• 한국표면공학회지
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• 제36권4호
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• pp.296-300
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• 2003

Extended cylindrical magnetron sputtering system with rotating 600-mm long and 90-mm diameter graphite cathode and pulsed power supply voltage generator were developed and fabricated. Time-dependent Langmuir probe characteristics as well as carbon films thickness were measured. It was shown that ratio of ions flux to carbon atoms flux for pulsed magnetron discharge mode was equal to $\Phi_{i}$ $\Phi$sub C/ = 0.2. It did not depend on the discharge current in the range of $I_{d}$ / = 10∼60 A since both the plasma density and the film deposition rate were found approximately proportional to the discharge current. In spite of this fact carbon film structure was found to be strongly dependent on the discharge current. Grain size increased from 100 nm at $I_{d}$ = 10∼20 A to 500 nm at $I_{d}$ = 40∼60 A. To deposit fine-grained hard nanocrystalline or amorphous carbon coating current regime with $I_{d}$ = 20 A was chosen. Pulsed negative bias voltage ($\tau$= 40 ${\mu}\textrm{s}$, $U_{b}$ = 0∼10 ㎸) synchronized with magnetron discharge pulses was applied to a substrate and voltage of $U_{b}$ = 3.4 ㎸ was shown to be optimum for a hard carbon film deposition. Lower voltages were not sufficient for amorphization of a growing graphite film, while higher voltages led to excessive ion bombardment and effects of recrystalization and graphitization.

• 한국표면공학회지
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• 제45권3호
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• pp.111-116
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• 2012

Oblique angle deposition (OAD) is a physical vapor deposition method which utilizes non-normal angles between the substrate and the vaporizing source. It has been known that tilting the substrate changes the properties of the film deposited on it, which was thought to be a result of morphological change of the film. In this study, OAD has been applied to prepare single and multilayer Al films by magnetron sputtering. The magnetron sputtering source of 4 inch diameter was used to deposit the films. Al films have been deposited on Si wafers and cold-rolled steel sheets. The multilayer films were prepared by changing the tilting angle upside down at each layer interval, which means that when the first layer was deposited at an angle of $+45^{\circ}$, the second layer was deposited at an angle of $-45^{\circ}$, and vice versa. The microstructure, surface roughness and reflectance of the films were investigated using a scanning electron microscope, a surface profiler and a spectrophotometer, respectively. The corrosion resistance was measured and compared using the salt spray test. The single layer film prepared at an oblique angle of $60^{\circ}$ prepared at other angles. However, for the multilayer films, the film prepared at an oblique angle of $45^{\circ}$ showed the most compact and featureless structure. The multilayer films were found to exhibit higher corrosion resistance than the single layer films.

• Journal of Industrial and Engineering Chemistry
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• 제68권
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• pp.274-281
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• 2018

Experimental studies of the hydrodynamic performance of the draft tube conical spout-fluid bed (DCSF) were conducted using pharmaceutical pellets. The experiments were carried out in a DCSF consisted of two sections: (a) a conical section with the cross section of $120mm{\times}250mm$ and the height of 270 mm, (b) a cylindrical section with the diameter of 250 mm and the height of 600 mm. The flow characteristics of solids were investigated with a high speed camera and a pezoresistive absolute pressure transducer simultaneously. These characteristics revealed different flow regimes in the DCSF: packed bed at low gas velocities, fluidized bed in draft tube at higher gas velocities until minimum spouting, and spouted bed. The stable spouting was identified by the presence of two dominant frequencies of the power spectrum density of pressure fluctuation signature: (i) the frequency band 6-9 Hz and (ii) the frequency band 12-15 Hz. The pressure drops across the draft tube as well as the annulus measured in order to better recognize the flow structure in the DCSF. It was observed that the pressure drop across the draft tube, the pressure drop across the annulus, and the minimum spouting velocity increase with the increase in the height of draft tube and distance of the entrainment zone, but with the decrease in the distributor hole pitch. Finally, this study provided novel insight into the hydrodynamic of DCSF, particularly minimum spouting and stable spouting in the DCSF which contains valuable information for process design and scale-up of spouted bed equipment.

• Current Optics and Photonics
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• 제2권2호
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• pp.125-133
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• 2018

We report an in-depth analysis of the design and fabrication of multilayer dielectric (MLD) diffraction gratings for spectral beam combining at a wavelength of 1055 nm. The design involves a near-Littrow grating and a modal analysis for high diffraction efficiency. A range of wavelengths, grating periods, and angles of incidence were examined for the near-Littrow grating, for the $0^{th}$ and $-1^{st}$ diffraction orders only. A modal method was then used to investigate the effect of the duty cycle on the effective indices of the grating modes, and the depth of the grating was determined for only the $-1^{st}$-order diffraction. The design parameters of the grating and the matching layer thickness between grating and MLD reflector were refined for high diffraction efficiency, using the finite-difference time-domain (FDTD) method. A high reflector was deposited by electron-beam evaporation, and a grating structure was fabricated by photolithography and reactive-ion etching. The diffraction efficiency and laser-induced damage threshold of the fabricated MLD diffraction gratings were measured, and the diffraction efficiency was compared with the design's value.

• 공업화학
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• 제30권1호
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• pp.39-42
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• 2019

본 연구에서는 PET 상용 소재를 기반으로 제작된 유수분리막을 오일 폐수 처리에 효과적으로 적용하기 위하여 유수분리장치 성능 향상 및 적절한 소재 선정에 대하여 검토하였다. PET 섬유 소재의 방수 능력과 선택성을 유지할 수 있는 최적 조건을 탐색하였으며, 밀도 $60g/m^2$ 이상의 PET 소재를 2겹 이상으로 사용하여야 분리 효율을 유지하면서 본 연구에서 설계한 단위 셀에 적합한 수준의 방수 능력을 보여주었다. 유수분리장치는 회전하는 타공 원통 구조로 설계되고, 외부에 유수분리막이 감싸는 구조로 장착되어 연속적인 흡착제거가 가능하며, 내부에 부유형 방해판을 설치하여 오일 성분을 강제적으로 유수분리막 방향으로 유도하여 제거 효율과 안정성을 극대화하였다.

• 한국축산식품학회지
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• 제39권1호
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• pp.23-34
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• 2019

Fat reduction in the formulation of cheese emulsion causes problems in its flowability and functional characteristics during spray-dried cheese powder production. In order to eliminate these problems, the potential of using microparticulated whey protein (MWP) in cheese emulsions was examined in this study. Reduced-fat white-brined cheese emulsions (RF) with different dry-matters (DM) (15%, 20%, and 25% excluding emulsifying salt) were produced using various MWP concentrations (0%-20% based on cheese DM of emulsion). Their key characteristics were compared to full-fat cheese emulsion (FF). MWP addition had no influence on prevention of the phase separation observed in the instable group (RF 15). The most notable effect of using MWP was a reduction in apparent viscosity of RF which significantly increased by fat reduction. Moreover, increasing the amount of MWP led to a decrease in the values of consistency index and an increase in the values of flow behavior index. On the other hand, using high amounts of MWP made the emulsion more liquid-like compared to full-fat counterpart. MWP utilization also resulted in similar lightness and yellowness parameters in RF as their full-fat counterparts. MWP in RF increased glossiness and flowability scores, while decreased mouth coating scores in sensory analyses. Fat reduction caused a more compact network, while a porous structure similar to FF was observed with MWP addition to RF. In conclusion, MWP showed a good potential for formulation of reduced-fat cheese emulsions with rheological and sensorial characteristics suitable to be used as the feeding liquid in the spray drying process.

• 한국재료학회지
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• 제29권3호
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• pp.183-188
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• 2019

Flexible dye-sensitized solar cells using binder free $TiO_2$ paste for low temperature sintering are developed. In this paste a small amount of titanium gel is added to a paste of $TiO_2$ nanoparticle. Analysis of titanium gel paste prepared at $150^{\circ}C$ shows that it has a pure anatase phase in XRD and mesoporous structure in SEM. The formation of the titanium gel 1-2 nm coated layer is confirmed by comparing the TEM image analysis of the titanium gel paste and the pristine paste. This coating layer improves the excited electron transfer and electrical contact between particles. The J-V curves of the organic binder DSSCs fabricated at $150^{\circ}C$ shows a current density of $0.12mA/cm^2$ and an open-circuit voltage of 0.47 V, while the titanium gel DSSCs improves electrical characteristics to $5.04mA/cm^2$ and 0.74 V. As a result, the photoelectric conversion efficiency of the organic binder DSSC prepared at low temperature is as low as 0.02 %, but the titanium gel paste DSSCs has a measured effciency of 2.76 %.

• 한국재료학회지
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• 제29권2호
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• pp.87-91
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• 2019

We report on stretchable electrochromic films of poly(3-hexylthiophene) (P3HT) fabricated on silver nanowire (AgNW) electrodes. AgNWs electrodes are prepared on polydimethylsiloxane (PDMS) substrates using a spray coater for stretchable electrochromic applications. On top of the AgNW electrode, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is introduced to ensure a stable resistance over the electrode under broad strain range by effectively suppressing the protrusion of AgNWs from PDMS. This bilayer electrode exhibits a high performance as a stretchable substrate in terms of sheet resistance increment by a factor of 1.6, tensile strain change to 40 %, and stretching cycles to 100 cycles. Furthermore, P3HT film spin-coated on the bilayer electrode shows a stable electrochromic coloration within an applied voltage, with a color contrast of 28.6 %, response time of 4-5 sec, and a coloration efficiency of $91.0cm^2/C$. These findings indicate that AgNWs/PEDOT:PSS bilayer on PDMS substrate electrode is highly suitable for transparent and stretchable electrochromic devices.

• Current Photovoltaic Research
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• 제7권3호
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• pp.55-60
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• 2019

Polymer:nonfullerene solar cells with an inverted-type device structure were fabricated by employing the bulk heterojunction (BHJ) active layers, which are composed of poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophene-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene-4,8-dione))] (PBDB-T) and 3,9-bis(6-methyl-2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3-d']-s-indaceno[1,2-b:5,6-b']dithiophene (IT-M). The BHJ layers were formed on a pre-patterned indium-tin oxide (ITO)-coated glass substrate by spin-coating using the blend solutions of PBDB-T and IT-M. The solar cell performances were investigated with respect to the cell position on the ITO-glass substrates. In addition, the short-term shelf lifetime of solar cells was tested by storing the PBDB-T:IT-M solar cells in a glovebox filled with inert gas. The results showed that the performance of solar cells was relatively higher for the cells close to the center of substrates, which was maintained even after storage for 24 h. In particular, the PCE of PBDB-T:IT-M solar cells was marginally decreased after storage for 24 h owing to the slightly reduced fill factor, even though the open circuit voltage was unchanged after 24 h.

• 한국표면공학회지
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• 제52권1호
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• pp.16-22
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• 2019

The structural change of DLC coatings during long-term wear test and dicing test under the low loading condition was investigated. DLC coatings were applied for the precision injection molds of a modified SNCM steel for the extension of life and the micro-diamond blades for the high cutting efficiency and the increase in life. A ball-on-disc wear tests in the mold steel and a dicing tests in the micro-diamond blades were conducted to understand degradation of DLC coatings. The degradation of DLC coatings for the injection mold steel and the micro-diamond blades during the wear and dicing tests were studied with Raman Spectroscopy. Raman peaks were divided two bands(D band and G band) to study the degradation process of DLC structure. By the wear test, polished condition of wear marks were observed to be maintained until 10 hrs of wear test period is given, but small striation marks appeared in 20 hours wear test. It was observed that $I_D/I_G$ ratios changed as the degradation of DLC coatings is proceeded during the wear tests and the dicing tests. It is suggested that the change in $I_D/I_G$ value possibly reflected from the composition of $sp^2$ and $sp^3$ bondings in DLC layers relevant to the change in mechanical and physical property.