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다중기포 소노루미네센스를 이용한 CdS/TiO₂ 나노입자의 제조
변기택(Ki-Taek Byun),이승수(Seung Soo Lee),심일운(Il-Wun Shim),곽호영(Ho-Young Kwak) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
Sonoluminescence (SL) is the light emission associated with the catastrophic bubble collapse of a gas bubble oscillating under an ultrasonic field. At the collapse, the bubble produces high temperature and pressure at liquid layer, where high energy chemical reaction can be possible. In the case of the MBSL, a lot of transient bubbles can be generated by the irradiation of high intensity ultrasound in aqueous solution. In this study, synthesis of cadmium sulfide(CdS) and a preparation of the nanoparticles coated on submicron titanium dioxide particles under ultrasonic field at the multibubble sonoluminescence(MBSL) condition were tried. At the optimal MBSL condition in aqueous solution containing cadium chloride of 8.8 wt%, thioacetamide of 11.5 wt% and TiO₂ of 0.8 wt%, CdS nanoparticles were synthesized first and subsequently nanoparticles of several nanometers of CdS/TiO₂(TiO₂ particles coated with CdS nanoparticles) particles were synthesized within 5 minutes. The prepared particles of CdS/TiO₂ were examined by XRD, EDS, UV-vis spectrophotometer, FE-SEM and TEM. The synthesized CdS/TiO₂ particles may be used for a material to reduce the recombination loss in dye solar cell unit.
다중기포 소노루미네센스를 이용한 β<SUB>bc</SUB> 형 수산화니켈의 제조
변기택(Ki-Taek Byun),서국원(Kook Won Seo),심일운(Il-Wun Shim),곽호영(Ho-Young Kwak) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Nanosized nickel hydroxide powder for alkine batteries was synthesized in aqueous or nonaqueous solution of nickel chloride with NaOH under ultrasound radiation at the multibubble sonoluminescence (MBSL) condition. Characterization by X-ray diffraction, transmission electron microscopy, FT-IR spectroscopy, as well as elemental analysis indicates the formation of β<SUB>bc</SUB>-type nickel hydroxide. The β<SUB>bc</SUB>-type nickel hydroxide synthesized in aqueous solution of NiCl₂ is slightly different that formed in nonaqueous solution of NiCl₂. The synthetic process of β<SUB>bc</SUB>-type nickel hydroxide at the MBSL condition was completed within 5 minutes. Coating of nickel hydroxide particles on various oxide particles such as Al₂O₃ and SiO₂ was also prepared at the MBSL condition.
변기택(Ki-Taek Byun),강상우(Sarng Woo Karng),김기영(Ki Young Kim),곽호영(Ho-Young Kwak) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
Sonoluminescence (SL) characteristics such as pulse shape, radiance and spectrum radiance from submicron bubbles were investigated. In this study, a set of analytical solutions of the Navier-Stokes equations for the gas inside bubble and equations obtained from mass, momentum and energy equations for the liquid layer adjacent the bubble wall were used to estimate the gas temperature and pressure at the collapse point, which are crucial parameters to determine the SL characteristics. Heat transfer inside the gas bubble as well as at the liquid boundary layer, which was not considered in the most of previous studies on the sonoluminescence was taken it into account in the calculation of the temperature distribution inside the bubble. It was found that bremsstrahlung is a very possible mechanism of the light emission from either micron or submicron bubbles. It was also found that the peak temperature exceeding 10^6 K in the submicron bubble driven at 1 MHz and 4 atm may be due to the rapid change of the bubble wall acceleration near the collapse point rather than shock formation.
박홍철,변기택,곽호영,Park, Hong-Chul,Byun, Gi-Taek,Kwak, Ho-Young 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.9
The maximum temperature limit at which liquid boils explosively is called the superheat limit of liquids. The superheat limits of hydrocarbon liquids and their mixtures were measured by the droplet explosion technique. Also the fully evaporated droplet at the superheat limit and subsequent bubble evolution from the fully evaporated droplet were visualized. The pressure wave emanating from the evaporating droplet and subsequent bubble evolution process were measured by a piezoelectric transducer.
강상우(Sarng Woo Karng),변기택(Gi-Taek Byun),곽호영(Ho-Young Kwak) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.5
The bubble behavior and the radiation mechanism from a laser-induced bubble have been studied<br/> theoretically. The calculated time dependent bubble radius is in good agreement with observed ones. The half<br/> width of the luminescence pulse at the collapse point, which was calculated with an assumption of black body<br/> source turned out to be good agreement with observed value of several nanoseconds.
물 속에서 레이저에 의하여 생성된 기포의 거동 및 복사현상
강상우(Sarng Woo Karng),변기택(Ki-Taek Byun),곽호영(Ho-Young Kwak) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
The bubble behavior and the radiation mechanism from a laser-induced collapsing bubble were investigated theoretically using the Keller-Miksis equation for the bubble wall motion and analytical solutions for the vapor inside bubble. The calculated time dependent bubble radius is in good agreement with observed ones. The half-width of the luminescence pulse at the collapse point, which was calculated under assumption that the light emission mechanism is black body radiation from the vapor bubble agreed well with observed value of several nanoseconds. The gas content inside the vapor bubble was too small to produce the light emission due to bremsstrahlung.
소산적 입자동력학을 이용한 계면활성제 수용액의 미셀 구조에 대한 메조스코픽 시뮬레이션
김기영(Ki Young Kim),변기택(Ki Taek Byun),곽호영(Ho-Young Kwak) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
Surfactant molecules which possess polar (head) and non-polar (tail) parts, spontaneously aggregate to form association structures such as micelles and vesicles in solutions. The association structures formed by the surfactant molecules play very important role in biological system. It is also known that the shape of micelles changes with increasing concentration from spherical to cylindrical and to lamellar. With a simple model surfactant which consists of hydrophilic head group and hydrophobic tail groups connected by harmonic springs. The structural change of the association structures in an aqueous surfactant solution has been studied using the dissipative particle dynamics (DPD) simulation. The effect of the hydrophilic interaction between the head and water molecules and the hydrophobic interaction between the tail and water molecules and between the head and tail on the structural change of the association structures was studied. For example, the change of the interaction parameters yields the various structures such as spherical micelle, cylindrical micelle and vesicle in the surfactant volume fraction of 20 %. Simulation results show that proper value of these interaction parameters could yield desirable change of the association structure depending on the concentration.
양협(Hyup Yang),변기택(Gi-Taek Byun),권용호(Yong-Ho Kwon),곽호영(Ho-Young Kwak) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.5
The cost structure of the CGAM system, a predefined cogeneration system suggested to unify the different<br/> methodologies of thermoeconomic analysis, was investigated by using a thermoeconomic method called<br/> MOPSA(Modified Productive Structure Analysis). An emphasis has been specially put on how the cost<br/> structure of the system is affected by the chosen level of aggregation that specifies the subsystems. It has<br/> been found that the unit cost of products is dependent on the chosen level of aggregation of the system only<br/> when one consider the negentropy flow as one of the parameters to determine the unit cost of products.