• Journal of Mechanical Science and Technology
• /
• 제19권6호
• /
• pp.1338-1346
• /
• 2005

Effects of thermal contact resistance between heater and susceptor, susceptor and graphite board in a MOCVD reactor on temperature distribution and film growth rate were analyzed. One-dimensional thermal resistance model considering thermal contact resistance and heat transfer area was made up at first to find the temperature drop at the surface of graphite board. This one-dimensional model predicted the temperature drop of 18K at the board surface. Temperature distribution of a reactor wall from the three-dimensional computational fluid dynamics analysis including the gap at the wafer position showed the temperature drop of 20K. Film growth rates of InP and GaAs were predicted using computational fluid dynamics technique with chemical reaction model. Temperature distribution from the three-dimensional heat transfer calculation was used as a thermal boundary condition to the film growth rate simulations. Temperature drop due to the thermal contact resistance affected to the GaAs film growth a little but not to the InP film growth.

• Carbon letters
• /
• 제25권
• /
• pp.78-83
• /
• 2018

Pyrolyzed fuel oil (PFO) and coal tar was blended in the feedstock to produce pitch via thermal reaction. The blended feedstock and produced pitch were characterized to investigate the effect of the blending ratio. In the feedstock analysis, coal tar exhibited a distinct distribution in its boiling point related to the number of aromatic rings and showed higher Conradson carbon residue and aromaticity values of 26.6% and 0.67%, respectively, compared with PFO. The pitch yield changed with the blending ratio, while the softening point of the produced pitch was determined by the PFO ratio in the blends. On the other hand, the carbon yield increased with increasing coal tar ratio in the blends. This phenomenon indicated that the formation of aliphatic bridges in PFO may occur during the thermal reaction, resulting in an increased softening point. In addition, it was confirmed that the molecular weight distribution of the produced pitch was associated with the predominant feedstock in the blend.

• 한국세라믹학회지
• /
• 제48권2호
• /
• pp.173-177
• /
• 2011

Decomposition promoting factors and decomposition mechanism in the zinc decomposition process of waste hard metals which are composed mostly of tungsten carbide and cobalt were evaluated. Zinc volatility amount was suppressed and zinc valatilization pressure was produced in the reaction graphite crucible inside an electric furnace for ZDP. Reaction was done for 2 h at $650^{\circ}C$, which 100 % decomposed the waste hard metals that were over 30 mm thick. As for the separation-decomposition of waste hard metals, zinc melted alloy formed a liquid composed of a mixture of ${\gamma}-{\beta}1$ phase from the cobalt binder layer (reaction interface). The volume of reacted zone was expanded and the waste hard metal layer was decomposed-separated horizontally from the hard metal. Zinc used in the ZDP process was almost completely removed-collected by decantation and volatilization-collection process at $1000^{\circ}C$.

• Tribology and Lubricants
• /
• 제25권1호
• /
• pp.20-24
• /
• 2009

TiC-derived carbon coatings have been synthesized at $600^{\circ}C$ temperature treatment with $H_2/Cl_2$ mixture gases. From Raman spectroscopy measurements, the modified layer was covered with carbon and the thick-ness of the layer was increased with increasing reaction time. And $I_D/I_G$ ratio was decreased with increasing reaction time. The superior tribological property was obtained from TiC reacted with $Cl_2$ gas for 2 hrs. And the tribological property measurements indicate that TiC-derived carbon layer has $0.9{\times}10_{-6}mm^3/Nm$ in wear coefficient and 0.13 in friction coefficient.

• Journal of Electrochemical Science and Technology
• /
• 제13권3호
• /
• pp.398-406
• /
• 2022

To satisfy the growing demand for high-performance batteries, diverse novel anode materials with high specific capacities have been developed to replace commercial graphite. Among them, cobalt hydroxides have received considerable attention as promising anode materials for lithium-ion batteries as they exhibit a high reversible capacity owing to the additional reaction of LiOH, followed by conversion reaction. In this study, we introduced graphene in the fabrication of Co(OH)₂-based anode materials to further improve electrochemical performance. The resultant Co(OH)₂/graphene composite exhibited a larger reversible capacity of ~1090 mAh g^-1, compared with ~705 mAh g^-1 for bare Co(OH)₂. Synchrotron-based analyses were conducted to explore the beneficial effects of graphene on the composite material. The experimental results demonstrate that introducing graphene into Co(OH)₂ facilitates both the conversion and reaction of the LiOH phase and provides additional lithium storage sites. In addition to insights into how the electrochemical performance of composite materials can be improved, this study also provides an effective strategy for designing composite materials.

• 공업화학
• /
• 제28권1호
• /
• pp.80-86
• /
• 2017

본 연구에서는 흑연섬유(GF)의 전기적 특성을 변화시키기 위하여 질소관능기 도입을 실시하였고, 처리조건에 따라 흑연섬유의 발열성능을 평가하였다. 흑연섬유는 $200^{\circ}C$에서 2 h 동안 열-고상반응법으로 처리되었다. 질소도핑 된 흑연섬유의 표면특성은 XPS로 조사되었으며, 저항 및 발열온도는 전위계 시스템과 열화상카메라를 이용하여 측정하였다. XPS 결과 우레아 함량이 증가함에 따라 흑연섬유 표면의 질소관능기가 증가하였으며, 이 질소관능기가 도입됨에 따라서 흑연섬유의 발열특성이 또한 향상되었다. 우레아 처리된 흑연섬유의 최대 발열온도는 60 V에서 $53.8^{\circ}C$로 나타났으며, 이는 미처리 흑연섬유와 비교하여 발열특성이 약 55% 향상됨을 알 수 있었다. 이러한 효과는 열고상반응법에 의해서 흑연섬유 표면에 도입된 질소관능기 때문에 기인한 것으로, 이는 흑연섬유의 열적 특성에 상당히 영향을 주었다.

• 전기화학회지
• /
• 제26권1호
• /
• pp.11-18
• /
• 2023

전기자동차 시장의 급속한 성장으로 이차전지의 사용이 급증함에 따라 사용 후 전지의 폐기 및 재활용이 심각한 문제로 제기되고 있다. 사용 후 리튬이온 전지를 처리하기 위해서는 저장된 에너지를 제거하기 위하여 효과적으로 방전하는 과정이 필수적이다. 본 연구에서는 흑연과 LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622)을 사용하여 코인셀 형태로 반쪽전지 및 완전지를 제조하였고, 이를 과방전할 때 발생하는 전기화학적 거동에 대하여 분석하였다. 반쪽전지를 사용하여 양극과 음극을 각각 과방전시키면, 양극에서는 먼저 전이금속 산화물이 금속으로 환원되는 전환반응을 겪게 되며, 음극에서는 SEI 피막의 분해에 이어 집전체인 Cu가 용출되는 부반응이 발생하였다. 또한, 이러한 과방전의 발생 시에는 큰 분극을 필요로 하였다. 완전지의 과방전 시에는 각각의 부반응이 진행되는 시점에 존재하는 큰 분극들로 인하여 부반응의 본격적인 발생 전에 0 V에 도달하여 방전이 종료되었다. 그러나, 사이클을 통하여 용량이 퇴화된 완전지의 경우에는 과방전거동이 변화하여 음극에서 Cu 집전체의 부식이 발생됨을 확인하였다. 따라서, 사용 후 전지는 사용 전의 전지와는 과방전 시에 다른 거동을 지니고 있으므로 이러한 점들이 고려되어야 한다.

• Korean Chemical Engineering Research
• /
• 제46권6호
• /
• pp.1113-1118
• /
• 2008

$CuFe_2O_4$와 $Fe_3O_4$의 탄소 침적 및 환원 특성을 $900^{\circ}C$에서 TGA, XRD, SEM, TEM 등의 분석 및 반응 후 가스조성분석을 통하여 연구하였다. XRD 분석결과 환원된 $Fe_3O_4$는 Fe(iron)와 graphite(C) 그리고 $Fe_3C$으로 구성되어 있는 것으로 나타났다. 반면에, 환원된 $CuFe_2O_4$에서는 graphite나 $Fe_3C$가 나타나지 않았다. SEM을 이용하여 표면 구조를 관찰한 결과 환원된 $Fe_3O_4$의 표면이 탄소로 뒤덮여 있는 것을 확인할 수 있었다. 이와 달리 $CuFe_2O_4$에서는 $CH_4$ 전환율 및 환원속도가 높았고, 환원반응 후 탄소량 추정결과 $Fe_3O_4$에서보다 훨씬 낮게 나타났다. TEM 분석결과 $Fe_3O_4$ 입자로부터 탄소가 판상구조의 형태로 성장한 것을 확인할 수 있었다.

• 대한기계학회논문집A
• /
• 제27권7호
• /
• pp.1132-1137
• /
• 2003

This study dealt with the suppression of interfacial reaction between Nb and MoSi$_2$ for the fabrication of high toughness Nb/MoSi$_2$ laminate composites, based on the results of a thermodynamical estimation. Especially, the effect of ZrO$_2$ particle on the interfacial reaction of Nb/MoSi$_2$ bonding materials has been examined. Nb/MoSi$_2$ bonding materials have been successfully fabricated by alternatively stacking matrix mixtures and Nb sheets and hot pressing in the graphite mould. The addition of ZrO$_2$ particle to MoSi$_2$ matrix is obviously effective for promoting both the interfacial reaction suppression and the sintered density of Nb/MoSi$_2$ bonding materials, since it is caused by the formation of ZrSiO$_4$ in the MoSi$_2$-ZrO$_2$ matrix mixture. The interfacial shear strength of Nb/MoSi$_2$ bonding materials also decreases with the reduction of interfacial reaction layer associated with the content of ZrO$_2$ particle and the fabrication temperature.

• 한국수소및신에너지학회논문집
• /
• 제25권6호
• /
• pp.620-628
• /
• 2014

Direct Carbon Fuel Cell(DCFC) is one of new power generation that the chemical energy of solid carbon can be converted into electrical energy directly. At the high temperature, the electrochemical reaction of the carbon takes place and the carbon reacts with oxygen to produce carbon dioxide as followed overall reaction ($C+O_2{\rightarrow}CO_2$). However, in case of using the raw coals as a fuel of DCFC, the volatile matter containing carbon, hydrogen, and oxygen produces at operating temperature. In this study, the electrochemical reaction of Adaro coal was compared with Graphite. This work focused on the electrochemical reaction of two kinds of solid carbon by Electrochemical Impedance Spectroscopy(EIS). The EIS results were estimated by equivalent circuit analysis. The constant phase element(CPE) was applied in Randle circuit to explain an electrode and fuel interface. The correlation between the fuel characteristic and electrochemical results was discussed by elements of equivalent circuit of each fuel.