• Journal of Sensor Science and Technology
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• v.30 no.4
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• pp.191-195
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• 2021

Pure ZnFe₂O₄ and Fe₂O₃-ZnFe₂O₄ hetero-composite spheres were prepared by ultrasonic spray pyrolysis of a solution containing Zn- and Fe-nitrates. Additionally, the sensing characteristics of these spheres in the presence of 5 ppm ethanol, benzene, p-xylene, toluene, and CO (within the temperature range of 275-350 ℃) were investigated. The Fe₂O₃-ZnFe₂O₄ hetero-composite sensor with a cation ratio of [Zn]:[Fe]=1:3 exhibited a high response (resistance ratio = 140.2) and selectivity (response to p-xylene/response to ethanol = 3.4) to 5 ppm p-xylene at 300 ℃, whereas the pure ZnFe₂O₄ sensor showed a comparatively lower gas response and selectivity. The reasons for the superior response and selectivity to p-xylene in Fe₂O₃-ZnFe₂O₄ hetero-composite sensor were discussed in relation to the electronic sensitization due to charge transfer at Fe₂O₃-ZnFe₂O₄ interface and Fe₂O₃-induced catalytic promotion of gas sensing reaction. The sensor can be used to monitor harmful volatile organic compounds and indoor air pollutants.

• Journal of Magnetics
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• v.7 no.1
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• pp.18-20
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• 2002

The charge structures of (LSMO) and of the combined system $(La_{ 0.6}Sr_{0.4}FeO_3$(LSMO) and of the combined system (La_{0.6}Sr_{0.4}MnO_3)_{0.7}(La_{0.6}Sr_{0.4}/FeO_3)_{0.3}$are investigated by using M$\ddot{o}$ssbauer spectroscopy. The antiferromagnetically ordered $(La_{0.6}Sr_{0.4}FeO_3$(LSFO) has possible charges of Fe^{3+} and Fe^{4+}$, which include a low-spin $Fe^{4+}$ state at and above 230 K. The temperature dependences of the M$\ddot{o}$ssbauer spectra for the $(La_{ 0.6}Sr_{0.4}FeO_3$ system and for the combined $(LSMO)_{ 0.7}(LSFO)_{0.3}$ system are fitted as three sets of Zeeman patterns corresponding to $Fe^{3+}$ and $Fe^{4+} below 230 K. At and above 230 K, the fitted M$\ddot{o}$ssbauer spectra for the combined system are the same in all temperature ranges. Above 230 K, $(La_{0.6}Sr_{0.4}FeO_3$ spectrum consists of two sets of six Lorentzians for $Fe^{3+}$ and one line for low spin $Fe^{4+}$. It is worth noting that large fields are induced in the combined system.

• Journal of the Korean Institute of Gas
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• v.2 no.2
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• pp.40-47
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• 1998

This study describes a synthesis of spinel-type $Fe_3O_4$ for decomposition of carbon dioxide, using $Fe_3O_4$ $7H_2O$ and NaOH, at $40^{\circ}C$ for 20 h. with change of their chemical equivalent ratio from 0.50 to 0.75, 1.00, 1.25 and 1.50, respectively. Addition of 0.1-1.00 mole percentage $NiCl_2,\;RhCl_3$ to the particles of $Fe_3O_4$, Prepared by reacting chemical equivalent ratio 1.00, afforced spinel $Fe_3O_4$. The structure of $Fe_3O_4$ and $NiCl_2,\;RhCl_3$-added $Fe_3O_4$ was investigated with XRD and SEM, respectively.

• Applied Chemistry for Engineering
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• v.18 no.5
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• pp.495-500
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• 2007

The inside wall of a coal gasifier is lined with refractory, and the corrosion of the refractory is an important factor affecting the refractory lifetime and the replacement period. This paper examines the changes in microstructure of a chromia refractory due to chemical reactions with slag having varying amounts of $Fe_2O_3$. Slag samples were prepared by adding $Fe_2O_3$ to KIDECO slag, and static corrosion experiments were carried out at $1550^{\circ}C$. The layer of $(Fe,Cr)_3O_4$ formation and the depth of Fe depletion in the infiltrating slag were determined. In addition, FactSage equilibrium calculations were carried out in order to determine the conditions of formation, and to compare with the experimental observations. In the sample exposed to KIDECO slag, which has about 10 wt% $Fe_2O_3$, the formation of $(Fe,Cr)_3O_4$ was not observed. As the $Fe_2O_3$ concentration in slag increased, $(Fe,Cr)_3O_4$ formation and Fe depletion depth increased. Increasing $Fe_2O_3$ concentration also made the slag/refractory interface indistinguishable. Equilibrium calculations predicted that higher $Fe_2O_3$ concentrations favor chromite formation at gasification temperatures. The chromite formation was most favorable when the amount of $Cr_2O_3$ was limited, as in the case of dissolved $Cr_2O_3$ in slag. When the concentration of $Fe_2O_3$ in slag was less than 20%, the formation of chromite was least favorable in the system with equal amounts of slag and refractory.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.18-22
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• 2006

Effects of V substitution of Fe on the magnetic properties of $Fe_3O_4$ have been investigated by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), conversion electron Mossbauer spectroscopy (CEMS), and vibrating sample magnetometry (VSM) measurements on sol-gel-grown films. XRD data indicates that the $V_xFe_{3-x}O_4$ films maintain cubic structure up to x=1.0 with little change of the lattice constant. Analyses on V 2p and Fe 2p levels of the XPS data indicate that V exist as $V^{3+}$ mostly in the $V_xFe_{3-x}O_4$ films with the density of $V^{2+}$ ions increasing with increasing V content. Analyses on the CEMS data indicate that $V^{3+}$ ions substitute tetrahedral $Fe^{3+}$ sites mostly, while $V^{2+}$ ions octahedral $Fe^{2+}$ sites. Results of room-temperature VSM measurements on the films reveal that the saturation magnetization for the x=0.14 sample is larger than that of $Fe_3O_4$, while it becomes smaller than that of $Fe_3O_4$ for $x{\geq}0.5$. The coercivity of the $V_xFe_{3-x}O_4$ films is found to increase with x, attributed to the increase of anisotropy by the substitution of $V^{2+}(d^3)$ ions into the octahedral sites.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.2
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• pp.185-190
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• 1999

An $Al_2O_3/Fe$ composite was synthesized through the double stage processes by a reaction sintering which requires simple process and equipments but provides near-net-shape, a reduction/oxidation process for 5 hrs at $650^{\circ}C$ was followed by sintering at $1200^{\circ}C$ to form an $Al_2O_3/Fe$ composite. The composite processed through the double stage sintering are mainly consists of $\alpha$-Fe and ${\alpha}Al_2O_3$ with minor amount of $FeAl_2O_4$, a spinnel structure which is known to prevent Fe from filling up the pores and good contact with $Al_2O_3/Fe$ particles.

• Journal of the Korean Chemical Society
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• v.56 no.4
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• pp.478-483
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• 2012

We successfully synthesized $Fe_3O_4/SiO_2$ nanoparticles with ultrathin silica layer of $1.0{\pm}0.5$ nm that was fine controlled by changing concentration of $Fe_3O_4$. Among various reaction conditions for silica coating, increasing concentration of $Fe_3O_4$ was more effective approach to decrease silica thickness compared to water-to-surfactant ratio control. Moreover, we found that concentration of the 1-octanol is also important factor to produce the homogeneous $Fe_3O_4/SiO_2$ nanoparticles. The present approach could be available to apply on preparation of other core/shell nanoparticles with ultrathin silica layer.

• Journal of the Korean Chemical Society
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• v.25 no.5
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• pp.318-324
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• 1981

The effects of$ Fe_2O_3$ aggregation on the sintering of Ba-ferrite (BaFe$_{12}O_{19}$) were studied. $BaCO_3-Fe_2O_3$ mixtures were prepared by partial precipitation mixing and ball-mill mixing method using two different $Fe_2O_3 $powders. Techniques employed were TG, XRD and SEM. X-ray diffraction analysis showed that the over all reaction basically consists of the two consecutive reaction; $BaCO_3 + 6Fe_2O_3\;{\longrightarrow}\;BaFe_2O_3 + 5Fe_2O_3 + CO_2{\uparrow}\;BaFe_2O_4 + 5Fe_2O_3 \;{\longrightarrow}\;BaFe_{12}O_{19}$ It is also shown that the aggregation state of $Fe_2O_3$ raw materials, as well as the mixing method, has a remarkable effect on solid state reaction between $BaCO_3\;and\;Fe_2O_3$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.1
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• pp.64-67
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• 2013

$Fe_3O_4$(magnetite) having half metallic property attracts great attention material with high curie temperature in spintronics. $Fe_3O_4$ thin films and nanowires were grown onto c-$Al_2O_3$(0001) at various substrate temperatures. $Fe_3O_4$ films deposited from 300 to $600^{\circ}C$ are influenced by thermal stress induced from mismatch of thermal expansion coefficient between $Fe_3O_4$ and $Al_2O_3$ (0001) substrate. The $Fe_3O_4$ nanowires grown at $640^{\circ}C$ showed a diameter of 130 nm and a length of $2-10{\mu}m$. The nanowire arrays fabricated by pulsed laser deposition technique have high coercivity($H_c$) of 608 Oe and Squareness($M_r/M_s$) of 0.68 in perpendicular direction.

• Journal of Powder Materials
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• v.24 no.4
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• pp.308-314
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• 2017

$Fe_3O_4$/Fe/graphene nanocomposite powder is synthesized by electrical wire explosion of Fe wire and dispersed graphene in deionized water at room temperature. The structural and electrochemical characteristics of the powder are characterized by the field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, field-emission transmission electron microscopy, cyclic voltammetry, and galvanometric discharge-charge method. For comparison, $Fe_3O_4$/Fe nanocomposites are fabricated under the same conditions. The $Fe_3O_4$/Fe nanocomposite particles, around 15-30 nm in size, are highly encapsulated in a graphene matrix. The $Fe_3O_4$/Fe/graphene nanocomposite powder exhibits a high initial charge specific capacity of 878 mA/g and a high capacity retention of 91% (798 mA/g) after 50 cycles. The good electrochemical performance of the $Fe_3O_4$/Fe/graphene nanocomposite powder is clearly established by comparison of the results with those obtained for $Fe_3O_4$/Fe nanocomposite powder and is attributed to alleviation of volume change, good distribution of electrode active materials, and improved electrical conductivity upon the addition of graphene.