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Hexagonal-Boron Nitride 강화 시멘트 복합체의 압축강도 향상에 대한 실험적 연구
최요민,신현규,Choi, Yomin,Shin, Hyun-Gyoo 한국분말재료학회 (*구 분말야금학회) 2020 한국분말재료학회지 (KPMI) Vol.27 No.6
The mechanical properties and microstructures of hexagonal boron nitride (h-BN)-reinforced cement composites are experimentally studied for three and seven curing days. Various sizes (5, 10, and 18 ㎛) and concentrations (0.1%, 0.25%, 0.5%, and 1.0%) of h-BN are dispersed by the tip ultrasonication method in water and incorporated into the cement composite. The compressive strength of the h-BN reinforced cements increases by 40.9%, when 0.5 wt% of 18 ㎛-sized h-BN is added. However, the compressive strength decreases when the 1.0 wt% cement composite is added, owing to the aggregation of the h-BNs in the cement composite. The microstructural characterization of the h-BN-reinforced cement composite indicates that the h-BNs act as bridges connecting the cracks, resulting in improved mechanical properties for the reinforced cement composite.
중공 유리 마이크로스피어 혼입 시멘트 복합체의 내열충격성 향상에 대한 실험적 연구
최요민,신현규 한국분말재료학회 2022 한국분말재료학회지 (KPMI) Vol.29 No.6
The thermal shock resistance of cement composites with hollow glass microspheres (HGM) is investigated. Cement composites containing various concentrations of HGM are prepared and their properties studied. The density, thermal conductivity, and coefficient of thermal expansion of the composites decrease with increasing HGM concentration. A thermal shock test is performed by cycling between -60 and 50oC. After the thermal shock test, the compressive strength of the cement composite without HGM decreases by 28.4%, whereas the compressive strength of the cement composite with 30 wt% HGM decreases by 5.7%. This confirms that the thermal shock resistance of cement is improved by the incorporation of HGM. This effect is attributed to the reduction of the thermal conductivity and coefficient of thermal expansion of the cement composite because of the incorporation of HGM, thereby reducing the occurrence of defects due to external temperature changes
김형섭,최요민,박윤찬,Rajendra C. Pawar,좌용호,이선영 한국물리학회 2017 Current Applied Physics Vol.17 No.4
Porous TiO2 films were deposited onto FTO (fluorine doped tin oxide) substrate through dry deposition method, and polystyrene (PS) beads used as a sacrificial material. In addition, pore size was controlled by introducing 50-nm- and 300-nm-sized PS beads. Moreover, the improved porous film was obtained by varying weight ratios of TiO2 and PS powders to enhance DSSCs (dye-sensitized solar cell) efficiency. The DSSC with improved porous structure has shown efficiency of 6.8% with weight ratio (71.5%), which higher than that of only TiO2 layer (6.08%) and other compositions. The IPCE analysis showed the maximum absorbance over the wavelength range of 550e800 nm resulted in higher efficiency. EIS results indicated that the electron generation and transfer properties of porous films were better than that of the TiO2 layer only. From photovoltage decay measurement, the carrier lifetime was found to be longer in the porous structure than that of TiO2 layer only. Then, we proposed formation mechanism of porous films and their relation for effective scattering/absorbance of light. Moreover, the porous structure also enhances the specific surface area for higher amount of dye loading. Therefore, deposition of porous films could improve the efficiency of DSSCs using facile process.
PdOx가 도핑된 나노 기공구조 SiO<sub>2</sub>/Si 기반의 수소 게터 제작 및 특성평가
엄누시아,임효령,최요민,정영훈,조정호,좌용호,Eom, Nu Si A,Lim, Hyo Ryoung,Choi, Yo-Min,Jeong, Young-Hun,Cho, Jeong-Ho,Choa, Yong-Ho 한국재료학회 2014 한국재료학회지 Vol.24 No.11
The existing metal getters are invariably covered with thin oxide layers in air and the native oxide layer must be dissolved into the getter materials for activation. However, high temperature is needed for the activation, which leads to unavoidable deleterious effects on the devices. Therefore, to improve the device efficiency and gas-adsorption properties of the device, it is essential to synthesize the getter with a method that does not require a thermal activation temperature. In this study, getter material was synthesized using palladium oxide (PdOx) which can adsorb $H_2$ gas. To enhance the efficiency of the hydrogen and moisture absorption, a porous layer with a large specific area was fabricated by an etching process and used as supporting substrates. It was confirmed that the moisture-absorption performance of the $SiO_2/Si$ was characterized by water vapor volume with relative humidity. The gas-adsorption properties occurred in the absence of the activation process.
초음파 분무 열분해와 화학적 변환 공정을 이용한 (GaN)<sub>1-x</sub>(ZnO)<sub>x</sub> 나노입자의 합성과 광학적 성질
김정현,류철희,지명준,최요민,이영인,Kim, Jeong Hyun,Ryu, Cheol-Hui,Ji, Myungjun,Choi, Yomin,Lee, Young-In 한국분말재료학회 (*구 분말야금학회) 2021 한국분말재료학회지 (KPMI) Vol.28 No.2
In this study, (GaN)<sub>1-x</sub>(ZnO)<sub>x</sub> solid solution nanoparticles with a high zinc content are prepared by ultrasonic spray pyrolysis and subsequent nitridation. The structure and morphology of the samples are investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The characterization results show a phase transition from the Zn and Ga-based oxides (ZnO or ZnGa<sub>2</sub>O<sub>4</sub>) to a (GaN)<sub>1-x</sub>(ZnO)<sub>x</sub> solid solution under an NH3 atmosphere. The effect of the precursor solution concentration and nitridation temperature on the final products are systematically investigated to obtain (GaN)<sub>1-x</sub>(ZnO)<sub>x</sub> nanoparticles with a high Zn concentration. It is confirmed that the powder synthesized from the solution in which the ratio of Zn and Ga was set to 0.8:0.2, as the initial precursor composition was composed of about 0.8-mole fraction of Zn, similar to the initially set one, through nitriding treatment at 700℃. Besides, the synthesized nanoparticles exhibited the typical XRD pattern of (GaN)<sub>1-x</sub>(ZnO)<sub>x</sub>, and a strong absorption of visible light with a bandgap energy of approximately 2.78 eV, confirming their potential use as a hydrogen production photocatalyst.