAR). The majority of the magnetic dissipation comes from the Neel relaxation, while the Brown contribution is small. A thermal steady state at the selected temperature (42 °C) can be achieved using synthesized maghemite particles with proper particle morphology and by controlling the magnetic field intensity or the frequency.
Keywords: magnetic nanoparticles, hyperthermia, magnetic properties
Published: 10.07.2015; Views: 1204; Downloads: 69
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Evaluation of mechanical properties of soft magnetic materials for axial flux permanent magnet synchronous machines
Zdravko Praunseis, Peter Virtič, 2013, original scientific article

Abstract: Accurate determination of real material mechanical properties is important for safe servicing of energy components. The aim of the paper is systematic experimental approach for determination of mechanical properties of high strenght low alloyed steels and mild carbon steel in the rolling, thickness and width direction.
Keywords: soft magnetic materials, mechanical properties, experimental testing
Published: 10.07.2015; Views: 1347; Downloads: 40
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Blaž Goričar, 2014, master's thesis

Abstract: This Master's thesis research is about the localized coercivity enhancement of Nd-Fe-B magnets, which are used in electric motors. Computer simulations show, that when magnets operate at high temperatures, they experience large demagnetizing fields. However, this happens only on specific parts of the body of the magnet. The demagnetization can be prevented by locally enhancing the coercivity only on these specific parts. The goal of this Master’s thesis was to research the localized coercivity enhancement by creating a magnet, where one half would have different magnetic properties compared to the other half. Commercially available Nd-Fe-B magnets were bought from Shin-Etsu, Japan. The magnetic properties of the magnets were measured on two very different devices – the permeameter and the vibrating sample magnetometer. The demagnetization curves were compared. The coercivity of the magnet was improved with the electrophoretic deposition of dysprosium on the surface. The dysprosium then diffused, at high temperature, from the surface to the inside of the magnet along the grain boundaries. The microstructure of the magnet was analysed on the scanning electron microscope, while the content of the elements was quantitatively analysed with the EDS method. The demagnetization curves of both devices were comparable. The grain-boundary diffusion process of dysprosium with the electrophoretic deposition increased the coercivity of the magnet by 25 %, without any significant loss in remanence. The research on the localized grain-boundary diffusion was first done with measurements on the vibrating sample magnetometer and then confirmed with the Hall probe. We discovered that one part of the magnet could have different magnetic properties compared to the other half. There was a clear border between the two.
Keywords: Nd-Fe-B magnet, coercivity, magnetic properties, electrophoretic deposition, grain-boundary diffusion process.
Published: 09.09.2014; Views: 1600; Downloads: 93
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Subsolidus phase equilibria and the Li[sub]5Nd[sub]4FeO[sub]10 phase in the Li[sub]2O-Nd[sub]2O[sub]3-Fe[sub]2O[sub]3 system
Irena Ban, Mihael Drofenik, Danilo Suvorov, Darko Makovec, 2005, original scientific article

Abstract: A survey of the subsolidus phase equilibria in the system Li2O-Nd2O3-Fe2O3 wasmade at subsolidus temperatures in the range 1000-1050 °C. A ternary phase was identified. The phase is centered on Li5Nd4FeO10, with a cubic lattice a =11.9494 A. The compound melts incongruently at 1105 °C. The magnetic susceptibility was measured in the temperature range 4-300 K. The compound is paramagnetic in the temperature range 150-300 K and follows the Curie-Weiss law. At about TN = 10 K, a long-range magnetic ordering is observed.
Keywords: lithium ferrites, differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction, magnetic properties, phase equilibrium
Published: 01.06.2012; Views: 1607; Downloads: 23
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The synthesis of iron-nickel alloy nanoparticles using a reverse micelle technique
Irena Ban, Mihael Drofenik, Darko Makovec, 2006, original scientific article

Abstract: Nanosized Fe0.2Ni0.8 particles were prepared by reducing their salts with sodium borohydride (NaBH4) in cationic water-in-oil (w/o) microemulsions of water/cetyl-trimethyl-amonium bromide (CTAB) and n-butanol/isooctane at 25 °C.According to the TEM and X-ray diffraction analyses, the synthesized particles were around 4-12 nm in size. Due to their nanodimensions, the particles had a primitive cubic (pc) structure rather than the body-centered cubic (BCC) structure of the bulk material. An examination of the synthesis from the reverse micelle reveals that the morphology of the iron-nickel alloy nanoparticles depends mainly on the microemulsion`s composition. The magnetization of the nanoparticles was much lower than that of the bulk material, reflecting the influence of the nanodimensions on the particlesć magnetizations.
Keywords: magnetic materials, nickel/iron alloys, nanoparticles, synthesis, microemulsions, magnetic properties, reverse micelles
Published: 31.05.2012; Views: 1514; Downloads: 85
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