• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.84-84
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• 2009

$BaTiO_3$는 perovskite 구조를 가지는 대표적인 강유전체 재료로서 MLCC (Multi Layer Ceramic Capacitor), PTC thermistor등에 널리 사용되어지고 있다. 최근 고용량 MLCC의 상업화와 함께 나노크기를 갖는 tetragonal phase의 $BaTiO_3$ 입자를 합성하기 위한 다양한 제조방법이 제시되고 있다. 또한 유전특성과 온도특성 및 신뢰성을 향상시키기 위해 많은 첨가제들이 연구되어지고 있다. 따라서 본 연구에서는 희토류 원소인 $Y_2O_3$를 첨가하여 유전특성 및 온도특성을 향상시키고자 하였다. 본 실험에서는 150nm 크기를 갖는 pure $BaTiO_3$ 분말을 사용하고 $Y_2O_3$의 양은 0.02 ~ 0.1wt%로 변수를 주어 첨가하였으며, 최적의 소결 조건을 찾기 위하여 1200, 1230, $1250^{\circ}C$에서 소결을 진행하였다. 실험방법으로는 균일한 혼합을 위하여 Iso-alcohol을 이용하여 48시간 ball-mill 하였으며 오븐에서 건조 후 ${\Phi}15$로 성형하여 소결을 진행하였다. 실험결과로는 $Y_2O_3$ 첨가량이 0.02wt% 부터 상온부터 상전이 온도 부근의 유전율 기울기는 완만해 지는 것을 확인할 수 있었으며, 소결시편의 정방정비 (tetragonality)도 뚜렷하게 나타났다. $Y_2O_3$ 첨가랑이 0.1 wt% 일 때는 첨가량의 증가로 인해 강유전성이 상쇄됨을 나타냈다. 이는 $2450^{\circ}C$에 이르는 매우 높은 용융온도와 $2350^{\circ}C$까지 상전이가 는 $Y_2O_3$를 미량 첨가할 때, 고온에서 높은 화학적 안정성과 내열성을 가져 온도 안정성이 향상된 것으로 판단된다.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.191.1-191.1
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• 2015

최근에 백색 발광다이오드를 개발하기 위한 고효율의 형광체 개발에 많은 연구가 집중되고 있다. 본 연구에서는 $La_2WO_6$ 모체 결정에 다양한 활성제 이온인 $Eu^{3+}$, $Dy^{3+}$, $Sm^{3+}$, $Tb^{3+}$를 각각 도핑하여 다양한 발광 파장을 갖는 고효율의 형광체를 제조하였다. 합성한 형광체 분말은 초기물질 $La_2O_3$, $WO_3$, 희토류 원소 ($Eu_2O_3$, $Dy_2O_3$, $Sm_2O_3$, $Tb_4O_7$)를 각각 화학양론적으로 준비하여 고상반응법으로 제조하였으며, 이때 하소 공정은 $400^{\circ}C$에서 3시간, 소결 공정은 $1050^{\circ}C$에서 5시간 유지하여 합성하였다. $La_2WO_6:Eu^{3+}$ 형광체 분말의 경우에 320, 395, 465 nm에서 강한 흡광 파장이 발생하였으며, 파장 320 nm로 여기 시켰을 때 최대 발광 세기는 618 nm에서 관측되었다. $Sm^{3+}$을 도핑한 형광체의 흡광 스펙트럼은 310, 375, 406, 475 nm에서 발생하였으며, 310 nm로 여기 시켰을 때 602 nm의 강한 주황색 발광 신호가 나타났다. $Dy^{3+}$가 도핑된 $La_2WO_6$ 형광체는 575 nm에 강한 발광 피크를 갖는 황색을 나타내었으며, 흡광 파장은 313 nm 이었다. $Tb^{3+}$를 도핑한 형광체의 주 흡광 스펙트럼은 316 nm에서 발생하였고, 발광 스펙트럼은 545 nm에 피크를 갖는 녹색 발광 신호가 나타났다. 활성제이온의 종류에 따른 형광체의 흡광과 발광, 결정 구조의 특성을 체계적으로 제시하고자 한다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.2
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• pp.145-151
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• 2000

The sintering behaviour of monolithic zirconium diboride (ZrB$_{2 }$) and ZrB$_{2 }$-based composite ZrB$_{2 }$-ZrC were studied using a pressureless sintering technique. The specimens were prepared using commercially available ZrB$_{2 }$ and ZrC powder which were pressed and subjected to pressureless sintering. The effects of lanthanum and neodymium used as sintering aids in the sintering processes were investigated. The sintered specimens were characterized using X-ray diffraction analysis and scanning electron microscopy. The ZrB$_{2 }$ specimen prepared using and addition of 1 wt% lanthanum and pressurelessly sintered at $2200^{\circ}C$ showed the maximum relative density of 96%. The ZrB$_{2 }$-ZrC composite specimen without the addition of any sintering aids exhibits the maximum sintered density but contains significantly detectable amount of secondary phase.

• Journal of Environmental Science International
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• v.18 no.6
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• pp.621-632
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• 2009

Rare earth contents(REE) were analysed for the plants, M. sinensis. A. vulgaris and R. crataegitolius, from two different soils serpentine area consisting of serpentinite(SP) and non-serpentine area, containing amphibole schist(AS) of Gapyeong area, and were compared with soils and host rocks. The AS were high with the differences of several times in the top soils, and with the differences of several to ten times in the host rocks relative to the SP. In the same area, the SP were high in the soil, but the rocks for the AS. In the plants, the A. vulgaris were high, but low in the R. crataegitolius. Root parts were higher than the upper parts. Differences between the upper and root parts were big in the SP rather than the AS, and were big in the R. crataegitolius, but small in the M. sinensis. Among the parts of the plants, high elements were shown in the R. crataegitolius of the SP, and the A. vulgaris and M. sinensis of the AS. In the correlation coefficients, most of the REE showed positive relationships among the element pairs, especially high positive correlation coefficients in the upper parts of the SP.Differences of the soils and plants(average) were smalle in the M. sinensis and big in the R. crataegitolius. In the upper parts. contents of the A. vulgaris were close to the soils while the R. crataegitolius showed large discrepancies with the soils. In the root parts, contents of the A. vulgaris showed discrepancies with the soils regardless of soil types, but close in the R. crataegitolius of the SP and M. sinensis of the AS.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.5 no.1
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• pp.1-7
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• 2007

Electrorefining experiments were successfully carried out in LiCl-KCl eutectic molten salt with a graphite cathode. It was found that the formation of Uranium-Graphite intercalation compound(U-GIC) helped the self-scraping mechanism of the uranium dendrite and the efficiency of the electrorefiner increased due to an elimination of the stripping step. The contaminations of the uranium deposit by rare earth elements was negligible while about 300 ppm of carbon was observed. The carbon contamination is believed to be eliminated by further purification by yttrium reaction. The morphology characteristics of the recovered U deposit was compared to that of steel cathode. These are only qualitative preliminary experimental results, but we believe that further research on this type of activity change the direction of the electrorefining research on spent nuclear fuel.

• The Journal of the Petrological Society of Korea
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• v.28 no.4
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• pp.299-306
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• 2019

We estimated the provenance of the obsidian artifacts from Samgeori site at Yeoncheon, one of the prehistoric sites in South Korea. Pyroxene microlites are of hedenbergite to augite compositions, and intergrown and/or overgrown with Fe-oxides showing poikilitic texture. Major oxides contents for the matrix of the obsidian artifacts exhibit a narrow compositional range, especially SiO₂ contents being 73.0~75.5 wt.% of acidic rhyolitic composition. Also, rare earth element (REE) contents are relatively constant in the obsidian artifacts, and the chondrite-normalized REE patterns show a strong Eu negative anomaly. These mineralogical and geochemical features of the Samgeori obsidian artifacts were compared with those from both the Baekdusan obsidians and Japanese Kyushu obsidians which have been thought to be two major obsidian provenances around South Korea. It is suggested that the Samgeori obsidian artifacts were possibly originated from the Baekdusan obsidians.

• Journal of Korea Foundry Society
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• v.33 no.1
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• pp.13-21
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• 2013

The effects of rare earth element (R.E.) and cooling rate on the eutectic reaction of flake graphite cast irons were studied by combined analysis of macro/micro-structure and cooling curve data. The correlation between eutectic reaction parameter and macro/micro-structure was systematically investigated. Two sets of chemical compositions with the different addition of R.E. were designed to cast. Three types of molds for cylindrical specimens with the different diameters were prepared to analyze cooling rate effect. The difference between undercooling temperature and cementite eutectic temperature (${\Delta}T_1=T_{U}-T_{E,C}$), which is increased by adding R.E. and decreased by increasing cooling rate, is considered to be a suitable eutectic reaction parameter for predicting graphite morphology. According to the criterion, A-type graphite is mainly suggested to form for ${\Delta}T_1$ over $20^{\circ}C$. Eutectic reaction time (${\Delta}t$), which is decreased by adding R.E. or increasing cooling rate, is a suitable eutectic reaction parameter for predicting eutectic cell size. Eutectic cell size is found to decrease in a proportion to the decrease of ${\Delta}t$.

• Applied Chemistry for Engineering
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• v.20 no.1
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• pp.21-27
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• 2009

Resins were synthesized by mixing 1-aza-15-crown-5 macrocyclic ligand attached to styrene (a hazardous material) divinylbenzene (DVB) copolymer with crosslink of 1％, 2％, 5％ and 20％ by a substitution reaction. The characteristic of these resins was confirmed by the content of chlorine, element analysis, thermogravimetric analysis (TGA), surface area (BET), and IR-spectroscopy. The effects of pH, time, dielectric constant of solvents and crosslink on adsorption of metal ions by the synthetic resin adsorbent were investigated. The metal ion was showed a fast adsorption on the resins above pH 3. The optimum equilibrium time for adsorption of metallic ions was about two hours. The adsorption selectivity determined in ethanol was in increasing order of uranium ($UO_2^{2+}$) > manganese ($Mn^{2+}$) > praseodymium ($Pr^{3+}$). The adsorption was in the order of 1％, 2％, 5％, and 20％ crosslink resin and adsorption of resin decreased in proportion to the order of dielectric constant of solvents.

• Economic and Environmental Geology
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• v.36 no.6
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• pp.407-413
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• 2003

The geology of the Apdong Nb-Ta deposit, is hosted by alkali metasomatites, consist of Upper Proterozoic sedimentary rocks, alkali syenites(Hoamsan intrusive) of Phyonggang Complex(late Paleozoic to early Mesozoic), Jurassic granite and Quaternary basalt. Alkali syenites are distinguished as alkali amphibole-pyroxene syenite, alkali amphibole-biotite syenite, biotite-nepheline syenite, biotite syenite, and quartz-alkali amphibole-pyroxene syenite. Alkali metasomatites are the products of intense post-magnatic metasomatism, and form the Nb-Ta ore bodies as the belt, irregular vein and lenticular types in the southern part of Hoamsan intrusive. The ore mineralization is characterized by the occurrence of pyrochlore, zircon, and small amounts of columbite, fergusonite. magnetite, fluorite, molybdenite, ilmenite, titanite, apatite, and monazite. Pyrochlore is one of the niobium/tantalum oxides and contains substantial amounts of rare earths and radioactive elements. The compositional varieties of pyrochlore can be defined: (1) enriched in tantalum, uranium and cerium, (2) substantially tantalum- and fluorine-poor, and (3) enriched in thorium or barium. The geochemical characteristics, ore textures and mineral occurrences indicate that alkali metasomatism of the mineralizing fluid was the dominant ore-forming process.

• Journal of the Korean Chemical Society
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• v.27 no.5
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• pp.361-367
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• 1983

The selective separation and the quantitative recovery of uranium from Korean monazite sand have been studied by anion-exchange chromatography. It has been shown that method of anion-exchange chromatography under controlled conditions of elution can be applied to the production of relatively high purity of Uranium Oxide from monazite sand. Under the optimum separation conditions, the recoveries from standard sample were up to 99.3% as $U_3O_8$ on sulfate form anion resin bed and 99.2% as $U_2O_3{\cdot}P_2O_7$ on phosphate form anion resin bed. The possibility of recovering uranium from the monazite sulfate solution using a strong base anion exchange resin-Amberlite IRA-900. Uranium was successfully recovered about 92 percent. Phosphate ion did not seem to interfere with the process.