• Membrane Journal
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• v.26 no.3
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• pp.205-211
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• 2016

Performance of pyrophyllite-based ceramic membranes newly developed were investigated. Membrane fouling caused by microbial suspensions taken from a full-scaled MBR system at domestic wastewater treatment plant was observed at different airflow rate and distance between each membrane. For the pyrophyllite support, pore size was about $1.0{\mu}m$, but surface coating with $Al_2O_3$ solution decreased the pore size with the reduction of the pure water permeability. With the MLSS taken from the full-scaled MBR system (6 g/L), the fouling rate was decreased by increasing airflow rate under $20L/m^2{\cdot}hr$ of setpoint flux. However, the effectiveness of the airflow rate on the fouling control depends strongly upon the gap between each membrane. At fixed airflow rate, the fouling rate was decreased by increasing the gap between each pyrophyllite membrane. Nevertheless, further increasing the membrane distance from 3.5 to 5.4 cm resulted in higher fouling rate. Similar result was observed with the $Al_2O_3$ coated-pyrophyllite membrane. Nevertheless, the fouling rate was lower with the coated membrane than that observed with the uncoated pyrophyllite support. Regardless of surface coating, the suspended solids were removed almost completely and the surface coating on the pyrophyllite support improved organic rejection with PEG solution (MW : 8000 kDa) tested.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.421.2-421.2
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• 2016

고효율 태양전지에서 후면 반사 방지막은 장파장대(900nm~1200nm) 빛의 내부 반사를 증가시켜 광흡수도를 개선한다. 태양전지 후면에 박형 절연층 구조를 구성함으로써 특정 파장에서 높은 반사도를 얻을 수 있는 Bragg mirror 구조를 이론적으로 계산할 수 있다. Bragg mirror 구조를 이용하여 태양전지의 후면 반사층(Rear reflector layer)을 형성함으로써 태양전지 내부의 광흡수도를 개선할 수 있다. 후면 반사 방지막(Rear anti-reflection coating)으로 사용되는 Al2O3와 SiOxNy 또는 이러한 두 가지 물질의 겹층 구조를 구성하여 장파장대 빛의 반사도 차이에 의한 광흡수도 개선 정도를 광학 시뮬레이션을 통해 계산하였다. 광학 시뮬레이션은 TCAD를 이용하였으며 두 가지 겹층 구조에서 각 반사 방지막의 두께에 따른 단락 전류(Jsc)의 개선 정도, 후면 반사층 두께의 최적화 조건을 계산하였다. 후면 반사방지막을 제외한 기본적인 태양전지 구조는 n-type PERC 구조를 사용하였으며, 후면 반사방지막만의 광학적 특성을 살펴보기 위해 전극은 광학적으로 투명하다고 가정하였다. 반사방지막 두께의 범위는 Al2O3(5-30nm), SiNx(150-300nm), SiOxNy(150-300nm)에서 수행하였으며, 각각 1nm, 2nm 간격으로 진행하였다. Al2O3/SiOxNy 구조에서는 단락 전류가 32.45-32.87mA/cm2 값을 가진다. Al2O3/SiNx 구조에서는 단락 전류가 32.59-32.87mA/cm2 값을 가진다. 결론적으로, 후면 반사방지막의 겹층 구조를 통해 광흡수도를 증가 시킬 수 있으며, TCAD 시뮬레이션을 통하여 입사되는 태양광 스펙트럼에 최적화된 구조를 설계할 수 있다.

• Membrane Journal
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• v.18 no.2
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• pp.176-184
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• 2008

Nano-porous ceramic membranes was synthesized by the sol-gel method. Gas permeation of hydrogen and nitrogen was determined by single composition gas. Pore size $0.1{\mu}m$ and porosity 32% of flat type ${\alpha}-Al_2O_3$ substrate was manufactured. An intermediate ${\gamma}-Al_2O_3$ layer with pore size of 4 nm was formed by dip-coating. Polymeric silica sol was synthesized by acid catalyzed hydrolysis and condensation of tetra-ethyl-ortho-silicate. Supported membranes on alumina were prepared by dipping and calcining. He, $N_2$ permeation experiments with nanoporous sol-gel modified supported ceramic membranes were peformed to determine the gas transport characteristics. $He/N_2$ permselectivity around $100{\sim}160$ and helium permeation in the order of $10^{-7}mol/m^2{\cdot}s{\cdot}Pa$ were measured in the temperature range of $303{\sim}363K$.

• Journal of the Korea Institute of Building Construction
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• v.14 no.6
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• pp.505-513
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• 2014

The purpose of this study is to evaluate the corrosion protective properties of a Zn-Sn metal spray method according to the contents of Zn and Sn by a CASS test and the electrochemical theory. In the experiment, the CASS test and the electrochemical test were conducted to investigate the corrosion protective property of the Zn-Sn Metal Spray system, the Zinc galvanizing system, and the heavy duty coating system. As a result, it was confirmed that the Zn-Sn (65:35) Metal Spray system had very high corrosion protective property through the electrochemical characteristic as comparison with the other anti-corrosion systems and was very effective to prevent steel products from corrosion.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.6
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• pp.513-519
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• 2014

For depth machining in die and mold, Electrical Discharge Machining (EDM) is used generally. To make deep hole and deep shape efficiently, cemented carbide endmill for depth machining is necessary. For this purpose, cemented carbide endmill was designed using design of experiment (DOE). To improve cutting performance, endmill was coated with multilayer surface treatment, TiAlCrSiN and TiAlCrN, for higher wear resistance. In order to evaluate the endmill, Transverse Rupture Strength (TRS) test was tried for investigating the relationship between surface treatment and strength in endmill body. Scratch test was also used for measuring adhesion force of each surface treatment. To evaluate hardness of surface treatment, Atomic Force Microscope (AFM) analysis was carried out. Wear test was executed for characteristics of each surface treatment in high temperature. Consequently, TiAlCrSiN was superior to the TiAlCrN coating in case of high temperature environment such as cutting.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.1035-1040
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• 2011

This research was performed on a microfilter made of a hybrid material (ceramic + metal) that was coated with ceramics on the metal-filter surface by using the thermal spray method. The ceramic powders used were $Al_2O_3+40TiO_2$ powder with a particle size of $20{\mu}m$ and $Al_2O_3$ (98%+)powder with a particle size of $45{\mu}m$. The metal filters were filter-grade $20{\mu}m$, $30{\mu}m$, and $50{\mu}m$ sintered metal powder filters (SIKA-R 20 IS, 30 IS, 50 IS; Sinter Metals Filters) and filter-grade $75{\mu}m$ sintered mesh filter with five layers. Ceramic-coated filters that were coated using the thermal spray method had a great influence on powder material, particle size, and coating thickness. However, these filters showed a fine performance when used as micro-filters.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.2
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• pp.203-215
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• 2007

Statement of problem: Titanium and its alloy, with their excellent bio-compatibility and above average resistance to corrosion, have been widely used in the field of dentistry. However, the excessive oxidization of titanium which occurs during the process of firing on porcelain makes the bonding of titanium and porcelain more difficult than that of the conventional metal-porcelain bonding. To solve this problem related to titanium-porcelain bonding, several methods which modify the surfaces, coat the surfaces of titanium with various pure metals and ceramics, to enable the porcelain adhesive by limiting the diffusion of oxygen and forming the adhesive oxides surfaces, have been investigated. Purpose: The purpose of this study was to know whether the titanium-porcelain bonding strength could be enhanced by treating the titanium surface with gold and TiN followed by fabrication of clinically applicable porcelain-fused-to-titanium crown Material and method: The porcelain-fused-to-titanium crown was fabricated after sandblasting the surface of the casting titanium coping with $Al_2O_3$ and treating the surface with gold and TiN coating followed by condensation and firing of ultra-low fusing porcelain. To compare with porcelain-fused-to-titanium crowns, porcelain-fused-to-gold crowns were fabricated and used as control groups. The bonding strengths of porcelain-fused-to-gold crowns and porcelain-fused-totitanium crowns were set for comparison when the porcelain was fractured on purpose to get the experimental value of fracture strength. Then, the surface were examined by SEM and each fracturing pattern were compared with each other Result:Those results are as follows. 1. The highest value of fracture strength of porcelain-fused-to-titanium crowns was in the order of group with gold coating, group with TiN coating, group with $Al_2O_3$ sandblasting. No statistically significant difference was found among the three (P>.05). 2. The porcelain-fused-to-gold crowns showed the highest value in bonding strength. The bonding strength of crowns porcelain-fused-to-titanium crowns of rest groups showed bonding strength reaching only 85%-94% of that of PFG, though simple comparision seemed unacceptable due to the difference in materials used. 3. The fracturing patterns between metal and porcelain showed mixed type of failure behavior including cohesive failure and adhesive failure as a similar patterns by examination with the naked eye and SEM. But porcelain-fused-to-gold crowns showed high incidence of adhesive failure and porcelain-fused-to-titanium crowns showed high incidence of cohesive failure. Conclusion: Above results proved that when fabricating porcelain-fused-to-titanium crowns, treating casting titanium surface with gold or TiN was able to enhance the bonding strength between titanium and porcelain. Mean value of masticatory force was found to showed clinically acceptable values in porcelain bonding strength in all three groups. However, more experimental studies and evaluations should be done in order to get better porcelain bonding strength and various surface coating methods that can be applied on titanium surface with ease.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.3
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• pp.57-61
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• 2016

In order to protect the solar cells from the moisture and oxygen, we evaluated the electrical and optical properties for the $Cu(In,Ga)Se_2$ (CIGS) solar cells which were prepared by the spray coating method. Generally, the EVA (ethylene-vinyl acetate) films are laminated to protect the CIGS flexible solar cells, which results in a high cost process due to complicated devices. In this study, we tried to prepare the protection layers of the flexible CIGS flexible solar cells by using spray coating method instead of conventional laminating films in order to reduce the device weight as well as the process time. The CIGS solar cells with spray coating method showed an enhanced efficiency than the before treated sample (2.77% to 2.93%) and relatively proper water vapor transmission rate of the solar cells about 62.891 gm/[$m^2-day$].

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.271-272
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• 2012

Bulk Metallic Glasses (BMGs or amorphous alloy) exhibit high strength and good corrosion resistance. Applications of thin films and micro parts of BMGs have been used a lot since its inception in the research of BMGs. However, Application and fabrication of BMGs are limited to make structural materials. Thin films of BMGs which is sputtered on the surface of structural materials by sputtering process is used to improve limits about application of BMGs. In order to investigate the difference of properties between designed alloys and thin films, we identified that thin films deposited on the surface that have the characteristic of the amorphous films and the composition of designed alloys. Zr-Cu (Cu=30, 35, 38, 40, 50 at.%) and Zr-Cu-Al (Al=10 at.% fixed, Cu=26, 30, 34, 38 at.%) alloys were fabricated with Zr (99.7% purity), Cu (99.997% purity), and Al (99.99% purity) as melting 5 times by arc melting method before rods 2mm in diameter was manufactured. In order to analyze GFA (Glass Forming Ability), rods were observed by Optical Microscopy and SEM and $T_g$, $T_x$, ($T_x$ is crystallization temperature and $T_g$ is the glass transition temperature) and Tm were measured by DTA and DSC. Powder was manufactured by Gas Atomizer and target was sintered using powder in large supercooled liquid region ($=T_x-T_g$) by SPS(Spark Plasma Sintering). Amorphous foil was prepared by RSP process with 5 gram alloy button. The composition of the foil and sputtered thin film was analyzed by EDS and EPMA. In the result of DSC curve, binary alloys ($Zr_{62}Cu_{38}$, $Zr_{60}Cu_{40}$, $Zr_{50}Cu_{50}$) and ternary alloys ($Zr_{64}Al_{10}Cu_{26}$, $Zr_{56}Al_{10}Cu_{34}$, $Zr_{52}Al_{10}Cu_{38}$) have $T_g$ except for $Zr_{70}Cu_{30}$ and $Zr_{60}Al_{10}Cu_{30}$. The compositions with $T_g$ made into powders. Figure shows XRD data of thin film showed similar hollow peak.

• Journal of the Korean Ceramic Society
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• v.30 no.10
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• pp.829-837
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• 1993

Chemically and geometrically homogeneous mixing of Si3N4 powders with sintering additives(YAG, 3Y2O3$.$5Al2O3) was attempted via coprecipitation method. X-ray dot maps for the additive elements(Al and Y) showed that the additives are evenly distributed in the powder mixture prepared by coprecipitation method(CP). TEM observation of the coprecipittion-treated Si3N4 powders revealed that they are covered with extremely fine crystallites of additive. The shift in isoelectric point(IEP) of Si3N4 powders from pH 6.7 to pH 7.9 after coprecipitation mixing gave another evidence for coating of Si3N4 powders with YAG additives. SIMS analysis for composition on the surface and in the matrix of mixed powders showed that the YAG additives are highly enriched on the surface of coprecipitation-treated Si3N4 powders. Especially when a small amount of additive was used, the effect of homogeneous additive distribution on densification was preceptible: After pressureless-sintering of powder compacts containing 5 mol% YAG at 1800$^{\circ}C$ for 0.5h, a sintered density of 96.5% theoretical was obtained from the specimens prepared bycoprecipitation in comparison with 93.8% from the mechanically-mixed one.