• Applied Chemistry for Engineering
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• v.17 no.2
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• pp.125-131
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• 2006

Dimethyl ether (DME) is a new clean fuel as an environmentally-benign energy resource. DME can be manufactured from various energy sources including natural gas, coal, biomass and spent plastic. In addition to its environmentally friendly properties, DME has similar characteristics to those of LPG. Therefore, it is considered as an excellent substitute fuel for LPG, fuel cells, power plant, and especially diesel and is expected to be the alternative fuel by 2010. The experimental study of the direct synthesis of DME was investigated under various conditions over a temperature range of $220{\sim}280^{\circ}C$, syngas ratio 1.2~3.0. All experiments were carried out with a hybrid catalyst, composed of a methanol synthesis catalyst ($Cu/ZnO/Al_2O_3$) and a dehydration catalyst (${\gamma}-Al_2O_3$). The observed reaction rate follows qualitatively a Langmiur-Hinshellwood model as the reaction mechanism. Such a mechanism is considered with three reactions; methanol synthesis, methanol dehydration and water gas shift reaction. From a surface reaction with dissociative adsorption of hydrogen, methanol, and water, individual reaction rate was determined.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.373-373
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• 2014

Resistive-change random access memory (ReRAM) device is one of the promising candidates owing to its simple structure, high scalability potential and low power operation. Many resistive switching devices using transition metal oxides materials such as NiO, Al2O3, ZnO, HfO2, $TiO_2$, have attracting increased attention in recent years as the next-generation nonvolatile memory. Among various transition metal oxides materials, HfO2 has been adopted as the gate dielectric in advanced Si devices. For this reason, it is advantageous to develop an HfO2-based ReRAM devices to leverage its compatibility with Si. However, the annealing temperature of these high-k thin films for a suitable resistive memory switching is high, so there are several reports for low temperature process including microwave irradiation. In this paper, we demonstrate the bipolar resistive switching characteristics in the microwave irradiation annealing processed Ag/HfO2/Pt ReRAM device. Compared to the as-deposited Ag/HfO2/Pt device, highly improved uniformity of resistance values and operating voltage were obtained from the micro wave annealing processed HfO2 ReRAM device. In addition, a stable DC endurance (>100 cycles) and a high data retention (>104 sec) were achieved.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.4 no.1
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• pp.59-64
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• 2006

Ion exchange resin particles should not be found in steam generator(S/G) sludge. The suspicious spherical resin particles observed in S/G sludge sample were characterized for particle size distribution under optical microscope using the micro-technique, for element analysis by the electron probe micro analysis (EPMA), and for molecular identification by the IR spectroscopy. The particle sizes are distributed from 1 to $200{\mu}m$ for the sludge, while 40 to $500{\mu}m$ for the spherical resin particles. The results of the elemental analysis showed different major impurities: Si, Al, Mn, Cr, Ni, Zn and Ti for the sludge particles, while Si, Cu, Zn for the spherical resin particles. However, both particles contain Fe as a matrix of magnetite $(Fe_3O_4)$. IR spectrum of the spherical particles was not quite similar to the IR spectrum of ion exchange resins used in S/G system. These results indicate that the spherical particles are not related to ion exchange resin particles and may be formed by the process of the sludge formation.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2005.06a
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• pp.129-136
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• 2005

There should not be ion exchange resin particles in S/G sludge. The suspicious spherical resin particles observed in S/G sludge sample were characterized for particle size distribution under optical microscope using the micro-technique, for element analysis by the electron probe micro analysis (EPMA), and for molecular identification by the IR spectroscopy The particle sizes are distributed from 1 to 200 ${\mu}m$ for the sludge, while 40 to 500 ${\mu}m$ for the spherical resin particles. The results of the elemental analysis showed different major impurities: Si, Al, Mn, Cr, Ni, Zn and Ti for the sludge particles, while Si, Cu, Zn for the spherical resin particles. However, both particles contain Fe as a matrix of hematite ($Fe_{3}O_4$). IR spectrum of the spherical particles was quite different from that of ion exchange resins used in S/G system. These results indicate that the spherical particles are not related to ion exchange resin particles and formed by the process of the sludge formation.

• Clean Technology
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• v.6 no.1
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• pp.61-69
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• 2000

In this study, generation process and properties of inorganic industrial waste which can be used in cement industry were investigated. The scheme of recycling to use the selected waste as raw materials, mineralizer and flux, admixture and raw materials for special cement was decided and then various experiments were carried out. The experimental results were as follows ; In the use of industrial waste as raw materials, ferrous materials could be substituted by Cu-slag, Zn-slag, electric arc furnace or convertor furnace slag etc., and a siliceous material could be substituted by sand from cast-iron industry. By-products from sugar or fertilizer industry, which has $CaF_2$ as the main component, and jarosite from Zn refinery enabled clinker phases to be formed at lower temperature by $100{\sim}150^{\circ}C$. Adding Cu slag and STS sludge in proper proportion to cement improved properties of cement. Fly ash and limestone powder as admixture had the same effect on cement. As a raw material for special cement, aluminium waste sludge could be used in making ultra early strength cement, which had the compressive strength of $300kg/cm^2$ within 2hours. And two different ashes from municipal incinerator could be raw materials of the cement which was mainly composed of $C_3S$ and $C_{11}A_7{\cdot}CaCl_2$ as clinker phases.

• Economic and Environmental Geology
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• v.56 no.6
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• pp.745-764
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• 2023

In the Republic of Congo, Banded iron formations (BIFs) occur in two areas: the Chaillu Massif and the Ivindo Basement Complex, which are segments of the Archean Congo craton outcropping in the northwestern and southwestern parts of the country. They show interesting potential with significant mineral resources reaching 2 Bt and grades up to 60% Fe. BIFs consist mostly of oxide-rich facies (hematite/magnetite), but carbonate-rich facies are also highlighted. They are found across the country within the similar geological sequences composed of amphibolites, gneisses and greenschists. The Post-Archean Australian Shale (PAAS)-normalized patterns of BIFs show enrichment in elements such as SiO₂, Fe₂O₃, CaO, P₂O₅, Cr, Cu, Zn, Nb, Hf, U and depletion in TiO₂, Al₂O₃, MgO, Na₂O, K₂O, Sc, Th, Ba, Zr, Rb, Ni, V. REE diagrams show slight light REEs (rare earth elements; LREEs) compared to heavy REEs (HREEs), and positive La and Eu anomalies. The lithological associations, as well as the very high (Eu/Eu^*)_SN ratios> 1.8 shown by the BIFs, suggest that they are related to Algoma-type BIFs. The positive correlations between Zr and TiO₂, Al₂O₃, Hf suggest that the contamination comes mainly from felsic rocks, while the absence of correlations between MgO and Cr, Ni argues for negligeable contributions from mafic sources. Pr/Pr^* vs. Ce/Ce^* diagram indicates that the Congolese BIFs were formed in basins with redox heterogeneity, which varies from suboxic to anoxic and from oxic to anoxic conditions. They were formed through hydrothermal vents in the seawater, with relatively low proportions of detrital inputs derived from igneous sources through continental weathering. Some Congolese BIFs show high contents in Cr, Ni and Cu, which suggest that iron (Fe) and silicon (Si) have been leached through hydrothermal processes associated with submarine volcanism. We discussed their tectonic setting and depositional environment and proposed that they were deposited in extensional back-arc basins, which also recorded hydrothermal vent fluids.

• Journal of the Korean Geosynthetics Society
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• v.11 no.2
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• pp.31-38
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• 2012

The recycled aggregate for construction, slag, coal ash and such may elute leachates by chemical reaction when in touch with water, and to confirm this, generally the waste process test is executed. If the test result criteria are met, it can be used as replacement aggregate. In case of steel slag, however, the chemical reaction does not end in a short term, but occurs over a long time, generating eluted leachate. Thus, in this study, the leachate from steel slag were analyzed for heavy metal, and the pH change and environmental characteristics of eluted leachate were analyzed. According to the experiment result, the chemical reaction of free CaO and water within the steel slag occurred more actively when stirred, and the smaller the grain size, the higher the pH was. As the result of waste process test, all test items for the two types of specimen were found to have no heavy metal, but from the ICP test analysis result, heavy metals such as Al, Pb, Zn, Fe were detected. It could be confirmed that chemical reaction would occur upon contact of steel slag and water, and heavy metal may be detected depending on experiment conditions and analysis methods, the long-term environmental characteristics should be examined for utilization of steel slag.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.174-174
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• 2009

현재 전자부품용으로 사용되는 유리프리트의 경우 PbO계를 주로 사용하고 있다. 최근 환경규제에 따른 PbO 사용이 제한됨에 따라 이를 대체할 Pb-free 유리 조성에 대한 연구가 활발히 진행 중이다. Pb-free계로서는 $Bi_2O_3$계, $B_2O_3$계가 주로 연구되고 있으나 소성 온도가 $500^{\circ}C$이상으로 높고 또한 $Bi_2O_3$ 계는 중금속이기 때문에 문제가 있다. 본 연구에서는 $400^{\circ}C$ 미만 소성이 가능한 SnO-$P_2O_5$계를 기본 조성계로 선택하고 열적, 전기적, 화학적 특성을 개선하기 위해 $R_2O_3$(R=Al, B), RO(R=Mg, Zn, Ca, Ba) 를 첨가하였다. 개선된 조성으로 샘플을 만들고 이를 대상으로 실제 전자부품 생산 공정에 적용 실험을 진행 하였다. 실험에 사용된 전자 부품은 소형 칩 베리스터로 생산 공정에서 코팅용 유리프리트와 파우더를 절연체로서 전면에 코팅하게 된다. 유리프리트를 코팅함으로서 누설 전류를 차단하고 생산 공정시 베리스터 내부를 보호하게 된다. 실험에 사용된 샘플의 열적 특성은 TMA로, 전기적 절연 특성은 고 절연저항 측정기로 측정하였고 내 산성과 내 알칼리성도 측정하였다. 샘플을 이용하여 완성된 칩 베리스터의 성능은 고온, 내습 신뢰성 TEST(고온:$150^{\circ}C$ 12HR, 내습:$85^{\circ}C$-85%12HR)로 실험하여 합부판정 (Leakage current <10uA)을 내려 완성품과 불량품을 가려내었다.

• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.2 s.17
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• pp.81-87
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• 2004

Semiconductor thick film gas sensors based on tin oxide are fabricated and their gas response characteristics are examined for four simulant gases of chemical warfare agent (CWA)s. The sensing materials are prepared in three different sets. 1) The Pt or Pd $(1,\;2,\;3\;wt.\%)$ as catalyst is impregnated in the base material of $SnO_2$ by impregnation method.2) $Al_2O_3\;(0,\;4,\;12,\;20\;wt.\%),\;In_2O_3\;(1,\;2,\;3\;wt.\%),\;WO_3\;(1,\;2,\;3\;wt.\%),\;TiO_2\;(3,\;5,\;10\;wt.\%)$ or $SiO_2\;(3,\;5,\;10\;wt.\%)$ is added to $SnO_2$ by physical ball milling process. 3) ZnO $(1,\;2,\;3,\;4,\;5\;wt.\%)$ or $ZrO_2\;(1,\;3,\;5\;wt.\%)$ is added to $SnO_2$ by co-precipitation method. Surface morphology, particle size, and specific surface area of fabricated sensing films are performed by the SEM, XRD and BET respectively. Response characteristics are examined for simulant gases with temperature in the range 200 to $400^{\circ}C$, with different gas concentrations. These sensors have high sensitivities more than $50\%$ at 500ppb concentration for test gases and also have shown good repetition tests. Four sensing materials are selected with good sensitivity and stability and are fabricated as a sensor array A sensor array Identities among the four simulant gases through the principal component analysis (PCA). High sensitivity is acquired by using the semiconductor thick film gas sensors and four CWA gases are classified by using a sensor array through PCA.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.310-310
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• 2007

Mg-Si-O계 세라믹스에 glass frit 조성을 첨가하여 저온에서의 소결 특성 및 마이크로파 유전 특성을 연구하였다. 기존의 Mg-Si-O계 세라믹스는 우수한 유전특성을 가지고 있으나 높은 소결온도로 인하여 LTCC용 기판 소재로 적용이 어려웠다. 본 연구에서는 MgO, $SiO_2$를 이용하여 $Mg_2SiO_4$을 합성한 후, $B_2O_3-ZnO-Na_2O-SiO_2-Al_2O_3$계 glass 조성을 20~40wt%로 첨가하여 소결온도를 감소시켜 LTCC 기판 소재로서의 적용성을 고찰하였다. glass frit 함량이 증가함에 따라 밀도($g/cm^3$) 및 유전율(${\varepsilon}_r$)은 증가하였고 품질계수($Qxf_0$)값은 감소하였다. glass frit 함량이 40wt%일때 $900^{\circ}C$에서 1시간 소결한 소결체의 유전톡성은 유전율 (${\varepsilon}_4$) = 6.5. 품질계수 ($Qxf_0$) = 4,000(GHz), 온도계수 $(\tau_t)\;=\;{\pm}\;10ppm/^{\circ}C$로 우수한 특성을 확인하였다.