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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, izvirni znanstveni članek

Opis: 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.
Ključne besede: cobalt ferrite, nanoparticles, co-precipitation, colloidal suspensions, magnetic properties
Objavljeno: 30.08.2017; Ogledov: 1875; Prenosov: 58
.pdf Celotno besedilo (279,23 KB)
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Reactive sintering of $MnZn$ ferrites
Tomaž Kosmač, Mihael Drofenik, 2001, izvirni znanstveni članek

Opis: Reaction-formed $MnZn$ ferrite was prepared and the decrease in shrinkage after sintering due to the volume expansion accompanying iron oxidation was studied. Green compacts consisting of the milled raw oxides $Fe_2O_3$, $Mn_3O_4$, $ZnO$ and metallic iron powder were sintered at 1350 °C in air. During the first hold at 800 °C, $Fe$ was oxidized to $\alpha-Fe_2O_3$ and $Zn$ ferrite was formed. Above 1300 °C the reaction bonding was completed and $MnZn$ ferrite, exhibiting a relatively low shrinkage, was formed. The chemical reactions involved during reaction bonding were associated with a volume expansion and porosity formation, compensating for the shrinkage on sintering. Intensive milling decreases the porosity after sintering but induces the oxidation of iron, and partially removes the shrinkage compensation caused by the presence of metallic iron.
Ključne besede: reaction-forming, $MnZn$ ferrite, inorganic technology, ferrite ceramics, reaction bonded ceramics, sintering, iron oxides, iron
Objavljeno: 25.08.2017; Ogledov: 520; Prenosov: 70
.pdf Celotno besedilo (441,54 KB)
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Synthesis of nanocrystalline nickel-zinc ferrites within reverse micelles
Vuk Uskoković, Mihael Drofenik, 2003, izvirni znanstveni članek

Opis: Nanocrystalline nickel-zinc ferrites were synthesized via a reverse micelle microemulsion route. The precursor cations were precipitated in the microemulsion system CTAB/1-hexanol/water. A subsequent oxidizing reaction was used to synthesize the nickel-zinc ferrite. The obtained nanoparticles were less than 20 nm in size.
Ključne besede: nanomaterials, ferrite, powders synthesis, microemulsion, reverse micelle
Objavljeno: 23.03.2017; Ogledov: 595; Prenosov: 71
.pdf Celotno besedilo (109,33 KB)
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2014, doktorska disertacija

Opis: Cobalt ferrite (CoFe2O4) nanoparticles prepared via co-precipitation method were modified with tetraethoxysilane (TEOS) and additional funkcionalized with 3-mercaptopropyl trimethoxysilane (MPTMS) with purpose of cleaning waste water contaminated with heavy metal ions (Pb2+ and Hg2+). The influence of different experimental parameters (reaction time, reaction temperature and different TEOS:MPTMS ratios) on silica coating of CoFe2O4 nanoparticles and additional on thiol group was systematically studied. Silanes adsorb to the particle surface with alkoxy (Si(OR)4) groups at one end, while functional substituents (-SH) at the opposite end stay extended into surrounding aqueous medium and chemically interact with heavy metal contaminates. Thiol functionalized CoFe2O4 nanoparticles were characterized using IR spectroscopy, X-ray diffraction (XRD), transmission electron microscopy/high-resolution transmission electron microscopy (TEM/HRTEM), energy-dispersive X-ray spectroscopy (EDXS) and vibrating-sample magnetometer (VSM). The thiol functionalized CoFe2O4 nanoparticles were used for Pb2+ and Hg2+ions adsorption from aqueous media. Effect of treatment has been demonstrated using atomic absorption spectroscopy (AAS).
Ključne besede: cobalt ferrite, magnetic nanoparticles, tetraethoxysilane, 3-mercaptopropyl trimetoxysilane, thiol group, lead, mercury, adsorption
Objavljeno: 02.12.2014; Ogledov: 1890; Prenosov: 118
.pdf Celotno besedilo (5,22 MB)

Charpy toughness and microstructure of vibrated weld metal
Bogdan Pučko, Vladimir Gliha, 2006, izvirni znanstveni članek

Opis: Vibration during welding can be used to obtain certain changes in mechanical properties of weld metal. Research work on the influence of vibration on the secondary microstructure of welds and hence on the Charpy toughness was performed. Vibration during welding exhibits positive effects on the microstructure constituent formation. Multipass welding was simulated with reheating of the original single pass weld in order to obtain similar microstructure to multipass welds. Microstructures were examined with an optical microscope. Additionally, fractographic examination of the rupture of Charpy specimens was performed. Changes in the microstructure according to vibration were observed which affect toughness of the weld metal. Vibration during welding was rated more effective in the case of reheating the weld metal, which is the case in multipass welding.
Ključne besede: welding, welded joints, mechanical properties of metals, ferrite, vibration, microstructure, toughness, notched bar testing, weld metal
Objavljeno: 31.05.2012; Ogledov: 1742; Prenosov: 84
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