• Title/Summary/Keyword: ${\beta}-Fe_2O_3$

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Structural properties of β-Fe2O3 nanorods under compression and torsion: Molecular dynamics simulations

  • Kilic, Mehmet Emin;Alaei, Sholeh
    • Current Applied Physics
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    • v.18 no.11
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    • pp.1352-1358
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    • 2018
  • In recent years, one-dimensional (1D) magnetic nanostructures, such as magnetic nanorods and chains of magnetic nanoparticles have received great attentions due to the breadth of applications. Especially, magnetic nanorods has been opened an area of active research and applications in medicine, sensors, optofluidics, magnetic swimming, and microrheology since they possess the unique magnetic and geometric features. This study focuses on the molecular dynamics (MD) simulations of an infinitely long crystal ${\beta}-Fe_2O_3$ nanorod. To elucidate the structural properties and dynamics behavior of ${\beta}-Fe_2O_3$ nanorods, MD simulation is a powerful technique. The structural properties such as equation of state and radial distribution function of bulk ${\beta}-Fe_2O_3$ are performed by lattice dynamics (LD) simulations. In this work, we consider three main mechanisms affecting on deformation characteristics of a ${\beta}-Fe_2O_3$ nanorod: 1) temperature, 2) the rate of mechanical compression, and 3) the rate of mechanical torsion.

Effects of Heat Treatment Conditions of FeC2O4·2H2O on the Formation of Fe3O4-δ (FeC2O4·2H2O의 열처리 조건이 Fe3O4-δ 형성에 미치는 영향)

  • Oh, Kyoung-Hwan;Park, Won-Shik;Rhee, Sang-In;Suhr, Dong-Soo
    • Korean Journal of Materials Research
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    • v.22 no.11
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    • pp.620-625
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    • 2012
  • A general synthetic method to make $Fe_3O_{4-{\delta}}$ (activated magnetite) is the reduction of $Fe_3O_4$ by $H_2$ atmosphere. However, this process has an explosion risk. Therefore, we studied the process of synthesis of $Fe_3O_{4-{\delta}}$ depending on heat-treatment conditions using $FeC_2O_4{\cdot}2H_2O$ in Ar atmosphere. The thermal decomposition characteristics of $FeC_2O_4{\cdot}2H_2O$ and the ${\delta}$-value of $Fe_3O_{4-{\delta}}$ were analyzed with TG/DTA in Ar atmosphere. ${\beta}-FeC_2O_4{\cdot}2H_2O$ was synthesized by precipitation method using $FeSO_4{\cdot}7H_2O$ and $(NH_4)_2C_2O_4{\cdot}H_2O$. The concentration of the solution was 0.1 M and the equivalent ratio was 1.0. ${\beta}-FeC_2O_4{\cdot}2H_2O$ was decomposed to $H_2O$ and $FeC_2O$4 from $150^{\circ}C$ to $200^{\circ}C$. $FeC_2O4$ was decomposed to CO, $CO_2$, and $Fe_3O_4$ from $200^{\circ}C$ to $250^{\circ}C$. Single phase $Fe_3O_4$ was formed by the decomposition of ${\beta}-FeC_2O_4{\cdot}2H_2O$ in Ar atmosphere. However, $Fe_3C$, Fe and $Fe_4N$ were formed as minor phases when ${\beta}-FeC_2O_4{\cdot}2H_2O$ was decomposed in $N_2$ atmosphere. Then, $Fe_3O_4$ was reduced to $Fe_3O_{4-{\delta}}$ by decomposion of CO. The reduction of $Fe_3O_4$ to $Fe_3O_{4-{\delta}}$ progressed from $320^{\circ}C$ to $400^{\circ}C$; the reaction was exothermic. The degree of exothermal reaction was varied with heat treatment temperature, heating rate, Ar flow rate, and holding time. The ${\delta}$-value of $Fe_3O_{4-{\delta}}$ was greatly influenced by the heat treatment temperature and the heating rate. However, Ar flow rate and holding time had a minor effect on ${\delta}$-value.

Color Evolution and Phase Transformation of α-FeOOH@SiO2 and β-FeOOH@SiO2 pigments (SiO2가 코팅된 α-FeOOH와 β-FeOOH의 상전이를 통한 SiO2가 코팅된 α-Fe2O3의 색상 연구)

  • Yu, Ri;Choi, Kyoon;Pee, Jae-Hwan;Kim, YooJin
    • Journal of Powder Materials
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    • v.20 no.3
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    • pp.210-214
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    • 2013
  • This manuscript reports on compared color evolution about phase transformation of ${\alpha}-FeOOH@SiO_2$ and ${\beta}-FeOOH@SiO_2$ pigments. Prepared ${\alpha}$-FeOOH and ${\beta}$-FeOOH were coated with silica for enhancing thermal properties and coloration of both samples. To study phase and color of ${\alpha}$-FeOOH and ${\beta}$-FeOOH, we prepared nano sized iron oxide hydroxide pigments which were coated with $SiO_2$ using tetraethylorthosilicate and cetyltrimethyl-ammonium bromide as a surface modifier. The silica-coated both samples were calcined at high temperatures (300, 700 and $1000^{\circ}C$) and characterized by scanning electron microscopy, CIE $L^*a^*b^*$ color parameter measurements, transmission electron microscopy and UV-vis spectroscopy. The yellow ${\alpha}$-FeOOH and ${\beta}$-FeOOH was transformed to ${\alpha}-Fe_2O_3$ with red, brown at 300, $700^{\circ}C$, respectively.

Fabrication of Sintered Thermistor Body of Fe-Al-Si-O System by Solid Reaction Method (고상반응법에 의한 Fe-Al-Si-Ti-O계 써어미스터 소결체 합성)

  • Gam, Kee-Sool;Gang, Gi-Hun
    • Korean Journal of Materials Research
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    • v.1 no.4
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    • pp.198-205
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    • 1991
  • Sintered thermistor body was fabricated by solid reaction method using $Fe_2O_3, \;Al_2O_3, \;TiO_2$ and Si powder. Surface matrix of sintered body was investigated by SEM and $\beta$-constant was obtained from measurement of resistance variation in liquid bath. The values of thermistor constant $\beta$ of samples in the temperature range $-50~+50^{\circ}C$ were distributed from 927 to 4005k. This thermistor body can be used as temperature sensor for radiosonde.

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Oxidation Behavior of $Ni_xFe_{1-x}(OH)_2$ in $C\Gamma$-containing Solutions

  • Chung, Kyeong Woo;Kim, Kwang Bum
    • Corrosion Science and Technology
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    • v.2 no.3
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    • pp.148-154
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    • 2003
  • The addition of Ni leads to the formation of protective rust layer on steel and subsequently high corrosion resistance of steel in $Cl^-$-containing environment. $\alpha$-FeOOH, $\beta$-FeOOH, $\gamma$-FeOOH and $Fe_3O_4$ are formed mainly on steels exposed to $Cl^-$-containing environment. As the first work of this kind, this study reports the influence of Ni on the oxidation behavior of $Ni_xFe_{1-x}(OH)_2$ in $Cl^-$-containing solution at two different pH regions(condition I under which the solution pH is allowed to decrease and condition I under which solution pH is maintained at 8) where $\gamma$-FeOOH and $Fe_3O_4$ are predominantly formed, respectively, upon oxidation of $Fe(OH)_2$, In the presence of Ni(II) in the starting solution, the formation of $\beta$-FeOOH was facilitated and the formation of $\gamma$-FeOOH was suppressed with increasing Ni(II) content and with increasing oxidation rate of Fe(II). Ni(II) was found to have $Fe_3O_4$-suppressing effect under condition II.

Preparation and Magnetic Properties of Amorphous Spinel Ferrite (비정질 Spinel Ferrite의 제조와 그 자기적 특성)

  • 김태옥;김창곤
    • Journal of the Korean Magnetics Society
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    • v.2 no.1
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    • pp.29-36
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    • 1992
  • The fundamental research about the amorphous ferrite, which is expected as the important material for electronic and information imdustry in future, was carried out in this work. Because the ferromagnetic amorphous ferrites reported recently are very inferior in magnetic properties than the crystalline ferrites, the development of the more ferromagnetic amorphous ferrites is required. In order to obtain the fundamental data for the preparation of amorphous ferrites, the hand-made twin-roller quenching apparatus was used for rapid quenching. Investigation on amorphous ferrite in the system $CaO-Bi_{2}O_{3}-Fe_{2}O_{3}$ has been carried out in the composition of 10-50 mole% CaO, 10-50 mole% $Bi_{2}O_{3}$, 40-70 mole% $Fe_{2}O_{3}$. Large magnetization values were obtained near the composition of the mixture of $BiFeO_{3}$ and $CaFe_{4}O_{7}$. Especially, an amorphous ${(CaO)}_{20}{(Bi_{2}O_{3})_{15}{(Fe_{2}O_{3})}_{65}$ specimen has a magmetization value of about 21.84 emu/g at 0K(10 kOe). Fe $M\"{o}ssbauer$ absorption spectrum indicates that this specimen is compsed of two amorphous phases, antiferromagnetic phase($\alpha$-phase) and ferromagnetic phase($\beta$-phase). Crystallization of this amorphous ferrite was happened in steps-$550^{\circ}C$ and $775^{\circ}C$, then observed crystal phases were perovskite phase of $BiFeO_{3}$ and $Fe_{2}O_{3}$ phase.

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Effects of Harmaline and Harmalol on the Oxidative Injuries of Hyaluronic Acid, Lipid and Collagen by $Fe^{2+}$ and $H_2O_2$ ($Fe^{2+}$$H_2O_2$에 의한 Hyaluronic Acid, Lipid와 Collagen의 산화성 손상에 나타내는 Harmaline과 Harmalol의 영향)

  • Cho, In-Sung;Shin, Yong-Kyoo;Lee, Chung-Soo
    • The Korean Journal of Pharmacology
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    • v.31 no.3
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    • pp.345-353
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    • 1995
  • ${\beta}-Carboline$ alkaloids including harmaline have been shown to inhibit enzymatically or nonenzymatically induced-lipid peroxidation of microsomes. This study was done to explore the antioxidant ability of harmaline and harmalol on the oxidative injuries of hyaluronic acid, lipid and collagen by $Fe^{2+}$ and $H_2O_2$. Their scavenging actions on reactive oxygen species were also examined. Harmaline, harmalol, superoxide dismutase, catalase and DMSO inhibited both degradation of hyaluronic acid by $Fe^{2+}$ and $H_2O_2$ and lipid peroxidation of microsomes by $Fe^{2+}$. In these reactions, DABCO inhibited degradation of hyaluronic acid but did not affect lipid peroxidation. ${\beta}-Carbolines$ inhibited degradation of cartilage collagen by $Fe^{2+}$, $H_2O_2$ and ascorbic acid. The reduction of ferricytochrome c due to autoxidation of $Fe^{2+}$, which is inhibited by superoxide dismutase, was not affected by harmaline and harmalol. They also did not have a decomposing action on $H_2O_2$. Hydroxyl radical production in the presence of $Fe^{2+}$ and $H_2O_2$ was inhibited by harmaline, harmalol and DMSO. Harmaline and harmalol may inhibit the oxidative injuries of hyaluronic acid, lipid and cartilage collagen by $Fe^{2+}$ and $H_2O_2$ through their scavenging actions on reactive oxygen species, OH and probably iron-oxygen complexes and exert antioxidant abilities.

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Oxidation Resistance of SPS (Spark Plasma Sintering) Sintered β-FeSi2Bodies at High Temperature (방전플라즈마 소결법으로 제작한 β-FeSi2 소결체의 고온 내산화성)

  • Chang, Se-Hun;Hong, Ji-Min;Oh, Ik-Hyun
    • Korean Journal of Materials Research
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    • v.17 no.3
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    • pp.132-136
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    • 2007
  • Oxidation resistance of sintered ${\beta}-FeSi_{2}$ was investigated at intermediate temperature range in air atmosphere. Fully dense and porous bodies of ${\beta}-FeSi_{2}$ samples were fabricated by using the Spark Plasma Sintering (SPS). They were annealed at $900^{\circ}C$ for 5days to obtain ${\beta}-FeSi_{2}$ phase. The bulk samples were oxidized at $800,\;900\;and\;950^{\circ}C$ in air atmosphere. The high temperature oxidation tests reveal that amorphous $SiO_{2}$ layer, similar to Si was formed and grew parabolically on ${\beta}-FeSi_{2}$. Accelerated oxidation is not observed as well as cracks and grain boundary oxidation. Granular ${\varepsilon}-FeSi$ was developed below the oxide layer as a result of oxidation of ${\beta}-FeSi_{2}$. Oxidation resistance of sintered ${\beta}-FeSi_{2}$ was excellent for high-temperature thermoelectric application.

Characteristics of the sintered body of the Al2TiO5 with addition of LAS (β-spodumene) and Fe2O3 (LAS (β-spodumene)와 Fe2O3 첨가에 따른 Al2TiO5의 소결체 특성 연구)

  • Kim, Sang-Hun;Kang, Eun-Tae;Kim, Ung-Soo;Hwang, Kwang-Taek;Cho, Woo-Seok
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.22 no.1
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    • pp.57-63
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    • 2012
  • $Al_2TiO_5$ ceramics were sintered by a solid-state reaction. LAS (${\beta}$-spodumene) and $Fe_2O_3$ were added to the $Al_2TiO_5$ composition for enhancement of sintering behavior such as mechanical strength and thermal shock resistance. The sintered body was much densified by addition of LAS and $Fe_2O_3$ because LAS formed the liquid-phase and $Fe_2O_3$ suppressed the grain growth. We have systematically investigated the sintering characteristics, microstructures, mechanical properties, and thermal shock resistance according to the change of the amount of additive. When the additive of LAS (20 wt%)-$Fe_2O_3$ was added to $Al_2TiO_5$, it confirmed that superior mechanical properties of the fracture strength of over 120 MPa and the thermal shock resistance of over $1,200^{\circ}C$ were achieved.