• 한국자기학회지
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• 제5권5호
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• pp.778-781
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• 1995

The mixed ferrite $Ni_{x}Co_{1-x}Fe_{2}O_{4}$ have been investigated by X-ray and $M\"{o}ssbauer$ spectoscpy. From the results of X-ray diffraction measurement the structure for this system is spinel, and the lattice constant is in accord with Vegard's law. $M\"{o}ssbauer$ spectra of $Ni_{x}Co_{1-x}Fe_{2}O_{4}$ have been taken at various temperature ranging from 13 to 800 K. The isomer shifts indicate that the valence states of the irons at both A(tetrahedral) and B(octahedral) sithe are found to be in ferric high-spin states. The variation of magnetic hyperfine fields at the A and B sites are explained on the basis on A-B and B-B supertransferred hyperfine interactions. It is found that Debye temperatures for the A and B sites of $CoFe_{2}O_{4}$ and $NiFe_{2}O_{4}$ are found to be ${\theta}_{A}=734{\pm}5K,\;{\theta}_{B}=248{\pm}5K,\;and\;{\theta}_{A}=378{\pm}5K,\;{\theta}_{B}=357{\pm}5K$, respectively. Atomic migration of $Ni_{0.3}Co_{0.7}Fe_{2}O_{4}$ starts near 450 K and increases rapidly with increasing temperature to such a degree that 61 % of the ferric ions at the A site have moved over to the B site by 700 K.

• 한국세라믹학회지
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• 제35권4호
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• pp.378-384
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• 1998

We investigated the possibility of systemizing data for the colour gradation of classical ceramics by build-ing program and D-basing each data information in pottery field that has been fall behind in forming data be-cause of many variable and lacking of data system. In this study we manufactured $CoAl_2O_4$ stain that has stable spinel structure at high temperature and then mixed base glaze with stain for the additive per-centage of 0.5 , 1, 5, 10, 15 wt% In thie colouring of Lime base glaze with the wide ranged melting tem-perature the colour development of cobalt-blue sintered at $1250^{\circ}C$ is better than that of $1150^{\circ}C$ $1350^{\circ}C$ The experimental conditions and data are D-based simulated programming of computer. The result of -based data appeared to be more smoothed fusion-adherence in the Matt glaze range of Lime base glaze, The variation of colouring is not found when additive content of glaze is more than 5 wt% and the stable colour development of stain was shown at the content that RO, $R_2O$ percentage is high (the content that R2O3 per-centage is low)

• 한국자기학회지
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• 제4권2호
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• pp.114-121
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• 1994

$Ba_{2}Co_{2-x}Zn_{x}Fe_{12}O_{22}(x\;=\;0.0~2.0,\;Co_{2-x}Zn_{x}Y)$ 분말을 공침법으로 합성하고 $1150~1250^{\circ}C$에서 4시간 동안 소결을 하였다. 소결체의 미세구조와 자기적 특성(포화자화, Curie 온도)과 복소투자율을 측정하였다. $Co_{2-x}Zn_{x}Y$의 조성식에서 x=0에서 x=2.0까지 x의 증가에 따라 복소투자율의 실수항은 증가하였고, 공명주파수는 7 GHz에서 1 GHz 감소하였다. Y-형 육방정 페라이트는 수 GHz대역에서 공명이 일어나므로 스피넬 페라이트보다 더 높은 주파수에서 사용가능하고, 회전공명보다 높은 주파수에서 관찰된 2차공명 기구에 대한 더 많은 연구가 필요하다.

• 한국세라믹학회지
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• 제37권2호
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• pp.164-167
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• 2000

Flue gases in the iron foundry consist of 15~20% CO2 as an air pollution gas whose emission should be mitigated in order to protect the environment. In the present study, ultrafine powders of NixZn1-xFe2O4 as a potential catalyst for the CO2 decomposition were prepared by the coprecipitation methods. Oxygen deficient ferrites (MeFe2O4-$\delta$) can decompose CO2 as C and O2 at a low temperature of about 30$0^{\circ}C$. The XRD result of synthesized ferrites showed the spinel structure of ferrites and ICP-AES and EDS quantitative analyses showed the composition similar with initial molar ratios of the mixed solution prior to reaction. The BET surface area of the (Ni, Zn)-ferrites was about 77~89.5$m^2$/g and their particle size was observed about 10~20 nm. The CO2 decomposition efficiency of the oxygen deficient (Nix, Zn1-x)-ferrites was the highest at x=0.3, and the ternary (Ni, Zn)-ferrites was better than that of binary Ni-ferrites.

• 한국재료학회지
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• 제25권11호
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• pp.598-601
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• 2015

Using reverse micelle processing, $ZnAl_2O_4$ nanopowders were synthesized from a mixed precursor(consisting of $Zn(NO_3)_2$ and $Al(NO_3)_3$). The $ZnAl_2O_4$ was prepared by mixing the aqueous solution at a molar ratio of Zn : Al = 1 : 2. The average size and distribution of the synthesized powders with heat treatment at $600^{\circ}C$ for 2 h were in the range of 10-20 nm and narrow, respectively. The average size of the synthesized powders increased with increasing water to surfactant molar ratio. The XRD diffraction patterns show that the phase of $ZnAl_2O_4$ was spinel(JCPDS No. 05-0669). The synthesized and calcined powders were characterized using a thermogravimetric - differential scanning calorimeter(TG-DSC), X-ray diffraction analysis (XRD), and high resolution transmission electron microscopy(HRTEM). The effects of the synthesis parameter, such as the molar ratio of water to surfactant, are discussed.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.294-294
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• 2007

Spinel cathode material $LiMn_2O_4$ is currently studied as a promising cathode material for lithium ion secondary batteries for future applications because of it is low cost, easy to be prepared and capable to be operated in high voltage range. However as a cathode material, $LiMn_2O_4$ performs a poor capacity retention which leads to short cycle life. In this study, stoichiometric $LiMn_2O_4$ was synthesized with granulation method with ion substitution to stabilize its structure and niobium doping to improve its conductivity. These well-mixed powders were calcined at $850^{\circ}C$ for 6 hours and its properties were investigated. Correlations of dopant and electrochemical properties were examined as well.

• 한국재료학회지
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• 제16권12호
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• pp.719-724
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• 2006

Ultrafine mullite powder was prepared from aluminium-secbutoxide and tetraethyl orthosilicate(TEOS) in the molar $Al_2O_3/SiO_2$=3/2. Sol-gel method by partial hydrolysis technique, as it were, first, TEOS was partially hydrolysized and then mixed with Al-secbutoxide for complete hydrolysis was used. X-ray diffraction, infrared spectroscopy and transmission electron microscopy, etc. confirmed that the mullite powder prepared by this method is in the stoichiometric $Al_2O_3/SiO_2$ ratio. Al-Si spinel was formed at $980^{\circ}C$ and ultrafine mullite powder with about 20 nm particle size was obtained above $1,200^{\circ}C$. Also mullite powders calcined at $1,600^{\circ}C$ had a stoichiometric composition, $3Al_2O_3{\cdot}2SiO_2$ and the lattice constants of the mullite powders calcined above $1,200^{\circ}C$ were almost coincided with theoretical values.

• Metals and materials international
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• 제24권6호
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• pp.1285-1292
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• 2018

Microstructural properties of as-grown and annealed CoCrFeMnNi high entropy alloy (HEA) oxynitride thin films were investigated. The CoCrFeMnNi HEA oxynitride thin film was grown by magnetron sputtering method using an air gas, and annealed under the argon plus air flow for 5 h at $800^{\circ}C$. The as-grown film was homogeneous and uniform composed of nanometer-sized crystalline regions mixed with amorphous-like phase. The crystalline phase in the as-grown film was face centered cubic structure with the lattice constant of 0.4242 nm. Significant microstructural changes were observed after the annealing process. First, it was fully recrystallized and grain growth happened. Second, Ni-rich region was observed in nanometer-scale range. Third, phase change happened and it was determined to be $Fe_3O_4$ spinel structure with the lattice constant of 0.8326 nm. Hardness and Young's modulus of the as-grown film were 4.1 and 150.5 GPa, while those were 9.4 and 156.4 GPa for the annealed film, respectively.

• 대한금속재료학회지
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• 제47권2호
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• pp.99-106
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• 2009

The high temperature corrosion properties of heat resistant steels were investigated in oxidation atmosphere including sulfur dioxide. The heat resistant steels of T22, T92, T122, T347HFG and T304H were evaluated at 620, $670^{\circ}C$ for 400 hours. The corrosion rates showed a decreasing tendency while chrome contents of those steels increased from 2 mass.% to 19 mass.%. The in crease in temperature increasement has an more effect on the corrosion rates of low chrome steels than high chrome steels. The weight gains of T22, T92, T304H at $670^{\circ}C$ were 3.7, 1.65, 1.23 times compared with those at $620^{\circ}C$. The external scale formed on T22 was composed of hematite, magnetite and Fe-Cr spinel and internal layer including iron oxide mixed with sulfide. The scales formed on T92, T122, T304H consisted of an outer layer of hematite and inner layer of chrome oxide and hematite. The proportion of chrome oxide at inner layer was increased when the chrome contents in heat resistant steels were increased.

• 청정기술
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• 제21권3호
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• pp.184-190
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• 2015

대부분의 LNT 촉매는 낮은 온도 영역에서의 NO_x 산화를 위하여 Pt와 같은 귀금속류를 사용하는 것은 경제적인 부담을 가지고 있다. 따라서, 본 연구는 이러한 문제를 해결하기 위하여 시도되었다. 즉, Pt, Pd, Rh 등과 같은 귀금속류(platinum group metal, PGM)를 사용하지 않는 LNT (lean NO_x trap)용 DeNO_x 촉매를 개발하기 위해 시도하였다. 이를 위해서 예비실험을 통해 Pt등 귀금속류등의 PGM (platinum group metal)을 사용하지 않는 Al/Co/Ni 혼합 금속 산화물을 선정하였다. 궁극적으로는, 선정된 촉매의 소성온도에 따른 물리화학적 특성 변화가 NO_x 전환율에 미치는 영향을 살펴보고자 하였다. 이들의 물리화학적인 성질을 평가하기 위해 XRD, EDS, SEM, BET 분석을 실시하였다. 이러한 평가를 실시한 결과, 모든 소성온도에서 혼합금속 산화물은 Co₂AlO₄ 및 NiAl₂O₄의 스피넬 구조가 혼재되어 있는 것으로 나타났고, NO_x 기체들의 산화-환원 반응이 이루어지기에는 충분한 기공부피와 기공크기를 갖고 있음을 알 수 있었다. 그러나 NH₃-TPD 분석 결과에서는 소성온도가 700 ℃ 이하를 유지해야 하는 것으로 판단되었다. 더욱이 ramp test를 통해서는 NO 및 NO_x 전환율을 동시에 만족할 수 있는 시료는 소성온도는 500 ℃에서 처리된 경우임을 알 수 있었다. 이러한 결과 등을 바탕으로, Al/Co/Ni=1.0/2.5/0.3 혼합 금속 산화물의 최적 소성온도는 500 ℃임을 알 수 있었다.