• Resources Recycling
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• v.33 no.3
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• pp.12-20
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• 2024

The global cement industry emits approximately 2.9 billion tons of greenhouse gases, of which 1.74-1.89 billion tons are emitted from limestone, which is the main raw material for clinkers. Therefore, the feasibility of using slag, a non-carbonated CaO-based raw material, must be investigated, and the physical properties of cement must be considered. In this study, the mixing ratios of the raw mix and properties of cement were analyzed. The CaCO₃ replacement ratio was limited when one type of slag was used; however, when the mixed slag was utilized, the CaCO₃ replacement ratio increased by more than 12 %. The compressive strength of the slag-incorporated cement was lower than that of Ordinary Portland Cement (OPC). Therefore, the lime saturation factor (LSF) of the raw mix and fineness of the cement were increased to improve the compressive strength. The compressive strength of cement with improved fineness was similar to that of OPC for a CaCO₃ replacement ratio of up to 6 %, and it decreased as the CaCO₃ replacement ratio was increased to 9 %. When both fineness and LSF were increased, the compressive strength and flow value of the cement with a CaCO₃ replacement ratio of 12 % were similar to that of OPC.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.249-249
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• 2010

핵융합로에서는 디버터의 열부하에 대한 안전성을 고려하기 위해 열전도도 및 열 저항성이 높은 텅스텐이 대면 물질로 고려되고 있으며, 경제적인 측면과 실용성 측면에서 텅스텐블록을 직접 제작하여 사용하는 것보다 텅스텐코팅이 효과적이라는 의견이 지배적이다. 또한 ASDEX Upgrade 에서는 탄소블럭에 텅스텐을 코팅하여 챔버 외벽 및 디버터 영역까지 구성하여 캠페인을 진행하였고, 재료적인 측면에서 안정성을 확인 하였다. 따라서 본 연구에서는 디버터 및 챔버외벽 등에 대한 대면물질을 구성하기 위해 상압 열플라즈마 제트를 이용하여 고온에서의 용융 및 냉각을 통해 모재에 텅스텐 피막을 적층하는 과정을 수행하고 있다. 기존의 연구를 통해 일부 공정 변수에 대해서는 이미 적정한 범위의 공정조건을 확보하였고, 기공도와 산화도 및 부착력 등의 물성치에 대한 추가적인 향상을 위해 주요 공정 변수에 집중하여 최적의 조건을 탐색하는 과정이 진행 중이다. 이를 위해 출력증가실험의 일환으로서 기존 36kW급 플라즈마 토치 전력을 한 단계 끌어 올려 48kW급 전력까지 단계적으로 상승시킴으로써 이에 따른 물성치 변화를 검증하고 있다. 현재 44kW 급까지 실험이 수행되었으며, 이를 통해 공극률 감소 및 미세구조 변화에 대한 결과를 얻었다. 실제로 토치의 출력을 증가시킴으로서 텅스텐 피막의 물성치가 변화하는 메커니즘은 플라즈마 제트의 중심부 온도 및 축방향 속도에 의해 결정된다. 중심부 온도가 상승하게 될수록 코팅을 위해 분사되는 분말의 용융률은 증가하지만 분말 외벽에 산화텅스텐이 형성될 가능성은 증가하게 되며, 플라즈마 제트의 모재를 향상 축방향 속도가 증가할수록 용융 된 분말이 모재에 증착 시 형성하는 형태가 원형에 가깝게 되므로 기공이 감소하는 효과가 발생한다. 특히 용융된 분말의 증착 형태는 모재의 온도 및 분말의 입사속도에 결정적이 영향을 받게 되며, 결국 모재와 분말사이의 습윤성에 의한 분말 분산속도가 분말의 입사속도에 버금갈 경우 분말은 모재 위에서 효과적으로 원형으로 전이하며 적층하게 된다. 이러한 전이 현상은 앞에서 언급한 모재의 온도 등에 의해 결정적으로 영향을 받게 되며, 모재의 온도가 전이온도 이하일 경우 폭파형태에서 원형으로 분말의 증착 형태가 전이하게 된다. 이외에 추가적으로 진행하고 있는 연구는 코팅 전처리에 해당하는 분말 효과이며, 특히 탄화텅스텐 분말을 통한 재료적 auto-shroud 효과와 미세분말을 이용한 분말 표면열속의 증가에 따른 용융률 증가효과를 연구에 포함할 계획이다. 이러한 연구는 열적, 그리고 재료적 해석을 바탕으로 해석적 접근을 통해 이루어진다.

• Korean Journal of Materials Research
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• v.6 no.9
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• pp.919-924
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• 1996

사염화우라늄을 제조하기 위한 가장 효율적인 반응계는 이산화우라늄, 염소가스와 탄소분말이다. 여러 가지 실험변수 가운데 이산화우라늄의 염소화반응에 사용된 염소가스 주입량과 탄소의 양이 사염화우라늄 제조에 미치는 영향에 관하여 연구하였다. 각각의 실험변수들에 대한 전화율과 휘발률 계산을 통해 효율적인 반응을 위한 적정 염소가스 주입량과 탄소의 양을 구하였고, 이산화우라늄의 증가함에 따라 직접접촉에 의한 기체-고체반응에서는 전화율과 휘발률은 증가했으나 이후 과량을 첨가함에 따라 감소하였고, 용융염내의 기체-액체반응에서는 전화율의 미미한 증가와 휘발률의 감소를 확인하였가. 염소주입량이 증가함에 따라 전화율과 휘발률이 증가했으며, 과량의 염소가수 주입시 고이온가 염화물의 생성량이 증가하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.11
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• pp.5357-5364
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• 2011

The objective of this study is development of carbon recycle technology which convert carbon dioxide captured from flue gas to carbon monoxide or carbon and reuse in industrial fields. Since carbon dioxide is very stable and difficult to decompose, metal oxide was used as activation agent for the decomposition of carbon dioxide at low temperature. Metal oxides which convert $CO_2$ to CO or carbon were prepared using Ba-ferrite by solid and hydrothermal synthesis. TPR/TPO and TGA were used in this study. The results of TPR by H2 and TPO by $CO_2$ showed that Ba-ferrite powders synthesized by hydrothermal method were better than those by solid method. TGA showed contrary results that reduction of Ba-ferrite powders synthesized using solid method by $H_2$ was 21.96 wt%, oxidation by $CO_2$ was 21.24 wt% and 96.72 wt% of $CO_2$ decomposition efficiency showing excellent oxidation-reduction characteristics at $500^{\circ}C$.

• Resources Recycling
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• v.31 no.6
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• pp.60-65
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• 2022

This study presents the carburization process for recycling sludge, which was formed during silicon wafer machining. The sludge used in the carburization process is a mixture of silicon and silicon carbide (SiC) with iron as an impurity, which originates from the machine. Additionally, the sludge contains cutting oil, a fluid with high viscosity. Therefore, the sludge was dried before carburization to remove organic matter. The dried sludge was washed by acid cleaning to remove the iron impurity and subsequently carburized by heat treatment under vacuum to form the SiC powder. The ratio of silicon to SiC in the sludge was varied depending on the sources and thus carbon content was adjusted by the ratio. With increasing SiC content, the carbon content required for SiC formation increased. It was demonstrated that substoichiometric SiC_x (x<1) was easily formed when the carbon content was insufficient. Therefore, excess carbon is required to obtain a pure SiC phase. Moreover, size reduction by high-energy milling had a beneficial effect on the suppression of SiC_x, forming the pure SiC phase.

• Journal of the Korean Electrochemical Society
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• v.18 no.4
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• pp.143-149
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• 2015

Carbon-coated $Li_2MnSiO_4$ powders as the active materials for the cathode were synthesized by planetary ball milling and solid-state reaction, and their phase formation behavior and charge-discharge properties were investigated. Calcination temperature and atmosphere were controlled in order to obtain the ${\beta}-Li_2MnSiO_4$ phase, which was active electrochemically, and the carbon-coated $Li_2MnSiO_4$ active material powders with near single phase ${\beta}-Li_2MnSiO_4$ could be fabricated. The particles of the synthesized powders were secondary particles composed of primary ones of about 100 nm size. The carbon incorporation was essential to enable the Li ions to be inserted and extracted from $Li_2MnSiO_4$ active materials, and the initial capacity of 192 mAh/g could be obtained in the $Li_2MnSiO_4$ active materials with 4.8 wt% of carbon.

• Applied Chemistry for Engineering
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• v.24 no.1
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• pp.49-54
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• 2013

We fabricated a composite carbon electrode to remove nitrate ions selectively from a mixed solution of anions. The electrode was fabricated by coating the surface of a carbon electrode with the nitrate-selective anion exchange resin (BHP55, Bonlite Co.) powder. We performed capacitive deionization (CDI) experiments on a mixed solution containing chloride, nitrate, and sulfate ions using a BHP55 cell constructed with the fabricated electrode. The removal of nitrate ions in the BHP55 cell was compared to that of a membrane capacitive deionization (MCDI) cell constructed with ion exchange membranes. The total quantity of ions adsorbed in BHP55 cell was $38.3meq/m^2$, which is 31% greater than that of MCDI cell. In addition, the number of nitrate adsorption in the BHP55 cell was $15.9meq/m^2$ (42% of total adsorption), 2.1 times greater than the adsorption in the MCDI cell. The results showed that the fabricated composite carbon electrode is very effective in the selective removal of nitrate ions from a mixed solution of anions.

• Polymer(Korea)
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• v.24 no.2
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• pp.237-244
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• 2000

Phenolic resin used as a precursor of carbonized matrix for carbon-carbon composites was modified by addition of molybdenum disilicide (MoSi$_2$) in various concentrations of 0, 4, 12 and 20% by weight to improve the anti-oxidation properties of the composites. The green body was manufactured by a prepreg method and was submitted to carbonization up to 110$0^{\circ}C$. In this work, the oxidation behavior of carbon-carbon composites with MoSi$_2$ as an oxidation inhibitor was investigated at the temperature range of 600-100$0^{\circ}C$ in an air environment. The carbon-carbon composites with MoSi$_2$ showed a significantly improved oxidation resistance due to both the reduction of the porosity formation and the formation of mobile diffusion barrier for oxygen when compared to those without MoSi$_2$. Carbon active sites should be blocked, decreasing the oxidation rate of carbon. This is probably due to the effect of the inherent MoSi$_2$ properties, resulted from a formation of the protective layer against oxygen attack in the composites studied.

• Journal of the Korean Vacuum Society
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• v.17 no.2
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• pp.170-174
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• 2008

We have studied, using Raman and photoluminescence (PL) spectroscopy, material property changes of single-walled carbon nanotubes (SWCNTs) dispersed in sodium dodecyl sulfate(SDS) aqueous solution by ultrasonication. Radial breathing mode Raman intensities of the dispersed SWCNTs shows different behavior depending on their chiralities as the sonication time increases. As the amount of SWCNTs dispersed in 1wt% SDS solution increases, both a downshift of the G-band Raman frequency and an enhancement in the PL intensity were observed.

• Composites Research
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• v.26 no.6
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• pp.373-379
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• 2013

The coating of metal surface with carbon nanotubes (CNTs) has been studied for the heat transfer enhancement of the boiling and condensation of refrigerant. The MWCNT/copper composite powder was made by the attrition ball milling, which has been coated on the copper wafer by electrostatic powder coating and sintered with electric furnace. In this paper, experiments were performed to assess the characterization and comparison of CNT before and after sinterning and the morphology changes of the CNT/Cu-coated surface. The samples were examined by the scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDAX) and raman spectroscopy. To verify the heat transfer enhancement, boiling heat transfer tests were performed.