• 한국정보전자통신기술학회논문지
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• 제12권3호
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• pp.218-223
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• 2019

높은 CVD 그래핀저항으로 인한 낮은 발열효과를 해결하기 위해 다층으로 그래핀을 적층하여, 저저항의 광학특성이 우수한 투명 면상 발열시스템을 구현하였다. 제작한 CVD 그래핀의 발열필름으로 $300{\times}400{\times}5mm$ 발열체를 제작하고, 효율적인 전력을 구동하기 위해 PWM 제어를 통한 회로를 구성하여 시스템을 구현하였다. 발열체로 사용한 4층의 CVD 그래핀 필름의 평균 면 저항 측정값은 $85.5{\Omega}/sq$이다. 따라서 저 저항의 CVD 그래핀의 구현 방법으로 열전사의 적층의 방법은 타당하다. 발열시험 결과, CVD 그래핀을 이용한 저저항 투명 면상 발열 시스템의 평균 발열상승은 $10^{\circ}C/min$ 이고, 86.44%의 CVD 그래핀 필름의 광투과율을 갖음을 보여준다. 따라서 제시한 발열 시스템은 대형창 유리 및 자동차 발열유리로서 적용가능하다.

• 대한원격탐사학회지
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• 제35권1호
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• pp.39-55
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• 2019

In this study, we have proposed an improved method to detect forest fires by correcting the reflected signals of day images using the middle-wavelength infrared (MWIR) channel. The proposed method is allowed to remove the reflected signals only using the image itself without an existing data source such as a land-cover map or atmospheric data. It includes the processing steps for calculating a solar-reflected signal such as 1) a simple correction model of the atmospheric transmittance for the MWIR channel and 2) calculating the image-based reflectance. We tested the performance of the method using the MODIS product. When compared to the conventional MODIS fire detection algorithm (MOD14 collection 6), the total number of detected fires was improved by approximately 17%. Most of all, the detection of fires improved by approximately 30% in the high reflection areas of the images. Moreover, the false alarm caused by artificial objects was clearly reduced and a confidence level analysis of the undetected fires showed that the proposed method had much better performance. The proposed method would be applicable to most satellite sensors with MWIR and thermal infrared channels. Especially for geostationary satellites such as GOES-R, HIMAWARI-8/9 and GeoKompsat-2A, the short acquisition time would greatly improve the performance of the proposed fire detection algorithm because reflected signals in the geostationary satellite images frequently vary according to solar zenith angle.

• 한국재료학회지
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• 제29권6호
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• pp.385-391
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• 2019

In the present study, vanadium oxide($V_2O_5$) films for electrochromic(EC) application are fabricated using sol-gel spin coating method. In order to optimize the EC performance of the $V_2O_5$ films, we adjust the amounts of polyvinylpyrrolidone(PVP) added to the solution at 0, 5, 10, and 15 wt%. Due to the effect of added PVP on the $V_2O_5$ films, the obtained films show increases of film thickness and crystallinity. Compared to other samples, optimum weight percent(10 wt%) of PVP led to superior EC performance with transmittance modulation(45.43 %), responding speeds(6.0 s at colored state and 6.2 s at bleached state), and coloration efficiency($29.8cm^2/C$). This performance improvement can be mainly attributed to the enhanced electrical conductivity and electrochemical activity due to the increased crystallinity and thickness of the $V_2O_5$ films. Therefore, $V_2O_5$ films fabricated with optimized amount of PVP can be a promising EC material for high-performance EC devices.

• 대한건축학회논문집:구조계
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• 제35권6호
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• pp.153-164
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• 2019

The presence of thermal bridges in a building envelope cause additional heat loss which increases the heating energy. Given that a higher building insulation performance is required in these cases, the heat loss via thermal bridges is a high proportion of the total heat energy consumption of a building. For the dry exterior insulation system that uses mullions and transoms to fix insulation and exterior materials such as stone and metal sheet, the occurrence of thermal bridges at mullions and transoms is one of the main reasons for heat loss. In this study, a dry exterior insulation system using the truss insulation frame (TIF) was proposed as an alternative to metal mullions. To evaluate the building envelope performance, structural, air-leakage, water-leakage, fire-resistance, thermal, and condensation risk tests were conducted. In addition, the annual energy consumption associated with heating and cooling was calculated, including the linear thermal transmittance of the thermal bridges. As a result, the dry exterior insulation system using TIF achieved the allowable value for all tests. It was also determined that the annual heating load of a building was reduced by 36.7 % when the TIF dry exterior insulation system was used, relative to the dry exterior insulation system using steel pipes without additional insulations.

• 공업화학
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• 제22권1호
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• pp.81-86
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• 2011

자기 조립성 염료인 Sunset Yellow-FCF 수용액은 상온에서 농도 25 wt%부터 schlieren 구조의 액정상을 보이기 시작하여, 28 wt% 이상이면 완전한 네마틱 액정상으로 관찰되었다. 전단배향에 의한 코팅으로 광학적 이방성 필름을 제조하기 위해서는 30 wt% 이상의 농도가 필요하였다. 액정 색소의 농도, 코팅속도, 건조 온도, 상대습도 등 코팅 변수가 최종 박막필름의 두께, 투과도에 미치는 영향 분석에 의하면, 최종 필름의 두께에는 용액의 농도가 가장 큰 영향을 주었으며, 평행방향의 투과도에는 건조 온도와 농도의 영향이 가장 컸다. 특히 Sunset Yellow-FCF의 농도 증가로 전단코팅에 의한 배향성이 개선되고 높은 편광도를 갖는 필름제조가 가능하였다. 본 실험에서는 33 wt%의 Sunset Yellow-FCF 수용액을 사용하면, 89.7~98.7%의 편광도를 갖는 광학적 이방성 필름이 제조되었다.

• 대한금속재료학회지
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• 제50권8호
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• pp.605-611
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• 2012

ZnO nanostructures were grown on R-plane sapphire substrates with seed layers annealed at different temperatures ranging from 600 to $800^{\circ}C$. The properties of the ZnO nanostructures were investigated by scanning electron microscopy, high-resolution X-ray diffraction, UV-visible spectrophotometer, and photoluminescence. For the as-prepared seed layers, ZnO nanorods and ZnO nanosheets were observed. However, only ZnO nanorods were grown when the annealing temperature was above $700^{\circ}C$. The crystal qualities of the ZnO nanostructures were enhanced when the seed layers were annealed at $700^{\circ}C$. In addition, the full width at half maximum (FWHM) of near-band-edge emission (NBE) peak was decreased from 139 to 129 meV by increasing the annealing temperature to $700^{\circ}C$. However, the FWHM was slightly increased again by a further increase in the annealing temperature. Optical transmittance in the UV region was almost zero, while that in the visible region was gradually increased as the annealing temperature increased to $700^{\circ}C$. The optical band gap of the ZnO nanostructures was increased as the annealing temperature increased to $700^{\circ}C$. It is found that the optical properties as well as the structural properties of the rod-shaped ZnO nanostructures grown on R-plane sapphire substrates by hydrothermal method are improved when the seed layers are annealed at $700^{\circ}C$.

• 반도체디스플레이기술학회지
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• 제21권1호
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• pp.79-84
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• 2022

As various flexible display products are released, the demand for high-performance colorless and transparent polyimide (CPI) film is continuously increasing. The primary purpose of this study is to establish a systematic procedure for optimizing the optical performance of CPI films by applying the response surface method. After selecting three key factors (monomer type, stirring time for varnish synthesis, and maximum temperature of vacuum furnace for film production) affecting optical performance based on experiences and references, CPI films were manufactured according to the experimental sequence designed by the central composite design, and then the yellowness index (YI) and optical transmittance (Tr) of the films were measured. When producing a CPI film by pouring varnish into a petri dish, the change in optical properties according to thickness should be considered, and there was a meaningful linear relationship between YI and Tr. The species of monomer and the maximum temperature were the critical factors that had an influence on YI and Tr, respectively. It is expected that the procedure proposed in this study can serve as a starting point for CPI film optimization studies considering the other factors that were not considered and responses such as thermal properties.

• 한국재료학회지
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• 제33권8호
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• pp.337-343
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• 2023

3Y-TZP (3 mol% yttria-stabilized tetragonal zirconia polycrystals) ceramics have excellent mechanical properties including high fracture toughness, good abrasion resistance as well as chemical and biological stability. As a result, they are widely used in mechanical and medical components such as bearings, grinding balls, and hip implants. In addition, they provide excellent light transmittance, biocompatibility, and can match tooth color when used as a dental implant. Recently, given the materials' resemblance to human teeth, these ceramics have emerged as an alternative to titanium implants. Since the introduction of CAD/CAM in the manufacture of ceramic implants, they've been increasingly used for prosthetic restoration where aesthetics and strength are required. In this study, to improve the surface roughness of zirconia implants, we modified the 3Y-TZP surface with a biocomposite of hydroxyapatite and forsterite using room temperature spray coating methods, and investigated the mixed effect of the two powders on the evolution of surface microstructure, i.e., coating thickness and roughness, and biological interaction during the in vitro test in SBF solution. We compared improvement in bioactivity by observing dissolution and re-precipitation on the specimen surface. From the results of in vitro testing in SBF solution, we confirmed improvement in the bioactivity of the 3Y-TZP substrate after surface modification with a biocomposite of hydroxyapatite and forsterite. Surface dissolution of the coating layer and the precipitation of new hydroxyapatite particles was observed on the modified surface, indicating the improvement in bioactivity of the zirconia substrate.

• 한국표면공학회지
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• 제34권5호
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• pp.503-509
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• 2001

Thin films of hydrogenated amorphous silicon (a-Si : H) and hydrogenated amorphous silicon carbide (a-SiC:H) of different compositions were deposited on Si(100) wafer and glass by RF plasma-enhanced chemical vapor deposition (RF-PECVD). In the present work, we have investigated the effects of the RF power on the properties, such as optical band gap, transmittance and crystallinity. The Raman data show that the a-Si:H material consists of an amorphous and crystalline phase for the co-presence of two peaks centered at 480 and $520 cm^{-1}$ . The UV-VIS data suggested that the optical energy band gap ($E_{g}$ ) is not changed effectively with RF power and the obtained $E_{g}$(1.80eV) of the $\mu$c-Si:H thin film has almost the same value of a-Si:H thin film (1.75eV), indicating that the crystallity of hydrogenated amorphous silicon thin film can mainly not affected to their optical properties. However, the experimental results have shown that$ E_{g}$ of the a-SiC:H thin films changed little on the annealing temperature while $E_{g}$ increased with the RF power. The Raman spectrum of the a-SiC:H thin films annealed at high temperatures showed that graphitization of carbon clusters and microcrystalline silicon occurs.

• 한국재료학회지
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• 제32권12호
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• pp.560-564
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• 2022

In this study, lanthanum boron silicate glasses were prepared with a composition of x Li₂O-(60-x)B₂O₃-5CaO-5BaO-7ZnO-10SiO₂-10La₂O₃-3Y₂O₃ where x = 1,3,5,7, and 9 mol%. Each composition was melted in a platinum crucible under atmospheric conditions at 1,400 ℃ for 2 h. Clear glasses with a transmittance exceeding 85 % were fabricated. Their optical, thermal, and physical properties, such as refractive index, Abbe number, density, glass transition (T_g) and Knoop hardness were studied. The results demonstrated that refractive index was between 1.6859 and 1.6953 at 589.3 nm. The Abbe number was calculated using an equation for 589.3 nm (nd), 656.3 nm (nf) and 486.1 nm (nc) and was observed to be in the range from 57.5 to 62.6. As the Li₂O content increased, the glass transition temperature of the optical glass decreased from 608 ℃ to 564 ℃. If glass mold pressing is performed using a material with a low transition temperature and high mechanical strength, then the optical glasses developed in this study can be completely commercialized.