• Nuclear Engineering and Technology
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• 제45권2호
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• pp.211-218
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• 2013

Large quantities of irradiated graphite waste from graphite-moderated nuclear reactors exist and are expected to increase in the case of High Temperature Reactor (HTR) deployment [1,2]. This situation indicates the need for a graphite waste management strategy. Of greatest concern for long-term disposal of irradiated graphite is carbon-14 ($^{14}C$), with a half-life of 5730 years. Fachinger et al. [2] have demonstrated that thermal treatment of irradiated graphite removes a significant fraction of the $^{14}C$, which tends to be concentrated on the graphite surface. During thermal treatment, graphite surface carbon atoms interact with naturally adsorbed oxygen complexes to create $CO_x$ gases, i.e. "gasify" graphite. The effectiveness of this process is highly dependent on the availability of adsorbed oxygen compounds. The quantity and form of adsorbed oxygen complexes in pre- and post-irradiated graphite were studied using Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Xray Photoelectron Spectroscopy (XPS) in an effort to better understand the gasification process and to apply that understanding to process optimization. Adsorbed oxygen fragments were detected on both irradiated and unirradiated graphite; however, carbon-oxygen bonds were identified only on the irradiated material. This difference is likely due to a large number of carbon active sites associated with the higher lattice disorder resulting from irradiation. Results of XPS analysis also indicated the potential bonding structures of the oxygen fragments removed during surface impingement. Ester- and carboxyl-like structures were predominant among the identified oxygen-containing fragments. The indicated structures are consistent with those characterized by Fanning and Vannice [3] and later incorporated into an oxidation kinetics model by El-Genk and Tournier [4]. Based on the predicted desorption mechanisms of carbon oxides from the identified compounds, it is expected that a majority of the graphite should gasify as carbon monoxide (CO) rather than carbon dioxide ($CO_2$). Therefore, to optimize the efficiency of thermal treatment the graphite should be heated to temperatures above the surface decomposition temperature increasing the evolution of CO [4].

• Carbon letters
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• 제8권3호
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• pp.207-213
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• 2007

The properties and electrochemical characteristics of anode material using pitch-coated graphite residue compounds by heat-treatment at $600^{\circ}C$ for 1 hour were investigated. The distance of layers of pitch-coated graphite residual compounds was 3.3539 ${\AA}$, which was as same as that of graphite. Its electrochemical and charge discharge characteristics were tested according to different four types of carbon material, natural graphite, pitch-coated graphite, amorphous graphite and pitch-coated graphite residual compounds, respectively. So it was shown the best charge-discharge characteristics in all of the samples. For the electrochemical and charge-discharge characteristics, although pitch-coated graphite residual compounds had different carbon contents 70% and 80%, these two samples were shown good electrochemical and charge-discharge characteristics.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.2
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• pp.1199-1202
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• 2004

리튬이온전지 음극활질용으로 Hybrid of pitch based graphite impregnating natural graphite와 Hybrid of pitch based carbon impregnating natural graphite로 탄소전극을 제작하여 전기화학적인 특성을 연구하였다. Natural graphite에 pitch based graphite나 pitch based carbon의 혼합은 흑연의 이론용량인 372 mAh/g를 초과하는 고용량을 나타내었다. 이것은 극소공동에 리튬종의 삽입과 탈삽입에 의한 것으로 파악된다. 그러나 충 방전이 계속 진행되면서 방전용량이 급격히 저하되는 현상이 관찰되었다. X-선 회절분석 결과로부터 Hybrid of pitch based carbon impregnating natural graphite 탄소전극에는 amorphous carbon이 상대적으로 다량 존재한다는 것을 확인하였고, 이는 리튬의 삽입된 상태의 전위에 분포가 있어 충 방전시에 완만한 전압의 구배를 만들며, 비가역용량을 증가시키는 요인으로 파악되었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 제6회 학술대회 논문집 일렉트렛트 및 응용기술연구회
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• pp.27-30
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• 2004

Different types of hybrid negative materials on pitch based carbon and natural graphite for lithium ion batteries were studied. Two types of active materials were prepared, that is, pitch based graphite carbon, and pitch based carbon impregnating natural graphite. The specific capacity, capacity recovery in high temperature condition, and other electrochemical properties were achieved for these materials. We found that addition of natural graphite type to the pitch based carbon can significant1y improve the specific capacity and interfacial resistance. However, use of natural graphite will cause a serious capacity loss in the high temperature condition owing to its increasing interface resistance. The specific capacity ranged from 321 to 348 mAh/g and the maximum specific capacity was obtained in the case of pitch based carbon impregnating natural graphite.

• 한국도로학회논문집
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• 제17권5호
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• pp.11-18
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• 2015

PURPOSES : The purpose of this study is to develop a deicing pavement system using carbon fiber or graphite with high electrical conductivity and thermal conductivity. METHODS: Based on literature reviews, in general, conventional concrete does not exhibit electrical and thermal conductivity. In order to achieve a new physical property, experiments were conducted by adding graphite and carbon fiber to a mortar specimen. RESULTS: The result of the laboratory experiment indicates that the addition of graphite can significantly reduce the compressive strength and improve the thermal conductivity of concrete. In the case of carbon fiber, however, the compressive strength of the concrete is slightly increased, whereas, the thermal conductivity is slightly decreased against the plain mortar irrespective of the length of the carbon fiber. In addition, a mixture of the graphite and carbon fiber can greatly improve the degree of heating test. CONCLUSIONS : Various properties of cement mortar change with the use of carbon fiber or graphite. To enhance the conductivity of concrete for deicing during winter, both carbon fiber and graphite are required to be used simultaneously.

• Carbon letters
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• 제7권3호
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• pp.196-200
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• 2006

Graphite has hexagonal closed packing structure with two bonding characteristics of van der Waals bonding between the carbon layers at c axis, and covalent bonding in the carbon layer at a and b axis. Graphite has high tolerant to the extreme conditions of high temperature and neutron irradiations rather than any other materials of metals and ceramics. However, carbon elements easily react with oxygen at as low as 400C. Considering the increasing production of today of hydrogen and electricity with a nuclear reactor, study of oxidation characteristics of graphite is very important, and essential for the life evaluation and design of the nuclear reactor. Since the oxidation behaviors of graphite are dependent on the shapes of testing specimen, critical care is required for evaluation of nuclear reactor graphite materials. In this work, oxidation rate and amounts of the isotropic graphite (IG-110, Toyo Carbon), currently being used for the Koran nuclear reactor, are investigated at various temperature. Oxidation process or principle of graphite was figured out by measuring the oxidation rate, and relation between oxidation rate and sample shape are understood. In the oxidation process, shape effect of volume, surface area, and surface to volume ratio are investigated at $600^{\circ}C$, based on the sample of ASTM C 1179-91.

• Carbon letters
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• 제11권2호
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• pp.90-95
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• 2010

Carbon materials such as graphite and graphene exhibit high electrical conductivity. We examined the electrical conductivity of synthetic and natural graphene powders after the chemical reduction of synthetic and natural graphite oxide from synthetic and natural graphite. The trend of electrical conductivity of both graphene (synthetic and natural) was compared with different graphite materials (synthetic, natural, and expanded) and carbon nanotubes (CNTs) under compression from 0.3 to 60 MPa. We found that synthetic graphene showed a marked increment in electrical conductivity compared to natural graphene. Interestingly, the total increment in electrical conductivity was greater for denser graphite; however, an opposite behavior was observed in nanocarbon materials such as graphene and CNTs, probably due to the differing layer arrangement of nanocarbon materials.

• Carbon letters
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• 제12권4호
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• pp.243-248
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• 2011

Two different types of graphite, such as flake graphite (FG) and spherical graphite (SG), were used as anode materials for a lithium-ion secondary battery in order to investigate their electrochemical performance. The FG particles were prepared by pulverizing natural graphite with a planetary mill. The SG particles were treated by immersing them in acid solutions or mixing them with various carbon additives. With a longer milling time, the particle size of the FG decreased. Since smaller particles allow more exposure of the edge planes toward the electrolyte, it could be possible for the FG anodes with longer milling time to deliver high reversible capacity; however, their initial efficiency was found to have decreased. The initial efficiency of SG anodes with acid treatments was about 90%, showing an over 20% higher value than that of FG anodes. With acid treatment, the discharge rate capability and the initial efficiency improved slightly. The electrochemical properties of the SG anodes improved slightly with carbon additives such as acetylene black (AB), Super P, Ketjen black, and carbon nanotubes. Furthermore, the cyclability was much improved due to the effect of the conductive bridge made by carbon additives such as AB and Super P.

• Carbon letters
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• 제4권1호
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• pp.36-39
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• 2003

Carbon and carbon-based materials are used in nuclear reactors and there has recently been growing interest to develop graphite and carbon based materials for high temperature nuclear and fusion reactors. Efforts are underway to develop high density carbon materials as well as amorphous isotropic carbon for the application in thermal reactors. There has been research on coated nuclear fuel for high temperature reactor and research and development on coated fuels are now focused on fuel particles with high endurance during normal lifetime of the reactor. Since graphite as a moderator as well as structural material in high temperature reactors is one of the most favored choices, it is now felt to develop high density isotropic graphite with suitable coating for safe application of carbon based materials even in oxidizing or water vapor environment. Carboncarbon composite materials compared to conventional graphite materials are now being looked into as the promising materials for the fusion reactor due their ability to have high thermal conductivity and high thermal shock resistance. This paper deals with the application of carbon materials on various nuclear reactors related issues and addresses the current need for focused research on novel carbon materials for future new generation nuclear reactors.

• The Korean Journal of Ceramics
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• 제2권4호
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• pp.221-225
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• 1996

In diamond synthesis by metal film growth method under high pressure and high temperature, the nucleation and growth of diamond was observed dependent on the carbon source variation from graphite powder to the heat treated powders of lamp black carbon. At the low driving force condition near equilibrium pressure and temperature line, nucleation of diamond did not occur but growth of seed diamond appeared in the synthesis from lamp black carbon while both nucleation and growth of diamond took place in the synthesis from graphite. Growth morphology change of diamond occurred from cubo-octahedron to octahedron in the synthesis from graphite but very irregular growth of seed diamond occurred in the synthesis from lamp block carbon. Lamp black carbon transformed to recrystallized graphite first and very nucleation of diamond was observed on the recrystallized graphite surface. Growth morphology of diamond on the recrystallized graphite was clear cubo-octahedron even at higher pressure departure condition from equilibrium pressure and temperature line.