• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2003.11a
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• pp.51-55
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• 2003

The thermal behavior of NiFe$_2$O$_4$ prepared by a solid-state reaction was investigated for H$_2$ generation by the thermochemical cycle. The reduction of NiFe$_2$O$_4$ started from 800 $^{\circ}C$, and the weight loss was 0.2-0.3 wt％ up to 1000 $^{\circ}C$. At this reaction, NiFe$_2$O$_4$ was reduced by release of oxygen bonded with the Fe$^3$ion in the B site of NiFe$_2$O$_4$. In the $H_2O$ decomposition reaction, H$_2$ was generated by oxidation of reduced NiFe$_2$O$_4$. The crystal structure of NiFe$_2$O$_4$ for redox reaction maintained spinel structure. Then, NiFe$_2$O$_4$ is excellent material in the thermochemical cyclic reaction due to release oxygen at low temperature for the reduction reaction and produce H$_2$ maintaining crystal structure for redox reaction.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.8
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• pp.708-712
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• 2002

The crystallization of amorphous $\alpha$-Fe$_2$O$_3$/$\alpha$-AI$_2$O$_3$(0001) thin films during thermal annealing in air has been studied using real-time synchrotron x-ray scattering. The well aligned (0.02$^{\circ}$/ FWHM) $\alpha$-Fe$_2$O$_3$and Fe$_3$O$_4$interfacial crystallites (50- -thick) coexist on the $\alpha$-AI$_2$O$_3$(0001) in the sputter-grown amorphous films at room temperature. The amorphous precursor is crystallized to the epitaxial $\alpha$-Fe$_2$O$_3$grains in three steps with annealing temperature; i ) the growth of the well aligned $\alpha$-Fe$_2$O$_3$interfacial crystallites, together with the transformation of the Fe$_3$O$_4$crystallites to the $\alpha$-Fe$_2$O$_3$ crystallites, ii ) the growth of the less aligned (3.08$^{\circ}$ FWHM)$\alpha$-Fe$_2$O$_3$grains on the well aligned grains (＞40$0^{\circ}C$), and iii) the nucleation of the other less aligned (1.39$^{\circ}$ FWHM) $\alpha$-Fe$_2$O$_3$grains directly on the $\alpha$-AI$_2$O$_3$substrate (＞$600^{\circ}C$). The effective thickness thinner than 230 may be very useful for enhancing the epitaxial quality of $\alpha$-Fe$_2$O$_3$/AI$_2$O$_3$(0001) thin films.

• Korean Chemical Engineering Research
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• v.45 no.3
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• pp.298-303
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• 2007

Several combinations of ozone based advanced oxidation processes were tested for the treatment of red water (RW) containing recalcitrant chemical pollutants produced from 2,4,6-trinitrotoluene (TNT) manufacturing process. $O_3$, $UV/O_3$, $UV/O_3/H_2O_2$, $UV/O_3/H_2O_2/Fe^{2+}$ processes were tested for the treatment of RW. The order of organic and color removal efficiency was found to be : $O_3{\leq}UV/O_3$ < $UV/O_3/H_2O_2$ < $UV/O_3/H_2O_2/Fe^{2+}$. The optimum conditions for the removal of organic and color in the $UV/O_3/H_2O_2/Fe^{2+}$ process were 0.053 g/min of ozone flow rate, 10 mM of $H_2O_2$ concentration and 0.1 mM of $FeSO_4$ concentration. Organic and color removal efficiencies were 96 and 100 % respectively in the $UV/O_3/H_2O_2/Fe^{2+}$ process. tert-butyl alcohol (t-buOH) was used as the hydroxyl radical scavenger. Enhancement of hydroxyl radical production was achieved by the combination of ozone with several oxidants such as UV, $H_2O_2$, $Fe^{2+}$.

• Korean Chemical Engineering Research
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• v.48 no.2
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• pp.157-163
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• 2010

A new etchant formulation was developed in this study to increase the shadow mask production rate, utilizing the $Fe(ClO_4)_3$ as an additive in the aqueous $FeCl_3$ solution. The shadow mask etch rate increased substantially with the increase of $Fe(ClO_4)_3$ concentration in the etchant. The etch rate difference between Ni and Invar steel was also reduced with the addition of $Fe{(ClO_4)_3}$ for most of the operating conditions, which was caused by the enhanced etch rate of both Ni and Fe by the new etchant. The increase in etch rate with the addition of $Fe(ClO_4)_3$ to aqueous ferric chloride solution was attributed to the superior electron transfer capability of $ClO^{4-}$ ion to that of $Cl^-$ ion.

• Advances in materials Research
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• v.3 no.4
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• pp.233-242
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• 2014

Magnetic and conducting aniline sulfide resin cross-linked (ASC-Fe3O4) nanocomposite has been prepared in the presence of aniline sulfide resin (ASR), aniline, $Fe_3O_4$ coated by polyethylene glycol (PEG) and initiator. The magnetic properties of the resulting composites showed ferromagnetic behavior, such as high-saturated magnetization (Ms= 41 emu/g), and coercive force (Hc=1.5 Oe). The saturated magnetization was increased by increasing of $Fe_3O_4$ content and decreased by increasing aniline ratio. The transmission electron micrograph (TEM) and X-ray diffraction proved that nanometer-sized about 20-30 nm $Fe_3O_4$ in the composite. The average size of ASC-$Fe_3O_4$ nanocomposite with core-shell structure was about 50-60 nm, and polydisperse. This approach may also be extended to the synthesis and modification of other polymers. Electrical conductivity of aniline sulfide resin cross-linked (ASC) nanocomposite has been studied by four-point probe method and produced $3.3{\times}10^{-4}S/cm$ conductivity for it. The conductivity of the composites at room temperature depended on the $Fe_3O_4$, aniline ratio and doping degree. The thermogravimetry analysis (TGA) results showed that this resin is thermal resistance near of $500^{\circ}C$. So, It can be used for resistance thermal coating for military applications. $Fe_3O_4$-PASC nanocomposite has been flexible structure with electrical and magnetic properties.

• Corrosion Science and Technology
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• v.22 no.2
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• pp.90-98
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• 2023

In this study, cobalt oxide (Co₃O₄) and cobalt-doped magnetite (CoFe₂O₄) nanoparticles were synthesized by a hydrothermal method. They were then used as corrosion inhibitors for corrosion protection of AA2024-T3 aluminum alloys. These obtained nanoparticles were characterized by x-ray diffraction, field-emission scanning electron microscopy, and Zeta potential measurements. Corrosion inhibition activities of Co₃O₄ and CoFe₂O₄ nanoparticles were determined by performing electrochemical measurements for bare AA2024-T3 aluminum alloys in 0.05 M NaCl + 0.1 M Na₂SO₄ solution containing Co₃O₄ or CoFe₂O₄ nanoparticles. Corrosion protection for AA2024-T3 aluminum alloys by a water-based epoxy with or without the synthesized Co₃O₄ or CoFe₂O₄ nanoparticles was investigated by electrochemical impedance spectroscopy during immersion in 0.1 M NaCl solution. The corrosion protection of epoxy coating deposited on the AA2024-T3 surface was improved by incorporating Co₃O₄ or CoFe₂O₄ nanoparticles in the coating. The corrosion protection performance of the epoxy coating containing CoFe₂O₄ was higher than that of the epoxy coating containing Co₃O₄.

• Bulletin of the Korean Chemical Society
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• v.9 no.6
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• pp.333-337
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• 1988

Spinel $CoFe_2O_4$ solid solutions containing up to 50 mol% CoO were synthesized with spectroscopically pure CoO and ${\alpha}-Fe_2O_3$ polycrystalline powders. The spinel structures of the $CoFe_2O_4$ solid solutions were analyzed from XRD patterns and the Mossbauer spectra showed that the quenched $CoFe_2O_4$ had a partially inversed spinel structure ($Co_{0.23}Fe_{0.77}$) < $Co_{0.77}Fe_{1.23}$ > $O_4$, while the slowly cooled $CoFe_2O_4$ was completely inversed spinel ($Co_{0.04}Fe_{0.96}$) <$Co_{0.96}Fe_{1.04}$ > $O_4$. The $CoFe_2O_4$ specimens containing 10, 20, 30 and 40 mol% CoO turned to be a mixture of corundum and spinel structures. Electrical conductivities were measured as a function of temperature from 300 to $900^{\circ}C$ under oxygen partial pressures from $10^{-3}$ to 1 atm. The temperature dependencies of the electrical conductivity show different behaviors in the low- and high-temperature regions. The average activation energies are 0.23 eV and 0.80 eV in the low- and high-temperature regions, respectively. It is suggested that $Co^{2+} {\to} CO^{3+} + e^-$ and $Fe^{2+} {\rightleftharpoons} Fe^{3+} + e^-$ are the main conduction mechanisms responsible for the electronic conduction in the low- and high-temperature regions, respectively.

• Resources Recycling
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• v.2 no.2
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• pp.9-15
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• 1993

In this study, magnetite($Fe_3$$O_4$) from the converter dust of the Kwangyang steel making factory has been recove-red by means of the magnetic separation and the sedimentation column. The magnetite recovered from the dust is used for the preparation of Sr-ferrite instead of hematite. The results obtained in this study as follows : 1. The converter EP dust of the Kwangyang steel making factory are composed of $\alpha$-Fe, ($Fe_3$$O_4$) wustite etc. Magnetite in the converter EP dust is recovered by using sedimentation column and plastic bonding magnet. 2. It was confirmed that Sr-ferrite synthesis could be possible without oxidizing roasting of the magnetite. The steps of Sr-ferrite formation are proposed as follows : I$SrCO_3$ $+Fe_3$O$_4$+1/2(1-X)$O_2$longrightarrow$\alpha$ $-Fe _2$$O_3$ $+SrFeO _3$\ulcorner+$CO_2$II. $5.5\alpha$ $-Fe_2$$O_3$ $+SrFeO_3$\ulcornerlongrightarrowSrFe\ulcornerO\ulcorner+1/2(1/2-X)$O_2$3. By using magnetite from the dust insted of hematite, the hard Sr-ferrite magnet of (B.H)\ulcorner=2.64MGOe in the magnetic characteristics was succesfully prepared.

• Particle and aerosol research
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• v.13 no.1
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• pp.33-40
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• 2017

Cobalt-iron oxides have emerged as alternative electrode materials for supercapacitors because they have advantages of low cost, natural abundance, and environmental friendliness. Graphene loaded with cobalt ferrite ($CoFe_2O_4$) nanoparticles can exhibit enhanced specific capacitance. In this study, we present three-dimensional (3D) crumpled graphene (CGR) decorated with $CoFe_2O_4$ nanoparticles. The $CoFe_2O_4$-graphene composites were synthesized from a colloidal mixture of GO, iron (III) chloride hexahydrate ($FeCl_3{\cdot}6H_2O$) and cobalt chloride hexahydrate ($CoCl_2{\cdot}6H_2O$) respectively, via one step aerosol spray pyrolysis. Size of $CoFe_2O_4$ nanoparticles was ranged from 5 nm to 10 nm when loaded onto 500 nm CGR. The electrochemical performance of the $CoFe_2O_4$-graphene composites was examined. The $CoFe_2O_4$-graphene composite electrode showed the specific capacitance of $253F\;g^{-1}$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.1
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• pp.21-27
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• 2018

Synthesis of ferromagnetic composite materials for the $Cu-BaFe_{12}O_{19}$ system by mechanical alloying (MA) has been investigated at room temperature. A mixture of copper and barium ferrite with a weight ratio of $Cu:BaFe_{12}O_{19}=4:1$, 3 : 2, 2 : 3 and 1 : 4 was used. It is found that $Cu-BaFe_{12}O_{19}$ composite powders in which $BaFe_{12}O_{19}$ is dispersed in copper matrix are successfully produced by mechanical alloying of $BaFe_{12}O_{19}$ with Cu for 80 min. in all composition. The change in X-ray diffraction patterns and magnetic properties reflects the details for the formation of ferromagnetic metal matrix composite of pure Cu and $BaFe_{12}O_{19}$ during mechanical alloying. Magnetization of $Cu-BaFe_{12}O_{19}$ composite powders gradually increases with increasing the amounts of barium ferrite, whereas coercive force of MA powders gradually decreases due to the refinement of barium ferrite powders with ball milling. However, it can be seen that the coercivity of $Cu-BaFe_{12}O_{19}$ MA composite powders with a weight ratio of $Cu:BaFe_{12}O_{19}=4:1$ and 3 : 2 ball-milled for 80 min. is still high value of 1400 Oe and 1450 Oe, respectively suggesting that the refinement of barium ferrite powders during ball milling process tend to be suppressed due to the ductile copper.