• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.610-610
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• 2013

그래핀을 구성하는 탄소 원자는 모두 표면에 존재하기 때문에, 맞닿아 있는 물질에 따라 그래핀의 물리적 특성에 민감한 영향을 미치기도 한다. 본 연구에서는 라만분광법과 원자 힘 현미경(atomic force microscopy, AFM)을 이용하여 통상적인 열처리 조건에서 그래핀에 탄화수소가 흡착될 수 있는 가능성을 탐구하였다. 산소가 없는 조건에서 열처리된 그래핀으로부터 D, G, 2D 봉우리와 겹쳐지는 폭이 넓은 새로운 라만 봉우리들이 관찰되었다. 열처리 시간, 온도 및 진공도에 따른 라만 스펙트럼의 변화와AFM에 의해 확인된 표면의 구조 변화로부터 새로이 관찰된 라만 봉우리는 탄화수소의 탄화에 의해 그래핀의 표면에 형성된 비결정성 탄소물질(amorphous carbon)임을 확인하였다. 기계적 박리법과 화학기상증착법으로 시료를 준비할 때 사용된 폴리머 잔유물이 열처리 과정에서 탄화수소를 배출하는 것으로 판단된다. 이 연구는 그래핀 소자의 작동에 있어서 환경적인 효과를 이해하고 탄화에 의해 그래핀 표면에 만들어진 비결정질 탄소를 정량화하는데 도움을 줄 것이다.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.150-155
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• 2004

The base material of optical disc is the amorphous polymer, polycarbonate. So crack growth on the rotating optical disc could happen by the static centrifugal force. This phenomenon is called static fatigue. Today's CD-R disc drive is being operated over 10,000 RPM. This is increasing the possibility of the disc fracture when operating. In this reason, new method to measure the static fatigue threshold quality and the way to calculate the threshold J-integral value and the safe crack length of the optical disc are studied. Finally the environmental effect to optical disc is also studied in this paper.

• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.443-450
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• 2015

This paper presents an investigation of the mechanical and microstructural properties of Class F fly ash based geopolymer containing sodium sulfate as an additive. Sodium sulfate was used as an chemical additive at the dosage levels of 0, 2, 4, and 6wt% of fly ash. Sodium hydroxide and sodium silicate solutions were used to activate fly ash. The compressive strengths of geopolymer pastes were measured at the age of 28 days. The microstructures of the geopolymer pastes were examined using XRD, MIP and SEM tests. The additions of 2wt% and 4wt% sodium sulfate produced geopolymers with high strength, while increasing the dosage of levels to 6% resulted in almost no changes in strength, comparing with the control geopolymer. The optimum increase in strength was obtained with the addition of 4wt% sodium sulfate. As the amount of sodium sulfate is increased, no additional crystalline phase was detected and no change of amorphous phase indicated despite the change in the strength development. The increase in the strength was due to the change of pore size distribution in samples. As addition of sodium sulfate altered the morphologies of reactive productions and Si/Al ratios of the reaction products, the strengths were thus affected. It was found that the strengths of geopolymer were larger for lower Si/Al ratios of reaction products formed in samples. The optimal amount of sodium sulfate in the fly ash based geopolymer helps to improve mechanical properties of the geopolymer, on the other hand, the high percentage of sodium sulfate could exist as an impurity in the geopolymer and hinder the geopolymer reaction.