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용액 연소법에 의한 광촉매용 나노크기의 ZnO 분말의 제조 및 특성
이강렬,김흥회,박성,Lee, Kang-Ryeol,Kim, Whung-Whoe,Park, Sung 한국세라믹학회 2001 한국세라믹학회지 Vol.38 No.8
광촉매용 ZnO 나노크기의 분말은 시작원료와 연료의 종류에 따라 용액연소법에 의해 제조되었다. 결정상은 XRD로부터 확인할 수 있었으며 분말의 하소온도는 TG 분석으로부터 결정되었다. 분말의 비표면적은 BET 법에 의해 측정되었으며 평균입자크기와 형태를 SEM과 TEM으로부터 조사하였다. 또한 분말의 순도를 조사하기 위해 적외선 흡수스펙트럼을 측정하였으며 광촉매 효율로서 은이 첨가된 사진현상액을 이용하여 은의 수거율을 측정하였다. 용액연소법으로 제조한 경우 시작원료와 연료에 관계없이 단상의 ZnO 분말을 쉽게 얻을 수 있었다. 그러나 합성된 ZnO 분말의 입자크기와 형태는 연료의 종류에 따라 서로 다르게 보였다. 특히, 연료로 glycine을 사용한 경우, ZnO 분말의 입자 형태는 균일한 나노 크기의 구형이었으나 carbohydrazide을 사용한 경우에는 판상과 같은 형태를 보였다. 이러한 결과를 기초로 하여 시작원료와 연료로 Zn(OH)$_2$와 glycine을 사용하여 합성된 ZnO 분말이 우수한 분말 특성을 보였으며 75nm의 입자크기와 94$m^2$/g의 비표면적을 보였다. 또한 사진현상액에 존재하는 은이 3분 이내에 완전히 제거되는 우수한 광촉매 성질을 보였다.
김경호(Kyeong Ho Kim),이민구(Min-Ku Lee),이창규(Chang Kyu Rhee),위명용(Myeong Yong Wey),김흥회(Whung Whoe Kim) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
In this research, fretting tests were conducted in air to investigate the wear characteristics of fuel cladding materials with the fretting parameters such as normal load, slip amplitude, frequency and the number of cycles. A high frequency fretting wear tester was designed for this experiment by KAERI. After the experiments, the wear volume and the shape of wear contour were measured by the surface roughness tester. Tribologically transformed structures(TTS) were analysed by means of optical and scanning electron microscopes to identify the main wear mechanisms. The results of this study showed that the wear volume were increased with increasing slip amplitude, and the shape of wear contour was transformed V-type to W-type. Also, it was found that the critical slip amplitude was 168㎛. This phenomena mean that wear mechanism transformed partial slip to gross slip to accelerate wear volume. The wear depth increased with an increase of friction coefficient due to increase of normal load and frequency. The fretting wear mechanisms were believed that, after adhesion and surface plastic deformation occurred by relative sliding motion on the contact between two specimens, TTS creation was induced by surface strain hardening and wear debris were detached from the contact surface which were produced by the micro crack propagation and creation.
나노 및 마이크로 알루미늄의 가수분해에 의한 알루미늄 수산화물의 형성
오영화,이근희,박중학,이창규,김흥회,김도향,Oh Young Hwa,Lee Geunhee,Park Joong Hark,Rhee Chang Kyu,Kim Whung Whoe,Kim Do Hyang 한국분말야금학회 2005 한국분말재료학회지 (KPMI) Vol.12 No.3
A formation of aluminum hydroxide by hydrolysis of nano and micro aluminum powder has been studied. The nano aluminum powder of 80 to 100 nm in diameter was fabricated by a pulsed wire evaporation (PWE) method. The micro powder was commercial product with more than $10\;{\mu}m$ in diameter. The hydroxide type and morphology depending on size of the aluminum powder were examined by several analyses such as XRD, TEM, and BET. The hydrolysis procedure of micro aluminum powder was different from that of nano aluminum powder. The nano aluminum powder after immersing in the water was transformed rapidly to a nano fibrous boehmite, accompanying with a remarkable temperature increase, and then further transformed slowly to a stable bayerite. However, the micro powder was changed to the stable bayerite slowly and directly. The formation of fibrous aluminum hydroxide from nano aluminum powder might be due to the fine cracks which were formed by hydrogen gas pressure on the surface hydroxide layer during hydrolysis. The nano powder with large specific surface area and small size reacted more actively and faster than the micro powder, and transformed to meta-stable hydroxide in relatively short reaction time. Therefore, the formation of fibrous boehmite is special characteristic of hydrolysis of nano aluminum powder.
알루미늄 나노 분말의 수화반응에 의한 수산화알루미늄 형성
이근희,오영화,이창규,김흥회,Lee Geunhee,Oh Young Hwa,Rhee Chang Kyu,Kim Whung Whoe 한국재료학회 2005 한국재료학회지 Vol.15 No.3
Formation of aluminum hydroxide by a hydrolytic reaction of nano aluminum powder synthesized by a pulsed wire evaporation (PWE) method has been studied. The type and morphology of the hydroxides were investigated with various initial temperatures and pHs. The nano fibrous boehmite (AlOOH) was formed predominantly over $40^{\circ}C$ of the hydrolytic temperature in acid solution, while the bayerite $(Al(OH)_3)$ was formed predominantly below $30^{\circ}C$ in alkali solution with a faceted crystalline structure. As a result the boehmite showed a much larger specific surface area (SSA) than that of bayerite. The highest SSA of the boehmite was about $409\;m^2/g$.
김경호,이민구,이창규,위명용,김흥회,Kim, Kyeong-Ho,Lee, Min-Ku,Rhee, Chang-Kyu,Wey, Myeong-Yong,Kim, Whung-Whoe 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.12
In this research, fretting tests were conducted in air to investigate the wear characteristics of fuel cladding materials with the fretting parameters such as normal load, slip amplitude, frequency and the number of cycles. A high frequency fretting wear tester was designed for this experiment by KAERI. After the experiments, the wear volume and the shape of wear contour were measured by the surface roughness tester. Tribologically transformed structures(TTS) were analysed by means of optical and scanning electron microscopes to identify the main wear mechanisms. The results of this study showed that the wear volume were increased with increasing slip amplitude, and the shape of wear contour was transformed V-type to W-type. Also, it was found that the critical slip amplitude was 168${\mu}{\textrm}{m}$. These phenomena mean that wear mechanism transformed partial slip to gross slip to accelerate wear volume. The wear depth increased with an increase of friction coefficient due to increase of normal load and frequency. The fretting wear mechanisms were believed that, after adhesion and surface plastic deformation occurred by relative sliding motion on the contact between two specimens, TTS creation was induced by surface strain hardening and wear debris were detached from the contact surface which were produced by the micro crack propagation and creation.
시험온도와 열처리 변화가 핵연료 봉의 파열강도에 미치는 영향
김경호(Kyeong Ho Kim),이민구(Min Ku Lee),이창규(Chang Kyu Rhee),위명용(Myeong Yong Wey),김흥회(Whung Whoe Kim) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8
The burst tests of low tin Zircaloy-4 claddings were conducted in order to obtain high temperature deformation behavior and burst strength characteristics with heat treatment condition and testing temperature, which varying room temperature to 50℃. While the uniform burst elongation and total circumferential elongation value of stress-relieved tube is small, the ultimate hoop stress of that tube are larger than that of fully recrystallized tube at all test temperature. The inflection point of elongation was 3000℃ for stress relived tubes and maximum elongation point was 4000℃ for fully recrystallized tube. The burst mechanism was believed that, after deformation was uniformly exerted on circumferentially until maximum circumferential stress reached, pin-hole fractured caused the fracture by the local stress concentration, which results from the decreasing tube thickness.
김광호(Gwang-Ho Kim),이민구(Min-Ku Lee),김경호(Kyeong-Ho Kim),김흥회(Whung-Whoe Kim),이창규(Chang-Kyu Rhee),김길무(Gil-Mu Kim) 한국표면공학회 2006 한국표면공학회지 Vol.39 No.2
In this study, the movable flame hardening process of 12Cr steel for a uniform hardness and desirable residual stress have been investigated. For this, the temperature cycles have been controlled accurately as a function of the three processing variables, the flame intensity If, the scanning velocity Vs and the initial flame holding time th, where the standard surface temperature Ts, max was maintained at 960°C. The optimized conditions were Vs = 0.68 ㎜/s and th = 67 sec for the C₃H?:O₂ = 5:20 l/min, Vs = 0.80 ㎜/s and th= 56 sec for the C₃H?:O₂ = 6:24 l/min, Vs = 1.01 ㎜/s and th= 48 sec for the C₃H?:O₂= 7:28 l/min, and Vs = 1.15 ㎜/s and th= 39 sec for the C₃H?:O₂= 8:32 l/min. The optimally flame-hardened surface exhibited uniform distributions of the hardness and residual compressive stress over the treated area with moderate levels of 470~490HV0.2 in hardness and ?300~?450 MPa in residual stress, which were acceptable on the basis of the acceptance criteria of Siemens AG-KWU and GE Power Generation Engineering.
화염급냉 표면처리된 Cu-9AI-4.5Ni-4.5Fe 합금의 β' 마르텐사이트 형성에 의한 케비테이션 침식 저항성 향상에 관한 연구
홍성모(Sung-Mo Hong),이민구(Min-Ku Lee),김광호(Gwang-Ho Kim),김경호(Kyeong-Ho Kim),김흥회(Whung-Whoe Kim),홍순익(Sun-Ig Hong) 한국표면공학회 2004 한국표면공학회지 Vol.37 No.4
Cavitation erosion properties of the Cu-9AI-4.5Ni-4.5Fe alloys (Al-bronze) surface-modified by flame quenching process have been investigated. After flame quenching at above T p, the surfaces of AI-bronze with α + κ structure have been changed into the α + β’ martensite phases by the eutectoid reaction of α + κ→β followed by the martensite transformation of β→’. As a result of cavitation test, the measured incubation time and erosion rate of the α + β’ alloy was 1.2 times higher and 1.5 times lower, respectively, compared to those of the conventional α + κ alloys, showing a remarkable increase of cavitation resistance with the formation of β martensite. This is attributed to a preferential erosion of the κ precipitates that show the lowest resistance among the α, κ, β’ phases under cavitation loading.