• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.137-141
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• 2005

The CMR properties and magnetic properties of sulphospinels $Zn_xFe_{1-x}Cr_2S_4$ have been explored by X-ray diffraction, magnetoresistance measurement, and $M\ddot{o}ssbauer$ spectroscopy. The crystal structures in the range of x=0.05, 0.1, 0.2 are cubic at room temperature. Magnetoresistance measurement indicates that these system is semiconducting below about 160 K. The temperature of maximum magnetoresistance is almost consistent with Curie temperature. The Zn substitutions for Fe occur to increase the Jahn-Teller relaxation and the electric quadrupole shift. CMR properties could be explained with Jahn-Teller effect, and half-metallic electronic structure, which is different from both the double exchange interactions of manganite La-Ca-Mn-O system and the triple exchange interactions of chalcogenide $Cu_xFe_{1-x}Cr_2S_4$.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1703-1707
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• 2018

Ferromagnetic ${\tau}-phase$ $Mn_{54}Al_{46}C_{2.44}$ particles were synthesized, and its composites with commercial $Sm_2Fe_{17}N_3$ and synthesized $Fe_{65}Co_{35}$ powders were fabricated. Smaller grain size than the single domain size of the $Mn_{54}Al_{46}C_{2.44}$ without obvious grain boundaries and secondary phases is the origin for the low intrinsic coercivity. It was confirmed that the magnetic properties of the $Mn_{54}Al_{46}C_{2.44}$ can be enhanced by magnetic exchange coupling with the hard magnetic $Sm_2Fe_{17}N_3$ and soft magnetic $Fe_{65}Co_{35}$. The high degrees of the exchange coupling were verified by calculating first derivative curves. Thermo-magnetic stabilities of the composites from 100 to 400 K were measured and compared. It was demonstrated that the $Mn_{54}Al_{46}C_{2.44}$ based composites containing $Sm_2Fe_{17}N_3$ and $Fe_{65}Co_{35}$ could be promising candidates for future permanent magnetic materials with the proper control of purity, magnetic properties, etc.

• Korean Journal of Environmental Agriculture
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• v.27 no.1
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• pp.35-43
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• 2008

The study was carried out to estimate runoff loads of heavy metals in the valley watershed at the middle of South Korea, during farming season. There were no other pollution sources except agricultural activity. From 27 April 2006 to 31 October 2007, water samples were collected using two methods. The first method was regular sampling wherein water samples were taken every two weeks; and the other method was through regular sampling when water were collected during each rainfall event. Results showed that heavy metals were found in the water from the regular samples, and were highest during May and June. It was presumed that this might have been contributed by farming activities. Heavy metal concentration of the irregular samples was lower than regular samples. The correlation coefficient between each heavy metal of the regular samples were as follows: Fe-Al>Cr-Al>Fe-Cr>Mn-Fe. The correlation coefficient of the irregular samples were the following: Fe-Al>Fe-Cu is positive; and Pb-Cu>Ni-Al is negative. Measured pollutant loads of heavy metals in the valley watershed were : 2.047 kg $day^{-1}$ of Al, 0.008 kg $day^{-1}$ of Cd, 0.034 kg $day^{-1}$ of Cr, 0.311 kg $day^{-1}$ of Cu, 0.601 kg $day^{-1}$ of Fe, and 0.282 kg $day^{-1}$ of Zn in 2006; while in 2007, the following were observed: 2.535 kg $day^{-1}$ of Al, 0.026 kg $day^{-1}$ of Cd, 0.055 kg $day^{-1}$ of Cu, 0.727 kg $day^{-1}$ of Fe, and 0.317 kg $day^{-1}$ of Zn. In the analysis of data gathered, the loading rates of effluents from the valley watershed during the rainy season were : 79.8% of Al, 69.1% of Cu, 82.5% of Fe, and 69.1% of Zn in 2006; while 69.9% of Al, 67.5% of Cu, 70.4% of Fe, and 67.5% of Zn in 2007.

• Journal of the Korean Ceramic Society
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• v.22 no.3
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• pp.35-40
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• 1985

The composition of the base glass was determined to be $Na_2O$ 15, $Fe_2O_3$ 35, $B_2O_3$ 0~20, $P_2O_5$ 30~50 by mole percent. The heating temperature for nucleation was determined by means of thermal expansion curve. Crystalline phases were investigated by X-ray diffraction method and I.R Spectra. Electrical conductivities of glass spec-imens were observed in the temperature range 25~20$0^{\circ}C$ The activation energies of these specimens were caculated. The results obtained were as follows : 1) The limit composition of the melts 15mol% $Na_2O$ 35mole% $Fe_2O_5$ 20mole% $B_2O_3$ 30mole% $P_2O_5$ was able to be formed into desired shapes during cooling, . 2) In the measurement of d. c conductivity($\delta$) on the glasses in the system $15Na_2O-35Fe_2O_3$-$B_2O_3$-(50-x) $P_2O_5$ the values decreased by replacing 5 mole% $P_2O_5$ with $B_2O_3$ 3) The d. c conducties of heat treated samples were increased by replacing $P_2O_5$ with $B_2O_3$ 4) $B_2O_3$ contributed to precipitate crystals such as${\gamma}$-$Fe_2O_3$ $Fe_3O_4$ which had the advantage of electronic conduction in heat treated samples. 5) The slope plotted Log($\delta$) versus 1/T in this glass system was linear in the measured temperature range.

• Korean Journal of Materials Research
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• v.27 no.11
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• pp.631-635
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• 2017

We report facile solution processing of mesoporous hematite (${\alpha}-Fe_2O_3$) thin films for high efficiency solar-driven water splitting. $Fe_2O_3$ thin films were prepared on fluorine doped tin oxide(FTO) conducting substrates by spin coating of a precursor solution followed by annealing at $550^{\circ}C$ for 30 min. in air ambient. Specifically, the precursor solution was prepared by dissolving non-toxic $FeCl_3$ as an Fe source in highly versatile dimethyl sulfoxide(DMSO) as a solvent. The as-deposited and annealed thin films were characterized for their morphological, structural and optical properties using field-emission scanning electron microscopy(FE-SEM), X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and UV-Vis absorption spectroscopy. The photoelectrochemical performance of the precursor (${\alpha}-FeOOH$) and annealed (${\alpha}-Fe_2O_3$) films were characterized and it was found that the ${\alpha}-Fe_2O_3$ film exhibited an increased photocurrent density of ${\sim}0.78mA/cm^2$ at 1.23 V vs. RHE, which is about 3.4 times higher than that of the ${\alpha}-FeOOH$ films ($0.23mA/cm^2$ at 1.23 V vs. RHE). The improved performance can be attributed to the improved crystallinity and porosity of ${\alpha}-Fe_2O_3$ thin films after annealing treatment at higher temperatures. Detailed electrical characterization was further carried out to elucidate the enhanced PEC performance of ${\alpha}-Fe_2O_3$ thin films.

• Korean Journal of Materials Research
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• v.15 no.4
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• pp.224-232
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• 2005

Dry sliding wear behavior of electro-pressure sintered Fe-Ni and Co-Fe-Ni compacts was investigated. Pin-on-disk wear tests were performed on the sintered Fe-Ni, Co-Fe-Ni disk specimens against alumina $(Al_2O_3)$ and silica $(SiO_2)$ ball counterparts at various loads ranging from 3N to 12N. A constant sliding speed of 0.1m/sec was employed. Wear rate was calculated by dividing the weight loss measured after the test by specific gravity and sliding distance. Worn surfaces and cross sections of them were examined by a scanning electron microscopy, and wear mechanism of the compacts was investigated. Wear characteristics of the compacts were discussed as a function of composition of the compacts. Relationship between the wear rate and mechancial properties of the compact was explored, and effects of the oxide layer that was formed on wearing surface of the compacts on the wear were also studied.

• Journal of Powder Materials
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• v.21 no.5
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• pp.382-388
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• 2014

Fe-TiC composite powder was fabricated by high-energy milling of powder mixture of (Fe, TiC) and (FeO, $TiH_2$, C) as starting materials, respectively. The latter one was heat-treated for reaction synthesis of TiC phase after milling. Both powders were spark-plasma sintered at various temperatures of $680-1070^{\circ}C$ for 10 min. with sintering pressure of 70 MPa and the heating rate of $50^{\circ}C/min$. under vacuum of 0.133 Pa. Density and hardness of the sintered compact was investigated. Fe-TiC composite fabricated from (FeO, $TiH_2$, C) as starting materials showed better sintered properties. It seems to be resulted from ultra-fine TiC particle size and its uniform distribution in Fe-matrix compared to the simply mixed (Fe, TiC) powder.

• Journal of the Korean Society for Heat Treatment
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• v.2 no.2
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• pp.38-45
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• 1989

The Cu-Fe permanent magnet were prepared in situ process, which has economic and mass productive merits in producing multi filamentary composites. The purpose of this research was to study the effect of reduction ratio and heat treatment on magnetic property. As the reduction ratio of Cu-Fe wire increased, the filament structure became finer and interfilament distances decreased and the morphology of filament cross section became ribbon shape. As Fe content increased significantly. The coercivity and squareness of Cu-55 wt%Fe composite increased as a reduction ratio became higher, whereas they increased to maximum values at 0.09 mm ${\phi}$ for Cu-30 wt%Fe, and 0.066 mm ${\phi}$ for CU-45 wt%Fe respectively, and decreased for further reduction. The magnetic properties of Cu-Fe composites can be more enhanced by intermediate heat treatment. The best magnetic properties were obtained from Cu-55 wt%Fe composite deformed to 0.054 mm ${\phi}$ and annealed.

• Journal of the Korean Chemical Society
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• v.58 no.2
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• pp.205-209
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• 2014

Hematite iron oxide (${\alpha}$-$Fe_2O_3$) nanowalls were fabricated on aluminum substrate by a facile solvent-assisted hydrothermal oxidation process. The XRD and EDS patterns indicate that the sample has a rhombohedral phase of hematite $Fe_2O_3$. FE-SEM, TEM, HR-TEM, SA-ED were employed to characterize the resulting materials. $N_2$ adsorption-desorption isotherms was used to study a BET surface area. Their capability of catalytic degradation of titan yellow GR azo dye with air oxygen in aqueous solution over $Fe_2O_3$ catalysts was studied. The result indicates that the as-prepared product has a high catalytic activity, because it has a larger surface area. Langmuir and Freundlich isotherms of adsorption dye on the catalysts surface were investigated and the decomposition of titan yellow GR follows pseudo-first order kinetic.

• Journal of the Korean Ceramic Society
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• v.24 no.6
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• pp.553-560
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• 1987

Amorphous ferrites with composition B2O3-mBaO-nFe2O3 were prepared by an ultra rapidquenching technique. X-ray patterns and SEM reveal the products to be amrophous at room temperature. BaFe12O19 fine particles extracted from amorphous Ba-ferrites which additived Al2O3, SiO2, TiO2 and CoO have narrow size distribution, average 0.2$\mu\textrm{m}$, and coercive force, average 1400 Oe, increased with increasing TiO2 amounts. The obtained BeFe12O19 fine particles would be appreciated as perpendicular magnetic recording media.