• Journal of the Korean Ceramic Society
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• v.47 no.2
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• pp.113-116
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• 2010

The silica coated $Fe_3O_4$ nanoparticles have been synthesized using a micro-emulsion method. The $Fe_3O_4$ nanoparticles with the sizes 6 nm in diameter were synthesized by thermal decomposition method. Hydrophobic $Fe_3O_4$ nanoparticles were coated silica using surfactant and tetraethyl orthosilicated (TEOS) as a $SiO_2$ precursor. Shell thickness of silica coated $Fe_3O_4$ can be controlled (11~20 nm) through our synthetic conditions. The $Fe_3O_4$ and silica coated $Fe_3O_4$ nano powders were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD) and vortex magnetic separation (VMS).

• Korean Journal of Materials Research
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• v.23 no.4
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• pp.219-226
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• 2013

Activated magnetite ($Fe_3O_{4-{\delta}}$) has the capability of decomposing $CO_2$ proportional to the ${\delta}$-value at comparatively low temperature of $300^{\circ}C$. To enhance the $CO_2$ decomposition capability of $Fe_3O_{4-{\delta}}$, $(Fe_{1-x}Co_x)_3O_{4-{\delta}}$ and $(Fe_{1-x}Mn_x)_3O_{4-{\delta}}$ were synthesized and then reacted with $CO_2$. $Fe_{1-x}Co_xC_2O_4{\cdot}2H_2O$ powders having Fe to Co mixing ratios of 9:1, 8:2, 7:3, 6:4, and 5:5 were synthesized by co-precipitation of $FeSO_4{\cdot}7H_2O$ and $CoSO_4{\cdot}7H_2O$ solutions with a $(NH_4)_2C_2O_4{\cdot}H_2O$ solution. The same method was used to synthesize $Fe_{1-x}Mn_xC_2O_4{\cdot}2H_2O$ powders having Fe to Mn mixing ratios of 9:1, 8:2, 7:3, 6:4, 5:5 with a $MnSO_4{\cdot}4H_2O$ solution. The thermal decomposition of synthesized $Fe_{1-x}Co_xC_2O_4{\cdot}2H_2O$ and $Fe_{1-x}Mn_xC_2O_4{\cdot}2H_2O$ was analyzed in an Ar atmosphere with TG/DTA. The synthesized powders were heat-treated for 3 hours in an Ar atmosphere at $450^{\circ}C$ to produce activated powders of $(Fe_{1-x}Co_x)_3O_{4-{\delta}}$ and $(Fe_{1-x}Mn_x)_3O_{4-{\delta}}$. The activated powders were reacted with a mixed gas (Ar : 85 %, $CO_2$ : 15 %) at $300^{\circ}C$ for 12 hours. The exhaust gas was analyzed for $CO_2$ with a $CO_2$ gas analyzer. The decomposition of $CO_2$ was estimated by measuring $CO_2$ content in the exhaust gas after the reaction with $CO_2$. For $(Fe_{1-x}Mn_x)_3O_{4-{\delta}}$, the amount of $Mn^{2+}$ oxidized to $Mn^{3+}$ increased as x increased. The ${\delta}$ value and $CO_2$ decomposition efficiency decreased as x increased. When the ${\delta}$ value was below 0.641, $CO_2$ was not decomposed. For $(Fe_{1-x}Co_x)_3O_{4-{\delta}}$, the ${\delta}$ value and $CO_2$ decomposition efficiency increased as x increased. At a ${\delta}$ value of 0.857, an active state was maintained even after 12 hours of reaction and the amount of decomposed $CO_2$ was $52.844cm^3$ per 1 g of $(Fe_{0.5}Co_{0.5})_3O_{4-{\delta}}$.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.21.2-21.2
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• 2011

$Fe_3O_4$ having half metallic property is one of the efficient spin filtering materials which are widely used in spintronic research field and ZnO is wide band gap semiconductor which can be used by tunnel barrier or semiconductor channel in spin MOSFET. We investigated the magnetic and the electric properties of $Fe_3O_4$/ZnO multilayer fabricated on c-$Al_2O_3$ substrate by pulsed laser deposition (PLD). For multilayer films, PLD was performed at variable temperatures such as $200{\sim}750^{\circ}C$ and at target distance from 40 to 80 mm, KrF eximer laser of 1.5 $J/cm^2$ and a reputation rate of 2Hz. $Fe_3O_4$/ZnO multilayers were deposited at $4{\times}10^{-6}$ Torr. After fabricating $Fe_3O_4$/ZnO multilayers, $Fe_3O_4$/ZnO multilayers were treated by RTA(Rapid Thermal Annealing) at various temperature to change magnetic phase. The magnetism of the multilayer is changed by thickness of the ZnO tunnel barrier. Magnetic phase of FexOy showed a very small magnetism due to $Fe_2O_3$ ${\alpha}$-phase, but large magnetism from $Fe_3O_4$ or $Fe_2O_3$ ${\gamma}$-phase was observed. In the present study, effect of the ZnO thickness on the MR (magnetoresistance) ratio was investigated in detail.

• Advances in materials Research
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• v.1 no.2
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• pp.161-168
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• 2012

Nanoflake composite multi core-shell $SrFe_{12}O_{19}/Fe_3O_4$/PEG/Polypyrrole was synthesized by in situ polymerization method. In this paper, the fabrication of $SrFe_{12}O_{19}$ nanoflake is as first core by solgel method. Then fabricated a shell layer from magnetic nanoparticles of $Fe_3O_4$, which synthesized by coprecipitation technique, onto the $SrFe_{12}O_{19}$ nanoflake. Polyethylene glycol (PEG) as a polymer layer and as second shell was coated onto the before core-shell. Than core-shell $SrFe_{12}O_{19}/Fe_3O_4$/PEG was used as template for the preparation of $SrFe_{12}O_{19}/Fe_3O_4$/PEG/Polypyrrole composite. Final composite has a conductive property among $4.23{\times}10^{-2}Scm^{-1}$ and magnetic property about $M_s$=2.99 emu/g. Also final composite in soluble at organic solvent such as DMF and DMSO and has a flake structure. Conductivity and magnetic property respectively determine by four-probe instrument and vibrant sample magnetometer (VSM), morphology and article size determined by FE-SEM, TEM and XRD.

• Transactions of the Korean hydrogen and new energy society
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• v.18 no.2
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• pp.124-131
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• 2007

Methane is partially oxidized to produce the syngas by the lattice oxygen of metal oxides in the absence of gaseous oxygen. The present work deals with ferrite including copper component, which does not chemisorb methane, to investigate the suppression of the carbon deposition during the reduction of metal oxides by methane. Iron-based oxides of $Cu_xFe_{3-x}O_4$(X=0.25, 0.5, 1.0) was synthesized by the co-precipitation method. Thermogravimetric Analysis(TGA) was used to observe the isothermal reduction behavior of $Cu_xFe_{3-x}O_4$ and $Fe_3O_4$ at $600-900^{\circ}C$ under methane atmosphere. The crystal structures of reduced specimens were characterized by X-rays powder diffraction(XRD) technique. From the analyses of TGA, it is concluded that the reduction kinetics of $CuFe_2O_4$ was the fastest among $Fe_3O_4$ and $Cu_xFe_{3-x}O_4$(X=0.25, 0.5, 1.0). The X-ray diffraction analyses indicated that $Cu_xFe_{3-x}O_4$ was decomposed to Cu and $Fe_3O_4$ phase at $600^{\circ}C$ and was reduced to Cu and Fe phase at $800^{\circ}C$. $Fe_3O_4$, which was reduced at $900^{\circ}C$, showed Fe, graphite and $Fe_3C$ phases. On the contrary, $Cu_xFe_{3-x}O_4$ does not show the graphite or $Fe_3C$ phases. This results infer that Cu component suppress the carbon deposition on Cu-ferrite.

• Journal of the Korean Magnetics Society
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• v.7 no.5
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• pp.232-236
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• 1997

We have gone into details about the velocity calibration of sinusoidal mode for Mossbauer spectrometer. Since sinusoidal Mossbauer spectrometer has a ${\gamma}$-ray source that oscillates at the end of loudspeaker with the natural frequency. Doppler velocity is accurate and stable. From the analyzing Mossbauer spectra of $Fe_3O_4$ and U $Fe_3O_4$ (unbalanced $Fe_3O_4$), we have shown the power of correct velocity for sinusoidal mode.

• Particle and aerosol research
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• v.14 no.3
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• pp.65-72
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• 2018

Core-shell structured $Fe_3O_4/graphene$ composites were synthesized by aerosol spray drying process from a colloidal mixture of graphene oxides and $Fe_3O_4$ nanoparticles. The structural and electrochemical performance of $Fe_3O_4/graphene$ were characterized by the field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, cyclic voltammetry, and galvanometric discharge-charge method. Core-shell structured $Fe_3O_4/GR$ composites were synthesized in different mass ratios of $Fe_3O_4$ and graphene oxide. The composite particles were around $3{\mu}m$ in size. $Fe_3O_4$ nanoparticles were encapsulated with a graphene. Morphology of the $Fe_3O_4/graphene$ composite particles changed from a spherical ball having a relatively smooth surface to a porous crumpled paper ball as the content of GO increased in the composites. The $Fe_3O_4/GR$ composite fabricated at the weight ratio of 1:4 ($Fe_3O_4:GO$) exhibited higher specific capacitance($203F\;g^{-1}$) and electrical conductivity than as-fabricated $Fe_3O_4/GR$ composite.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.12
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• pp.812-816
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• 2017

$Fe_3O_4$ was prepared on the $TiO_2-coated$ natural mica substrate. The natural mica has an average particle size of $22{\mu}m$. The substrate was coated on $TiO_2$ thin films using hydrothermal synthesis at pH 1.5-2.5 at $75^{\circ}C$. The Fe precursor solution was prepared by mixing $FeSO_4$ (for $Fe^{2+}$ ion) and $FeCl_3$ (for $Fe^{3+}$ ions) with different molar ratios such as 1/2, 1/1, 2/1, 3/0, and $Fe_3O_4$ only. X-ray diffraction analysis shows that the crystal structure depends on the $FeCl_3-to-FeSO_4$ molar ratio. $Fe_3O_4$ crystal phase could be obtained at higher $FeSO_4$ contents.

• Journal of the Korean Magnetics Society
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• v.10 no.4
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• pp.165-170
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• 2000

The purpose of this study is to investigate the effect of annealing conditions on physical and magnetic properties of Fe-Hf-N thin films. When the thin films were annealed in $N_2$ gas, a surface oxide layer, comprised of Fe$_2$O$_3$ and Fe$_3$O$_4$, was formed at the surface of the thin films and a Fe-Hf-O-N layer was also formed under this surface oxide layer. It was found that the thicknesses of the surface oxide layer and the Fe-Hf-O-N layer increased, as the annealing temperature increased. It was also found that if the thickness of the surface oxide layer was excluded in the property calculation, the soft magnetic properties of the annealed thin films were not much different from those of the as-deposited thin films. Therefore, it was suggested that the Fe-Hf-O-N layer formed under the surface oxide layer did not lose significantly the soft magnetic properties of the Fe-Hf-N films and the Fe-Hf-N films annealed in $N_2$gas showed the soft magnetic properties of the Fe-Hf-N and Fe-Hf-O-N multi-layers.

• Journal of the Korean Chemical Society
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• v.38 no.8
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• pp.547-551
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• 1994

A series of samples in the $Nd_{1-x}Ba_xFeO_{3-y}$ system has been prepared by heating the reactants to$1200^{\circ}C$ under an ambient atmosphere, and the solid solutions were identified by X-ray power diffraction analysis. The crystal systems of samples with x = 0.00 and 0.25 were found to be orthorhombic whose local symmetry is similiar to the distorted octahedral with orthoferrite type one, whereas those with x = 0.50 and 0.75 to be the cubic system. Since Fe ions in the solid solutions are a mixed valence state between $Fe^{3+}\;and\;Fe^{4+}$ ions, the nonstoichiometric chemical formulas could be determined from the mole ratio of $Fe^{4+}$ ion and oxygen vacacies. According to the Mossbauer spectroscopic analysis, the presence of 5-coordinated $FeO_5$ was evidenced only in the barium compounds along with $FeO_6,\;and\;FeO_4$, but not in the strontium and calcium compounds. The samples with x = 0.25 and 0.50 show a spectrum of superparamagnetism, which might be due to the formation of a domain of the ferromagnetic interaction between the $Fe^{3+}\;and\;Fe^{4+}$ ions. The electrical conductivities of all samples are within semiconducting range. Since the $Fe^{4+}$ ion acts as an electron acceptor level during the electron transfer between the Fe through intermediate $O^{2-}$ ions, the activation energy of the compounds decreases with the increment of $Fe^{4+}$ content.