• Journal of Magnetics
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• 제16권3호
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• pp.300-303
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• 2011

The effect of the hot-compaction temperature on the microstructure and magnetic properties of anisotropic nanocrystalline magnets was investigated. The hot-compaction temperature was found to impact both the magnetic properties and the microstructure of die-upset magnets. The remanence of the isotropic precursor increases slightly with the improved hot-compaction temperature, and the grains start to grow on the flake boundary at higher hot-compaction temperatures. After hot deformation, it was found that the change in the magnetic properties was the inverse of that observed with the hot-compaction temperature. Microstructural investigation showed that die-upset magnets inherit the microstructural characteristics of their precursor. For the die-upset magnets, hot pressed at low temperature, scarcely any abnormal grain growth on the flake boundary can be seen. For those hot pressed at higher temperatures, however, layers with large equiaxed grains could be observed, which accounted for the poor alignment during the hot deformation, and thus the poor magnetic properties.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.256-256
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• 2007

As a candidate for lead-free piezoelectric materials, dense ($(Na_{0.47}K_{0.47}Li_{0.06})NbO_3$ (LNKN6) ceramics were developed by conventional sintering process. Sintering temperature was lowered by adding $Li_2O$ as a sintering aid. Abnormal grain growth in the LNKN6 ceramics was observed with varying $Li_2O$ content. The electrical properties of LNKN6 ceramics were investigated as a function of $Li_2O$ concentration. When the sample sintered at $1000^{\circ}C$ for 4h with the addition of 1 mol% $Li_2O$, electromechanical coupling factor ($k_p$) and piezoelectric coefficient ($d_{33}$) of LNKN6 ceramics were found to reach the highest values of 0.40 and 184 pC/N, respectively.

• 생약학회지
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• 제6권1호
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• pp.43-47
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• 1975

Attempts were made to determine the characteristics of the morphology of Codonopsis lanceolata $T_{RAUT's}$ root. Its saponin and crude powder were examined by foaming and hemolytic tests and by observing transverse sections: 1) The cork-layer was consisted of multiple cells, and some of the cork cells contained monoclinic prism crystals of calcium oxalates. 2) The vascular bundle was formed of radial arrangement by the preminentic bursting pith and the irregular cambium ring with the abnormal growth. 3) The latex vessel and latex of the cortex were brown-gray or yellowish-brown. The latex vessel and sieve tube were consisted of the independent aggregates which had a number of layers. It had much more independent aggregates than Platycodi Radix. 4) The xylem was less than the phloem portion. The thick-walled vessels which had one to five lines ware more distributed than in Platycodi Radix. 5) The inulin distribution on a piece of section which is dipped in alcohol was observed through out the tissues, but starch grain was not found in it. 6) The duration time of foaming reaction of the crude powder in test tubes was shorter than that of Platycodi Radix. Foaming index of the foaming test of five percent decoctions was 3.33, 7) In the hemolytic test which used 10 percent decoction and one percent saponin solution, hemolytic action was very weak.

• Corrosion Science and Technology
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• 제22권4호
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• pp.232-241
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• 2023

The mechanical properties of the hydrogen valve responsible for supplying and blocking hydrogen gas in a hydrogen fuel cell electric vehicle (FCEV) were researched. Mechanical properties by hydrogen embrittlement were investigated by coating chromium nitride (CrN) and titanium nitride (TiN) on aluminum alloy by arc ion plating method. The coating layer was deposited to a thickness of about 2 ㎛, and a slow strain rate test (SSRT) was conducted after hydrogen embrittlement to determine the hydrogen embrittlement resistance of the CrN and TiN coating layers. The CrN-coated specimen presented little decrease in mechanical properties until 12 hours of hydrogen charging due to its excellent resistance to hydrogen permeation. However, both the CrN and TiN-coated specimens exhibited deterioration in mechanical properties due to the peeling of the coating layer after 24 hours of hydrogen charging. The specimens coated at 350 ℃ presented a significant decrease in ultimate tensile strength due to abnormal grain growth.

• 한국재료학회지
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• 제21권5호
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• pp.277-282
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• 2011

Negative temperature coefficient (NTC) materials have been widely studied for industrial applications, such as sensors and temperature compensation devices. NTC thermistor thick films of $Ni_{1+x}Mn_{2-x}O_{4+{\delta}}$ (x = 0.05, 0, -0.05) were fabricated on a glass substrate using the aerosol deposition method at room temperature. Resistance verse temperature (R-T) characteristics of the as-deposited films showed that the B constant ranged from 3900 to 4200 K between $25^{\circ}C$ and $85^{\circ}C$ without heat treatment. When the film was annealed at $600^{\circ}C$ 1h, the resistivity of the film gradually decreased due to crystallization and grain growth. The resistivity and the activation energy of films annealed at $600^{\circ}C$ for 1 h were 5.203, 5.95, and 4.772 $K{\Omega}{\cdot}cm$ and 351, 326, and 299 meV for $Ni_{0.95}Mn_{2.05}O_{4+{\delta}}$, $NiMn_2O_4$, and $Ni_{1.05}Mn_{1.95}O_{4+{\delta}}$, respectively. The annealing process induced insulating $Mn_2O_3$ in the Ni deficient $Ni_{0.95}Mn_{2.05}O_{4+{\delta}}$ composition resulting in large resistivity and activation energy. Meanwhile, excess Ni in $Ni_{1.05}Mn_{1.95}O_{4+{\delta}}$ suppressed the abnormal grain growth and changed $Mn^{3+}$ to $Mn^{4+}$, giving lower resistivity and activation energy.

• 한국기후변화학회지
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• 제4권4호
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• pp.371-384
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• 2013

최근 기후변화로 인해 잇따라 발생하는 전 지구적 이상기후의 출현은 사회 전반에 걸쳐 직 간접적으로 많은 영향을 미친다. 특히, 자연을 통해 기본 에너지를 얻는 농업은 기상환경에 따라 작물의 생장과 수확이 직접적으로 영향을 받기 때문에, 기후변화와 관련된 사회적 중요 관심사가 되었다. 본 연구에서는 국내 주요 수입곡물중 큰 부분을 차지하고 있는 옥수수와 밀에 대하여 주요 수출국인 미국과 중국을 대상으로 생산량에 많은 영향을 끼치는 온도의 변화 경향을 통해 취약성 평가를 하였다. 주요 곡물 생산국들의 곡물 생산성에 영향을 미치는 재배기간을 문헌 및 기존 연구를 통해 국가별로 파악하여 주요 재배기간으로 정하고, 옥수수와 밀에 대한 생산국별 주요 재배기간에 해당하는 미래 기상은 RCP8.5 기후변화 시나리오를 기반으로 구축하였다. 기온의 변화경향을 나타내는 적응성과 기온의 변화 정도를 나타내는 민감도를 이용하여 중국과 미국 간의 곡물별 생산취약성을 분석한 결과, 과거에 밀은 미국이 생산에 유리하고, 옥수수는 중국이 유리하였지만, 미래에는 두 곡물 모두 미국이 생산에 유리한 것으로 나타났다. 본 연구를 통해 도출된 생산성 취약성 평가 결과는 기후변화로 인한 미래 수입 곡물 가격변동에 대한 대비 자료로 이용될 수 있을 것으로 판단된다.

• 한국세라믹학회지
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• 제53권2호
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• pp.129-133
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• 2016

$MnO_2$ was added to the $0.95(Na_{0.5}K_{0.5})NbO_3-0.05CaTiO_3$ (NKN-CT) ceramics in order to promote the densification and improve the poling efficiency by increasing the resistance of the specimens. Densification and abnormal grain growth occurred in the $MnO_2$-added NKN-CT ceramics sintered at $1020^{\circ}C$, indicating that $MnO_2$ assisted the liquid-phase sintering of these materials. $Mn^{3+}$ ions were considered to enter the A-site of the matrix, thereby producing the free electrons, which interacted with the holes resulting from the evaporation of alkali ions. This interaction results in an increase in the resistance of the specimens. The increased resistance improved the poling efficiency and, hence, the dielectric and piezoelectric properties of the NKN-CT ceramics. A few of the $Mn^{3+}$ ions that entered the B-site of the NKN-CT matrix led to a slight increase in the mechanical quality factor.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1230-1231
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• 2008

The effect of content of $Al_2O_3+Y_2O_3$ sintering additives on the densification behavior, mechanical and electrical properties of the pressureless-sintered $SiC-ZrB_2$ electroconductive ceramic composites was investigated. The $SiC-ZrB_2$ electroconductive ceramic composites were pressureless-sintered for 2 hours at 1,700[$^{\circ}C$] temperatures with an addition of $Al_2O_3+Y_2O_3$(6:4 mixture of $Al_2O_3$ and $Y_2O_3$) as a sintering aid in the range of 8${\sim}$20[wt%]. Phase analysis of $SiC-ZrB_2$ composites by XRD revealed mostly of ${\alpha}$-SiC(6H), $ZrB_2$ and In Situ YAG($Al_5Y_3O_{12}$). The relative density, flexural strength, Young's modulus and vicker's hardness showed the highest value of 89.01[%], 81.58[Mpa], 31.437[GPa] and 1.34[GPa] for $SiC-ZrB_2$ composites added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at room temperature respectively. Abnormal grain growth takes place during phase transformation from ${\beta}$-SiC into ${\alpha}$-SiC was correlated with In Situ YAG phase by reaction between $Al_2O_3$ and $Y_2O_3$ additive during sintering. Compositional design and optimization of processing parameters are key factors for controlling and improving the properties of SiC-based electroconductive ceramic composites. In this paper, it is convinced that ${\beta}$-SiC based electroconductive ceramic composites for heaters or ignitors can be manufactured by pressureless sintering.

• 한국분말재료학회지
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• 제21권3호
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• pp.215-221
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• 2014

Translucent alumina is a potential candidate for high temperature application as a replacement of the glass or polymer. Recently, due to the increasing demand of high power light emitting diode (LED), there is a growing interest in the translucent alumina. Since the translucent property is very sensitive to the internal defect, such as voids inside or abnormal grain growth of sintered alumina, it is important to fabricate the defect-free product through the fabrication process. Powder injection molding (PIM) has been commonly applied for the fabrication of complex shaped products. Among the many parameters of PIM, the flowability of powder/binder mixture becomes more significant especially for the shape of the cavity with thin thickness. Two different positions of the gate were applied during PIM using the disc type of die. The binder was removed by solvent extraction method and the brown compact was sintered at $1750^{\circ}C$ for 3 hours in a vacuum. The flowability was also simulated using moldflow (MPI 6.0) with two different types of gate. The effect of the flowability of powder/binder mixture on the microstructure of the sintered specimen was studied with the analysis of the simulation result.

• 한국전기전자재료학회논문지
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• 제22권9호
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• pp.766-771
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• 2009

Lead-free $0.94(Na_{0.5}K_{0.5})NbO_3$-0.06Ba$(Ti_{0.9}Sn_{0.1})O_3$ [0.94NKN-0.06BTS] ceramics doped with 1 mol% $MnO_2$ were synthesized by a conventional solid state method. The phase transitional behavior and piezoelectric properties of the ceramics sintered at various temperatures were investigated. The 0.94NKN-0.06BTS ceramics sintered at $1050^{\circ}C$, having morphotropic phase boundary of orthorhombic and tetragonal phases, exhibited a microstructure with abnormal grain growth. A diffused phase transition behavior for all the specimens was verified as high degree of diffuseness (${\gamma}$) values from 1.45 to 1.79. A high piezoelectric constant of $d_{33}=256$ pC/N and a satisfactory electromechanical coupling factor of $k_p=42%$ were obtained for the relatively dense 0.94NKN-0.06BTS ceramics sintered at $1050^{\circ}C$.