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조동율 사단법인 한국지역사회연구소 2000 地域社會 Vol.2000 No.3
고속 인터넷 서비스회사가 이미 서비스를 제공하고 있거나 계획하고 있는 상황이므로 인터넷 이용의 하부 구조적인 면에 많은 개선이 이루어지고 있다. 따라서 광고매체로서의 인터넷의 중요성이나 활용성에 대한 인식이 우리나라에서도 충분히 무르익은 단계에 이미 도달했다고 보아도 무방할 것이다.
WC-Co 초고속 화염용사코팅 표면특성에 미치는 분말입자의 크기
조동율,윤재홍,윤상환,주윤곤,최원호,손영복 대한금속·재료학회 2017 대한금속·재료학회지 Vol.55 No.4
The effects of particle size on the surface properties of HVOF spray coating were studied to improve of the durability of metal components. Micro and nano sized WC-12Co powders were coated on the surface of Inconel718, and the effects of particle size on surface properties were studied. Surface hardness was reduced when the particle sizes of the powder were decreased, because the larger specific surface area of the smaller particles caused greater heat absorption and decomposition of the hard WC to less hard W2C and graphite. Porosity was increased by decreasing the particle size, because the larger specific surface area of the smaller particles caused a greater decomposition of WC to W2C and free carbon. The free carbon formed carbon oxide gases which created the porous surface. The friction coefficient was reduced by decreasing the particle size because the larger specific surface area of the smaller particles produced more free carbon free Co and Co oxide which acted as solid lubricants. The friction coefficient increased when the surface temperature was increased from 25 to 500 ℃, due to local cold welding. To improve the durability of metal mechanical components, WC-Co coating with the proper particle size is recommended.
조동율,천희곤,주윤곤,윤재홍 한국정밀공학회 2014 International Journal of Precision Engineering and Vol. No.
HVOF thermal spray coating of micron-sized WC-metal powder onto Inconel718 surface was carried out for the durabilityimprovement of magnetic shaft of turbo-blower. Porous coating of porosity 2.2±0.4% was formed, but the surface properties wereimproved, such as surface hardness from 400±10 Hv (In718) to 1250±50 Hv (coating), friction coefficient from 0.46±0.06 to0.32±0.04 at surface temperature 25oC and from 0.38±0.04 to 0.28±0.04 at surface temperature 450oC. Wear resistance improveddecreasing the wear trace by coating. Corrosion resistance improved by coating in 3.5% NaCl solution (sea water) and in acid, butit worsened in base. The coating was CO2 laser heat-treated for further improvement of the properties of the coating. By laser heatingof 0.6 second with power density 20 W/mm2, coating thickness was decreased, porosity decreased more than five times from 2.2±0.4%to 0.4±0.1%, the surface hardness increased to 1830±100 Hv the interface (coating/substrate) was compacted, and elements diffusedfrom both coating and substrate inconel718 to interface, forming metal rich buffer zone(interface) and enhancing the adhesion ofcoating. For the improvement of durability of the magnetic shaft, HVOF WC-metal power coating and laser heat-treatment arerecommended.
UV/Cl₂(g)에 의한 Si-wafer 표면금속 오염물의 건식세정에 관한 연구
손동수,정광진,최성호,천희곤,조동율 울산대학교 1998 공학연구논문집 Vol.29 No.2
본 연구에서는 실리콘 웨이퍼 표면에 존재하는 미량의 Zn, Fe, Ti 금속 오염물들이 UV-excited chlorine radical을 이용한 건식세정 방법으로 제거되는 반응과정을 연구 하였다. 실리콘 웨이퍼 상에 진공증착법으로 원형패턴이 있는 Zn, Fe, Ti 박막을 증착시켜 상온 및 200℃에서 UV/CI₂세정하였을 때, 염소 래디컬(CI*)이 Fe, Zn, Ti와 반응하여 제거되는 것을 반응 전후 광학현미경과 SEM을 통해 표면 형상 변화를 관찰하였고, in-line으로 연결된 XPS를 통해서 반응 후 웨이퍼 표면에 남아있는 화합물의 화학적 결합상태를 관찰하였으며, UV/CI₂세정 후 실리콘 기판이 손상받는 정도를 알기 위해 AFM으로 표면 거칠기를 측정하였다. 광학현미경과 SEM의 분석에 의하면 Zn와 Fe는 쉽게 제거되는 반면 염화물을 형성하기 보다는 휘발성이 적은 산화물을 형성하는 경향이 강한 Ti은 약간만 제거되는 것을 확인하였다. XPS 분석을 통해서 이들 금속 오염물들이 chlorine radical과 반응하여 웨이퍼 표면에 금속 염화물을 형성하고 있는 것을 확인하였고, UV/CI₂세정처리를 하였을 때 실리콘 웨이퍼의 표면 거칠기가 약간 증가하는 것을 알 수 있었다. 지금까지의 결과를 통해 볼 때, 습식세정과 UV/CI₂건식세정을 병행하면 플라즈마 및 레이저를 사용하는 다른 건식세정 방법에 비하여 보다 저온에서 실리콘 기판의 큰 손상 없이 비교적 용이하게 금속 오염물을 제거할 수 있음을 알수 있었다. The reaction mechanisms of dry cleaning of Zn, Fe and Ti trace contaminants on the Si wafer using UV/CI₂ have been studied by SEM, AFM and XPS analyses. The patterned Zn, Fe and Ti films were deposited on the Si wafer surface by thermal evaporation and changes in the surface morphology after dry cleaning using CI₂and UV/CI₂at 200℃ were studied by optical microscopy and SEM. In addition changes in surface roughness of Si wafer by the cleaning was observed by AFM. The chemical bonding states of the Zn, Fe and Ti deposited silicon surface were observed with in-line XPS analysis. Zn and Fe were easily cleaned in the form of volatile zinc-chloride and iron-chloride as verified by the surface morphology changes. Ti which forms involatile oxides was not easily removed at room temperature but was slightly removed by UV/CI₂at elevated temperature of 200℃. It was also found that the surface roughness of the Si wafer increased after CI₂and UV/CI₂cleaning. Therefore, the metallic contaminants on the Si wafer can be easily removed at lower temperature by continuous processes of wet cleaning followed by UV/CI₂dry cleaning.
초고속 회전체 내구성 향상을 위한 Co-alloy(T800)의 초고속 용사코팅
조동율(Tong Yul Cho),윤재홍(Jae Hong Yoon),김길수(Kil Su Kim),박봉규(Bong Kyu Park),윤석조(Suk Jo Youn),백남기(Nam Ki Back) 한국생산제조학회 2006 한국생산제조시스템학회 학술발표대회 논문집 Vol.2006 No.5
The traditional high wear resistant coatings such as hard chrome plating and ceramic coatings have been replacing progressively by other coating methods such as HVOF thermal spray coating because of the environmental pollution of very toxic hex-Cr known as carcinogen having toxicity greater than arsenic and cadmium by chrome plating and chrome plated products and the brittleness of ceramic coatings(6, 7). Co-alloy(T800) micron size powder was coated on Inconel 718 by HVOF thermal spraying for the studies of the improvement of durability of high speed air bearing spindle. Coatings were prepared by Taguchi program for the parameters of spray distance, flow rates of hydrogen and oxygen and powder feed rate. Optimal coating process was determined by the studies of coating properties such as micro-structure, porosity, surface roughness and micro hardness. Friction and wear behaviors of coatings were investigated by sliding wear test with counter sliding stainless steel 304 ball at room temperature and at elevated temperature of 1000°F(538℃). At room temperature wear debris of the coating were roughly reduced to 15 times less and friction coefficients were decreased to more than a half compared with the surface of non-coated parent material. At high temperature of 538℃ wear debris and friction coefficients of the coatings were drastically decreased compared with non-coated surface of parent material. These drastic decreases of both wear debris and friction coefficient of the coatings compared with those of non-coated surface of parent material shows that Co-alloy(T800) coating is highly recommendable for the durability improvement surface coating of high speed air-bearing spindle. At high temperature wear traces and friction coefficients of both coating and non-coating were drastically reduced compared with those of room temperature since the oxides such as CoO, CO₃O₄, MoO₂, MoO₃, and etc were formed easily on the surface, and the brittle oxide phases were attrited by the reciprocating sliding wear according to the complicated mixed mechanisms such as oxidative wear by direct reaction with oxygen, abrasion by scratching or gouging at the asperities by the sliding ball, slurry erosion by the mixture of solid particles and small drops of the melt of the attrited particles, cavitation by the relative motions among the coating, sliding ball and melt, and corrosive wear by the corrosion environment induced by the frictional heat and local high temperature(8, 17). These oxide particles and the melt play role as lubricant and reduce the wear and friction coefficient. This also shows that Co-alloy(T800) coating is highly recommendable for the durability improvement surface coating on the surface vulnerable to frictional heat such as high speed air-bearing spindles.