• 한국세라믹학회지
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• 제23권5호
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• pp.1-8
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• 1986

This paper is concerned with a gas sensor composed of semi-conducting ${\gamma}$-$Fe_2O_3$ ceramics made by oxidizing $Fe_2O_3$ sintered body. Acicular $\alpha$-FeOOH powder prepared by precipitation of $FeSO_4$.$7H_2O$ solution was transformed to $FeSO_4$ sintered at 700$^{\circ}$-850$^{\circ}$C for 1 hr. and then oxidized to ${\gamma}$-$Fe_2O_3$ The gas sensitive properties of ${\gamma}$-$Fe_2O_3$ ceramic bodies based on the lectrical resistance change was measured in 0.5-2 vol% $H_2$ and $C_2$ $H_2$ gas at 35$0^{\circ}C$ The specific surface area of sintered specimen largely dependent on the sintering temperature and grain shape directly affected the gas sensitive pro-perties of ${\gamma}$-$Fe_2O_3$gas sensor. Specimens having larger specific surface area showed better sensitivity which means the electrical resistance change due to oxidation and reduction process occurs on ly at the surface of grains microscopically in the ${\gamma}$-$Fe_2O_3$ceramics. Micropores made in $Fe_2O_3$ powder during dehydration of $\alpha$-FeOOH can not prompt the gas sensitive properties of sintered ${\gamma}$-$Fe_2O_3$ because they are sintered or closed in the grains during sintering process and dose not affect the specific surface area of sintered body.

• 한국재료학회지
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• 제27권11호
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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.

• 한국재료학회지
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• 제16권11호
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• pp.687-691
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• 2006

Synthesis of Iron oxides by air oxidation of $FeSO_4$ solutions in the presence of NaOH, Diethylenetriamine (DETA), Butylamine (BA) and influence of ultrasonic wave were investigated by XRD, SEM and particle size analyzer. As the DETA addition increased to 0.05 mol, $Fe_3O_4$ was formed with goethite($\alpha$- FeOOH) and $Fe_3O_4$ single phase was formed above 0.18mol of DETA. As the BA addition increased, the XRD peak intensity of (020) face of lepidocrocite($\gamma$-FeOOH) was developed until the formation of $Fe_3O_4$ and reduced the size of the iron oxide particles formed. Ultrasonic wave reduced the size of the iron oxide particles but gave little effects on the iron oxide particles synthesized by amine.

• The Korean Journal of Ceramics
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• 제6권4호
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• pp.401-404
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• 2000

Mimicking the bacterial synthesis of magnetosomes, in which the functionalized surface of a cytoplasmic (lipid) membrane is considered to be stimulating the crystal growth of magnetite, we have successfully grown magnetite films at $30^{\circ}C$ using an arachic acid monomolecular layer as a functionalized surface. The lipid monomolecular layer was spread on an aqueous solution of FeCl$_2$ which was oxidized by flowing a mixed gas, with ratio $O_2$/$N_2$=1/2000, on the surface of the lipid layer. Mossbauer and X-ray diffraction analyses revealed that the Fe$_3$O$_4$ films contain small amounts of ferric hydroxyl impurity phases of ${\alpha}$-FeOOH and ${\tau}$-FeOOH. This is because the oxygen partial pressure at the ferrite/aqueous interface changed as the film (through which the gas penetrated) increased in thickness. Methods to obtain single phase magnetite films are proposed.

• 대한환경공학회지
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• 제27권6호
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• pp.657-662
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• 2005

황화철은 자연 퇴적토와 공극수에서 생물학적 과정이나 무생물학적 과정에 의해서 상당량 생성된다. 본 연구에서는 6가 크롬과 황화철로부터 용해되어 나온 이가 철과 6가 크롬의 반응에 관하여 알아보기 위해 6가 크롬의 초기농도를 다르게 하여 pH 4와 8에서 수용액상과 고체상으로 나누어 실험을 수행하였다. 또한 철산화물인 ${\alpha}-Fe_2O_3$, ${\alpha}-FeOOH$, $Fe_3O_4$와 0가 철을 이용하여 황화철에 의한 6가 크롬의 제거효율을 비교하였다. 6가 크롬의 제거율은 pH 4일 때가 pH 8일 때 높았으며 이는 낮은 pH에서 황화철로부터 용해되어 나온 이가 철의 양의 pH 4에서 더 많기 때문인 것으로 판단된다. 투과전자 현미경(Transmission Electric Microscopy)을 이용한 황화철의 표면 분석을 통하여 고체 표면에 형성된 침전물을 확인하였다. 이는 황화철에 의한 6가 크롬의 환원 작용에 의하여 iron(oxyhyoxide) 침전이 형성된 것으로 판단된다. 황화철은 철 산화물 및 영가 철에 비하여 그 제거능이 월등하며 이는 이가 철과 함께 황화물의 상호작용인 것으로 사료된다.

• 한국지하수토양환경학회지:지하수토양환경
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• 제11권6호
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• pp.35-42
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• 2006

본 연구는 시멘트/Fe(II) 시스템에서 TCE의 환원성 탈염소화에 관여하는 유효반응성분을 규명하기 위하여 수행되었다. 먼저 시멘트 자체에 존재하거나 혹은 그 수화물에 존재하는 성분을 다량 함유하고 있는 hematite(${\alpha}-Fe_2O_3$), lepidocrocite(${\gamma}$-FeOOH), akaganeite(${\beta}$-FeOOH), ettringite($Ca_6Al_2(SO_4)_3(OH)_{12}$)를 대상으로 TCE 분해실험을 수행하여 이러한 물질이 시멘트/Fe(II) 시스템에서 탈염소반응에 관여할 수 있는지 고찰한 결과, hematite가 잠재적 유효반응성분으로 선정되었다. 각 시스템의 반응속도상수를 비교해 본 결과 200 mM Fe(II)에 hematite와 CaO를 1 : 4(몰비)로 주입한 시스템($k\;=\;0.637\;day^{-1}$)이 기존의 cement와 Fe(II)을 이용한 경우($k\;=\;0.645\;day^{-1}$)와 가장 비슷한 동력학적 분해경향을 보인다는 것을 알 수 있었다. 처음에 pH 조절이 주목적으로 주입되었던 CaO 역시 분해반응에서 중요한 역할을 담당하는 것으로 나타났는데, CaO 첨가량이 증가할수록 hematite/CaO/Fe(II) 시스템의 분해능은 증가하다가 CaO 양이 일정 수준에 다다르면 증가세가 둔화되는 경향을 보여 주었다. SEM(Scanning Electron Microscopy) 분석을 통해서는 hematite/CaO/Fe(II) 시스템 내에서 분해능이 커질수록 육각형 판상의 결정이 새롭게 형성된다는 것을 확인 할 수 있었으며 이 결정은 portlandite, green rust($SO_4$), Friedel's salt 등일 가능성이 높은 것으로 판단되었다. 그리고 동일 시료의 XRD(X-Ray Diffraction) 분석을 통해서는 hematite, magnetite/maghemite, green rust($SO_4$)의 존재를 확인할 수 있었다. SEM 및 XRD 분석에서 공통적으로 나타나는 green rust($SO_4$)가 유효반응성분일 가능성이 높다고 판단되었다.

• 한국환경보건학회지
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• 제21권2호
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• pp.68-74
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• 1995

The optimum conditions was synthesized for the formation of Magnetite ($Fe_3O_4$) by air bubbling with the suspensions obtained by mixing Ferrous sulfate ($FeSO_4\cdot 7H_2O$) and Sodium Hydroxide (NaOH) solution in various values equivalent ratio($R=2NaOH/FeSO_4$) were studied. The changes of the structure were measured with XRD, $EM and BET. Equivalent ratio R: 0.65 was synthesized Goethite ($\alpha$-FeOOH), which becomes Maghemite ($\gamma=Fe_2O_3$) by dehydration, reduction and oxidation process. At the equivalent ratio over 1 (R>1), Magnetite ($Fe_3O_4$) was synthesized directly. The oxygen-deficient Magnetite ($Fe_3O_{4-\delta}$), which is obtained by flowing $H_2$ gas(100 ml/min) through the synthesis Magnetite at 350$\circ$C for 4 hr. By using it, was researched the decomposition reaction of $CO_2$. $CO_2$ was decomposed nearly 100% in 45 minutes by the oxygen-deficient Magnetite.

• 한국지하수토양환경학회지:지하수토양환경
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• 제19권1호
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• pp.54-62
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• 2014

To better understand dissimilatory iron and sulfate reduction (DIR and DSR) by subsurface microorganisms, we investigated the effects of sulfate and electron donors on the microbial goethite (${\alpha}$-FeOOH) reduction. Batch systems were created 1) with acetate or glucose (donor), 2) with goethite and sulfate (acceptor), and 3) with aquifer sediment (microbial source). With 0.2 mM sulfate, goethite reduction coupled with acetate oxidation was limited. However, with 10 mM sulfate, 8 mM goethite reduction occurred with complete sulfate reduction and x-ray absorption fine-structure analysis indicated the formation of iron sulfide. This suggests that goethite reduction was due to the sulfide species produced by DSR bacteria rather than direct microbial reaction by DIR bacteria. Both acetate and glucose promoted goethite reduction. The rate of goethite reduction was faster with glucose, while the extent of goethite reduction was higher with acetate. Sulfate reduction (10 mM) occurred only with acetate. The results suggest that glucose-fermenting bacteria rapidly stimulated goethite reduction, but acetate-oxidizing DSR bacteria reduced goethite indirectly by producing sulfides. This study suggests that the availability of specific electron donor and sulfate significantly influence microbial community activities as well as goethite transformation, which should be considered for the bioremediation of contaminated environments.

• Journal of Magnetics
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• 제5권2호
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• pp.40-43
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• 2000

Acicular $\alpha-FeOOH\; and\; Ba(OH)_2\cdot8H_2O$ are starting materials in this study. This paper presents the characteristics of the contents of citric acid and heating condition for preparing acicular barium ferrite powder. They control particle shape, crystalline phase, magnetic properties of acicular barium ferrite powder So the effects of the contents of citric acid and heating condition are studied. The experimental condition for starting materials were 800~1000$\circ C$ in firing and 0~40 wt% citric acid, respectively, Ba-ferrite particles fired at the range of 800 $\circ C$to 900 $\circ C$ were maintained as acicular particle shape, but there were mixed particles of acicular and round shape after fired at 950 $\circ C$. Ba-ferrite powder of the single phase was obtained in firing at 900~1000$\circ C$ and with 20 wt.% citric acid. There were unreacted phase of $\alpha-Fe_2O_3 \;and \; BaFe_2O_4$ phases as a second phase in case of sintering at below 850 $\circ C$. Acicular barium ferrite powder of single phase was also produced in firing at 900 $\circ C$ with 20 wt.% citric acid. The saturation magnetization of single phase of acicular $BaFe_12O_19$powder was about 51 emu/g and coercivity was about 4200 Oe.

• 한국재료학회지
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• 제14권5호
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• pp.353-357
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• 2004

The influences of the ozone oxidation, reaction temperature and NaOH equivalent ratio on the iron oxide formation were studied with fixed ferrous sulfate concentration(0.5M $FeSO_4$ㆍ$7H_2$O). Geothite($\alpha$-FeOOH) and/or Magnetite ($Fe_3$$O_4$) were synthesized depending on the reaction conditions. The characteristics of the synthesized powders were evaluated by XRD, SEM and quantitative phase analysis. The synthetic conditions to get Goethite were quite different from the results of Kiyama's and the Goethite was conveniently synthesized at low temperature and at low NaOH equivalent ratio.