• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권3호
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• pp.179-184
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• 1999

In the past ten years, $LiMn_2O_4$-based spinels have been extensively studied as positive electrode materials for lithium-ion batteries. To improve the cycle performance of spinel $LiMn_2O_4$ as the cathode of 4V class lithium secondary batteries, spinel phases $LiMn_2O_4$ were prepared at various temperatures ranging form 600-900$^{\cire}C$ in air. The results showed that charge.dischare capacity of $LiMn_2O_4$ varied at 1st temperature from $200^{\circ}C to 600^{\circ}C$ increase with increasing temperature. $LiMn_2O_4$ synthesized at 2nd temperature $750^{\circ}C$excellent charge.discharge capacity, efficiency and cyclability compared to the samplesynthesized different temperatures. The value of lst charge.discharge capacity was 121mAh/g, 118mAh/g, Also, the efficiency value was about 97%.

• 한국자기학회지
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• 제5권1호
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• pp.21-26
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• 1995

비화학양론 조성의 니켈-아연 페라이트 소결체 시편에서 투자율과 유전율을 체계적으로 변화 시킴에 따라 전파흡수특성에 미치는 영향을 조사하였다. ${(Ni_{0.5}Zn_{0.5}O)}_{1-x}(Fe_{2}O_{3})_{1+x}$ 시편은 일반적인 세라믹 제조공정에 의해 제조 하였다. 본 연구에서는 니켈-아연 페 라이트에서 ${\alpha}-Fe_{2}O_{3}$ 함량을 변화시킴에 따라 복수투자율과 복소유전율의 조절 방안 을 조사하였다. 철과잉량의 효과는 유전상수 증가였으며 철결핍량의 효과는 ${\mu}_{r}"$ 감소이었다. 니켈-아연 페라이트에서 ${\alpha}-Fe_{2}O_{3}$ 함량 변화에 따라 정합주파수와 정합두께 조절이 가능함을 제시하였다.

• Corrosion Science and Technology
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• 제11권4호
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• pp.141-150
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• 2012

Stress corrosion cracks in Alloy 600 compact tension specimens tested at $325^{\circ}C$ in a simulated primary water environment of pressurized water reactor were analyzed by analytical transmission electron microscopy and secondary ion mass spectroscopy (SIMS). From a fine-probe chemical analysis, oxygen was found on the grain boundary just ahead of the crack tip, and chromium oxides were precipitated on the crack tip and the grain boundary attacked by the oxygen diffusion, leaving a Cr/Fe depletion (or Ni enrichment) zone. The oxide layer inside the crack was revealed to consist of a double (inner and outer) layer. Chromium oxides existed in the inner layer, with NiO and (Ni,Cr) spinels in the outer layer. From the nano-SIMS analysis, oxygen was detected at the locations of intergranular chromium carbides ahead of the crack tip, which means that oxygen diffused into the grain boundary and oxidized the surfaces of the chromium carbides. The intergranular chromium carbide blunted the crack tip, thereby suppressing the crack propagation.

• 한국세라믹학회지
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• 제55권1호
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• pp.21-35
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• 2018

Spinel $LiNi_{0.5}Mn_{1.5}O_4$ has received great attention as one of the most outstanding cathode materials for Li-ion batteries (LIBs) because of its high energy density resulting from the operating voltage of ~ 4.7 V (vs. $Li^+/Li$) based on the $Ni^{2+}/Ni^{4+}$ redox reaction. However, $LiNi_{0.5}Mn_{1.5}O_4$ is known to suffer from undesirable side reactions with the electrolyte at high voltage as well as Mn dissolution from the structure. These issues prevent the realization of the optimal electrochemical performance of $LiNi_{0.5}Mn_{1.5}O_4$. Extensive research has been conducted to overcome these issues. This review presents an overview of the various surface-modification methods available to improve the electrochemical properties of $LiNi_{0.5}Mn_{1.5}O_4$ and provides perspectives on further research aimed at the application of $LiNi_{0.5}Mn_{1.5}O_4$ as a cathode material in commercialized LIBs.

• Journal of Magnetics
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• 제15권4호
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• pp.165-168
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• 2010

$Li_{0.1}Zn_{0.9}O$ and $MgFe_2O_4$ powders were synthesized using chemical methods and mixed in different proportions to prepare a mixture of $Li_{0.1}Zn_{0.9}O$ and $MgFe_2O_4$ that was thermally treated between 900 to $1100^{\circ}C$ for 1 hour. Structural characterization was done using X-ray powder diffraction measurements. Grain sizes and morphologies of $Li_{0.1}Zn_{0.9}O$, $MgFe_2O_4$, and $Li_{0.1}Zn_{0.9}O+MgFe_2O_4$ samples were observed using a scanning electron microscope. Variation of magnetic properties of the $Li_{0.1}Zn_{0.9}O+MgFe_2O_4$ samples due to the addition of $Li_{0.1}Zn_{0.9}O$ was studied in relation to the structural changes occurring due to the thermal treatment. In particular, changes in the cationic distribution between the tetrahedral and octahedral positions were studied with respect to the increase of the annealing temperature. Magnetization was found to be dependent on the cations distributed in the tetrahedral and octahedral sites of the $MgFe_2O_4$.

• 보존과학회지
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• 제38권1호
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• pp.1-13
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• 2022

Colour consistency is an important consideration when selecting pigments used on works of art. In this study, we analyse the colour difference between two sets of synthetic blue glass pigments acquired at least 8 years apart from the same manufacturer in Japan. The old pigment set (unused, dry powder with four different grain sizes) appears faded compared to the new set. These pigments are made available for artistic use, commonly in Nihonga or Japanese paintings. Raman spectroscopy and SEM-EDS results characterize these pigments as cobalt aluminate spinels dissolved in leaded glaze, a special class of complex coloured inorganic pigments that is not well-understood in the field of conservation. Colour difference between the old and new pigments with four different grain sizes were quantified by analysing photomicrographs with image analysis software. Blue pigments with coarse and extremely fine grains showed significant colour change compared to pigments with medium and fine grain sizes. The high occurrence of crystallites in the finer grains give a final colour that is bluer and lighter. Possible causes for the colour difference including manufacturing methods and storage environment are discussed.

• 한국결정성장학회지
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• 제8권3호
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• pp.498-502
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• 1998

순수 스피넬$(MgAl_2O_4)$에 대하여 $1400^{\circ}C$에서 $1700^{\circ}C$까지에 내화온도 범위에서 입자크기(G), 밀도($\rho$), 활성에너지(Q)를 구하고 다른 실험값과 비교 분석하였다. 스피넬에 대한 입자크기와 상대밀도는 매우 유사한 경향을 나타내었다. 이들은 두 개의 뚜렷한 영역을 나타내었는데 상대밀도가 약 85~90%까지의 중간소결단계와 전이-밀도 수준 이상의 마지막 단계, 소결영역으로 나타난다. 입자크기(G)와 밀도($\rho$)의 관계에서 활성화에너지 값은 670-48kJ/mol이었으며 다른 스피넬에서는 넓은 온도 범위에서 약 590kJ/mol이었다. 이 값은 기존의 360~580kJ/mol의 값은 근접하였다.

• 한국수소및신에너지학회논문집
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• 제20권2호
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• pp.116-124
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• 2009

We investigated the influences of cobalt coating deposited by DC electroplating on the ferritic stainless steel, STS 430, as a protective layer on a metallic interconnect for SOFC applications. Cobalt coated STS 430 revealed a uniform and denser-packing oxide surface and a reduced growth rate of $Cr_2O_3$ scales after oxidation at $800^{\circ}C$in air. Cobalt coating layer was oxidized to $CoCo_2O_4$ and Co containing mixed oxide spinels such as $Co_2CrO_4$, $CoCr_2O_4$, and $CoCrFeO_4$. The area specific resistance value of Co coated sample was $0.020\;{\Omega}cm^2$ lower than that of uncoated at $800^{\circ}C$ in air during 500 h. After 1000 h oxidation, cobalt oxide coating layer suppressed chromium outward diffusion.

• 한국세라믹학회지
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• 제14권3호
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• pp.187-192
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• 1977

For the purpose researching to the influence of tetrahedral and octahedral preference of cations of $Ni^{2+}$, $Ti^{4+}$ upon the formation and the color development of the $ZnO-SnO_2$ spinel containing $Ni^{2+}$ and $Ti^{4+}$ ions, the gradual substitution of $Ni^{2+}$ ions for $Zn^{2+}$ ions and of $Ti^{4+}$ ions for $Sn^{4+}$ ions of the spinel in NiO-ZnO-$SnO_2$-$TiO_2$ system was carried out. On samples prepared by calcining the oxide and basic cabonate mixtures at $1300^{\circ}C$ for 2 hours, the X-ray analysis, measurement of reflectance and the test of their stabilaity as a glaze pigment were also carried out. The results are summarized as follows 1) Single spinel was formed completely to x=1 in the $xNiO\cdot(2-x)ZnO\cdot{SnO}_2$system, and gave brilliant lightgreen hue. Moreover, $NiO\cdot{ZnO}\cdot{SnO}_2$ formed easily spinel than $NiO\cdot{MgO}\cdot{SnO}_2$ because Zn^{2+}$ ions had more strong tetrahedral preference than $Mg^{2+}$ ions. 2) As the gradual substitution of $Ti^{4+}$ ions for $Sn^{4+}$ ions in $NiO\cdot{MgO}\cdot{SnO}_2$ system, the spinels formed well and was nearly not changed in the hue. 3) The results of glaze test. (1) As the gradual substitution of $Ni^{2+}$ ions for $Zn^{2+}$ ions, the color changed from dull white to graish broun gradually in calcium-zinc glaze and calcium glaze, and from white to beige in tile glaze. (2) As the gradual substitution of $Ti^{4+}$ ions for $Sn^{4+}$ ions in $NiO-ZnO-SnO_2-TiO_2$ system, the color was become dull generally and was not change in tile glaze.

• 한국재료학회지
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• 제25권2호
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• pp.95-99
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• 2015

$NiAl_2O_4$ nanoparticle was synthesized by a reverse micelle processing for inorganic pigment. $Ni(NO_3)_2{\cdot}6H_2O$ and $Al(NO_3)_3{\cdot}9H_2O$ were used for the precursor in order to synthesize $NiAl_2O_4$ nanoparticles. The aqueous solution, which consisted of a mixing molar ratio of Ni/Al, was 1:2 and heat treated at $800{\sim}1100^{\circ}C$ for 2h. The average size and distribution of synthesized $NiAl_2O_4$ powders are in the range of 10-20 nm and narrow, respectively. The average size of the synthesized $NiAl_2O_4$ powders increased with an increasing water-to-surfactant molar ratio and heating temperature. The crystallinity of synthesized $NiAl_2O_4$ powder increased with an increasing heating temperature. The synthesized $NiAl_2O_4$ powders were characterized by X-ray diffraction analysis(XRD), a field emission scanning electron microscopy(FE-SEM), and a color spectrophotometer. The properties of synthesized powders were affected as a function such as a molar ratio and heating temperature. Results indicate that synthesis using a reverse miclle processing is a favorable process to obtain $NiAl_2O_4$ spinels at low temperatures. The procedure performed suggests that this new synthesis route for producing these oxides has the advantage of being fast and simple. Colorimetric coordinates indicate that the pigments obtained exhibit blue colors.