• Journal of the Mineralogical Society of Korea
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• v.31 no.3
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• pp.161-172
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• 2018

Multi-anvil press (MAP) is one of the high pressure apparatuses and often generates the pressure-conditions ranging from 5 to 25 GPa and temperature-conditions up to $2,300^{\circ}C$. The MAP is, therefore, suitable to explore the pressure-induced structural changes in diverse earth materials from Earth's mantle and the bottom of the mantle transition zone (~660 km). In this study, we present the experimental results for pressure-load calibration of the 1,100-ton multi-anvil press equipped in the authors' laboratory. The pressure-load calibration experiments were performed for the 14/8 step, 14/8 G2, 14/8 HT, and 18/12 assembly sets. The high pressure experiments using ${\alpha}$-quartz, wollastonitestructure of $CaGeO_3$, and forsterite as starting materials were analyzed by powder X-ray diffraction spectroscopy. The phase transition of each mineral indicates the specific pressure that is loaded to a sample at $1,200^{\circ}C$: a transition of ${\alpha}$-quartz to coesite at 3.1 GPa, that of garnet-structure of $CaGeO_3$ to perovskite-structure at 5.9 GPa, that of coesite to stishovite at 9.2 GPa, and that of forsterite to wadsleyite at 13.6 GPa. While the estimated pressure-load calibration curve is generally consistent with those obtained in other laboratories, the deviation up to 50 tons is observed at high pressure above 10 GPa. This is partly because of the loss of oil pressure at high pressure resulting from the differences in a sample chamber, and the frictional force between pressure medium and second anvil. We also report the ${\sim}200^{\circ}C/mm$ of thermal gradient in the vertical direction of the sample chamber of 14/8 HT assembly. The pressure-load calibration curve and the observed thermal gradient within the sample chamber can be applied to explain the structural changes and the relevant macroscopic properties of diverse crystalline and amorphous earth materials in the mantle.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.8
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• pp.144-149
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• 2005

In this paper, insulations characteristics by temperature changes($+30{\sim}-40[^{\circ}C]$) of $SF_6$ gas in the experimental chamber were studied. From this result, The breakdown characteristics classify the vapor stage of $SF_6$ according the Paschen's law, the gas & liquid coexisted stage of voltage value increases & much deviation and the VB low stage as the interior of chamber gets filled with mixture of $SF_6$ that are not liquefacted and remaining air which couldn't be ventilated. In addition the ability of insulation of liquid $SF_6$ was higher than that of the highly pressurized $SF_6$ gas. In this research, we want to provide the base data on designing insulation of high-temperature superconductor and the cryogenic equipments by investigating the insulation characteristics of $SF_6$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.5
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• pp.213-218
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• 2014

An investigation of the influence of $WO_3$ addition with different precursors and preparation methods on the phase formation and selective catalytic reduction (SCR) efficiency of anatase-$TiO_2$ powders has been carried out. An anatase-$TiO_2$ synthesized by precipitation process was used as a catalyst support. For $WO_3(10wt%)/TiO_2$, the W loading to the $TiO_2$ support led to the lower in anatase to rutile transition temperature to ${\sim}900^{\circ}C$ from $1200^{\circ}C$ of the $TiO_2$ support alone. In the case of $WO_3(10wt%)/TiO_2$ SCR powders obtained from a wet process with ammonium meta-tungstate (AMT) precursor, the highest $NO_X$ conversion efficiency was achieved at $450^{\circ}C$ remaining high efficiency at $500^{\circ}C$, while the same composition prepared from a dry process with $WO_3$ addition showed the lowered efficiency with temperature after reaching the efficiency maximum at $350^{\circ}C$. The same tendency has been found that the $V_2O_5(5wt%)-WO_3(10wt%)/TiO_2$ SCR powders obtained from the wet process with AMT precursor has shown the superior $NO_X$ conversion efficiency over 90 % in a wider temperature range of $300{\sim}500^{\circ}C$.

• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.817-821
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• 1998

$BaTiO_3$ particles were prepared using $Ba(OH)_2{\cdot}8H_2O$ and $Ti(OC_2H_5)O_4$ by the hydrothermal method and their characteristics treated at the various temperatures have been investigated. This prepared $BaTiO_3$ powder includes a very small amount of $H_2O$ and $OH^-$. By increasing the treated temperature from $200^{\circ}C$ to $1000^{\circ}C$, the mean particle size was accordingly increased from $0.022{\mu}m$ to $0.072{\mu}m$ and the tetrogonality(c/a)was increased from 1.02 to 1.2 so that the phase transition to tetroganal takes place. $BaTiO_3$ sintered at $1250^{\circ}C$ after heat treatment at $400^{\circ}C$ for 3 hrs showed a specific dielectric constant of 8120 and surface activation energy was 9680 kcal/mol.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.2
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• pp.134-139
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• 2000

Ternary system of 40PMN-30PT-30PMW was prepared by using different reaction process. The PMN-PT was synthesized firstly, then it reacted to $PbWO_4$ as PbO and $WO_3$ sources. The dielectric constants were dependent on the density of sintered body and decreased with sintering temperature above $950^{\circ}C$. The highest dielectric constant was 24,000 in a sample sintered at $950^{\circ}C$ with the dielectric loss of 3 %. The temperature dependence of the dielectric constant were decreased with the increase of sintering temperature due to the appearance of double peak maxima. The lowest change in dielectric constant was -37-0 % from -55 to $125^{\circ}C$in a sample sintered at $1150^{\circ}C$ with dielectric constant of 9,900 at room temperature.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.198-198
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• 2003

본 연구는 활성알루미나, 베이어라이트, 미세결질베마이트, 슈도베마이트, 깁사이트 등의 수산화알루미늄을 각각 출발물질로 하여 알파알루미나를 제조하였고 출발물질에 따라 알파알루미나로의 전이온도와 결정성의 차이 및 비표면적, 밀도를 관찰하였다 베이어라이트는 상온에서 5시간 동안 수화반응 시켜 제조하였고, 미세결정질베마이트는 활성알루미나를 수열처리 하여서 제조하였다. 실험결과 활성알루미나, 베이어라이트, 슈도베마이트가 깁사이트와 미세결정질베마이트보다 낮은 온도에서 알파알루미나로의 전이가 일어났음을 알 수 있었고 알파알루미나의 결정성에서는 슈도베마이트가 가장 높은 것을 알 수 있었다. 그리고 130$0^{\circ}C$에서는 미세결정질 베미이트를 제외한 모든 출발물질이 알파알루미나로 전이되었음을 확인할 수 있었다.

• Journal of the Korea Concrete Institute
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• v.28 no.6
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• pp.665-672
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• 2016

This study is conducted to investigate the effect of phase change materials (PCM) on hydration heat and strength characteristics of cement mortar. Two types of Barium and Strontium-based PCMs were used in this study and the addition ratio of each PCM to the cement mortar ranged from 1% to 5% by cement weight. Flow test, semi-adiabatic temperature rise test, compressive strength and flexural strength test were carried out to examine the PCM effect on heat and mechanical properties of cement mortar. Test results indicated that PCMs used in this study were effective to control hydration heat of cement mortar, and Barium-based PCM slightly reduce flow value. The compressive and flexural strength of cement mortar with PCM decreased with increasing the adding mount of PCM. The prediction model for compressive strength of cement mortar with different addition levels of PCMs are suggested in this study.

• Journal of the Korean Chemical Society
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• v.39 no.10
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• pp.806-811
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• 1995

The electrical properties for $(Ba,Sr)_{1-x}Y_xTiO_3$(x=0.001∼0.009, BSYT) with a positive temperature coefficient of resistivity(PTCR) effect were investigated. The BSYT powder was prepared by oxalate coprecipitation method. It was found that the large PTCR effect was appeared up to 0.3 mol% and decreased above 0.5 mol% of the yttrium concentration. The plot of temperature vs. $1{\varepsilon}$m(T) above Curie temperature($T_c$) was agreed with Curie-Weiss law. The potential barrier calculated from measured resistivity and dielectric constant of specimens was high up to 0.3 mol% and reduced above 0.5 mol% of yttrium concentration as the curve of PTCR effect.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.3
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• pp.239-244
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• 2000

Synthesis and high temperature phase stability of $_{1+x}$ Co$_{y}$ Mn$_{2-y}$ $O_4$(0$\leq$x$\leq$0.2,y=0,1/9,1/6) spinel, both the excess lithium and cobalt added, have been studied. The spinel was prepared by oxalate precipitation method as the wet chemical process. Oxalate derived spinel was synthesized by heating of precipitates at temperature lower than $600^{\circ}C$. As a result of the TG-DTA and XRD analysis of prepared and quenched powders, it was found that reversible phase transitions started at temperatures $T_1$, $T_2$및 $T_{2'}$. The transitions involved weight (oxygen) loss and gain during heating and cooling. The effects of Li excess and Co doping on the spinel lattice constant, phase stability and transition temperatures of the prepared powders are investigated. This study would provide important data for determining the spinel preparation process such as synthesis temperature and cooling speed.

• Journal of the Korean Magnetics Society
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• v.6 no.5
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• pp.294-297
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• 1996

We have carried out a $^{31}P$ nuclear magnetic resonance (NMR) study on the electrooptic material $KTiOPO_{4}(KTP)$. From the spin -lattice relaxation time ($T_{1}$) measurements at 17.9 MHz in the temperature range 77-390 K, two phase transitions associated with the change of the dominant charge carriers were observed and the activation energies were obtained in each phase.