• 전기학회논문지
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• 제66권11호
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• pp.1651-1656
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• 2017

This paper deals with the thermal and mechanical properties of ceramic coating material for bus bars. A ceramic coated samples were prepared for the mechanical properties test. There are two types of samples. One is a square shape and the other is a busbar shape. Each sample was deteriorated for 30 days to compare the thermal and mechanical properties with the non-degraded samples. Two thermal properties tests are TGA and flammability tests, and four mechanical properties tests are drop impact test, cross cut, tensile test, and bend test. The ceramic coating material was never damaged by impact and did not separate from aluminum in the cross cut test. In the tensile test, the breakage of the insulating material did not occur until aluminum fractured, and the breakage of the insulating material did not occur until the maximum load in the bending test. The decomposition temperature (melting point) of the ceramic coating material was higher than that of other epoxy insulators. This ceramic coating material is nonflammable and it has excellent fire stability.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.379-379
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• 2013

본 논문에서는 Normal ink jetting 공법으로 OTFT를 제작할 때 coffee stain effect에 의해서 반도체 소자의 특성이 저하되는 것을 극복하기 위해서 동일한 위치에 동일한 부피로 Droplet을 형성하는 Multiple ink jetting 공법을 통해 TIPS pentacene 결정의 Morphology와 전기적 특성이 어떻게 변화하는지 알아 보았다. Multiple ink jetting의 drop 횟수가 증가할수록 coffee stain effect에 의해서 형성된 가운데 영역의 Dendrite grain이 점점 작아지다가 7 Drops 이후로는 Big grain 만 남게 되었다. Active layer의 표면 Roughness는 drop 횟수가 증가할수록 낮아지다가 일정 count 이후로는 다시 높아지는 것을 확인할 수 있었다. 전계 이동도(mobility)는 drop 횟수가 증가할수록 커지다가 일정 count 이후로는 saturation되는 것을 확인할 수 있었다. Multiple ink jetting에 의해서 만들어진 OTFT 소자의 전계 이동도(mobility)는 1 drop과 10 drops에서 각각 0.0059, 0.036 cm2/Vs 로 6배 정도 차이가 있었다. 이것은 첫 drop에 의해 만들어진 가운데 Dendrite grain 영역이 Multiple ink jetting을 반복하면서 점점 작아지게 되어 사라지고 두꺼운 Grain 영역만 남게 된 것으로 판단된다. Vth 와 On/Off ratio는 1 drop과 10 drops에서 각각 -3 V, -2 V 그리고 $3.3{\times}10^3$, $1.0{\times}10^4$를 보였다. OTFT의 substrate로 Flexible한 polyethersulfone (PES) 기판을 사용하였고, 절연체로 Spin coating된 Poly-4-vinylphenol (PVP)가 사용되었으며, Gate 및 Source/Drain 전극은 Au를 50 nm 두께로 증착하였다. Channel의 width와 length는 각각 100 um, 40 um 였고, Gate 전극 위에 Active layer를 형성한 Bottom gate 구조로 제작되었다. Ink jet으로 제작된 TIPS pentacene의 결정성은 x-ray diffraction (XRD)와 광학 현미경으로 분석하였고 Thickness profile은 알파스텝 측정기를 이용하였으며, OTFT의 전기적 특성은 Keithley-4,200을 사용하여 측정하였다.

• Journal of Electrochemical Science and Technology
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• 제12권2호
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• pp.225-229
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• 2021

Commercially available continuous glucose sensors require the operation stability for more than two weeks. Typically, the sensor comprises a sensing layer and an over-coating layer for the stable operation inside the body. In the sensing layer, enzymes and mediators are cross-linked together for the effective sensing of the glucose. The over-coating layer limits the flux of glucose and works as a biocompatible layer to the body fluids. Here, we report the simple preparation of the flux-limiting layer by the condensation of polyethyleneimine (PEI), tri-epoxide linker, and trimethylolpropane triglycidyl ether (PTGE). The sensor is constructed by a layer-by-layer drop-coating of the sensing layer containing glucose dehydrogenase and the PEI-derived blocking layer. It is stable for more than 14 days, which is enough for the sensor in the continuous monitor glucose monitoring (CGM) system.

• International Journal of Korean Welding Society
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• 제4권1호
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• pp.15-22
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• 2004

Metal transfer behavior of three shielded metal arc welding electrodes, AWS El1018, E6013 and E6010, were investigated through the characterization of size distribution of droplets and measurement of arc voltage signals. Of the three electrodes, Ell018 electrode showed the largest droplet size with the smallest amount of spatter, while E6010 electrode showed the smallest droplet size with the largest amount of spatter. Even though Ell0l8 electrode showed a good agreement between the frequencies of voltage drop in FFT processed voltage signals and the transfer rate of droplets, E6013 and E6010 electrodes showed weaker correlation because of their dominant explosive transfer behavior. The type of cathode used and electrode baking time also influenced the metal transfer behavior. Compared to bead-on-plate welding using steel plate as a cathode, welding on a water-cooled copper pipe showed less short-circuiting and higher melting rate in all electrodes because of higher arc potential and/or anode drop. When baked for a long time, E6010 electrode showed much more stable arc with less short-circuiting and explosion due to the loss of gas formation ingredients.

• 한국입자에어로졸학회지
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• 제18권1호
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• pp.9-21
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• 2022

In this study, a novel antiviral coating method for the air filtration system of subway station was investigated. Using dry aerosol coating process, we developed a high-performance antiviral air filter with spark discharger and carbon brush type ionizer. Silver nanoparticles were produced by a spark discharge generation system with ion injection system and were used as antiviral agents coated onto a medium grade air filter. The pressure drop, filtration efficiency, and antiviral ability of the filter against aerosolized MS2 virus particles as a surrogate of SARS-CoV-2 virus were tested with dust contamination. Dust contamination caused the increase of the filtration efficiency and pressure drop, while the antiviral agents (in this study, silver nanoparticles) coating did not have any significant effect on the filtration efficiency and pressure drop. Using these properties, we suggested a novel method to maximize the antiviral performance of the antiviral air filter that was contaminated by dust particles. Moreover theoretical analysis of antiviral ability with dust contamination and re-coated antiviral agents was carried out using a mathematical model to calculate the time-dependent antiviral effect of the filter under actual conditions of subway station. Our model can be used to apply on antiviral air filtration system of subway station for prevention of pandemic diffusion, and predict the life cycle of an antiviral filter.

• Advances in materials Research
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• 제9권3호
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• pp.219-231
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• 2020

The aim of this study is to investigate the durability of fly ash based geopolymer mortar with and without protective coatings in aggressive chemical environments. The source materials for geopolymer are Fly ash and Ground Granulated Blast furnace Slag (GGBS) and they are considered in the combination of 80% & 20% respectively. Two Molarities of NaOH solution were considered such as 8M and 10M. The ratio of binder to sand and Sodium silicate to Sodium hydroxide solution (Na₂SiO₃/NaOH) are taken as 1:2 and 2 respectively. The alkaline liquid to binder ratio is 0.4. Compressive strength tests were conducted at various ages of the mortar specimens. In order to evaluate the performance of coatings on geopolymer mortar under aggressive chemical environment, the mortar specimens were coated with two different types of coatings such as epoxy and Acrylic. They were then subjected to different chemical environments by immersing them in 10% standard solutions of each ammonium nitrate, sodium chloride and sulphuric acid. Drop in compressive strength as a result of chemical exposure was considered as a measure of chemical attack and the drop in compressive strength was measured after 30 and 60 days of chemical exposure. The compressive strength results following chemical exposure indicated that the specimens containing the acrylic coating proved to be more resistant to chemical attacks. The control specimen without coating showed a much greater degree of deterioration. Therefore, the application of acrylic coating was invariably much more effective in improving the compressive strength as well as the resistance of mortar against chemical attacks. The results also indicated that among all the aggressive attacks, the sulphate environment has the most adverse effect in terms of lowering the strength.

• 한국재료학회지
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• 제18권5호
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• pp.259-265
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• 2008

The corrosion and degradation factors of a current collector in a molten carbonate fuel cell (MCFC) were investigated to determine the optimized coating thickness of nickel on STS316L. The results show that the surface morphology and electrical properties depended on the nickel coating thickness. The surface morphology gradually changed from a flat to a porous structure along as the nickel coating thickness decreased, and the electrical resistance of the nickel-coated STS316L increased as the nickel coating thickness decreased. This can be attributed to the diffusion of elements of Fe and Cr from the substrate through the nickel grain boundaries. Additionally, carburization in the metal grains or grain boundaries in an anodic environment was found to influence the electrical properties due to matrix distortion. The resistance of Cr-oxide layers formed in an anodic environment causes a drop in the potential, resulting in a decrease in the system efficiency.

• Steel and Composite Structures
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• 제16권6호
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• pp.703-718
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• 2014

The initial clamping forces of high strength bolts subjected to different faying surface conditions drop within 500 hours regardless of loading, any other external force or loosening of the nut. This study develops a mathematical model for relaxation confined to creep on a coated faying surface after initial clamping. The quantitative model for estimating relaxation was derived from a regression analysis for the relation between the creep strain of the coated surface and the elapsed time for 744 hours. This study establishes an expected model for estimating the relaxation of bolted joints with diverse coated surfaces. The candidate bolts are dacro-coated tension control bolts, ASTM A490 bolt, and plain tension control bolts. The test parameters were coating thickness, species of coating. As for 96, 128, 168, and $226{\mu}m$ thick inorganic zinc, when the coating thickness was increased, relaxation after the initial clamping rose to a much higher range from 10% to 18% due to creep of the coating. The amount of relaxation up to 7 days exceeded 85% of the entire relaxation. From this result, the equation for creep strain can be derived from a statistical regression analysis. Based on the acquired creep behavior, it is expected that the clamping force reflecting relaxation after the elapse of constant time can be calculated from the initial clamping force. The manufacturer's recommendation of inorganic zinc on faying surface as $75{\mu}m$, appears to be reasonable.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2067-2072
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• 2007

Understanding of the impinging behavior of an electrically charged spray is essential in determining appropriate operating conditions for electro-spraying of paints, surface coating materials and insecticides. In the present work, as an initial step, the wall impact of an electrically charged droplet has been experimentally investigated. The charged drops were directed on the surface of a paraffin wax, and the impinging behavior was visualized and recorded using a CCD camera to identify the impingement regime. The spread-rebound boundary for the charged drop turned out to be smaller compared to that for an electrically neutral droplet under the same surface condition. The shift of the transition criterion is considered to be due to the discrepancy between the maximum spread ratio of the electrically charged droplet and that of the neutral droplet.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2010년도 춘계학술발표대회
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• pp.20.2-20.2
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• 2010

Recently inkjet printing technology has been developed in the areas of low cost fabrication in environmentally friendly manufacturing processes. Although inkjet printing requires the interdisciplinary researches including development of materials, manufacturing processes and printing equipment and peripherals, manufacturing a printhead is still core of inkjet technology. In this study, a piezoelectric driven DOD (drop on demand) inkjet printhead has been fabricated on three layers of the silicon wafer in MEMS Technology because of its chemical resistance to industrial inks, strong mechanical properties and dimensional accuracy to meet the drop volume uniformity in printed electronics and display industries. The flow passage, filter and nozzles are precisely etched on the layers of the silicon wafers and assembled through silicon fusion bonding without additional adhesives. The piezoelectric is screen-printed on the top the pressure chamber and the nozzle plate surface is treated with non-wetting coating for jetting fluids. Printheads with nozzle number of 16 to 256 have been developed to get the drop volume range from 5 pL to 80 pL in various industrial applications. Currently our printheads are successfully utilized to fabricating color-filters and PI alignment layers in LCD Flat Panel Display and legend marking for PCB in Samsung Electronics.