• Korean Chemical Engineering Research
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• v.46 no.6
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• pp.1113-1118
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• 2008

Characteristics of reduction properties and carbon deposition of $CuFe_2O_4$ and $Fe_3O_4$ were investigated by using TGA, XRD, SEM, TEM and gas analysis at $900^{\circ}C$. XRD analyses indicated that the reduced $Fe_3O_4$ was composed of Fe, graphite and $Fe_3C$ phases. In contrast, the reduced $CuFe_2O_4$ did not show the graphite or $Fe_3C$ phases. It was observed by SEM analysis that the surface of the $Fe_3O_4$ was completely covered with carbon, after methane partial oxidation. From gas analysis, $CuFe_2O_4$ showed much higher methane conversion and reduction kinetics as compared to the $Fe_3O_4$ under the same reaction conditions and the estimated carbon deposition amounts on the reduced $CuFe_2O_4$ was much lower than those on the reduced $Fe_3O_4$ during the syngas production process. It was found by TEM that carbon on the reduced $Fe_3O_4$ particles has a platelet shape.

• Journal of the Korean Ceramic Society
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• v.28 no.4
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• pp.305-314
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• 1991

This study was conducted to research the formation and the color development of NiO-ZnO-Fe2O3-TiO2-SnO2 system for the purpose of synthesizing the spinel pigments which are stable at high temperature. After preparing ZnO-Fe2O3 as a basic composition, {{{{ chi }}NiO.(l-{{{{ chi }})ZnO.Fe2O3 system, {{{{ chi }}NiO.(l-{{{{ chi }})ZnO.TiO2 system, and {{{{ chi }}NiO.(l-{{{{ chi }})ZnO.SnO2 system were prepared with {{{{ chi }}=0, 0.2, 0.5, 0.7, 1 mole ratio respectively. The manufacturing was carried out at 128$0^{\circ}C$ for 30 minutes. The reflectance measurement and the X-ray analysis of these specimens were carried out and the results were summarized as follows. 1. In the specimens which included NiO, it was difficult for the spinel structure to be formed. 2. As increasing the contents of NiO and Fe2O3, all the groups which were yellow or green colored changed to brown. 3. NiO-ZnO-Fe2O3 system and NiO-ZnO-TiO2 system formed the spinel structure and the illmenite structure appeared in NiO-TiO2 system.

• Journal of the Korean Ceramic Society
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• v.45 no.3
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• pp.179-184
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• 2008

(40-x)BaO${\cdot}xFe_2O_3{\cdot}60P_2O_5$ glasses with $5{\leq}x{\leq}35mol%$ were investigated by ESR spectroscopy. Two resonances observed near g=2.0 and g=4.3. The line at g=4.3 disappeared with the increase of the $Fe_2O_3$ content. The resonance at $g{\approx}2.0$ displayed characteristic signal consisting of superposed extremely broad and narrow components. The broader one indicates the presence of the association of two or more $Fe^{3+}$ ions, antiferromagnetically and the narrow one is related to the microclusters involving iron ions. Temperature dependence of the ESR integrated intensity revealed short-range antiferromagnetic character for $x{\geq}15mol%$.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2003.11a
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• pp.373-378
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• 2003

As a part of assessment of the structural material for the molten salt handling system, corrosion behavior of austenitic alloys, Fe-base and Ni-base in the molten salt of $LiCl-Li_2O_2$ was investigated in the range of temperature; 650~$725^{\circ}C$, time; 24- 168h, $Li_2O$; 3wt%, mixed gas; Ar-10%$O_2$. In the molten salt of $LiCl-Li_2O_2$, Ni-base alloys showed higher corrosion resistance than Fe-base alloys. Fe-base alloy with low Fe and high Ni contents exhibited better corrosion resistance. The scales of $Cr_2O_3$, $FeCr_2O_4$ on Fe-base alloys were showed, and $Cr_2O_3$, $NiFe_2O_4$ on Ni-base alloys were also showed.

• Journal of the Korean Magnetics Society
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• v.14 no.2
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• pp.71-75
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• 2004

$\alpha$-LiFe $O_2$ powders have been prepared by a sol-gel method. The crystallographic and magnetic properties were characterized with a x-ray diffractometry, Mossbauer spectroscopy, and vibrating Samples magnetometry. The ${\gamma}$-LiFe $O_2$+LiFe$_{5}$ $O_{8}$ phase is observed in the Samples annealed at $600^{\circ}C$ for 3h in air and $\alpha$-LiFe $O_2$ phase is observed in the Samples annealed at $600^{\circ}C$ for 3 h in $H_2$(5％)/Ar(Bal.) gas atmosphere. The crystal structure of $\alpha$-LiFe $O_2$ is found to be cubic with a lattice a=4.193$\pm$0.0005 $\AA$. The Neel temperature of $\alpha$-LiFe $O_2$ is found to be 130$\pm$3 K.

• Journal of the Korean institute of surface engineering
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• v.49 no.1
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• pp.69-74
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• 2016

In order to investigate the effect of NiO on the ethanol gas sensing performance of ${\alpha}-Fe_2O_3$ nanoparticles, NiO and ${\alpha}-Fe_2O_3$ nanoparticles are synthesized by hydrothermal method. The sensor with ${\alpha}-Fe_2O_3$ and NiO nanoparticles mixed at an optimum ratio of 7:3 showed 3.8 times improved sensing performance for 200ppm ethanol gas at $200^{\circ}C$. The enhanced gas sensing performance can be considered to be caused by pn heterojunction at the grain boundaries of ${\alpha}-Fe_2O_3$ and NiO nanopartcles.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.28-33
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• 2006

La substituted perovskite $BiFeO_3$ have been prepared by a sol-gel method. Magnetic and structural properties of the powders were characterized with Mossbauer spectroscopy, XRD, SEM, and TG-DTA. The crystal structure is found to be a rhombohedrally distorted perovskite structure with the lattice constant $\alpha=3.985{\AA}\;and\;\alpha=89.5^{\circ}.\;Bi_{2/3}La_{1/3}FeO_3$ powders that were annealed at and above $600^{\circ}C$ have a single-phase perovskite structure. However, powders annealed at $900^{\circ}C$ have a typical perovskite structure with small amount of $Bi_2O_3$ phase. The Neel temperature of $Bi_{2/3}La_{1/3}FeO_3$ is found to be $680\pm3K$. The isomer shift value at room temperature is found to be 0.27 mm/s relative to the Fe metal, which is consistent with high-spin $Fe^{3+}$ charge states. Debye temperature far$Bi_{2/3}La_{1/3}FeO_3$ is found to be $305\pm5K$. The average hyperfine field $H_{hf}(T)$ of the $Bi_{2/3}La_{1/3}FeO_3$, shows a temperature dependence of $[H_{hf}(T)-H_{hf}(0)]/H_{hf}(0)=-0.42(T/T_N)^{3/2}-0.13(T/T_N)^{5/2}$ for $T/T_N<0.7$ indicative of spin-wave excitation.

• Journal of the Korean Magnetics Society
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• v.9 no.6
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• pp.296-300
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• 1999

Cross-shape structures of spin tunneling junctions were fabricated using DC magnetron sputtering and metal masks. The film structures were $substrate/Ta/NiFe/FeMn/NiFe/CoFe/Al_2O_3/CoFe/NiFe$ and $substrate/Ta/NiFe/CoFe/ Al_2O_3/CoFe/NiFe/FeMn/NiFe$. Fabrication conditions of insulating layer ($Al_2O_3$) and thickness and sputtering power of each film layer were varied, and maximum magnetoresistance ratio of 24.3 % was obtained. Magnetic characteristic variations in the above mentioned two structures and two types of substrates (Corning glass 7059 and Si(111)) were compared. Annealing of the junctions was performed to find out magnetic characteristic variations expected from the device fabrication. Magneoresistance Ratio were observed to maintain as-deposited value up to 150 $^{\circ}C$ annealing and then to drop rapidly after 180 $^{\circ}C$ annealing.

• Journal of the Mineralogical Society of Korea
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• v.20 no.4
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• pp.367-376
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• 2007

Aenigmatite, $Na_4(Fe^{2+},Ti,Fe^{3+}){_{12}}(Fe^{3+},Si){_{12}}O_{40}$, is a common constituent of sodium-rich alkaline igneous rocks and is classified a an open-branched single-chain silicate. $M\ddot{o}ssbauer$ spectroscopy of three natural aenigmatite specimens were done and the detailed crystal chemistry was obtained. Fitting of $M\ddot{o}ssbauer$ spectra led to the resolution of nine peaks. They consist of three doublets of $Fe^{2+}/oct$ and one merged peak at low velocity matching to two small peaks at high velocity which were assigned to $Fe^{3+}/tet\;and\;Fe^{2+}/oct$, respectively. Using the peak area for $Fe^{2+}\;and\;Fe^{3+}$ peaks, analytical data were recalculated. Precise assignment of $Fe^{2+}\;and\;Fe^{3+}$ ions in tetrahderal and octahedral sites revealed detailed crystal chemistry of aenigmatite. The existence of significant amounts of $Fe^{3+}/tet$ indicates that $Fe^{3+}$ has preference over $Al^{3+}$ for the tetrahedral sites. Crystal chemistry of aenigmatite (AEN1) yields the formula of $(Na_{3.97}Ca_{0.03})(Ca_{0.11}Mn_{0.59}Fe^{2+}{_{8.07}}Ti_{2.07}Mg_{0.70}Fe^{3+}{_{0.43}}Al_{0.04})(Fe^{3+}{_{0.56}}Al_{0.18}Si_{11.26})O_{40}$.

• Resources Recycling
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• v.28 no.3
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• pp.45-52
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• 2019

$TiO_2$ as a raw material for producing titanium can be produced by carbon reduction of natural ilmenite ores over 1823 K and acid leaching of the obtained titanium-rich slag. However, the conventional process can cause very high energy consumption and a large amount of leaching residues. In the present study, we proposed the sulfurization of $FeTiO_3$ with $Na_2SO_4$ at temperatures below 1573 K, which can separate Fe in $FeTiO_3$ as the FeS based sulfide phase and Ti as the $TiO_2-Na_2O$ based oxide phase. This study is a fundamental study for sulfurization of $FeTiO_3$ to investigate the influence of reducing atmosphere, reaction temperature and the sulfur/Fe ratio on the separability and distribution behaviors of of Fe, Ti, and Na between the oxide phase and the sulfurized phase. At 1573 K and carbon saturation condition, the Fe can be separated from $FeTiO_3$ as Fe-C-S metal and a part of FeS, and the concentration of Fe in oxide decreased to 4 mass% after sulfurization.