• Title/Summary/Keyword: $\delta$-FeOOH

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The Thermal Decomposition Process of $\delta$-FeOOH Prepared by Rapid Oxidation Method (급격산화법에 의해 제조된 $\delta$-FeOOH의 열분해과정)

  • 박영도;이훈하;김태옥
    • Journal of the Korean Ceramic Society
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    • v.31 no.12
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    • pp.1501-1506
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    • 1994
  • The precipitate of FeCl2.4H2O and NaOH, Fe(OH)2 was rapidly made to oxidize by H2O2 to prepare $\delta$-FeOOH. The particle size, surface and morphology of $\delta$-FeOOH, and the shape and structure of thermally decomposed $\delta$-FeOOH were investigated by the use of high resolution STEM. $\delta$-FeOOH prepared under the condition of reaction temperature of Fe(OH)2 at 4$0^{\circ}C$, [OH-][Fe2+]=5 and aging time of 2 hr Fe(OH)2, had 630$\AA$ mean particle size, 4~5 aspect ratio, 20.8 emu/g saturation magnetization and 210 Oe coercivity. The edges of $\delta$-FeOOH were inclined to (001) about 41$^{\circ}$, 60$^{\circ}$ and coincident with (102), (101) respectively. When $\delta$-FeOOH was thermally decomposed at 25$0^{\circ}C$ for 2 hr in vacuo, which had micropores of 0.9 nm thickness and crystallites of 2.4 nm thickness. (001)hex, [10]hex. of $\delta$-FeOOH parallel with (001)hex, [100]hex. of $\alpha$-Fe2O3 respectively. This showed three dimensional topotaxial structure transition, which was investigated by SADP (Selected Area Diffraction Pattern) of STEM.

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Preparation of $\delta$-FeOOH by Coprecipitation Method and Its Magnetic Properties (공침법에 의한 $\delta$-FeOOH의 제조 및 자기 특성)

  • 김성재;김태옥
    • Journal of the Korean Ceramic Society
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    • v.33 no.3
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    • pp.327-331
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    • 1996
  • $\delta$-FeOOH was prepared by rapid oxidation method of Fe(OH)2 using H2O2. The effects of reaction temperature and mole ratio ([OH-]/[Fe2+])의 몰비를 제조 변수로 하여 최종 생성된 $\delta$-FeOOH의 입자크기 입자형태, 자기특성을 조사하였다. Fe(OH)2 의 반응온도 및 [OH-]/[Fe2+] 비가 $\delta$-FeOOH의 입자크기 및 형상에 많은 영향을 미침을 알수 있었으며 입자 크기는 이 두인자에 비례하여 증가하였다 Fe(OH)2 의 반응온도가 4$0^{\circ}C$ [OH-]/[Fe2+]=5 Fe(OH)2 숙성 시간 2시간에서 제조된 $\delta$-FeOOH를 TEM, VSM으로 입자의 크기 및 자기특성을 조사한결과 평균 입경이 630$\AA$ 정도이고 입도 분포가 양호하였으며 포화자화 및 보자력은 각각 20.8emu/g 210 Oe였다.

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The Preparation and Magnetic Properties of Single-Crystallite of Ba-Ferrite from Ba-Sol Coated $\delta$-FeOOH (Ba-Sol을 도포한 $\delta$-FeOOH로부터 Ba-Ferrite 단결정 미리자의 제조와 그 자기적 특성)

  • 박영도;이훈하;이재형;오영우;김태옥
    • Journal of the Korean Ceramic Society
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    • v.32 no.12
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    • pp.1383-1391
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    • 1995
  • Hexagonal $\delta$-FeOOH was coated with Ba-Sol, which was produced by hydrolizing Ba(OC2H5)2, Ba-Sol coated $\delta$-FeOOH spread on a stainless plate, dried at 8$0^{\circ}C$ and then heat-treated. In this way, Ba-ferrite fine particles were produced. although there was a difference in a degree of hydrolysis of Ba(OC2H5)2, crystalline phase of Ba-ferrite appeared around 617$^{\circ}C$, and Ba-ferrite single phase was obtained after heat treatment at 80$0^{\circ}C$ for 2 hr. When Ba-ferrite was made from Ba-Sol coated $\delta$-FeOOH, $\delta$-FeOOH was thermally decomposed to $\alpha$-Fe2O3 at $700^{\circ}C$, producing a porous structure which was observed by TEM photographs. But the porous structure was not observed at 80$0^{\circ}C$. Ba-ferrite, heat-treated at 80$0^{\circ}C$ for 2 hr, had mean particle size of 1000$\AA$, lattice parameter of a0=5.889243 $\AA$ and c0=23.214502 $\AA$, a saturation magnetization ($\sigma$8) of 45.3 emu/g and a coercive force (Hc) of 5200Oe.

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Formation Process of Barium Ferrite Crystallites in Molten Salts and its Magnetic properties (용융염내에서의 Ba-ferrite 결정의 생성과정 및 그 자기적 특성)

  • 정지형;김창곤;윤석영;신학기;김태옥
    • Journal of the Korean Ceramic Society
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    • v.38 no.11
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    • pp.1015-1022
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    • 2001
  • In this study, formation process of Ba-ferrite by using molten salt synthesis and its magnetic properties were investigated. Among starting materials, BaC $O_3$was only soluble in the molten salts, but other starting material such as $\delta$-FeOOH or F $e_2$ $O_3$was not soluble even at 105$0^{\circ}C$. It implies that the dissolved $Ba^{2+}$ diffused on surfaces of F $e_2$ $O_3$(or $\delta$-FeOOH), therefore, Ba-ferrtites were formed through surface reaction. However, the magnetic properties of Ba-ferrite prepared by two starting materials (F $e_2$ $O_3$and $\delta$-FeOOH) were not different. On the other hand, compared $\delta$-FeOOH with F $e_2$ $O_3$m, morphologies and dispersibility of Ba-ferrites prepared by using $\delta$-FeOOH were good and Ba-ferrites were obtaioned at lower temperature.

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Synthesis and Particle Size Control of δ-FeOOH Using H2O2 Oxidizing Agent (H2O2 산화제를 이용한 δ-FeOOH의 합성과 입자 크기 제어)

  • Seongmin Shin;Kyunghwan Kim;Jeongsoo Hong
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.37 no.3
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    • pp.292-296
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    • 2024
  • In this study, Iron (III) oxide-hydroxide (δ-FeOOH) was successfully synthesized using hydrogen peroxide (H2O2) as an oxidizing agent. The synthesis of δ-FeOOH was carried out by controlling the amount of H2O2, and pure δ-FeOOH was successfully synthesized in ranges from 0.2 mL to 0.6 mL of H2O2. The size of the synthesized δ-FeOOH particles was compared by controlling the amount of oxidant H2O2. The average particle size of the synthesized pure δ-FeOOH particles increased from 875.1 nm to 897.2 nm as the amount of H2O2 was increased. The optical properties of δ-FeOOH synthesized under these specific conditions were investigated. All δ-FeOOH showed a similar trend of increasing and decreasing light absorption from 800 nm to 400 nm, although there was a slight difference in the amount of light absorption, with the largest amount of light absorption at 410 nm. The band gap energy of δ-FeOOH through the Tauc plot method was about 2.1~2.2 eV when H2O2 was 0.2~1.4mL. With a sufficient small particle size, simple control of that particle size, and a small band gap energy enough to absorb light in the visible spectrum, δ-FeOOH could be useful in a variety of applications, including photoelectrochemistry and battery electrodes.

Atmospheric Corrosion Process for Weathering Steel

  • Nagano, Hiroo;Yamashita, Masato
    • Corrosion Science and Technology
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    • v.7 no.2
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    • pp.119-124
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    • 2008
  • Steel is generally not corrosion resistant to water with formation of non protective rusts on its surface. Rusts are composed of iron oxides such as $Fe_3O_4$, $\alpha-$, $\beta-$, $\gamma-$and ${\delta}-FeOOH$. However, steel, particularly weathering steel containing small amounts of Cu, Ni and Cr etc., shows good corrosion resistance against rural, industrial or marine environment. Its corrosion rate is exceedingly small as compared with that of carbon steel. According to the exposure test results undertaken in outdoor environments, the atmospheric corrosion rate for weathering steel is only 1 mm for a century. Atmospheric corrosion for steels proceeds under alternate dry and wet conditions. Dry condition is encountered on steel surface on fine or cloudy days, and wet condition is on rainy or snowy days. The reason why weathering steel shows superior atmospheric corrosion resistance is due to formation of corrosion protective rusts on its surface under very thin water layer. The protective rusts are usually composed of two layer rusts; the upper layer is ${\gamma}-FeOOH$ termed as lepidocrocite, and inner layer is nano-particle ${\alpha}-FeOOH$ termed as goethite. This paper is aimed at elucidating the atmospheric corrosion mechanism for steel in comparison with corrosion in bulky water environment by use of empirical data.The summary is as follows: 1. No corrosion protective rusts are formed on steel in bulky water. 2. Atmospheric corrosion for steel is the corrosion under wetting and drying conditions. Corrosion and passivation occur alternately on steel surface. Steel, particularly weathering steel with small amounts of alloying elements such as Cu, Ni and Cr etc. enhances forming corrosion protective rusts by passivation.

Comparision between Synthesis Processes of Ba-Ferrite from Coprecipitates $Fe(OH)_2-BaCO_3$ and $Fe(OH)_3-BaCO_3$ ($Fe(OH)_2-BaCO_3$$Fe(OH)_3-BaCO_3$ 의 공심물로부터 Ba-Ferrite 생성과정의 비교)

  • 김태옥
    • Journal of the Korean Ceramic Society
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    • v.19 no.3
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    • pp.223-228
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    • 1982
  • For the preparation of ferroxidure BaO.5.5 $Fe_2O_3$ with high coercive force, the green and calcined coprecipitates, which were obtained by neutralizing the mixed salt solution $FeCl_2-BaCl_2$ and $FeCl_3-BaCl_2$ with alkali solution $NaOH-Na_2CO_3$, were investigated about the thermal reaction, crystal growth, and the magnetic properties of the sintered specimens. The very single-domain crystallites of Ba-ferrite with high coercive force are formed from the coprecipitate of amorphous $Fe(OH)_3$ and amorphous $BaCO_3$ at lower temperature than that of subnucleus crystalline $\delta$-FeOOH and amorphous $BaCO_3$.

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The Decomposition of Carbon-dioxide Using the Oxygen Deficient Magnetite (산소 결함 Magnetite를 이용한 이산화탄소의 분해)

  • 김승호;박영구;이승훈
    • Journal of Environmental Health Sciences
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    • v.21 no.2
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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.

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Formation of Hexagonal Ferrite $Co_2$Z(${Ba_3}{Co_2}{Fe_{24}}{O_{41}}$) Prepared by Coprecipitation-oxidation Method (공침산화법에 의한 육방정 페라이트 $Co_2$Z(${Ba_3}{Co_2}{Fe_{24}}{O_{41}}$)의 생성)

  • 신형섭
    • Journal of the Korean Ceramic Society
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    • v.38 no.11
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    • pp.1023-1029
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    • 2001
  • Hexagonal ferrite $Co_2$Z(B $a_3$ $Co_2$F $e_{24}$ $O_{41}$ ) was prepared by various coprecipitation-oxidation methods. The formation of $Co_2$Z was studied in order to determine the optimal method. The $Co_2$Z composition hydroxides were prepared with the different oxidation and precipitation from the aqueous solution of $Ba^{2+}$, $Co^{2+}$ and F $e^{2+}$ chloride mixture. The coprecipitates were heat-treated at various temperatures, and their formation phases and microstructures were investigated from the analyses of DTA/TGA, powder XRD and SEM. The $Co_2$Z phase was observed in the case where the precursor will have the amorphous like oxyhydoxide($\delta$-FeOOH), and formed from $Ba_3$F $e_{32}$ $O_{51}$ , BaF $e_{12}$ $O_{19}$ (M-type) and $Ba_2$ $Co_2$F $e_{12}$ $O_{22}$ (Y-type). The $Co_2$Z was synthesized by the heat-treatment of the coprecipitate, which was prepared from the precipitation after oxidizing the chloride mixed solution, above 110$0^{\circ}C$.EX>.

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