• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.184-185
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• 2007

We investigated the growth behaviors of ZnO epilayers on sapphire substrates fabricated sing RF magnetron puttering and RTA. The effects of deposition temperature and oxygen partial pressure in plasma on the structural and electrical properties were measured by XRD, AFM, SEM, and Hall effect measurement. It was found that ZnO thin films became denser and smoother with increasing deposition temperature and $O_2$ content in the puttering gas. ZnO thin film of oxygen and argon with a ratio of 5:5 had an electron concentration of $8.048{\times}10^{18}cm^{-3}$, resistivity of $0.0141{\Omega}{\cdot}Cm$, and mobility of $55.07cm^2/V{\cdot}s$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.1
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• pp.12-17
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• 1998

The heteroepitaxial growth of InP and GaInAs on GaAs substrates has been studied by using a new combination of source materials: ethyldimethylindium (EDMIn) and trimethylgallium (TMGa) as group III sources, and tertiarybutylarsine (TBAs) and tertiarybutylphosphine (TBP) as group V sources. Device quality InP heteroepitaxial layers were obtained by using a two-step growth process under atmospheric pressure, involving a growth of an initial nucleation layer at low temperature followed by high temperature annealing and the deposition of epitaxial layer at a growth temperature. The continuity and thickness of nucleation layer were important parameters. The InP layers deposited at 500$^{\circ}$- 55$0^{\circ}C$ are all n-type, and the electron concentration decreases with decreasing TBP/EDMIn molar ratio. The excellent optical quality was revealed by the 4.4 K photoluminescence (PL) measurement with the full width at half maximum (FWHM) of 4.94 meV. Epitaxial Ga\ulcorner\ulcorner\ulcornerIn\ulcorner\ulcorner\ulcornerAs layers have been deposited on GaAs substrates at 500$^{\circ}$ - 55$0^{\circ}C$ by using InP buffer layers. The composition of GaInAs was determined by optical absorption measurements.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.138-143
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• 2006

The peculiarity of ice slurry, such as liquidity, high heat transfer rate and easy storage can also find to supercooled type dynamic ice storage system(DISS) which is one of the DISS. However, in order to accomplish continuous ice formation in the system without mechanical moving parts, supercooled aqueous solutionshould be formed stable through cooling heat exchanger and be dissoluted in storage tank. In previous research, the time of ice slurry increased as the pressure of the cooling heat exchanger(PHX) increased. In this study, a cooling experiment of an ethylene glycol 7mass% solution was performed with various inlet temperature of the PHX, which has constant brine inlet temperature of $-7^{\circ}C$. The temperature in the storage tank maintained to freezing point of the solution. At results, the time of ice slurry formation increased as the supercooling degree decreased and the cooling rate increased.

• Journal of the Semiconductor & Display Technology
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• v.16 no.2
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• pp.55-60
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• 2017

The supercritical $CO_2$ (sc-$CO_2$) mixture and the sc-$CO_2$-based Photoresist(PR) stripping(SCPS) process were applied to the removal of the post etch/ash PR residue on aluminum patterned wafers and the results were observed by scanning of electron microscope(SEM). In the case of MDII wafers, the carbonized PR was able to be effectively removed without pre-stripping by oxygen plasma ashing by using sc-$CO_2$ mixture containing the optimum formulated additives at the proper pressure and temperature, and the same result was also able to be obtained in the case of HDII wafer. It was found that the efficiency of SCPS of ion implanted wafer improved as the temperature of SCPS was high, so a very large amount of MEA in the sc-$CO_2$ mixture could be reduced if the temperature could be increased at condition that a process permits, and the ion implanted photoresist(IIP) on the wafer was able to be removed completely without pre-treatment of plasma ashing by using the only 1 step SCPS process. By using SCPS process, PR polymers formed on sidewalls of metal conductive layers such as aluminum films, titanium and titanium nitride films by dry etching and ashing processes were removed effectively with the minimization of the corrosion of the metal conductive layers.

• Journal of Soil and Groundwater Environment
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• v.25 no.4
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• pp.58-66
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• 2020

Since the typical horn-type ultrasonic equipment induces a reaction at the probe tip, the sonochemical reaction has a limitation that it occurs only in a specific area. As one of the ways to overcome this limitation, an ultrasonic device with multi-stepped horn equipped with several oscillators has been developed. The objective of this study was to investigate the sonochemical effects induced by acoustic cavitation system in 20 kHz multi-stepped ultrasonic horn using calorimetry, KI dosimetry and the luminol test. The sonochemical effects of multi-stepped ultrasonic horn were compared with that of the typical horn-type 20 kHz ultrasonic device. The effect of immersion depth and power on the sonochemical reaction was investigated in the ultrasonic system with multi-stepped ultrasonic horn. Higher calorimetric energy was obtained at higher immersion depth and power conditions. Sonochemical effects increased significantly when using the high immersion depth and input power. However, as the input power increased, the cavitation reaction zone concentrated around the ultrasonic horn. Additionally, the experiments to examine the effect of liquid temperature was conducted. The smaller sonochemical reaction was obtained for the higher liquid temperature. The effect on temperature seems to be closely related to liquid conditions such as viscosity and vapor pressure of water.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2836-2846
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• 2020

During severe nuclear power plant (NPP) accidents, a H₂/CO mixture can be generated in the reactor pressure vessel by core degradation and in the containment as well by molten corium-concrete interaction. In spite of its importance, a state-of-the-art methodology predicting H₂/CO combustion risk relies predominantly on empirical correlations. It is therefore necessary to develop a proper methodology for flammability evaluation of H₂/CO mixtures at ex-vessel phases characterized by three factors: CO concentration, high temperature, and diluents. The developed methodology adopted Le Chatelier's law and a calculated non-adiabatic flame temperature model. The methodology allows the consideration of the individual effect of the heat transfer characteristics of hydrogen and carbon monoxide on low flammability limit prediction. The accuracy of the developed model was verified using experimental data relevant to ex-vessel phase conditions. With the developed model, the prediction accuracy was improved substantially such that the maximum relative prediction error was approximately 25% while the existing methodology showed a 76% error. The developed methodology is expected to be applicable for flammability evaluation in chemical as well as NPP industries.

• Journal of ILASS-Korea
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• v.28 no.3
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• pp.143-149
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• 2023

Amidst the drive towards carbon neutrality, interest in renewable synthetic e-fuels is rising rapidly. These fuels, generated through the synthesis of atmospheric carbon and green hydrogen, offer a sustainable solution, showing advantages like high energy density and compatibility with existing infrastructure. The physical properties of e-fuels can be different from those of conventional gasoline based on manufacturing methods, which requires investigations into how the physical properties of e-fuels affect the fuel injection characteristics. This study performs a comparative analysis between conventional and Fischer-Tropsch (F-T) synthetic gasoline (e-gasoline) across various fuel temperatures, including the cold start condition. The fuel properties of F-T synthetic and conventional gasoline are analyzed using a gas chromatography-mass spectrometry technique and the injection rates are measured using a Bosch-tube injection rate meter. The F-T synthetic gasoline exhibited higher density and kinematic viscosity, but lower vapor pressure compared to the conventional gasoline. Both fuels showed an increase in injection rate as the fuel temperature decreased. The F-T synthetic gasoline showed higher injection rates compared to conventional gasoline regardless of the fuel temperature.

• Korean Journal of Materials Research
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• v.33 no.7
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• pp.279-284
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• 2023

One-dimensional MgO nanostructures with various morphologies were synthesized by a thermal evaporation method. The synthesis process was carried out in air at atmospheric pressure, which made the process very simple. A mixed powder of magnesium and active carbon was used as the source powder. The morphologies of the MgO nanostructures were changed by varying the growth temperature. When the growth temperature was 700 ℃, untapered nanowires with smooth surfaces were grown. As the temperature increased to 850 ℃, 1,000 ℃ and 1,100 ℃, tapered nanobelts, tapered nanowires and then knotted nanowires were sequentially observed. X-ray diffraction analysis revealed that the MgO nanostructures had a cubic crystallographic structure. Energy dispersive X-ray analysis showed that the nanostructures were composed of Mg and O elements, indicating high purity MgO nanostructures. Fourier transform infrared spectra peaks showed the characteristic absorption of MgO. No catalyst particles were observed at the tips of the one-dimensional nanostructures, which suggested that the one-dimensional nanostructures were grown in a vapor-solid growth mechanism.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.8
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• pp.401-406
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• 2020

NOx (nitrogen oxide) in the exhaust gas engines causes severe air pollution. NOx is produced under high-temperature combustion conditions. EGR (exhaust gas recirculation) is normally used to reduce the combustion temperature and NOx production. As the EGR ratio increases, the NOx level becomes low. On the other hand, an excessively high EGR ratio makes the combustion unstable resulting in other air pollution problems, such as unburned hydrocarbon and higher CO levels. In this study, the improvement of fuel droplets moving by the radiation of sonic waves was studied for the stable combustion using analytic and experimental methods. For the analytical study, the effects of the radiation of a sonic wave on the fuel droplet velocity were studied using Fluent software. The results showed that the small droplet velocity increased more under high-frequency sonic wave conditions, and the large droplet velocity increased more under low-frequency sonic wave conditions. For the experimental study, the combustion chamber was made to measure the combustion pressure under the sonic wave effect. The measured pressure was used to calculate the heat release rate in the combustion chamber. With the heat release rate data, the heat release rate increased during the initial combustion process under low-frequency sonic wave conditions.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.4
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• pp.339-345
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• 2008

The heat exchanger tube in nuclear power plants is mainly fabricated from nonferromagnetic material such as a copper, titanium, and inconel alloy, but the moisture separator & reheater tube in the turbine system is fabricated from ferromagnetic material such as a carbon steel or ferrite stainless steel which has a good mechanical properties in harsh environments of high pressure and temperature. Especially, the moisture separator & reheater tubes, which use steam as a heat transfer media, typically employ a tubing with integral fins to furnish higher heat transfer rates. The ferromagnetic tube typically shows superior properties in high pressure and temperature environments than a nonferromagnetic material, but can make a trouble during the normal operation of power plants because the ferrous tube has service-induced damage forms including a steam cutting, erosion, mechanical wear, stress corrosion cracking, etc. Therefore, nondestructive examination is periodically performed to evaluate the tube integrity. Now, the remote field testing(RFT) technique is one of the solution for examination of ferromagnetic tube because the conventional eddy current technique typically can not be applied to ferromagnetic tube such as a ferrite stainless steel due to the high electrical permeability of ferrous tube. In this study, we have designed RFT probes, calibration standards, artificial flaw specimen, and probe pusher-puller necessary for field application, and have successfully carry out RFT examination of the moisture separator & reheater tube of nuclear power plants.