• Journal of the Korean Applied Science and Technology
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• v.33 no.1
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• pp.67-74
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• 2016

The Prussian Blue Analogue(PBA) has three dimensional structure and the metal - organic framework material, and it has a variety configurations depending on the type of organic ligands. PBA has been receving an attention in the fields of biosensors, optical, catalytic, and hydrogen storage device. Also, it is an environmental friendly substance with a chemical stability. In addition, PBA is widely used in the filed of adsorption art since we can adjust the size of the fine pores. In this study, we synthesized $Mn_3[Fe(CN)_6]_2$, an organometallic framework chains by using a hydrothermal synthesis method. We used $K_4[Fe(CN)_6]$ and $MnCl_2$ as precursors. We also produced a manganese iron oxide, by baking the synthesized material. The effect of the size and shape of the particles was examined by controling pH of the precursor solution, the molar concentration of the precursor, and reaction time as the experimental variables. Synthesized absorbent was analyzed by XRD, SEM, FT-IR, UV-Vis, and TG / DTA to evaluate the adsorption properties of several dyes.

• Applied Chemistry for Engineering
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• v.22 no.2
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• pp.185-189
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• 2011

In this work, nano-sized M-ferrites (M=Co, Ni, Cu, Zn) for the decomposition of carbon dioxide were synthesized by the chemical co-precipitation. From the thermogravimetric analysis, it was clear that the maximum weight loss of each sample took place below $350^{\circ}C$. High temperature calcination resulted in more systematic crystallines, smaller specific surface area and larger particle size. An analysis by FTIR in the range of $375{\sim}406cm^{-1}$ revealed the presence of chelates at the octahedral site, which implies the formation of spinel structure in the ferrites. The current work showed that a $500^{\circ}C$ is the optimum heat treatment temperature of metal ferrites for $CO_2$ decomposition reaction.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.533-536
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• 2003

YIG(Yttrium Iron Garnet) is one of the most widely used ferrites for microwave telecommunication. It used as a passive devices such as isolators and circulators. In order to reduce the insertion losses of these passive devices, it is very important to reduce magnetic loss of the ferrites. In general, the magnetic losses of ferrites is closely related to the microstructure of the ceramics. In the sintering of YIG, pores are easily trapped in grains and grain boundaries. These pores cause to increase magnetic losses of the sinterted bodies. In this paper, the effect of the $SiO_2$ addition on the microstructure was discussed. Increasing the $SiO_2$ addition, the grain size was reduced, which means that added acts as a grain-growth inhibitor. During the sintering, $SiO_2$ settled down on the grain boundaries, and drag the grain growth. Therefore, there is enough time for pores to move out. The relative density of YIG sintered at $1350^{\circ}C$ with 1 mol% $SiO_2$ addition was 99.6%. $\Delta$H of these samples was under 50 Oe.

• Journal of the Korean Ceramic Society
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• v.39 no.8
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• pp.789-794
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• 2002

In this study, nano-sized Si-C-N precursor powders were synthesized by Chemical Vapor Condensation Method(CVC) using TMS(Tetramethylsilane: $Si(CH_3)_4$), $NH_3$ and $H_2$ gases under the various reaction conditions of the reaction temperature, TMS/$NH_3$ ratio and TMS/$H_2$ ratio. XRD and FESEM were used to analysis the crystalline phase and the average particle size of the synthesized powders. It was found that the obtained powders under the considering conditions were all spherical amorphous powder with the particle size of 87∼130 nm. The particle size was decreased as the reaction temperature increased and TMS/$NH_3$ and TMS/$H_2$ ratio decreased. As the results of EA analysis, it was found that the synthesized powders had been formed the powders composed of Si, N, C and H. Through FT-IR results, it was found that the synthesized powders were Si-C-N precursor powders with Si-C, Si-N and C-N bonds.

• Journal of the Korean Magnetics Society
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• v.22 no.1
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• pp.19-22
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• 2012

$Ba_2Mg_{0.5}Co_{1.5}(Fe_{0.99}In_{0.01})_{12}O_{22}$ was prepared by the conventional solid-state reaction method, and studied by x-ray diffractometer, vibrating sample magnetometer, and Mossbauer spectrometer. The crystal structure was determined to be a single-phased rhombohedral with space group R-3m. Magnetization value were $M_s$ = 28.6 emu/g at 295 K. The hysteresis loops indicate that all the samples are ferrimagnetic behaviors. Mossbauer spectra of $Ba_2Mg_{0.5}Co_{1.5}(Fe_{0.99}In_{0.01})_{12}O_{22}$ have been 6-sextet taken at various temperatures ranging from 4.2 to 620 K. Based on the isomer shift (${\delta}$) values of all samples, the charge states were found to be $Fe^{3+}$ state at all temperatures, the Curie temperature was determined to be 630 K by the ZVC curve.

• Journal of the Korean Chemical Society
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• v.33 no.5
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• pp.445-451
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• 1989

A series of solid solutions with formula $Er_{1-x}Sr_xFeO_{3-y}, where x is from 0.0 to 1.0, has been synthesized by heating at $1200^{\circ}C$ for 24 hours. X-ray diffraction shows these samples to be orthorhombically distorted perovskites for compositions up to x = 0. 6 and apparantly simple cubic perovskite structures from $0.8{\leq}x{\leq}1.0$. Lattice volumes are increased with the introduction of Sr. The mixed valence state of two kinds of Fe ion in these ferrite systems is analyzed by the Mohr salt titration method. Mossbauer spectra measured at room temperature for x = 0.0 and 0.5 compositions shows hyperfine splitting for iron (III) due to magnetic ordering and indicates that these samples contain octahedrally and tetrahedrally coordinated iron sites. Electrical conductivity measurements indicate that conduction in these samples apparantly occurs over the octahedral sites by a hopping mechanism.

• Journal of the Korean institute of surface engineering
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• v.34 no.2
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• pp.89-96
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• 2001

N- or O-doped STS304 stainless films were synthesized by an unbalanced magnetron sputtering process with various argon and reactive gas ($N_2$, $O_2$) mixtures. These films were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), Auger electron spectroscopy (AES) and Knoop microhardness tester. The Results from X-ray diffraction (XRD) analysis showed that a STS304 stainless steel film synthesized without reactive gas using a bulk STS304 stainless steel target had a ferrite bcc structure ($\alpha$ phase), while the N-doped STS304 stainless film was consisted of a nitrogen supersaturated fcc structure, which hsa a strong ${\gamma}$(200) phase. In the O-doped films, oxide Phases ($Fe_2$$O_3$ and $Cr_2$$O_3$) were observed from the films synthesized under an excess $O_2$ flow rate of 9sccm. AES analysis showed that nitrogen content in N-doped films increased as the nitrogen flow rate increased. Approximately 43 at.%N in the N-doped film was measured using a nitrogen flow rate of 8sccm. In O-doped film, approximately 15 at.%O was detected using a $O_2$ flow rate of 12sccm. the Knoop microhardness value of N-doped film using a nitrogen flow rate of 8 sccm was measured to be approximately $H_{ k}$ 1200 and this high value could be attributed to the fine grain size and increased residual stress in the N-doped film.

• Applied Chemistry for Engineering
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• v.8 no.6
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• pp.954-959
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• 1997

The solid solutions of the $Sr_{1-X}M_XFeO_{3-y}$ (x=0.1, 0.2, 0.3, 0.4, 0.5, M=Ca) system having perovskite structures were prepared in air by heat treatment at 1473 K for 18hr. X-ray diffraction assigns cubic system for all the samples and shows that the lattice volume of each system decreases with increasing x value until x=0.3, but increases abruptly from x=0.4. The mole fractions of $Fe^{4+}$ ion($\tau$ value), the amounts of oxygen vacancy (y value) and finally nonstoichiometric chemical formulas for each composition were determined from Mohr salt analysis. TG/DTA thermal analysis (temperature range: 300~1173K) exhibits that 3-y values of the samples having x=0.1 and 0.2, decrease with temperature and increase almost reversibly with decreasing temperature. The samples of $x{\geq}0.3$, however, didn't show the reversible weight change and the 3-y values of them were nearly 2.5 in cooling process. Conductivities of each sample were varied within the semiconductivity range at relatively low temperature. And the conductivity at constant temperature decreases steadily with x value. The conduction mechanism of this ferrite system may be proposed as a hopping model of conducting electrons between the mixed valence states. At high temperature semiconductivity of each sample changed into metallic property.

• Journal of Aerospace System Engineering
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• v.17 no.1
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• pp.42-50
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• 2023

In this study, hexagonal ferrite powder with chemical formula SrZn_2-xCo_xFe₁₆O₂₇ was synthesized by a solid-state reaction method and its electromagnetic (EM) wave absorption characteristics were evaluated in the frequency range of 0.1-18 GHz with absorber thickness range of 0 - 10 mm. Reflection loss (RL) affecting electromagnetic wave absorption performance was calculated based on the transmission line theory using measured complex permeabilities and permittivities. RL spectra were also directly measured for some samples. They were well matched with calculated results. High-frequency complex permeability characteristics were changed gradually according to the amount of Co substitution (x). The EM wave absorption frequency band could be tuned accordingly. Hexaferrite samples with x = 1.0, 1.25, and 1.5 exhibited remarkable maximum electromagnetic wave absorption performances with minimum RL (RL_min) lowered than -50 dB. They also showed a very broad frequency band (Δf > 10 GHz) in which more than 90% of the EM wave energy absorption occurred (RL ≤ -10 dB).