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수열 압력 제조 조건이 MoS2 촉매 특성과 직접 메탄화 반응에 미치는 영향
박정환,김성수,김진걸 한국수소및신에너지학회 2018 한국수소 및 신에너지학회논문집 Vol.29 No.2
After MoS2 catalyst was prepared at 1, 30, and 70 atm, the hydrothermal pressure effect over preparation of MoS2 was investigated in terms of catalyst characterization and direct methanation. Multifaceted characterization techniques such as XRD, BET, SEM, TPR, EDS, and XPS were used to analyze and investigate the effect of high pressure over the preparation of surface and bulk MoS2 catalyst. Result from XRD, SEM, and BET demonstrated that MoS2 was more dispersed as preparation pressure was increased, which resulted finer MoS2 crystal size and higher surface area. EDS result confirmed that bulk composition was MoS2 and XPS result showed that S/Mo mole ratio of surface was about 1.3. TPR showed that MoS2 prepared at 30 atm possessed higher active surface sites than MoS2 prepared at 1 atm and these sites could contribute to higher CO yield during methanation. Direct methanation was used to evaluate the CO conversion of the both catalysts prepared at 1 atm and 30 atm and reaction condition was at feed mole ratio of H2/CO=1, GHSV=4800, 30 atm, temperature(℃) of 300, 350, 400, and 450. MoS2 prepared at 30 atm showed more stable and higher CO conversion than MoS2 prepared at 1 atm. Faster deactivation was occurred over MoS2 prepared at 1 atm, which indicated that preparation pressure of MoS2 catalyst was the dominant factor to improve the yield of direct methanation.
이황화몰리브덴(MoS2) 적용된 광섬유기반 습도 센서 개발
문종주,김현승,홍광식,고영민,권민기,안태정 한국물리학회 2022 새물리 Vol.72 No.7
In this study, a humidity sensor was developed by combining an etched multimode optical fiber with MoS2 nanoparticles. We measured the change in optical properties due to the interaction of MoS2 and H2O molecules. MoS2 was synthesized with Na2MoO4·2H2O and CH3CSNH2 at 200 °C for 24 h. To obtain high sensitivity to humidity, we selected DMF solution as a solvent. Etched optical fiber was downsized to 50 µm, thereby improving the responsivity to humidity. The optical loss of the fiber-optic humidity sensor to human breathing was to 0.5 dB. The response rate was approximately 0.85 s, and the recovery rate was approximately 5.82 s. We confirmed the performance of the sensor for humidity changes from 40 to 80% in a thermo-hygrostat. In addition, we determined that the simultaneous measurement of temperature and humidity is feasible by combining the optical humidity sensor with a fiber Bragg grating. 본 연구는 MoS2 나노 입자와 식각된 다중모드 광섬유를 결합한 광기반 습도센서에 관한 것이다. MoS2와 H2O 간 상호작용으로 인한 광학적 특성 변화를 측정했다. MoS2는 Na2MoO4·2H2O과 CH3CSNH2을 200 °C 에서 24시간 합성하여 얻었다. 코팅 용액은 MoS2와 디메틸포름아미드(DMF)를 혼합한 직후 사용하였을 때 가장 높은 민감도를 보였다. 다중모드 광섬유의 직경을 약 50 µm까지 식각하여 반응성을 항상시켰다. 이 광기반 습도센서의 호흡에 대한 반응도는 최대 0.5 dB이다. 호흡에 대한 반응 속도는 약 0.85 초였고, 회복 속도는 약 5.82 초였다. 개발된 센서의 습도 변화에 대한 성능 확인을 위해 습도 챔버를 이용한 실험을 진행했다. 센서의 신호 변화는 습도 챔버 내 40 - 80%의 습도 변화를 주어 모니터링했다. 또한 광섬유격자 온도센서와 결합하여 온습도 동시 측정이 가능함을 보였다.
이황화몰리브덴(MoS2) 코팅된 측면연마 광섬유 기반 습도센서 개발
안태정,문종주,김현승,홍광식,서정민,고영민,권민기 조선대학교 공학기술연구원 2022 공학기술논문지 Vol.15 No.4
In this study, a humidity sensor was developed by combining a side-polished optical fiber with the molybdenum disulfide (MoS2) nanoparticles. We quantified the change in optical properties due to the interaction of MoS2 and water (H2O) molecules. As the hole carrier concentration related to the amount of H2O increased, the refractive index of MoS2 decreased and the attenuation coefficient increased. Synthesized MoS2 in a Dimethylformamide (DMF) solution as a suspension solvent was coated on the surface of a side-polished optical fiber(SPF). DMF solution makes the sensitivity to humidity decreased over time. Thus, the highest sensitivity can be obtained when coated immediately after MoS2 and DMF were mixed.
구형 및 평면 원자현미경 탐침에 대한 2차원 소재의 마찰 특성
Bien-Cuong Tran Khac,정구현 한국트라이볼로지학회 2019 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.35 No.4
Two-dimensional materials such as graphene, h-BN, and MoS2 have attracted increased interest as solid lubricant and protective coating layer for nanoscale devices owing to their superior mechanical properties and low friction characteristics. In this work, the frictional properties of single-layer graphene, h-BN, and MoS2 are experimentally investigated under various normal forces using atomic force microscope (AFM) tips with a spherical and flat end, with the aim to gain a better understanding of frictional behaviors. The nonlinear relationship between friction and normal force friction was clearly observed for single-layer graphene, h-BN, MoS2 specimens slid against the spherical and flat AFM tips. The results also indicate that single-layer graphene, h- BN, MoS2 exhibit low frictional properties (e.g., friction coefficient below 0.1 under 70~100 nN normal force). In particular, graphene is found to be superior to h-BN and MoS2 in terms of frictional properties. However, the friction of single-layer graphene, h-BN, MoS2 against the flat tip is larger than that against the spherical tip, which may be attributed to the relatively large adhesion. Furthermore, it is shown that the fluctuation of friction is more significant for the flat tip than the spherical tip. The resutls of this study may be helpful to elucidate the feasibility of using two-dimensional materials as solid lubricant and protective coating layer for nanoscale devices.
CVD 방법으로 성장시킨 MoS₂ 스핀 밸브의 자성-수송 특성
전병선(Byong Sun Chun) 한국자기학회 2017 韓國磁氣學會誌 Vol.27 No.5
We have investigated magneto-transport properties in a MoS₂ lateral spin-valve structures for different ferromagnetic CoFe electrode shapes and MoS₂ channel lengths. For these devices, high quality and large-scale MoS₂ thin films were synthesized through sulfurization of epitaxial MoO₃ films and these sulfurized-MoO₃ thin films properties are in good agreements with measurements on exfoliated MoS₂ film. Magneto-transport measurements show a clear rectangular magnetoresistance signal of 0.16% and a spin polarization of 0.00012%. By using the one-dimensional spin diffusion equation, we extracted the spin diffusion length and coefficient, finding them to be 12 ㎚ and 1.44 × 10<SUP>−3</SUP> ㎠/s, respectively. These small values of magnetoresistance and spin polarization could be enhanced by appeasement of conductivity mismatch between the ferromagnet and semiconductor interface.
마찰력현미경을 이용한 나노스케일 마멸시험 시 다이아몬드 탐침으로의 MoS₂ 마멸입자 전이현상
송현준(Hyunjun Song),임형우(Hyeongwoo Lim),성권일(Kwon Il Seong),안효석(Hyo Sok Ahn) 한국트라이볼로지학회 2019 한국윤활학회지(윤활학회지) Vol.35 No.5
In friction and wear tests that use friction force microscopy (FFM), the wear debris transfer to the tip apex that changes tip radius is a crucial issue that influences the friction and wear performances of films and coatings with nanoscale thicknesses. In this study, FFM tests are performed for bilayer MoS₂ film to obtain a better understanding of how geometrical and chemical changes of tip apex influence the friction and wear properties of nanoscale molecular layers. The critical load can be estimated from the test results based on the clear distinction of the failure area. Scanning electron microscopy and energy-dispersive spectroscopy are employed to measure and observe the geometrical and chemical changes of the tip apex. Under normal loads lower than 1000 nN, the reuse of tips enhances the friction and wear performance at the tip-sample interface as the contact pair changes with the increase of tip radius. Therefore, the reduction of contact pressure due to the increase of tip radius by the transfer of MoS₂ or Mo-dominant wear debris and the change of contact pairs from diamond/MoS₂ to partial MoS₂ or Mo/MoS₂ can explain the critical load increase that results from tip reuse. We suggest that the wear debris transfer to the tip apex should be considered when used tips are repeatedly employed to identify the tribological properties of ultra-thin films using FFM.
자동차 에어컨용 압축기 사판의 표면 형태에 따른 마찰 마모 거동
권윤기(Yunki Kwon),이건호(Geonho Lee),이기천(Kichun Lee) 한국트라이볼로지학회 2011 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.27 No.2
The tribological characteristics of the swash plate surface of a compressor which is for automobile were investigated. For surface treatments, PTFE and MoS2 are used as a solid lubricant, together with copper alloy. Test condition is set considering actual driving condition. Wear testing is conducted using pin on disk type tester, and the coefficient of friction and the temperature on friction surface are measured. Also, to determine the wear patterns, cross-section of friction surface is analyzed by SEM(scanning electrode microscope). The MoS2, both at dry and lubricated conditions, friction surface and the coefficient of friction maintained rather stable results. But, the PTFE, at oil less condition, sample resulted in rather unstable condition. In case of copper alloy, quite higher friction coefficients(higher than 0.1) were obtained at dry condition. At the temperature of 125oC, seizure has occurred.