• Journal of the Korean Applied Science and Technology
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• v.18 no.3
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• pp.174-179
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• 2001

The spinel $Fe_{3}O_{4}$ powders were synthesized using 0.2 $M-FeSO_4{\cdot}7H_{2}O$ and 0.5 M-NaOH by oxidation in air and the spinel $LiMn_{2}O_{4}$ powders were synthesized at 480 $^{\circ}C$ for 12 h in air by a sol-gel method using manganese acetate and lithium hydroxide as starting materials. The synthesized $LiMn_{2}O_{4}$ powders were mixed at portion of 5, 10, 15 and 20 wt% of $Fe_{3}O_{4}$ powders using a ball-mill. The mixed catalysts were dried at room temperature for 24 hrs. The mixed catalysts were reduced by hydrogen gas at 350 $^{\circ}C$ for 2 h. The carbon dioxide decomposition rates of the mixed catalysts were 90% in all the mixed catalysts but the decomposition rate of carbon dioxide was increased with adding $LiMn_{2}O_{4}$ powders to $Fe_{3}O_{4}$ powders.

• Journal of the Korean Ceramic Society
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• v.35 no.1
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• pp.23-32
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• 1998

Al2O3/Al composites were produced by immersing the sintered silica preform in molten aluminum which contained magnesium as impurity. Three distinct regions existed in the penetration behavior of molten me-tal with changing the reaction temperature. These regions are denoted as low temperature regime(75$0^{\circ}C$-85$0^{\circ}C$) intermediate regime(90$0^{\circ}C$-95$0^{\circ}C$) and high temperature regime(100$0^{\circ}C$$\leq$) In the low temperature regime the penetration speed of molten aluminum increased with increasing reaction temperature whereas it decreased in the intermediate regime due to the phase transition of alumina formed by displacement reac-tion. In the high temperature regime the penetration speed of molten aluminum was the highest at 100$0^{\circ}C$ which was 3.6 mm/hr But above 105$0^{\circ}C$ molten aluminum did not penetrate into the silica preform because of the formation of a dense spinel layer at the preform surface by magnesium in molten Al.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.5
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• pp.182-187
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• 2005

The FT-IR absorption spectrum by the lattice vibrations of ruby and garnet obtained from FT-IR shows quite different characteristics. By the UV-VIS spectroscopy it was found that the ruby has two transmission bands in red and blue region, while garnet has only one transmission band in red region. The color filter to distinguish ruby from garnet was developed and named HWANG JI HO filter. Through the HWANG JI HO filter, ruby was shown in blue color and garnet was shown in dark red color because of the only the blue region transmittance of the filter. Other red stones, such as spinel, tourmaline were shown in dark red color like as garnet. The ruby could be recognized easily from the red stone.

• Transactions of the Korean hydrogen and new energy society
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• v.20 no.6
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• pp.455-463
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• 2009

코발트 보호막 코팅이 적용된 페라이트계 스테인리스 스틸인 STS 430과 STS 444 소재에 대해 고체산화물 연료전지용 금속연결재로서의 고온 산화 특성에 대해 살펴보았다. 코발트 코팅층은 $800^{\circ}C$ 고온 산화 후 코발트 산화물 및 $Co_2CrO_4$, $CoCr_2O_4$, $CoCrFeO_4$ 등과 같은 코발트가 함유된 스피넬 상을 형성하였다. 또한 페라이트계 스테인리스 스틸과 코발트 코팅의 계면에서 크롬과 철이 함유된 치밀한 산화층을 형성하여 금속연결재 표면의 스케일 성장속도를 감소시키고 금속연결재 내에 함유된 크롬의 외부 확산을 효과적으로 억제하였다. 한편 STS 430은 고온 산화 후 표면에 형성된 스케일 하부에 $SiO_2$와 같은 내부 산화물이 형성된 반면 STS 444는 표면 스케일 이외에 다른 내부 산화물은 확인되지 않았으며 고온에서의 면저항 측정 결과, 코발트가 코팅된 STS 444의 전기 전도성이 STS 430 보다 우수한 것으로 나타났다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.10
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• pp.834-839
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• 2000

The structural properties that SEM photograph of ZnO varistors surface studied by fractal mathematics program were investigated to verify the relations of electrical characteristics. The SEM photograph of ZnO varistors surface were changed by binary code and the grain shape of that were analyzed by fractal dimension. The void of ZnO varistors surface was found by fractal program. The relation between grain density and electrical properties depend on fractal dimension. The grain size in ZnO varistors surface was decreased by increasing of Sb$_2$O$_3$ addition. The spinel structure was formed by Sb$_2$O$_3$addition and it was depressed the ZnO grain formation. The grain size of ZnO by Sb$_2$O$_3$addition were from 5 to 10[${\mu}{\textrm}{m}$]. Among of ZnO varistors, fractal dimension of ZnO4 was very high as a 1.764. The density of grain boundary in ZnO2 and ZnO3 varistors surface was 15[%] by formed spinal structure. The breakdown electric field of ZnO2 that fractal dimension has 1.752 was very high to be 8.5[kV/cm]. When the fractal dimensin was high, the grain shape of ZnO varistors was complex and the serial layers of ZnO grain was increased.

• Journal of the Korean Magnetics Society
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• v.17 no.6
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• pp.238-241
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• 2007

Ni-Cu-Zn ferrites were prepared by the co-precipitation. Physical properties and Microwave absorbing properties were investigated in Ni-Cu-Zn ferrite for the aim of microwave absorbers. From the analysis of X-ray diffraction patterns, we can see that all the particles have only a single phase spinel structure. The loss factor was maximum at sintering temperature $1100^{\circ}C$. The initial permeability of sintered ferrite obtained was an average of 50. We found that the $(Ni_{0.7}Cu_{0.2}Zn_{0.1}O)_{1.02}(Fe_2O_3)_{0.98}$ can be used in ferrite rubber composite microwave absorber when sintering temperature at $1100^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.44 no.5 s.300
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• pp.160-165
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• 2007

This research studied the most suitable synthesis condition of mineral pigments of black spinel, which have a stable chromogenic characteristic also ata high temperature of $1400^{\circ}C$ (it is not currently producedin the country) to meet not only functionality of ceramics but also an individual's aesthetic. It was synthesized by the plastic synthetic method on the basis of basic formation of $Fe_2O_3,\;Cr_2O_3$, Quartz, Kaolin, CoO, $MnO_2$, and plasticity was made at $1500^{\circ}C,\;1550^{\circ}C,\;1600^{\circ}C,\;1650^{\circ}C$. We researched the most suitable condition of plasticity and composition which make crystallization of spinel system and chromogenic characteristic close to black in every composition. And for the experiment of application to Zirconia, after adding synthesized pigments to Zirconia and plasticizing them, we analyzed their color and property of matters. The most suitable synthesis conditions of mineral pigments of black spinel system require composition of $Fe_2O_3-32.01%,\;Cr_2O_3-30.47%$, Quartz-9.66%, Kaolin-18.53%, CoO-3.71%, $MnO_2-5.62%$ and condition of plasticity kept for 1 h at $1600^{\circ}C$. When we added pigments synthesized in this way to Zirconia with 5 wt% and plasticized them at $1410^{\circ}C$, the result was that the degree of $strength-32.6kgf/mm^2$, absorptance-0.108%, $luminosity-L^*:37.54,\;color-a^*:1.31,\;b^*:2.61$ and their use suited for artificial jewelry or decoration Zirconia goods.

• Journal of the Korean Ceramic Society
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• v.45 no.4
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• pp.214-219
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• 2008

The zirconia ceramics are widely used because of their excellent mechanical properties. Recently, many researches to make a colored zirconia was achieved to satisfy the individual aesthetic requirements. In this study, the synthesis of black-color spinel-based inorganic pigments which are stable above $1400^{\circ}C$ and the fabrication of black-colored zirconia using the synthesized pigments are investigated. Inorganic pigments which have spinel structure and near black color were synthesized by a solid state reaction method using a $Fe_2O_3,\;Cr_2O_3$, CoO and NiO powder as a starting materials at $1600^{\circ}C$. Most of synthesized pigments were black colored spinel phases and single spinel phase was successfully synthesized at the composition range of $Cr_2O_3:25{\sim}35%,\;Fe_2O_3:45{\sim}55%$, CoO:20% and NiO:$6{\sim}10%$. The black-colored zirconia was fabricated at $1410^{\circ}C$ with the 5 wt% synthesized pigments and their properties were evaluated. The results showed that the strength value was more than 848 MPa, absorption rate was 0.1%, the brightness of color was $L^*:40{\sim}42$, the tone of color is $a^*:0.2{\sim}0.8$ and $b^*:-1.1{\sim}2.4$. As a result, the black-colored zirconia was suitable for a artificial jewelry or decoration zirconia goods.

• Journal of Conservation Science
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• v.6 no.1 s.7
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• pp.3-14
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• 1997

Twelve Punchong sherds collected in Hakbongni, Kongju where the well known iron-painted on white slip were manufactured from late 15C to early 16C were analyzed for their composition and microstructure. The composition of the body was analyzed by X-ray fluorescence and that of glaze by electron probe micro-analyzer. Microstructure was observed by optical microscope, polarizing microscope, EPMA, and X-ray diffractometer. The results of composition of body and glaze of Hakbongni were compared with those of Punchong from Yongsuri, Boryong which was close to Hakbongni. The composition of body and glaze of these two areas were compared by principal component analysis using SPSS program. Hakbongni bodies have higher silica and flux materials but lower alumina and their glaze have higher silica, soda, iron oxide but lower alumina, calcia. Hakbongni punchong itself is divided into two groups. Their glaze is lime type. There are many remnant minerals, such as quartz, large feldspar mass with partially melted surrounding area, albite, biotite, and iron-oxide. From such a microstructure we can assume that preparation of raw material was rather crude and firing temperature quite low. Iron-painted material is identified as Mg/Fe/Al spinel by composition analysis and XRD pattern.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.294-295
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• 2005

다중 코어를 이용한 대전류 변압기용 Mn-Zn ferrite를 제조하고 전자기적 특성을 분석하였으며, 제조된 자심재료를 이용하여 변압기를 제조하고 전원장치에 탑재하여 효율특성을 분석하였다. ZnO의 몰비가 증가할수록 혼합 스피넬의 형성을 통한 보아 자자의 증가로 인해 투자율은 증가하고 상대적으로 전력손실이 감소하여 $Fe_2O_3$ : MnO : ZnO = 53 : 36 : 11 mo\% 일 때 가장 우수한 특성을 나타냈고, 열처리 공정의 승온 과정에서부터 산소 분압을 제어하고 최적의 대기압 상수를 산출함으로써 Zn-loss 현상을 최소화하여 ZnO 11 mol%, 대기압 상수 7.7일 때 투자율 2350, 밀도 4.9 $g/cm^3$, 비저항 480 ${\Omega}cm$, 300 mT의 최대 자속 밀도 특성을 갖는 우수한 자심 재료를 개발하였다. 그리고 최소 손실 온도를 $90^{\circ}C$ 이하로 감소시켰으며 100 kHz에서 250 $kW/m^3$의 낮은 전력손실을 나타냈다. 또한 개발된 자심재료를 이용하여 제조된 전원장치는 30~80A의 출력 전류에서 85% 이상의 고효율을 얻었다.