• 한국재료학회지
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• 제28권10호
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• pp.601-609
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• 2018

To study the effects of graphite shape and the composite fabricating method on the mechanical properties of graphite/copper (Gr/Cu) composites, a copper composite using graphite flakes or graphite granules as reinforcing phases is fabricated using mechanical mixing or electroless plating method. The mechanical properties of the Gr/Cu composites are evaluated by compression tests, and the compressive strength and elongation of the Gr/Cu composites using graphite granules as a reinforcing phase are compared with those of Cu composites with graphite flakes as a reinforcing phase. The compressive yield strength or maximum strength of the Gr/Cu composites with graphite granules as a reinforcing phase is higher than that of the composites using graphite flakes as a reinforcing phase regardless of the alignment of graphite. The strength of the composite produced by the electroless plating method is higher than that of the composite material produced by the conventional mechanical mixing method regardless of the shape of the graphite. Using graphite granules as a reinforcing phase instead of graphite flakes improves the strength and elongation of the Gr/Cu composites in all directions, and reduces the difference in strength or elongation according to the direction.

• Bulletin of the Korean Chemical Society
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• 제33권1호
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• pp.209-214
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• 2012

In this work, the reduced graphene nanosheets were synthesized from pre-exfoliated graphite flakes. The pristine graphite flakes were firstly pre-exfoliated to graphite nanoplatelets in the presence of acetic acid. The obtained graphite nanoplatelets were treated by Hummer's method to produce graphite oxide sheets and were finally exfoliated to graphene nanosheets by ultrasonication and reduction processes. The prepared graphene nanosheets were studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). From the results, it was found that the preexfoliation process showed significant influence on preparation of graphite oxide sheets and graphene nanosheets. The prepared graphene nanosheets were applied to the preparation of conductive materials, which yielded a greatly improved electrical resistance of $200{\Omega}/sq$.

• 한국재료학회지
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• 제24권3호
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• pp.159-165
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• 2014

This study is research on the thermal emissivity depending on the alignment degrees of graphite flakes. Samples were manufactured by a slurry of natural graphite flakes with organic binder and subsequent dip-coating on an aluminum substrate. The alignment degrees were controlled by applying magnetic field strength (0, 1, and 3 kG) to the coated samples. The alignment degree of the sample was measured by XRD. The thermal emissivity was measured by an infrared thermal image camera at $100^{\circ}C$. The alignment degrees were 0.04, 0.11, and 0.17 and the applied magnetic field strengths were 0, 1, and 3 kG, respectively. The thermal emissivities were 0.829, 0.837, and 0.844 and the applying magnetic field strengths were 0, 1, and 3 kG, respectively. In this study the correlation coefficient, $R^2$, between thermal emissivity and alignment degree was 0.997. Therefore, it was concluded that the thermal emissivities are correlated with the alignment degree of the graphite flakes.

• 한국주조공학회지
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• 제3권3호
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• pp.174-180
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• 1983

The matrix changes and graphite formation in high manganese cast iron (Fe-12Mn-3.5C) are studied with increasing nickel and silicon content. Also, the decomposition of carbides and graphite precipitation are studied by adequate heat treatment.The results obtained in this work are as follows. 1. In high manganese cast iron, fine flakes graphite appeared by adding 5 wt% nickel and A-type flakes graphite can be obtained by adding 7 wt% nickel. 2. Nodular graphite are obtained by graphite spheroidizing treatment with same melt. 3. In high manganese cast iron containing 7 wt% nickel, full austenitic matrix with nodular graphite can be achieved by water quenching after 10 hours' solution heat treatment at $1050^{\circ}C$ in case of containing 2.0 wt% silicon, and 6 hours' at the same temperature in case of containing 2.5 wt% silicon.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2008년도 춘계학술대회 논문집
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• pp.623-624
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• 2008

• 청정기술
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• 제28권4호
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• pp.293-300
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• 2022

그래핀의 우수한 기계적, 전기적, 열적 성질은 최근 몇 년 동안 여러 연구 분야에서 지대한 관심을 불러일으켰다. 그래핀을 생산하는 대표적인 방법인 습식공정 중 액상박리(liquid-phase exfoliation, LPE)는 초음파 및 높은 전단응력을 이용하여 벌크흑연을 그래핀으로 박리하는 기술이다. 액상박리에 의해 생산된 그래핀 분산액은 그래핀 잉크로 전환되어 그 활용폭을 더 넓힐 수 있는 장점이 있지만 고품질의 그래핀을 생산하고 가격경쟁력을 확보해야 한다. 위 조건을 만족하기 위해서 그래핀을 효율적으로 박리할 수 있는 공정 확보와 더불어 상대적으로 가격이 저렴한 천연흑연 기반의 그래핀 분산액 및 잉크를 생산해야 한다. 본 연구에서는 합성흑연 보다 약 3배 정도 저렴하고 그 크기는7배 이상 큰 천연흑연을 흐름반응기 액상박리 공정을 이용하여 박리를 시도하고 공정의 최적화와 박리된 그래핀의 구조적, 전기적 특성을 분석하였다. 천연흑연 기반 그래핀의 전기적 특성을 분석하기 위해 잉크 정제화 공정을 거쳐 그래핀 잉크를 생산하고 인쇄 장비를 사용하여 그래핀 패턴을 제작하였다. 본 연구를 통해 보다 경제적인 그래핀 분산액 및 잉크를 생산하고 그래핀 인쇄 소자를 개발할 수 있는 방법을 제시할 수 있을 것으로 기대된다.

• 한국재료학회지
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• 제28권11호
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• pp.615-619
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• 2018

To produce carbon electrodes for use in perovskite solar cells, electrode samples are prepared by mixing various weight ratios of 35 nm nano carbon(NC) and $1{\mu}m$ graphite flakes(GF), GF/(NC+GF) = 0, 0.5, 0.7, and 1, in chlorobenzene(CB) solvent with a $ZrO_2$ binder. The carbon electrodes are fabricated as glass/FTO/carbon electrode devices for microstructure characterization using transmission electron microscopy, optical microscopy, and a field emission scanning electron microscopy. The electrical characterization is performed with a four-point probe and a multi tester. The microstructure characterization shows that an electrode with excellent attachment to the substrate and no surface cracks at weight ratios above 0.5. The electrical characterization results show that the sheet resistance is <$70{\Omega}/sq$ and the interface resistance is <$70{\Omega}$ at weight ratios of 0.5 and 0.7. Therefore, a carbon paste electrode with microstructure and electrical properties similar to those of commercial carbon electrodes is proposed with an appropriate mixing ratio of NC and GF containing a CB solvent and $ZrO_2$.

• 대한화학회지
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• 제7권1호
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• pp.51-57
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• 1963

It is well known that the graphite flakes become spherulite, when a suitable amount of nodulizing element, such as cerium or magnesium, is added to the cast iron. The change of graphite from flake to nodular shape improves not only the tensile strength but the ductility as well. However, the mechanism of spheroidization of graphite in cast iron has not yet been clearly understood, and various theories proposed by a number of investigators were such that it may be due to the special nucleation effect, prevention of flake formation by the adsorption of magnesium vapour on the graphite surface or file surface free energy difference between plain graphite and magnesium-adsorbed graphite. Regardless of the speculations of spheroidizing mechanism of the graphite in the cast iron, the final phenomenon comes to the conclusion that it may be due to the lack of wettability between graphite and iron matrix. In order to collaborate this fact through an experimental method, the authors have constructed a vacuum arc furnace for the wettability measurement as its first step. Our study and experiments were then directed to the comparison of the wettability between iron and graphite on the two cases (namely, the one where magnesium was preliminarily coated on the graphite surface and the other not coated), by means of contact angle measurements. The result was such that a significant difference of the contact angles has been shown between the above two cases. indicating the spheroidization of graphite which might have resulted from the lack of wettability between magnesium-adsorbed graphite and iron matrix.

• 한국표면공학회지
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• 제42권2호
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• pp.95-101
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• 2009

This study is the research on the thermal emissivity depending on the bulk graphite's alignment degree. Bulk graphites were manufactured by uni-axial pressing and subsequent heat treatment of natural graphite flakes with organic binder. The samples were prepared to be $0^{\circ}$ (relative to the 002 c-face), $45^{\circ}$, and $90^{\circ}$ (relative to the 100 a-face) for measuring alignment degree. The alignment degree of the sample was measured by XRD. The thermal emissivity was measured by infrared thermal image camera at $100^{\circ}C$ and compared with the value obtained by Infrared spectroscopy. The alignment degree and thermal emissivity of $0^{\circ}$ sample were measured to be 0 and 0.70 respectively. And those of $90^{\circ}$ sample were 0.73 and 0.80 respectively. The emissivity value was correlated with obtained by IR spectroscopy. Therefore it was considered that the thermal emissivity of the bulk graphite is correlated with the alignment degree.

• 한국세라믹학회지
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• 제25권4호
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• pp.408-414
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• 1988

This thesis is 2nd thesis from "Mechanism of Intercalation Compounds in Graphite with Hydrogen sulfate(J. Korea Cer. Soc. Vol. 22. No.6, 1985). We have oxidized natural Graphite flakes(0.1~0.2mm., Kropfm hl passau in Deutchland. S40) with a solution of CrO3 in H2SO4. Whilst persulfate ions were intercalated, too, below 7$^{\circ}C$, no evidence for intercalation of a peroxo compound was found at 22$^{\circ}C$. The reaction was interrupted after various times by filtering and washing with concentrated H2SO4. X-ray diffraction showed that the 2nd stage compound had already been formed after 2 minutes. We could only follow further oxidation to the blue stage compound which was completed after 35 minutes. We have found six distinct intermediate stage between 2nd stage and 1 stage. Experiments are described on the formation of intermediate stage color and X-ray diffraction analysis.ysis.