• 한국세라믹학회지
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• 제23권1호
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• pp.67-73
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• 1986

SiC and $SiC-Si_3N_4$ powder were synthesized via the carbiding and carbiding-nitriding reaction of Jecheon quartz respectively using graphite as a reducing agent. $\beta$-SiC+($\alpha$+$\beta$)-$Si_3N_4$ composite was obtained by the carbiding-nitriding reaction of Jecheon quartz-graphite mixture at 1, 35$0^{\circ}C$ in $H_2$ atmosphere. $\beta$-SiC+($\alpha$+$\beta$)-$Si_3N_4$ composite was obtained by the carbidint-nitriding reaction of Jecheon quartz-graphite mixture at 1, 35$0^{\circ}C$ in $N_2-H_2$ atmosphere. The ratio of $\beta$-SiC+($\alpha$+$\beta$)-$Si_3N_4$ content in a produced composite could be controlled by adjusting the reaction time and gaseous mixture.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2004년도 학술논문집
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• pp.105-114
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• 2004

This study investigated the thermal behavior of the nuclear graphite waste generated from the decommissioning of the Korean nuclear research reactor, The first part study investigated the decomposition rate of the nuclear graphite waste up to $1000^{\circ}C$ under various oxygen partial pressures using a thermo-gravimetric analyzer (TGA). Tested graphite waste sample not easily destroyed in the oxygen-deficient condition. However, the gas-solid oxidation reaction was found to be very effective in the presence of oxygen. No significant amount of the product of incomplete combustion was formed even in the limited oxygen concentration of 4% $O_2$. The influence of temperature and oxygen partial pressure was evaluated by the theoretical model analysis of the thermo-gravimetric data. The activation energy and the reaction order of graphite oxidation were evaluated as 128 kJ/mole and 1.1, respectively. The second part of this study investigated the behavior of radioactive elements under graphite oxidation atmosphere using thermodynamic equilibrium model. $^{22}Na$, $^{134}Cs$ and $^{137}Cs$ were found be the semi-volatile elements. Since volatile uranium species can be formulated at high temperatures above $1050^{\circ}C$, the temperature of incinerator furnace should be minimized. Other corrosion/activation products, fission products and uranium were found to be the non-volatile species.

• 공업화학
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• 제2권4호
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• pp.393-398
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• 1991

실제 실험 시간에 따른 시료의 무게변화와 생성가스의 조성 측정을 동시에 진행할 수 있는 실험실 규모의 장치를 칸 발란스를 이용하여 제작하였다. 급속 가열이 가능하도록 텅스텐 할로겐 등을 이용한 복사가열 방식을 채택하였고 시료 접시는 복사열을 충분히 흡수하도록 흑연을 사용하였다. 석탄가스화 실험조건에서 이 흑연이 반응기체와 반응하는 것을 막기위하여 실리콘나이트로 코팅하였고, 시료접시 바로 밑에 위치한 열전쌍에도 같은 방식으로 제작된 흑연 모자를 씌워 복사열 흡수능력이 서로 다른 흑연(시료접시)과 금속체(열전쌍) 사이에서 생길 수 있는 온도 측정의 오차를 최소화 하도록 하였다. 이 장치를 사용한 결과 상온에서 섭씨 800도까지 3 분 이내에 온도상승이 가능하였으며 시료 접시의 무게변화없이 실험중 석탄 시료의 무게 변화와 가스조성을 동시에 측정할 수 있었다.

• 한국세라믹학회지
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• 제44권8호
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• pp.445-450
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• 2007

A conversion layer of SiC was fabricated on the graphite substrate by a chemical vapor reaction method in order to enhance the oxidation resistance of graphite. The effect of boron carbide containing powder bed on the morphology of SiC conversion layer was investigated during the chemical vapor reaction of graphite with the reactive silicon-source at $1650^{\circ}C\;and\;1700^{\circ}C$ for 1 h. The presence of boron species enhanced the conversion of graphite into SiC, and altered the morphology of the conversion layer significantly as well. A continuous and thick SiC conversion layer was formed only when the boron source was used with the other silicon compounds. The boron is deemed to increase the diffusion of SiOx in SiC/C system.

• 대한화학회지
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• 제41권1호
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• pp.1-11
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• 1997

0.5 M $K_2SO_4$ 용액에서 여러 가지 세 탄소전극(glassy carbon, 인조흑연, graphite foil)에 대하여 양극분극에 따른 전극표면반응에 대한 연구를 임피던스 스펙트로스코피를 통하여 실시했다. Graphite foil 전극의 경우 이중츨 capacotance는 다른 두 전극재료에 비하여 높게 나타났으며, 양극분극시 glassy carbon과 인조 흑연(PVDF 혼합 graphite)은 전극계면에서 흡착현상에 의한 capacitance C의 영향이 현저하게 나타남을 알 수 있었다. 3종류 전극재료의 전기화학적 거동은 전극표면 조직의 차이에 의해 glassy carbon의 경우는 분극시 파라데이 임피던스의 영향을 받으며, graphite foil의 경우는 field transport의 지배를 받아 전압의 변화에 의한 임피던스 파라미터의 변화는 거의 나타나지 않았다.

• 한국주조공학회지
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• 제20권4호
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• pp.247-253
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• 2000

Titanium was melted in the CaO-coated alumina crucible and the reaction between the melt and the coating layer was negligible. The volume fraction of the gas porosity was decreased with increasing pressure and the sound bar castings with no porosity was obtained under the Ar atmosphere of the pressure of $300kN/mm^2$. The surface of the casting obtained from CaO-coated graphite mold was slightly rougher than that from graphite without coating. The reaction product of titanium melt with the layer of CaO was mainly titanium oxide and that with graphite crucible was titanium cabide with small amount of titanium nitride.

• 한국결정성장학회지
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• 제12권3호
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• pp.120-125
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• 2002

Si-wafers for solar cells were cast in a size of $50{\times}46{\times}0.5{\textrm}{mm}^3$ by vacuum casting method. The graphite mold coated by BN powder, which was to prevent the reaction of carbon with the molten silicon, was used. Without coating, the wetting and reaction of Si melt to graphite mold was very severe. In the case of BN coating, SiC was formed in the shape of tiny islands at the surface of Si wafer by the reaction between Si-melt and carbon of the graphite mold on the high temperature. The grain size was about 1 mm. The efficiency of Si solar cell was lower than that of Si solar cell fabricated on commercial single and poly crystalline Si wafer. The reason of low efficiency was discussed.

• 한국세라믹학회지
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• 제29권10호
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• pp.785-790
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• 1992

A study of the pack cemcented SiC coating on graphite was performed and the process conditions were evaluated by means of experimental design. The content of Si, P2O5, B and Al2O3 reaction temperature, reaction time and acid treatment wast tested as the experimental variables. The results were analyzed and compared by the characteristic value of 10% weight loss by oxidation. The acid treatment exhibited the most effective anti-oxidation property and the optimum conditions were the powder composition of 20% Si, 3% B and 77% SiC, the reaction temperature of 1550$^{\circ}C$ for 7 hours with phosphoric acid treatment. The pack coating performed under this condition improved the 10% weight loss oxidation temperature by 514$^{\circ}C$ compared to the bare graphite.

• Bulletin of the Korean Chemical Society
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• 제28권4호
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• pp.635-646
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• 2007

The reaction of gas-phase hydrogen atoms H with H atoms chemisorbed on a graphite surface has been studied by the classical dynamics. The graphite surface is composed of the surface and 10 inner layers at various gas and surface temperatures (Tg, Ts). Three chains in the surface layer and 13 chains through the inner layers are considered to surround the adatom site. Four reaction pathways are found: H2 formation, H-H exchange, H desorption, and H adsorption. At (1500 K, 300 K), the probabilities of H2 formation and H desorption are 0.28 and 0.24, respectively, whereas those of the other two pathways are in the order of 10-2. Half the reaction energy deposits in the vibrational motion of H2, thus leading to a highly excited state. The majority of the H2 formation results from the chemisorption-type H(g)-surface interaction. Vibrational excitation is found to be strong for H2 formed on a cold surface (~10 K), exhibiting a pronounced vibrational population inversion. Over the temperature range (10-100 K, 10 K), the probabilities of H2 formation and H-H exchange vary from 0 to ~0.1, but the other two probabilities are in the order of 10-3.

• 한국세라믹학회지
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• 제22권6호
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• pp.5-8
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• 1985

Graphite has been oxidized to graphite hydrogen sulfate in concentrated $H_2SO_4$. Anodic oxidation and chemical oxidation of graphite in $H_2SO_4$ generally leads to the formation of intercalation compounds of the ionic salt type through incorporation of $H_2SO_4^-$ions and $H_2SO_4$ molecules into the graphite. Several other reactions also accur at various points of the charging cycle. But there is no satisfactory kinetics and mechanism of intercalationin graphite. We have studied them with anodic oxidation and chemical oxidation. We found six distinct phenomena between 2nd stage and 1st stage in chemical oxidation. We examined them in detail by the following in the measurements electrical oxidation. X-ray diffractions UV-Vis spectroscopy density measurements. We could obtained a equation for kinetic according to the reaction rate from this results and mechanism of intercalation between 2nd stage and 1st stage with hydrogen sulfate in graphite. Three thesis were written for the mechanism of intercalation compounds in graphite with hydrogen sulfate ; first thesis is anodic oxidation second thesis is chemical oxidation and definition of transit phase between 2nd etc the third thesis is the kinetic mechanism of intercalation compounds in graphite with Hydrogen sulfate. This thesis is the first paper among three thesis as anodic oxidation.