Al₂O₃:xCr₂O₃ 고용상의 발광특성과 적색형광체의 연색성 향상을 위한 첨가제로의 응용

채기웅,천채일,김정석,Chae, Ki-Woong,Cheon, Chae-Il,Kim, Jeong-Seog 한국세라믹학회 2010 한국세라믹학회지 Vol.47 No.2

In this article photoluminescence of the $Al_2O_3:xCr_2O_3$ solid solutions prepared by solid state reaction method are represented. The effect of $Cr_2O_3$-activator concentration and heat treatment time on the PL characteristics have been discussed in conjunction with microstructure of phosphor samples. The $Al_2O_3:xCr_2O_3$ phosphors show the highest PL intensity at x=0.003 mole when the samples are reacted at $1600^{\circ}C$ for 5 h. The PL emission and absorption spectra show the maximum peaks at 698 nm and at 398 nm respectively. The CIE color coordinate is (x=0.646, y=0.316) at 0.003 mole $Cr_2O_3$, which value is very close to the NTSC coordinate of red color. This characteristic feature of $Al_2O_3:xCr_2O_3$ has been applied for an additive to improve the color characteristic of other red phosphor $LiEuW_2O_8$ which has a relatively poor color purity with an emission peak centered at 615 nm and with a CIE coordinate (x=0.530, y=0.280). The $Al_2O_3:0.003Cr_2O_3$ phosphor has been mixed with the $LiEuW_2O_8$ phosphor powder and the PL characteristics and CIE color coordinates are characterized. The $Al_2O_3:xCr_2O_3$ phosphor was found effective for improving the CRI (color rendering index) of $LiEuW_2O_8$ phosphor.

수용액 합성법에 의한 ZnO 이중 나노구조물의 합성

채기웅,김정석,Chae, Ki-Woong,Kim, Jeong-Seog,Cao, Guozhong 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.6

Double-layered ZnO nanostructures have been synthesized by aqueous solution method on (001) plane of ZnO nanorod. A stepwise changing of aqueous solution concentration gave rise to a new nano-structured layer consisting of either multiple of nanorods or nanowires with much smaller radii than that of the ZnO nanorod on which the new layer was grown. As the first step the ZnO nanorods have been grown to have the (001) preferential orientation in the aqueous solution consisting of 0.1M zinc nitrate and 0.1 M HMT. This preferentially aligned ZnO nanorods have been regrown in either a less diluted solution of 0.01M zinc nitrate and 0.01 M HMT or a more diluted solution of 0.005M zinc nitrate and 0.01 M HMT. A new nano-layer consisting of numerous aligned nanorods or nanowires has been produced on the (001) planes of ZnO nanorods. The growth mechanism for this double layered ZnO nanostructure is ascribed to the (001) polar surface energy instability and inhibition of (001) plane growth due to the step-wise change of aqueous solution concentration; ZnO nuclei formed on the (001) plane grow preferentially in (010) plane instead of (001) plane to reduce the total surface energy. Surface area of ZnO nanostructure can be increased in orders of magnitudes by forming a new layer consisting of smaller nanorods/nanowires on (001) plane of ZnO nanorods.

Rietveld 정밀화법과 SEM-EDS 분석에 의한 DPF용 코디어라이트 하니컴 세라믹스의 결정성장 과정 분석

채기웅,김강산,김정석,김신한,Chae, Ki-Woong,Kim, Kang San,Kim, Jeong Seog,Kim, Shin-Han 한국결정성장학회 2021 한국결정성장학회지 Vol.31 No.3

코디어라이트(Mg₂Al₄Si₅O₁₈) 하니컴 세라믹스의 대표적 응용분야는 자동차 배기가스 정화용 필터(diesel particulate filter(DPF))이다. 천연광물, 조공제, 유기바인더를 혼합한 슬러리를 압출하여 DPF용 하니컴 코디어라이트를 성형한 후 980~1450℃ 범위에서 소결하였다. 소결온도에 따른 결정상(indialite, cordierite, cristobalite, alumina, spinel, mullite, pro-enstatite)의 형성과정을 XRD Rietveld 정밀화법을 이용하여 정량분석 하였다. 동시에, 세라믹 에칭(etching) 방법으로 소결 시료 표면의 비정질상을 제거한 후 SEM/EDS법을 사용하여 결정상들의 형상과 조성을 확인하였다. 이들 결과로부터 DPF 하니컴에서 결정상 형성 과정을 명확히 밝힐 수 있었다. 또한, DPF 하니컴의 소결온도에 따른 열팽창계수(linear coefficient of thermal expansion, CTE) 변화를 분석하였고, 결정상의 정량분석결과를 바탕으로 계산된 CTE와 비교하였다. 소결된 DPF 하니컴 내의 결정상들이 CTE 특성에 미치는 영향을 고찰하였다. Diesel particulate filter (DPF) is a typical application field of cordierite (Mg₂Al₄Si₅O₁₈) honeycomb. Green body for DPF honeycomb was extruded using slurry paste and sintered at the temperature range of 980~1450℃. Quantitative crystal phase analysis was carried out by using Rietveld refinement method for powder XRD data. In conjunction with the quantitative Rietveld analysis, SEM-EDS analysis was carried for the crystal phases (indialite, cordierite, cristobalite, alumina, spinel, mullite, pro-enstatite). After removing amorphous phase on the sintered surfaces by chemical etching method, the shape and composition of the crystal phases can be clearly identified by SEM-EDS method. By combining the Rietveld refinement method and SEM-EDS analysis, crystal phase evolution process in DPF cordierite ceramics could be clarified. In addition, the coefficient of thermal expansion (CTE) of the DPF honeycombs were measured and compared with the calculated CTEs based on the quantitative crystal phase analysis results.

NFT를 활용한 음원 수익 정산권 거래 시스템

채기웅(Gi-Woong Chae),김민수(Minsu Kim),김영환(Younghwan Kim),김상균(Sang-Kyun Kim) 한국방송·미디어공학회 2023 한국방송공학회 학술발표대회 논문집 Vol.2023 No.6

WC-Co계 미세조직에 따른 CVD 다이아몬드 코팅막의 접착력 변화

이동범,채기웅,Lee, Dong-Beum,Chae, Ki-Woong 한국세라믹학회 2004 한국세라믹학회지 Vol.41 No.10

평균입자크기가 서로 다른 WC-Co계 모재위에 고온 열처리법과 화학적 에칭방법을 이용하여 다이아몬드 막을 코팅하고 압흔법을 통해 그 접착력(adhesion strength)을 평가하였다. $1450^{\circ}C$의 고온 열처리 방법에 의해 준비된 WC-Co 시편표면에서는 WC 입자가 성장하였으며, 그 결과 20$\mu$m 이상의 다이아몬드 막이 증착된 경우에도 100kg의 하중에서도 우수한 접착력이 얻어졌다. 그러나, 모재 표면입자의 과도한 입성장으로 시편 인선부에는 변형이 발생하였으며, 증착된 다이아몬드 막은 거친 표면조도를 보였다. 이와 비교하여, 화학적 부식의 경우에는 submicron 크기의 WC 입자를 제외하고, 2$\mu$m 이상의 WC 입자를 가지는 모재를 이용하여 10$\mu$m의 다이아몬드 코팅막을 증착시킨 경우에는, 60kg의 하중에서도 양호한 접착력이 유지되었다 특히, WC 입자가 클수록 접착력의 신뢰성이 대폭 향상되었다. 이는 수 $\mu$m 이내의 비교적 얇은 두께의 다이아몬드 막을 증착하는 경우 화학적 에칭방법이 시편 형상의 변형을 방지하고, 양호한 표면조도를 얻을 수 있어 고온 열처리 방식에 비해 효과적임을 의미한다. The effect of microstructure of WC-Co substrates which have different WC grain sizes from submicron to 5 $\mu$m on the diamond-substrate adhesion strength was investigated. The substrates were pre-treated by two methods : chemical etching with Murakami's solution and subsequently with $H_2SO_4$, and thermal heat-treatment. The adhesion strength was estimated by degree of peeling after Rockwell indentation. Diamond films of 20 $\mu$m thickness deposited on the heat-treated substrates showed an excellent adhesion strength at the load of 100 kg, which ascribed to the large and elongated WC grains. However, the cutting edge of insert was deformed after heat treatment and the surface morphology of heat treated substrate strongly affected on the surface roughness of the deposited diamond films. On the contrary, the diamond film of 10 $\mu$m in thickness on the chemically etched substrates of average WC grain size over 2 $\mu$m showed good adhesion strength enough not to peel-off under a load of 60 kg. Especially, the substrate of average WC grain size over 5 $\mu$m exhibited much improved reliability of adhesion comparing with the substrate of average grain size under 2 $\mu$m. No substrate deformation was observed in this case after the chemical etching, which is more advantageous and more practical in terms of precious machining than the heat treatment case.

수용액 합성법의 2단계 성장온도 변화를 통한 ZnO 결정의 선택적 용해 현상

김정석,채기웅,Kim, Jeong-Seog,Chae, Ki-Woong 한국세라믹학회 2011 한국세라믹학회지 Vol.48 No.4

ZnO hexagonal rods grown in aqueous solution can be changed into a tubular shape by two-step aging in the course of the growing process. In the first step, hexagonal ZnO rods is grown by aging at $90^{\circ}C$ under a highly supersaturated aqueous solution giving rise to a fast precipitation rate. Meanwhile, during the second step aging at $60^{\circ}C$ in the same aqueous solution, the hexagonal polar face (001) having higher surface energy than (010) side planes dissolves to minimize surface energy. Hence the flat (001) face changes to a craterlike face and the hexagonal rod length of ZnO decreases at an initial-stage of this step aging. The formation of the (101) wedge-type faces is ascribed to the resultant of competitive reactions between the dissolution of polar face minimizing the surface energy which is a dominant reaction at the initial stage and the precipitation reaction dissipating supersaturation. At a later stage of the second-step the reaction rates of these two processes in the aqueous solution become similar and the overall reaction is terminated.

열처리 분위기가 Eu 이온이 첨가된 Li-Al-O계 형광체 특성에 미치는 영향

김정석,천채일,채기웅,Kim, Jeong Seog,Cheon, Chae Il,Chae, Ki-Woong 한국세라믹학회 2014 한국세라믹학회지 Vol.51 No.1

New green phosphor is synthesized by reducing $LiAlO_2:xEu^{3+}$ phosphors in a low pressure $H_2$ atmosphere. The $LiAlO_2:xEu^{3+}$ prepared by a solid state reaction method is reported as red phosphor. The effect of the reduction treatment on the $LiAlO_2:xEu^{3+}$ on the crystalline phase change and photoluminescence (PL) property are characterized. The reduced phosphor had a broad green light spectrum centered at 524 nm. The PL intensity of the reduced phosphor increased to a maximum at the reduction temperature of $1100^{\circ}C$. The PL intensity decreased with a further increase in the reduction temperature. The crystalline phase constituting the reduced phosphor varied with the temperature. A new crystalline phase $Li_2Al_4O_7$ was observed at $1100^{\circ}C$. The origin of the green-light emission is discussed in relation to the crystalline phase change.

비대칭 마그네트론 스퍼터링 방법으로 증착한 초경도 탄화규소 박막

배경은 ( Kyung Eun Bae ),채기웅 ( Ki Woong Chae ),박종극 ( Jong Keuk Park ),이욱성 ( Wook Seong Lee ),백영준 ( Young Joon Baik ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.8

The effect of sputter target power and substrate bias voltage on the deposition of silicon carbide thin film was investigated. Films were deposited using unbalanced magnetron sputtering method with sintered silicon carbide target connected to a direct current electric power from 50 to 200 W. Ar gas was used as a sputtering gas. The distance between the target and the substrate was 7.5 cm and the deposition pressure was 3 m Torr. We used a Si single crystal wafer as a substrate, which was heated at 450℃. The substrate bias voltage was varied between 0 and -100V. Deposited films consisted of columnar grains with several nm width, which formed a texture whose orientation was influenced by the bias voltage. Most of the grains were crystalline which was confirmed by transmission electron microscopy. The hardness measured by a nano-indentation method showed a super-hardness of about 50 GPa. (Received September 17, 2014)

소규모 급수 시설의 불소 및 질산성질소 이온 제거를 위한 탄소나노튜브 전극을 활용한 전기흡착 연구

한송희(Han, Song-Hee),장인성(Chang, In-Soung),채기웅(Chae, Ki-Woong),정선용(Chung, Son-Young),이철구(Lee, Chul-Ku) 한국산학기술학회 2011 한국산학기술학회논문지 Vol.12 No.6

본 연구에서는 소규모 수도시설에서 수질기준을 자주 초과하는 항목으로 지적되고 있는 불소와 질산성질소 를 효과적으로 제거하기 위하여, 탄소나노튜브를 이용한 전극을 제작하여 전기흡착 공정에 적용함으로써 두 종류의 무기이온 제거 가능성을 평가하였다. 탄소나노튜브를 활용한 전극을 제작하기 위해 코팅 (coating)법과 소결(sintering) 법을 이용하여 전극을 제작하였다. 코팅전극은 바인더의 종류, 소결전극은 소결온도를 변화시켜 각각의 전극을 제작 하였다. 제작된 전극을 이용하여 전류밀도 및 반응시간 등을 변화시켜가며 전기흡착 실험을 진행한 결과 유기바인더 를 이용해 제작된 전극의 이온제거율은 불소 46%, 질산성질소 99.9%로 무기바인더를 이용하여 제작된 전극보다 제거 효율이 우수하였다. 또한 소결하여 제작된 탄소나노튜브 중 1000℃ 고온에서 제작한 전극은 불소 77%, 질산성질소 87%의 제거율을 보여 850℃ 저온에서 제작한 전극보다 더 높은 제거효율을 보임을 확인하였다. 적당한 전류밀도 및 반응시간 하에서 모두 먹는 물 수질 기준에 적합한 농도로 처리될 수 있음을 보임으로써, 탄소나노튜브를 활용하여 제작한 전극을 채택한 전기흡착 공정이 소규모 수도시설에 적합한 공정으로 평가받을 수 있을 것으로 판단된다. Water qualities in the decentralized water treatment plants do not frequently satisfy the water standard limit, in particular, fluoride and nitrate are notorious for the poor removal. In this study, an electro-adsorption equipped with carbon nonotube (CNT) electrodes were carried out to effectively remove the nitrate and fluoride in the decentralized water treatment plants. Two types of CNT electrodes, coating and sintering electrodes were applied. Coating electrodes were made based on different kinds of binder and sintering electrodes were made based on different sintering temperature. Removal of fluoride and nitrate when the coated electrodes with organic binder were used for electro-adsorption were 46 and 99.9% respectively, which were better performances than the coated electrodes with inorganic binder were used. On the other hand, removal of fluoride and nitrate when the electrodes sintered at higher temperature (1,000℃) were 77 and 87% respectively, which were better performances than the electrodes sintered at lower temperature (850℃). As a consequences, the electro-adsorption equipped with a CNT electrodes could be an potential alternative process for the removal of fluoride and nitrate in a decentralized water treatment plants if proper current density and contact time were applied.

인공지능 기반 전력 수요 예측 방법에 관한 고찰 -앙상블 및 회귀 알고리즘을 기반으로-

김윤명 ( Yoon-myung Kim ),윤주영 ( Ju-young Yun ),김민주 ( Min-joo Kim ),채기웅 ( Gi-ung Chae ),최유정 ( Yu-jeong Choi ) 한국정보처리학회 2022 한국정보처리학회 학술대회논문집 Vol.29 No.2

본 연구는 인공지능 기반의 전력 수요 데이터 예측 모델을 구축하고 이를 최종적으로 웹의 형태로 구현하는 것을 목표로 하였다. 기상청 데이터의 기후 요소를 매개변수로 삼아 전력 수요를 예측하고, 그 결과를 가시적으로 시각화하는 것까지의 전 과정을 최대한 간결하게 진행하였다. 추후 한층 더 발전된 모델을 구축할 수 있다면, 전력시장의 효율성과 경제성을 향상시켜 불필요한 에너지 낭비를 미연에 방지할 수 있을 것이라고 기대한다. 나아가 시스템 상용화를 위해 계속 연구 활동에 정진할 수 있을 것이다.