• 한국분말재료학회지
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• 제8권2호
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• pp.104-109
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• 2001

The semiconducting ${\beta}-FeSi_2$ compound has been recognized as a thermoelectric material with excel-lent oxidation resistance and stable characteristics at elevated temperature. In the present work, we applied mechanical alloying(MA) technique to produce ${\beta}-FeSi_2$ compound using a mixture of elemental iron and silicon powders. The mechanical alloying was carried out using a Fritsch P-5 planetary mill under Ar gas atmosphere. The MA powders were characterized by the X-ray diffraction with Cu-K $\alpha$ radiation, thermal analysis and scanning electron microscopy. The single ${\beta}-FeSi_2$ phase has been obtained by mechanical alloying of $Fe_{33}Si_{67}$ mixture powders for 120 hrs or for 70 hrs coupled with the subsequent heat treatment up to $700^{\circ}C$. The grain size of ${\beta}-FeSi_2$ powders analyzed by Hall plot method was 44nm.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 추계학술대회 논문집 학회본부
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• pp.83-86
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• 1989

Electrical conductivity, I - V and DLTS have been measured on polycrystalline samples of $\alpha-Fe_{2}O_{3}$ containing small deviation from stoichiometry and small amounts of added titanium. DLTS (Deep Level Transient Spectroscopy) in the current transient mode has been applied to the measurement of the trap density at the grain boundary. Titanium enters the $\alpha-Fe_{2}O_{3}$ lattice substitutionally as $Ti^{4+}$, thus producing an $Fe^{2+}$ and maintaining the average charge per cation at three. The $Fe^{2+}$acts as a donor center with respect to the surrounding $Fe^{3+}$ions.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 C
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• pp.1500-1502
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• 2001

Plate-type ${\beta}-FeSi_2$ single crystals were grown using $FeSi_2$, Fe, and Si as starting materials by the chemical transport reaction method. The ${\beta}-FeSi_2$ single crystal was an orthorhombic structure. The direct optical energy gap was found to be 0.87eV at 300K. Hall effect shows a n-type conductivity in the ${\beta}-FeSi_2$ single crystal. The electrical resistivity values was 1.608$\Omega$cm and electron mobility was $3{\times}10^{-1}cm^2/V{\cdot}sec$ at room temperature.

• 한국표면공학회지
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• 제49권1호
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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.

• Bulletin of the Korean Chemical Society
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• 제10권1호
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• pp.27-30
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• 1989

Lithium has been intercalated into $FeMoO_4Cl$, and deintercalated from $LixFeMoO_4Cl$ both electrochemically and chemically. The inserted $Li^+$ ions are stabilized in the distorted octahedral field in interlayer space of $FeMoO_4Cl$. The crystal symmetry is reduced from tetragonal to monoclinic due to the reduction of ferric to ferrous ions in $LixFeMoO_4Cl$ upon lithium intercalation. From the magnetic and structural data, it has been concluded that the high-spin electronic configuration of $Fe^{2+}(d_{xz}^2{d_{y2}^1}{d_1}{2d_z^12}{\cdot}_y2)$, corresponding to $^5E_g$, group term in $D_{4h}$ symmetry, can be stabilized by the elongation of $FeO_4Cl_{2-}$octahedra in a weak ligand field.

• 반도체디스플레이기술학회지
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• 제7권2호
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• pp.45-48
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• 2008

An epitaxial $\beta-FeSi_2$ structure on Si (001) substrate was calculated by using density functional theory (DFT). Unit cell of orthorhombic $\beta-FeSi_2$ and $\sqrt{2}\times\sqrt{2}\times2$ supercell were calculated to find the energetically favorable structures first. The $\chi$- and y-direction axes of $\beta-FeSi_2$ were changed into y- and z-direction axes to match its structure with that of Si, to minimize the lattice mismatch between $\beta-FeSi_2$ and Si. Distance between the Si (001) surface and the $\beta-FeSi_2$ surface was varied to find an optimum distance between them, resulting in 0.825 $\AA$.

• 한국재료학회지
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• 제30권2호
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• pp.74-80
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• 2020

Synthesis of composite powders for the Fe₂O₃-Zn system by mechanical alloying (MA) has been investigated at room temperature. Optimal milling and heat treatment conditions to obtain soft magnetic composite with fine microstructure were investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that α-Fe/ZnO composite powders in which ZnO is dispersed in α-Fe matrix can be obtained by MA of Fe₂O₃ with Zn for 4 hours. The change in magnetization and coercivity also reflects the details of the solid-state reduction process of hematite by pure metal of Zn during MA. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine at 900 ~ 1,000 ℃ under 60 MPa. Shrinkage change after SPS of sample MA'ed for 5 hrs was significant above 300 ℃ and gradually increased with increasing temperature up to 800 ℃. X-ray diffraction results show that the average grain size of α-Fe in the α-Fe/ZnO composite sintered at 900 ℃ is in the range of 110 nm.

• 공업화학
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• 제16권2호
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• pp.206-211
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• 2005

백금과 티탄늄-이리듐전극으로 0.5 M의 철(II)과 코발트(II) 이온을 함유한 8.0 M의 질산용액 중에서 분자량이 1000, 4000, 20000인 폴리에틸렌글리콜류의 매개전해산화를 하였다. Fe(III)/Fe(II)와 Co(III)/Co(II) 산화환원계를 이용하여 전류밀도, 전극종, 전해질농도, 제거효율 등을 검토하였다. 백금전극 상에서 $0.67A/cm^2$의 전류밀도로 180~210 min 간 Fe(III)/Fe(II)와 Co(III)/Co(II) 전해환원계에서 매개전해산화에 의하여 폴리에틸렌글리콜류는 탄산가스로 분해되었다. 매개전해산화시 폴리에틸렌글리콜류의 제거효율은 Fe(III)/Fe(II) 산화환원계보다 Co(III)/Co(II) 산화환원계가 우수하였고 분자량이 1000, 4000, 20000인 폴리에틸렌글리콜류의 매개전해산화 제거효율은 100%이었다.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2000년도 창립총회 및 춘계학술발표회
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• pp.108-111
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• 2000

FeS/FeS$_2$ minerals have been known to be potentially useful reductant to the removal of common organic contaminants in groundwater and soil. This research is aimed at improving our understanding of factors affecting the pathways and rates of reductive transformation of Hexachloroethane by catalytical iron minerals in natural system. Hexachloroethane is reduced by FeS/FeS$_2$ minerals under anaerobic condition to tetrachloroethylene and trichloroethylene with pentachloroethyl radical as the intermediate products. The kinetics of reductive transformations of the Hexachloroethane have been investigated in aqueous solution containing FeS, FeS$_2$. The proposed reduction mechanism for the adsorbed nitrobenzene involves the electron donor-acceptor complex as a precursor to electron transfer. The adsorbed Hexachloroethane undergo a series of electron transfer, proton transfer and dehydration to achieve complete reduction. It can be concluded that the reductive transformation reaction takes place at surface of iron-bearing minerals and is dependent on surface area and pH. Nitrobenzene reduction kinetics is affected by reductant type, surface area, pH, the surface site density, and the surface charge. FeS/FeS$_2$-mediated reductive dechlorination may be an important transformation pathway in natural systems.

• 한국분말재료학회지
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• 제13권2호
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• pp.112-118
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• 2006

[ $R_{1/3}Sr_{2/3}FeO_{3}$ ](R=Pr, Nd, and Sm) was synthesized and their magnetic properties and charge ordering(CO) transition related with lattice dynamics and oxygen vacancy were systematically investigated. The charge disproportion ation(CD) in $R_{1/3}Sr_{2/3}FeO_{3}$(R=Pr,Nd) was in which two kins of iron with valence state $Fe^{3+}$ and $Fe^{5+}$ were found with ratio of 2:1. In this charge ordering state a sequence of $Fe^{3+}Fe^{3+}Fe^{5+}Fe^{3+}Fe^{3+}Fe^{5+}$ exists aligned along the [111] direction of the pseudocubic perovskite structure. The charge ordering exist in distorted structure involving $t_{pd}$ hybridization. The disordering phases coexist in distorted structure as temprature in creases that is controlled amount of oxygen vacancy. The magnetic hyperfine fields indicate charge tranfering temperature as it dissapeared drastically.