• 공업화학
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• 제25권6호
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• pp.592-597
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• 2014

본 연구에서는 리튬이차전지의 음극활물질로 graphite의 전기화학적 특성을 향상시키기 위하여 졸-겔 법에 의한 graphite/$SiO_2$ 복합소재를 제조하였다. 제조된 graphite/$SiO_2$ 합성물은 XRD, FE-SEM과 EDX를 사용하여 분석하였다. $SiO_2$에 의해 표면 개질된 graphite는 SEI 층을 안정화시키는데 장점을 보여 주었다. Graphite/$SiO_2$ 전극을 작업 전극으로, 리튬메탈을 상대전극으로 하여 리튬이차전지의 전기화학 특성을 조사하였다. $LiPF_6$ 염과 EC/DMC 용매를 전해질로 사용하여 제조한 코인 셀의 전기화학적 거동은 충방전, 사이클, 순환전압전류, 임피던스 테스트를 진행하여 평가하였다. Graphite/$SiO_2$ 전극을 사용한 리튬이차전지는 graphite 전극을 사용한 전지보다 우수한 특성을 보여주었으며, 0.1 C rate에서 465 mAh/g의 용량을 보여주었다. 또한 개질된 graphite 전극은 0.8 C rate에서 99%의 용량 보존율을 보여주었다.

• The Korean Journal of Ceramics
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• 제3권1호
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• pp.47-51
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• 1997

The dense sintered bodies of Si/SiC composite with various Si contents could be fabricated by changing the green density in the forming process. The Si/SiC/graphite composites with various graphite contents could be also fabricated by changing a graphite content in the starting composition. Their mechanical and tribological properties were characterized and wear mechanism was also studided. The hardness and strength of the Si/SiC and the Si/SiC/graphite were decreased with increasing the contents of free Si and graphite, respectively. However, the friction coefficient and specific wear rate had no specific relations to their hardness and strength. Adhesion of free Si was a main factor to determine a wear resistance of the Si/SiC composite. In the case of the Si/SiC/graphite, solid lubricationl and liquid reservoir of the graphite particles played the main role of the reduction of the friction force. In the torque test to estimate the possibility of practical of practical applications, the value of torque between the Al2O3 disk and Si/SiC/graphite disk was 1/6 lower compared with two $Al_2O_3$ disks on the basis of 100,000 cycles.

• 한국재료학회지
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• 제15권1호
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• pp.66-72
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• 2005

Surface modification of the silicon-coated graphite was carried out at $200^{\circ}C\~800^{\circ}C$ under hydrogen atmosphere. The silicon-coated graphites were prepared by fluidized-bed spray coating method. The components of silicon films prepared on the graphite consist of SiO, $SiO_x\;(1. The components of silicon films at $200^{\circ}C$ of heat treatment brought on the higher fraction of SiO and $SiO_x$ than that of $SiO_2$. However, inactive $SiO_2$ fraction increases with increase of the heat treatment temperature. The high content of SiO and $SiO_x$ in the silicon film on graphite leads to the higher discharge capacity in our experimental range.

• 한국세라믹학회지
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• 제34권12호
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• pp.1199-1204
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• 1997

SiC conversion layer was fabricated by the chemical vapor reaction between graphite substrate and silica powder. The CVR process was carried out in nitrogen atmosphere at 175$0^{\circ}C$ and 185$0^{\circ}C$. From the reduction of silica powder with graphite substrate, the SiO vapor was created, infiltrated into the graphite substrate, then, the SiC conversion layer was formed from the vapor-solid reaction of SiO and graphite. In the XRD pattern of conversion layer, it was confirmed that 3C $\beta$-SiC phase was created at 175$0^{\circ}C$ and 185$0^{\circ}C$. Also, in the back scattered image of cross-sectional conversion layer, it was found that the conversion layer was easily formed at 185$0^{\circ}C$, the interface of graphite substrate and SiC layer was observed. It was though that the coke particle size and density of graphite substrate mainly affect the XRD pattern and microstructure of SiC conversion layer. In the oxidation test of 100$0^{\circ}C$, the SiC converted graphites exhibited good oxidation resistance compared with the unconverted graphites.

• 한국분말재료학회지
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• 제16권6호
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• pp.389-395
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• 2009

A Si-CuO-graphite composite was prepared by a mechanical alloying (MA) method. The Si-CuO composite has a mixture structure, where CuO is homogeneously dispersed in Si. Also, $Cu_2O$ and $Cu_3Si$ phases were formed during MA and heat treatment. Graphite with the Si-CuO composite was mixed in the same mill for 30 minutes with weight ratio of Si-CuO composite and graphite as 1:1. The Si-CuO composite was homogeneously covered with graphite. SiC phase was not formed. Electrochemical tests of the composite have been investigated, and the first charge and discharge capacities of the material were about 870mAh/g and 660mAh/g, respectively. Those values are about 76% of the first cycle efficiency. The cycle life of the composite showed that the initial discharge capacity of 660 mAh/g could be maintained up to 92% after 20 cycles.

• 전기화학회지
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• 제15권3호
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• pp.154-159
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• 2012

Si계 음극소재는 리튬 삽입-탈착 중 일어나는 큰 구조적 부피변화와 입도변화로 인해 빠른 성능 퇴화가 일어나는 단점이 있다. 산화물 SiO 음극소재는 리튬과의 반응 중 비활성상인 $Li_2O$ 및 lithium silicate가 형성되어 Si의 부피변화를 완화시키는 버퍼 역할을 하므로 용량은 Si보다 적으나 개선된 용량 유지 특성을 보이는 것으로 알려져 있다. 본 연구에서는 Si의 부피변화 완화를 위하여 저가의 $SiO_2$와 입자간 전기전도성을 향상시키는 흑연을 구조안정화 기재로서 사용하여 Si-$SiO_2$-흑연 복합재 음극을 제작하였다. 구조안정화 뿐만 아니라 silane계 전해액 첨가제를 이용하여 Si-$SiO_2$-흑연 복합재 음극과 전해액간 계면을 안정화시킴으로써 용량 유지 특성이 개선되는 효과에 대해 보고하고자 한다.

• Nuclear Engineering and Technology
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• 제55권5호
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• pp.1855-1862
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• 2023

Graphite crucibles are used for melting uranium and its alloys in VIM furnace. Various coating materials namely Al₂O₃, ZrO₂, MgO etc. are applied on the inner surface of the crucibles using paint brush or thermal spray technique to mitigate U-C interaction. These leads to significant amount of carbon pick-up in uranium. In this study, the attempts are made to develop multilayer coatings comprising of SiC/Y₂O₃ and Mo/Y₂O₃ on graphite to study the feasibility of minimizing U-C interaction. The parameters are optimized to prepare SiC coating of about 70㎛ thickness using CVD technique on graphite coupons and subsequently Y₂O₃ coating of about 250㎛ thickness using plasma spray technique. Molybdenum and Y₂O₃ layers were deposited using plasma spray technique with 70㎛ and 250㎛ thickness, respectively. Interaction studies of the coated graphite with molten uranium at 1450℃ for 20 min revealed that Y₂O₃ coating with SiC interlayer provides physical barrier for uranium-graphite interaction, however, this led to the physical separation of coating layer. Y₂O₃ coating with Mo interlayer provided superior barrier effect showing no degradation and the coatings remained intact after interaction tests. Therefore, the Mo/Y₂O₃ coating was found to be a promising solution for minimizing carbon pick-up during uranium/uranium alloy melting.

• Bulletin of the Korean Chemical Society
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• 제31권5호
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• pp.1257-1261
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• 2010

The electrochemical performances of anode composites comprising elemental silicon (Si), silicon monoxide (SiO), and graphite (C) were investigated. The composite devoid of elemental silicon (SiO:C = 1:1) and its carbon coated composite showed reduced capacity degradation with measured values of 606 and 584 mAh/g at the fiftieth cycle. The capacity retention nature when the composites were cycled followed the order of Si:SiO:C = 3:1:4 < Si:SiO:C = 2:2:4 < SiO:C = 1:1 < SiO:C = 1:1 (carbon coated). A comparison of the capacity retention properties for the composites in terms of the silicon content showed that a reduced silicon content increased the stability of the composite electrodes. Even though the carbon-coated composite delivered low capacity during cycling compared to the other composites, its low capacity degradation made the anode a better choice for lithium ion batteries.

• Bulletin of the Korean Chemical Society
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• 제30권7호
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• pp.1607-1610
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• 2009

The carbon-coated Si/Cu powder has been prepared by mechanical ball milling and hydrocarbon gas decomposition methods. The phase of Si/Cu powder was analyzed using X-ray diffraction (XRD), dispersive Raman spectroscopy, electron probe microanalysis (EPMA) and transmission electron microscope (TEM). The carbon-coated Si/Cu powders were used as anode active material for lithium-ion batteries. Their electrochemical properties were investigated by charge/discharge test using commercial LiCo$O_2$ cathode and lithium foil electrode, respectively. The surface phase of Si/Cu powders consisted of carbon phase like the carbon nanotubes (CNTs) with a spacing layer of 0.35 nm. The carbon-coated Si/Cu/graphite composite anode exhibited a higher capacity than commercial graphite anode. However, the cyclic efficiency and the capacity retention of the composite anode were lower compared with graphite anode as cycling proceeds. This effect may be attributed to some mass limitations in LiCo$O_2$ cathode materials during the cycling.

• 한국세라믹학회지
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• 제34권4호
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• pp.380-386
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• 1997

The tribological properties of ceramics are very important in the application to engineering ceramic parts such as seal rings, pump parts, thread guides, and so on. In this study, the effects of graphite addition on the mechanical and tribological properties of alumina/graphite composites were investigated. The composites were prepared by the adding of graphite powder to the mixture of Al2O3, talc and calcium carbonate. Bending strength, water absorption, friction coefficient, the amount of worn out material at a certain time, and maximum surface roughness(Rmax) of the prepared composites were measured. Crystalline phases and microstructure were examined with XRD and SEM. The melt of Al2O3-CaO-MgO-SiO2 system was shown over 10 vol% graphite composition. As the amount of the graphite is increased, needle like crystals of mullite were formed and grown. We obtained the good properties of friction coefficients and wear resistance at the powder composition containing 15 vol% of graphite.