• Journal of the Korean Electrochemical Society
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• v.17 no.2
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• pp.124-129
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• 2014

In this article, we report the fabrication and characterization of carbon sphere/$Fe_3O_4$ nanocomposite for Li/air batteries. $Fe_3O_4$ nanoparticles are dispersed homogeneously on the surface of carbon spheres in an attempt to enhance the low conductivity of oxide catalyst ($Fe_3O_4$). The carbon sphere/$Fe_3O_4$ nanocomposite could offer wide surface area of $Fe_3O_4$ and increased carbon/catalyst contact area, which lead to enhanced catalytic activity. The electrode employing carbon sphere/$Fe_3O_4$ nanocomposite presented relatively low overpotential and stable cyclic performance compared with the electrode employing carbon sphere.

• Korean Journal of Optics and Photonics
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• v.28 no.3
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• pp.97-102
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• 2017

In this paper, we investigate the optical properties of $Ag@Fe_3O_4$ nanoparticles (NPs) composed of a plasmonic core and a magnetic shell. As the $Fe_3O_4$ shell with high refractive index (~2.42) is formed on the surface of the silver NPs having diameter of 60 nm, the wavelength of the localized surface-plasmon resonance (LSPR) is shifted from 420 nm to 650 nm, a so-called "redshift". Furthermore, through the use of three simulation models ($Ag@Fe_3O_4$ NP, $Fe_3O_4$ shell NP, and silver NP), the peak at 410 nm is seen to be the result of scattering by the $Fe_3O_4$ shell with 60 nm thickness, which would be useful in comprehending the complex optics in various nanoscale assemblies using similar NPs.

• Journal of the Korean Magnetics Society
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• v.7 no.5
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• pp.243-248
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• 1997

The effect of $O_2$ partial pressure on microstructure and soft magnetic properties of as-deposited Fe-Hf-O thin film alloys, which are produced by rf magnetron sputtering method in $Ar+O_2$ mixed gas atmosphere, are investigated. Saturation magnetization ($4{\pi}M_s$) of Fe-Hf-O film were decreased with increasing $O_2$ partial pressure, the best soft magnetic properties exhibit at $O_2$ partial pressure of 10%. With further increase of $O_2$ partial pressure, soft magnetic properties decreased continuously. The $Fe_{82}Hf_{3.4}O_{14.6}$ film with $P_{O2}=10%$ exhibits good soft magnetic properties with $4{\pi}M_s=17.7kG$, $H_c=0.7Oe$ and ${\mu}_ {eff}$ (1~100 MHz)=2,500, respectively. The addition of O is effective in grain refinement. In case of $P_{O2}=15%$, it is observed that $Fe_3O_4$ compound is formed and high frequency soft magnetic properties are decrease. The electrical resistvity($\rho$) of Fe-Hf-O film is increased with increasing $O_2$ partial pressure. Electrical resistivity of $Fe_{82}Hf_{3.4}O_{14.6}$ film was 5 times higher than that of the film without oxygen. Thus, it is considered that the good magnetic properties of $Fe_{82}Hf_{3.4}O_{14.6}$ film results from decreasing the $\alpha$-Fe grain size by precipitates (Hf and O), high electrical resistivity.

• Journal of the Korean Magnetics Society
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• v.6 no.4
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• pp.204-210
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• 1996

M type hexa-ferrites were prepared by means of a solid state reaction using mill scale, $Fe_{2}O_{3}$, and the mixture of mill scale and $Fe_{2}O_{3}$. The mixture of powders were calcined at $1150^{\circ}C$ for 2 hrs. and sintered at $1250^{\circ}C$ for 2 hrs, with varing the mole ratio of $Fe_{2}O_{3}$/$BaCO_{3}$, by 5.2~6.0. And the magnetic properties and morphologies of Baferrites with impurities such as $SiO_{2},\;Al_{2}O_{3},\;MgO,\;CaO\;and\;Na_{2}O$ in the mill scale were investigated. The magnetic properties were worsened by the addition of $Na_{2}O because of non-reacted iron oxide and intermediate compound of $BaFe_{2}O_{4}$ but they were improved apparently by the addition of $Si_{2}$ and $Al_{2}O_{3}$ in the composition of $BaO.5.6Fe_{2}O_{3}$. Moreover, $M_{s}$ decreased but $_{B}H_{C}$ increased through the addition of $Al_{2}O_{3}$ in Ba-ferrite. ${(BH)}_{max}$ of sintered BM($BaCO_{3}$, mill scale mixture) and BFM($BaCO_{3}$, $Fe_{2}O_{3}$, and null scale mixture) were 0.86 and 1.04 MGOe, respectively, and the magnetic properties were changed around $440^{\circ}C$.

• Journal of the Korean Institute of Telematics and Electronics
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• v.17 no.1
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• pp.36-39
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• 1980

Studies have been perfor mad on the normalization of V-I characteristics, the dependence of current runaway on the applied step voltage and the analysis of the current channet in the sintered 5Fe$_2$O$_3$-5Bi$_2$O$_3$. From the measurement of snitching Properties of the sintered 5Fe$_2$O$_3$-5Bi$_2$O$_3$, it is exe]twined that the electrical switching mechanism is that of thermal ionic breakolown.

• Journal of the Korean Institute of Telematics and Electronics
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• v.16 no.6
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• pp.11-15
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• 1979

Electrical switching phenomenon was observed in the Fe2O3-Bi2O3 system for the sintering temperature range of 700$^{\circ}$~85$0^{\circ}C$ for DC conductivity measurements of these sinterd materials in the ambient temperature range of 30$^{\circ}$~20$0^{\circ}C$ have shown that the conductivity increases with increasing the sitering temperature and ambient temperature. The formation of the current channel and the experimental evidence of the dependence of switching threshold voltage on the ambient temperature, strongly indicates that the main electrical switching mechanism of sintered Fe2O3-Bi2O3 is thermal effect.

• 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 $(Fe_{0.5}Co_{0.5})_3O_{4-{\delta}}$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.6
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• pp.245-251
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• 2015

We have applied mechanical alloying (MA) to produce soft magnetic composite material using a mixture of elemental $Fe_2O_3$-Mg powders. An optimal milling and heat treatment conditions to obtain soft magnetic ${\alpha}$-Fe/MgO composite with fine microstructure were investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that ${\alpha}$-Fe/MgO composite powders in which MgO is dispersed in ${\alpha}$-Fe matrix are obtained by MA of $Fe_2O_3$ with Mg for 30 min. The saturation magnetization of ball-milled powders increases with increasing milling time and reaches to a maximum value of 69.5 emu/g after 5 h MA. The magnetic hardening due to the reduction of the ${\alpha}$-Fe grain size by MA was also observed. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine at $800{\sim}1000^{\circ}C$ under 60 MPa. X-ray diffraction result shows that the average grain size of ${\alpha}$-Fe in ${\alpha}$-Fe/MgO nanocomposite sintered at $800^{\circ}C$ is in the range of 110 nm.

• 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.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.2
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• pp.69-73
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• 2018

Crystal growth of ${\alpha}-Fe_2O_3$ nanosized particles of 80~90 nm in size, which were hydrothermally prepared from 0.03 M $FeCl_3$ solution at $100^{\circ}C$, was investigated in Pb-containing and Pb-free frit. By heating ${\alpha}-Fe_2O_3$ nanosized particles in two frits at $800^{\circ}C$, the average diameter of particles in frits was increased to 200~210 nm and 150~160 nm, respectively, and the crystal growth due to the aggregation and sintering of several ${\alpha}-Fe_2O_3$ particles was observed. Formation ratios of larger particles over 100 nm in diameter were 54 % in Pb-free frit and 85 % in Pb-containing frit. After heating ${\alpha}-Fe_2O_3$ particles in frits at $800^{\circ}C$, 7~9 nm in average diameter of pores were formed in particles. Theses pores were derived from the porous structure of original ${\alpha}-Fe_2O_3$ particles and confined in particles during sintering.