• Carbon letters
• /
• 제21권
• /
• pp.51-60
• /
• 2017

Isotropic pitch-based fibers produced from coal tar pitch with the melt-blowing method were carbonized at temperatures ranging from 800 to $1600^{\circ}C$ to investigate their crystalline structure and physical properties as a function of the carbonization temperature. The in-plane crystallite size ($L_a$) of the carbonized pitch fiber from X-ray diffraction increased monotonously by increasing the carbonization temperature resulting in a gradual increase in the electrical conductivity from 169 to 3800 S/cm. However, the variation in the $d_{002}$ spacing and stacking height of the crystallite ($L_c$) showed that the structural order perpendicular to the graphene planes got worse in carbonization temperatures from 800 to $1200^{\circ}C$ probably due to randomization through the process of gas evolution; however, structural ordering eventually occurred at around $1400^{\circ}C$. For the carbonized pitch powder without stabilization, structural ordering perpendicular to the graphene planes occurred at around $800-900^{\circ}C$ indicating that oxygen was inserted during the stabilization process. Additionally, the shear stress that occurred during the melt-blowing process might interfere with the crystallization of the CPF.

• Carbon letters
• /
• 제13권4호
• /
• pp.230-235
• /
• 2012

In this study, reduced graphene oxide/polyimide (r-GO/PI) composite films, which showed significant enhancement in their electrical conductivity, were successfully fabricated. GO was prepared from graphite using a modified Hummers method. The GO was used as a nanofiller material for the preparation of r-GO/PI composites by in-situ polymerization. An addition of 20 wt% of GO led to a significant decrease in the volume resistivity of composite films by less than nine orders of magnitude compared to that of pure PI films due to the electrical percolation networks of reduced GO created during imidization within the films. A tensile test indicated that the Young's modulus of the r-GO/PI composite film containing 20 wt% GO increased drastically from 2.3 GPa to 4.4 GPa, which was an improvement of approximately 84% compared to that of pure PI film. In addition, the corresponding tensile strength was found to have decreased only by 12%, from 113 MPa to 99 MPa.

• Current Optics and Photonics
• /
• 제1권5호
• /
• pp.514-524
• /
• 2017

We proposed an integrated wavelength-selective photodetector based on a grating-assisted contradirectional coupler and a graphene absorption layer for a coarse wavelength division multiplexing (CWDM) communication system. The center wavelength of the absorption spectrum of the proposed device can be tuned simply by changing the period of the grating, and the proposed device structure is suitable to forming a cascaded structure. Therefore, an array of the proposed device of different grating periods can be used for simultaneous wavelength demultiplexing and signal detection in a CWDM communication system. Our theoretical study showed that the designed device with a grating length of $500{\mu}m$ could have an absorption of 95.1%, an insertion loss of 0.2 dB, and a 3 dB bandwidth of 7.5 nm, resulting in a -14 dB crosstalk to adjacent CWDM channels. We believe that the proposed device array can provide a compact and economic solution to receiver implementation in the CWDM system by combining functions of wavelength demultiplexing and signal detection.

• Journal of the Optical Society of Korea
• /
• 제17권1호
• /
• pp.5-9
• /
• 2013

We report on high-power continuous-wave operations of an Er:YAG ceramic laser in-band pumped by a cladding-pumped Er,Yb fiber laser at 1532 nm. With an output coupler of 10% transmission, the ceramic laser yielded 16.7 W of continuous-wave output at 1645 nm for 28.8 W of incident pump power, corresponding to a slope efficiency of 61.0% with respect to the incident pump power. The lasing wavelength switched to 1617 nm when output couplers of > 20% transmission were used. Up to 16.2 W of 1617 nm output was generated for 33.0 W of incident pump power, corresponding to a slope efficiency of 51.8%. Graphene Q-switched operation of Er:YAG cermic laser at 1645 nm was also demonstrated with stable pulses of 30-74 kHz repetition rates and 1.5-6.4 ${\mu}s$ pulse widths.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
• /
• pp.559-559
• /
• 2012

We developed a new scheme for the highly sensitive near-field scanning optical microscope (NSOM) by using a dithering sample stage rather than a dithering probe. In the proposed scheme, the sample is directly loaded on one prong surface of a dithering bare tuning fork. Gap control between probe and sample is performed by detecting the shear force between an immobile fiber probe and the dithering sample. In a conventional NSOM, the Q factor drastically decreases from 7783 to 1000 or even to 100 by attaching a probe to the tuning fork. In our proposed NSOM, on the contrary, the Q factor does not change significantly, 7783 to 7480, when the sample is loaded directly to the tuning fork instead of attaching a probe. Consequently, the graphene sheets that cannot be observed by a conventional NSOM were clearly observed by the proposed method with sub-nanometer vertical resolution due to the extremely high Q factor.

• Carbon letters
• /
• 제12권4호
• /
• pp.223-228
• /
• 2011

In this present work, the effect of additional heat-treatment (AHT) in the range from $1800^{\circ}C$ to $2400^{\circ}C$ on the chemical composition, morphology, microstructure, tensile properties, electrical resistivity, and thermal stability of commercial polyacrylonitrile (PAN)-based carbon fibers was explored by means of elemental analysis, electron microscopy, X-ray diffraction analysis, single fiber tensile testing, two-probe electrical resistivity testing, and thermogravimetric analysis (TGA). The characterization results were in agreement with each other. The results clearly demonstrated that AHTs up to $2400^{\circ}C$ played a significant role in further contributing not only to the enhancement of carbon content, fiber morphology, and tensile modulus, but also to the reduction of fiber diameter, inter-graphene layer distance, and electrical resistivity of "as-received" carbon fibers without AHT. The present study suggests that key properties of commercial PAN-based carbon fibers of an intermediate grade can be further improved by proprietarily adding heat-treatment without applying tension in a batch process.

• Composites Research
• /
• 제27권3호
• /
• pp.109-114
• /
• 2014

나노입자에 대한 복합재료 수요가 증가되면서 효과적인 나노입자 보강재를 이용한 나노복합재료 제조공정 단순화를 추구하고 있다. 본 연구에서는 나노입자를 활용하여 전도성과 계면 강도를 향상시킨 나노입자 강화유리섬유 소재에 대한 연구를 진행하였다. 탄소계 나노입자의 형상에 따른 유리섬유 표면에 흡착된 나노입자 상태를 FE-SEM으로 분석하였다. 나노입자 코팅층의 내구성을 평가하기 위한 방법으로 초음파 세척과정에 따른 나노입자의 세척 정도를 분석하여 탄소계 나노입자의 형상에 따른 나노입자 코팅층의 내구성을 분석하였다. 동적피로 실험을 통하여 나노입자 강화 유리섬유/에폭시의 계면강도를 나노입자 형상에 따른 차이에 따라 비교하였다. 나노입자 코팅층의 내구성은 단섬유 강화 복합재료시편을 이용하여 분석하였다. 겉보기 강성도 결과와 나노입자코팅층의 전도성 변화를 분석하여 코팅층의 다기능성을 분석할 수 있었다. 판상형의 나노입자 보다는 섬유 형태의 나노입자가 유리섬유 표면에 흡착성이 용이하였다. 계면 내구성 및 안정성에 효과가 있음을 확인하였다.

• Composites Research
• /
• 제33권3호
• /
• pp.91-100
• /
• 2020

폴리페닐렌설파이드(PPS)는 반결정성 엔지니어링 열가소성 수지로 뛰어난 열안정성, 우수한 기계적 강도, 고유의 난연성 및 내화학성, 전기적 특성을 갖고 있다. 이러한 우수한 특성으로 인해 PPS는 복합체의 매트릭스로 선호되고 있다. PPS의 기계적 물성을 향상시키며 기능성 부여를 위해 탄소섬유나 유리섬유와 같은 필러를 이용한 복합화 연구가 진행되어 오고 있다. 본 총설 논문에서는 PPS와 탄소나노튜브, 그래핀, 탄소섬유, 유리섬유 등과의 복합체 제조 및 응용에 대한 연구를 소개하고자 한다.

• 멤브레인
• /
• 제24권2호
• /
• pp.151-157
• /
• 2014

본 연구에서는, 산화그래핀(GO) 및 산화철이 기능화된 산화그래핀(M-GO)을 용매인 dimethylformamide (DMF)에 초음파분쇄법을 이용하여 완전히 분산시킨 후, 기질고분자인 polyacrylonitrile (PAN)에 첨가하여 전기방사함으로써, 나노섬유형태의 복합분리막을 제조하였다. 제조된 나노섬유 분리막은 적층수를 변화시켜 기공크기를 조절하였다. Scanning Electron Microscope (SEM) 분석 결과로부터 약 500 nm 크기의 고른 직경분포를 가진 나노섬유 복합분리막이 제조되었음을 확인하였다. 또한, Raman spectroscopy 분석과 Energy Dispersive x-ray Spectroscopy (EDS) 분석 결과로부터 GO 및 M-GO가 분리막 내에 분산되어 있음을 확인하였다. 최종 나노섬유 복합분리막은 상용막($0.27{\mu}m$, 55%)과 유사한 기공특성($0.21{\sim}0.24{\mu}m$, 40%)을 보여주었으며, 수투과도 측정결과 PAN 막에 비해 약 200% 향상된 성능을 보여주었다. 이러한 결과로부터, 전기방사법으로 제조된 나노섬유 복합분리막은 수처리용 분리막으로서 충분한 활용가능성이 있다고 판단된다.

• 멤브레인
• /
• 제30권5호
• /
• pp.293-306
• /
• 2020

물 부족을 포함한 기후 변화의 해로운 결과는 효과적인 정수에 대한 관심을 가져왔다. 또한, 수질 오염 수준이 높아지고 환경 파괴 수준이 심해지면서 오염 물질을 제거하려는 방안들이 요구되고 있다. 물을 정화하기 위해 반투막을 통한 삼투압 절차들을 사용할 수 있으며, 최근 연구에 따르면 탄소 양자점(CQD), 그래핀 양자점(GQD) 및 산화 그래핀 양자점(GOQD)을 포함한 나노입자를 복합 박막(TFC)에 합체하면 유사한 수준의 염 거부율을 유지하면서 물흐름을 증가시킬 수 있다. 이러한 효과 외의 여러 가지 효과가 있지만 그 중에서도 친수성을 높이고, 살균 성질을 보이고, 방오 특성으로 인해 박테리아 및 기타 미생물의 축적을 방지하면서 막의 효과가 감소하는 것을 막는 것을 보여준다. 이 보고서는 양자점이 합체된 정수용 복합 막에서 양자점의 제조 과정, 응용, 기능성, 성질 및 역할을 논의한다.