• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.336-337
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• 2005

ZnO varistor ceramics were fabricated as a function of the amount of $Y_2O_3$ addition and sintered at $1250^{\circ}C$ for 2 hour. The average grain size was decreased from 14.2 ${\mu}m$ to 8.3 ${\mu}m$ with the amount of $Y_2O_3$ addition, and varistor voltage was increased from 433 V to 563 V with $Y_2O_3$ addition. Nonlinear coefficient a of all specimens were increased with the amount of $Y_2O_3$ more than 67, in case of $Y_2O_3$ 0.01wt% addition showed the excellent results of 87. And leakage current was less than $1{\mu}A$ at 82% of varistor voltage. The clamping voltage ratio of the specimens added 0.01wt% $Y_2O_3$ was 1.41 at 25A [8/20${\mu}s$]. At the specimen 0.01wt% $Y_2O_3$ addition. endurance of surge current and deviation of varistor voltage were 5700A/$cm^2$ and $\Delta$-2.86%, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.211-214
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• 2001

The undesirable phase transformation of zirconium dioxide at high temperatures can be eliminated by stabilization of the cubic phase with an addition of a selected alkaline earth or rare-earth oxide. In this paper the ionic conductivity of cubic solid solutions in the stabilized ZrO$_2$ by CaO-Y$_2$O$_3$ system was examined. The higher ionic conductivity appears to be related to lower activation energy rather than to the number of oxygen vacancies dictated by composition. Those compositions of highest conductivity lie close to the cubic-monoclinic solid-solution phase boundary. Conductivity temperature data are presented that indicate a reversible order-disorder transition for Zr$_2$2-Y$_2$O$_3$cubic solid solutions containing 20 and 25 mole % $Y_2$O$_3$.

• Journal of the Korean Chemical Society
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• v.39 no.12
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• pp.946-954
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• 1995

The physico-chemical nature of the rare earth oxide which was produced by the caustic fritting of monazite was studied to furnish fundamental data that are required for its efficient use and processing. It was found that the material which was mainly constituted of light rare earths and thorium was a solid solution phase of oxide whose structure was fluorite-type face centered cubic. Its density was 6.75 g/$cm^3$ and it had a uniform particle size distribution at around 1 ${\mu}m.$ The crystallinity improved by heating to elevated temperatures, whereas the solubility in HCl decreased as the crystallinity improved. Complete dissolution in conc. HCl solution in short time (30 min.) was attained by heating to 70$^{\circ}C$. The measurement of zeta potential showed its I.E.P. to be at pH 8.6 of the suspension.

• Journal of Korea Foundry Society
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• v.35 no.5
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• pp.114-119
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• 2015

This paper reports the effect of a refractory crucible type on the microstructure of duplex stainless steel (DSS) cast with the addition of gadolinium using air-induction melting. Grade 4A DSSs with 1 wt% of gadolinium (Gd) were fabricated in various crucibles including alumina ($Al_2O_3$), magnesia (MgO), calcia (CaO) coated with yttria ($Y_2O_3$) and graphite. The standard free energies of the formation of calcium and yttrium oxide were lower than those of gadolinium oxide and other crucible elements based oxide. The yield of Gd in DSS using $Al_2O_3$, MgO, CaO-coated $Y_2O_3$ and graphite was 5, 19, 83 and 96%, respectively. As Gd yield increased, the amount of Gd-based inclusions increased, the size of the inclusions were reduced, and the inclusions became evenly distributed.

• Applied Science and Convergence Technology
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• v.26 no.2
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• pp.26-29
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• 2017

Thin films of europium-doped yttrium oxide ($Y_2O_3$:Eu) were prepared on Si (100) substrates by using a radio frequency (RF) magnetron sputtering. After the deposition, the films were annealed at $1000^{\circ}C$ in an air ambient for 1 hour. X-ray diffraction analysis revealed that the $Y_2O_3$:Eu films had a polycrystalline cubic ${\alpha}-Y_2O_3$ structure. The as-deposited films showed no photoluminescence (PL), which was due to poor crystalline quality of the films. The crystallinity of the $Y_2O_3$:Eu films was significantly improved by annealing. The strong red PL emission was observed from the annealed $Y_2O_3$:Eu films and the highest intensity peak was centered at around 613 nm. This emission peak originated from the $^5D_0{\rightarrow}^7F_2$ transition of the trivalent Eu ions occupying the $C_2$ sites in the cubic ${\alpha}-Y_2O_3$ lattice. The broad PL excitation band was observed at wavelengths below 280 nm, which was attributed to the charge transfer transition of the trivalent Eu ion.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.24 no.3
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• pp.321-329
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• 2014

Objectives: This study was performed to produce data on the pulmonary toxicity of neodymium oxide($Nd_2O_3$) by intratracheal instillation. Methods: Two groups of rats were exposed to neodymium oxide by intratracheal instillation with doses of 0.5 mg and 2.0 mg, respectively. At two days, four weeks and 12 weeks after exposure, body weight change, organ weight change and histopathological change were observed. At 12 weeks after exposure, lung function change was measured. Results: The body weight of rats in the high concentration group decreased after 12 weeks by 4-5% compared with the control group. At four weeks and 12 weeks after the administration of neodymium oxide, the absolute weight of the lungs of the high concentration group were significantly increased when compared with the control group(p<0.05). At 12 weeks after the injection of neodymium oxide, breath frequency and respiratory minute volume were increased, but inhalation time and expiratory time were decreased. Bronchiolar epithelial hyperplasia, alveolar type II cell hypertrophy/hyperplasia and foreign body granulomatous inflammation were observed in the high exposure group. Conclusions: Body weight decrease, lung absolute weight and breath frequency increase, and pathological lung change were all observed. We found that pulmonary toxicity of neodymium oxide nanoparticles by intratracheal instillation could be confirmed.

• Journal of the Mineralogical Society of Korea
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• v.28 no.2
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• pp.147-163
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• 2015

Chemical and mineralogical properties of coal ash samples from the nine thermal power plants of Korea were investigated to acquire basic data for estimating the potential of rare metal recovery. Chemical compositions of coal ash were consistent with those of average shale and foreign coal ashes. However, there were small differences between the metal contents of domestic anthracitic and imported bituminous coal ashes. Unburned coal particles were much abundant in the ash of domestic anthracitic coal. Chalcophile elements were relatively enriched in the fly ash compared to bottom ash. Silicate glass was the major component of coal ash with minor minerals such as quartz, illite (muscovite), mullite, magnetite, lime, and anhydrite. Al and Si were the major components of the glass with varying contents of Ca, Fe, K, and Mg. Glass occurred in a form of porous sphere and irregular pumace-like grain often fused with iron oxide spheres or other glass grains. Iron oxide spheres were fine intergrowth of fast-grown iron oxide crystals in the matrix of silicate glass. Chemical, microstructural, and mineralogical properties would guide successful rare metal recovery from coal ash.

• Economic and Environmental Geology
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• v.20 no.2
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• pp.85-95
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• 1987

The host rocks of titaniferous magnetite deposits in Gonamsan are alkaline gabbros, which are typical of undersaturated alkaline rocks in terms of the lack of normative quartz. According to field occurrences and petrographic features, these alkaline gabbros are divided into 3 rock types: coarse-grained and pegmatitic rock, medium-grained rock with equigranular texture, and layered cumulate rock. All these rocks mainly contain clinopyroxene(salite), plagioclase(An 43-66), pargasite, and ilmenite. The accessory minerals are apatite, sphene, quartz, and sometimes titaniferous magnetite. Pargasite, sphene, and quartz are considered to be secondary minerals formed by the reaction among clinopyroxene, plagioclase and Fe-Ti oxide at deuteric stage. Fe-Ti oxides generally occur as ilmenite in the alkaline rocks, and titaniferous magnetite in the ore deposits. Layered cumulate rocks are characterized by a recurrence of discontinuous thin mesolayer of clinopyroxene-pargasite within leucolayer mainly composed of plagioclase. Clinopyroxene is cumulus mineral whereas plagioclase, ilmenite and apatite occur as intercumulus minerals. According to the variation diagrams of oxide and trace element contents against the differentiation index, incompatible elements, such as Na, Ba and Sr, show positive correlations whereas compatible elements, such as Mg and Cr, show negative correlations. However some compatible elements, such as Co, Ni and V show irregular variations, reflecting relative cumulate status of cumulus and intercumulus minerals. On the de la Roche multicationic diagram, these alkaline gabbros are distributed along the differentiation curve of undersaturated alkaline series from alkaline basaltic composition through basanitic composition to tephritic composition. Layered cumulate rocks, which are distributed between basanitic composition and tephritic composition, reflect their cumulate character, slightly scattering away from the curve. The medium-grained rock shows higher contents in Ba, Sr and light rare earch elements than the coarse-grained and pegmatitic rock. The former shows two times higher contents of total rare earth elements than the latter, $while(La/Lu)_{cn}$ ratios maintain fairly constant values of 5.08~5.06 in these two rocks. This means that coarse-grained and pegmatitic rock, as compared with the medium-grained rock, was formed by the earlier differentiated magma but rare-earth element distribution pattern remained almost parallel during differentiation. From the data the above mentioned, these alkaline gabbros are considered to be comagmatic and to be formed by intrusions of differentiated magmas in its reservoir.

• Economic and Environmental Geology
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• v.41 no.6
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• pp.773-795
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• 2008

The major import minerals of South Korea are copper ore, lead-zinc ore, iron ore, manganese ore and molybdenum ore. Oversea resources development of South Korea have 92 projects in 14 nations of Asia, 29 projects in 10 nations of America and Europe, and 14 projects in 9 nations of Middle Asia and Africa. But, most projects of them are found in Australia, China, Mongolia and Indonesia. The most projects of the Australia, China and Indonesia are interested in coal and a little projects of them have manganese, iron, lead-zinc, nickel, copper, gold, molybdenum, rare earth elements and uranium. The most projects of the Mongolia are interested in gold and rare earth elements. Representative ore deposits models of metal resources are Orogenic lode deposits, Volcanogenic massive sulphide deposits, Porphyry deposits, Sedimentary exhalative deposits, Mississippi valley type deposits, Iron oxide copper-gold deposits and Magmatic nickel-copper-platinum group element deposits based on global distribution, reverses and grades of their deposits models. If oversea mineral resources will be examined the mineral reserves, mineral mine production and ore deposits models of nations and then survey and investigate of mineral resources, we may be maintained ore body of high grade at survey area and decrease the investment risk.

• Korean Chemical Engineering Research
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• v.53 no.2
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• pp.145-149
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• 2015

The electrochemical behavior of $Nd_2O_3-La_2O_3-NiO$ mixed oxide including rare earth resources has been studied to synthesize $La_{0.5}Nd_{0.5}Ni_5$ alloy in a LiCl molten salt. The $Nd_2O_3-La_2O_3-NiO$ mixed oxide was converted to $NiNd_2O_4$ (spinel) and $LaNiO_3$ (perovskite) structures at a sintering temperature of $1100^{\circ}C$. The spinel and perovskite structures led a speed-up in the electrolytic reduction of the mixed oxide. Various reaction intermediates such as Ni, $NiLa_2O_4$ were observed during the electrochemical reduction by XRD analysis. A possible reaction route to $La_{0.5}Nd_{0.5}Ni_5$ in the LiCl molten salt was proposed based on the analysis result.