• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.365-365
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• 2010

Similar to the superhydrophobic surfaces of lotus leaf, water strider leg is attributed to hierarchical structure of micro pillar and nano-hair coated with low surface energy materials, by which water strider can run and even jump on the water surface. In order to mimick its leg, many effort, especially, on the fabrication of nanohairs has been made using several methods such as a capillarity-driven molding and lithography using poly(urethane acrylate)(PUA). However most of those effort was not so effective to create the similar structure due to its difficulty in the fabrication of nanoscale hairy structures with hydrophobic surface. In this study, we have selected a low surface energy polymeric material of polytetrafluoroethylene (PTFE, or Teflon) assisted with surface modification of CF4 plasma treatment followed by hydrophobic surface coating with pre-cursor of hexamethyldisiloxane (HMDSO) using a plasma enhanced chemical vapor deposition (PE-CVD). It was found that the plasma energy and duration of CF4 treatment on PTFE polymer could control the aspect ratio of nano-hairy structure, which varying with high aspect ratio of more than 20 to 1, or height of over 1000nm but width of 50nm in average. The water contact angle on pristine PTFE surface was measured as approximately $115^{\circ}$. With nanostructures by CF4 plasma treatment and hydrophobic coating of HMDSO film, we made a superhydrophobic nano-hair structure with the wetting angle of over $160^{\circ}C$. This novel fabrication method of nanohairy structures has been applied not only on 2-D flat substrate but also on 3-D substrates like wire and cylinder, which is similarly mimicked the water strider's leg.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.6
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• pp.319-326
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• 2017

In this study, a lightweight geopolymer was prepared using by slag discharged from IGCC (Integrated Gasification Combined Cycle) power plant and its physical properties, the density and compressive strength, were analyzed as a function of the concentration of alkali activators, W/S ratio and aging times. Also the possibility of applying it to lightweight materials by adding Si sludge as a foaming agent to the geopolymerg was investigated. In particular, a complex composition of alkali activator and a pre-curing process were applied to improve the strength properties of lightweight geopolymers. While the compressive strength of the lightweight geopolymer using a single activator was 9.5 MPa, the specimen made with a complex composition of alkali activator had compressive strength of 2~5 times higher. In addition, the lightweight geopolymer with pre-curing process showed a compressive strength value of 18~48 % higher than that of specimen made with no precuring process. In this study, by using a complex activator and a pre-curing process. the maximum compressive strength of lightweight geopolymer was obtained as 40 MPa (The specimen was aged for 3 days and had density of $1.83g/cm^3$), which is comparable to cement concrete. By analyzing the crystal phase and microstructure of geopolymers obtained in this study using by XRD and SEM, respectively, it was confirmed that the flower-bud-like zeolite crystal was homogeneously distributed on the surface of the C-S-H gel (sodium silicate hydrate gel) in the geopolymer.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.6
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• pp.61-69
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• 2000

Indium-Tin Oxide (ITO) films were prepared on the commercial glass substrate by the Magnetron Sputtering method. The target was a 90wt.% $In_2O_3$-10wt.% $SnO_2$with 99.99% purity. The ITO films deposited by changing the partial pressure of oxygen gas ($O_2$/(Ar+$O_2$)) of 2, 3 and 5% as well as by changing the substrate temperature of $300^{\circ}C$ or $500^{\circ}C$. The influence of substrate pre-annealing and pre-cleaning on the quality of ITO film were examined, in which the substrate temperature was $500^{\circ}C$ and oxygen partial pressure was 3%. The characteristics of films were examined by the 4-point probe, Hall effect measurement system, SEM, AFM, Spectrophotometer, and X-ray diffraction. The optimum ITO films have been obtained when the substrate temperature is $500^{\circ}C$ and oxygen partial pressure is 3%. At optimum condition, the film showed transmittance of 81%, sheet resistivity of $226\Omegatextrm{cm}^2$, resistivity($\rho$) of $5.4\times10^{-3}\Omega$cm, carrier concentration of $1.0\times10^{19}cm^{-3}$, and carrier mobility of $150textrm{cm}^2$Vsec. From XRD spectrum, c(222) plane was dominant in the case of substrate temperature at $300^{\circ}C$, without regarding to oxygen partial pressure. However, in the case of substrate temperature at $500^{\circ}C$, c(400) plane was grown together with c(222) plane, only for oxygen partial pressure of 2 and 3%. In both case of chemical and ultrasonic cleaning without pre-annealing the substrate, it showed much almost same sheet resistivity, resistivity($\rho$), transmittance, carrier concentration, and carrier mobility. In case of $500^{\circ}C$/60min pre-annealing before ITO film deposited, both transimittance and carrier mobility are better than no pre-annealing, because pre-annealing is supposed to remove alkari ions diffusion from substrate. ITO film deposited on the Corning 0080 sybstrate showed a little bit better sheet resistivity, resistivity($\rho$), transimittance, carrier concentration than the film deposited on commercial glass. But no differences between Corning substrate and pre-annealed commercial glass substrate are found.

• Journal of Korea Foundry Society
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• v.18 no.6
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• pp.534-540
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• 1998

6061Al-matrix composite with TiNi shape memory fiber as reinforcement has been fabricated by Permanent Mold Casting to investigate the mechanical properties of the smart composites. The composites have showed good interface bonding as a result of the analysis of SEM and EDX. The smartness of composite is given due to the shape memory effect of the TiNi fiber which generates compressive residual stresses in the matrix material when heated after being prestrained. The tensile strength of the composites was tested at temperatures between $90^{\circ}C$ and room temperature with increasing amount of pre-strain, and it showed that the tensile strength at $90^{\circ}C$ was higher than that of the room temperature. Especially, the tensile strength of the composite increases with increasing pre-strain. It showed that hardness of matrix was higher than that of common 6061Al alloy.

• Journal of the Korean Ceramic Society
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• v.44 no.12
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• pp.733-739
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• 2007

NiO-YSZ anode-supported single cell was prepared by spin-coating YSZ and LSM slurries as electrolyte and cathode, respectively. Dense YSZ electrolyte film was successfully prepared on the porous NiO-YSZ anode substrate by tuning pre-sintering temperature of NiO-YSZ and co-firing temperature. The thickness of YSZ film was controlled by the solid content of slurry and coating cycles. The experimental conditions affecting on the thickness of YSZ film was discussed. Single cells with the active electrode area ${\sim}0.8\;cm^2$ were prepared by spin-coating the cathode layers of LSM-YSZ mixture and LSM consequently as well. The effects of the pre-sintering temperature and thus the microstructure of NiO-YSZ substrate on the current-voltage characteristics of co-fired cell were investigated.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.4
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• pp.275-281
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• 2016

One of the most important things for quality to meet ship-production schedule is an accuracy control. A ship is assembled by welding through whole production process, so it is important that loss by correction will not happen as much as possible by using some engineering skills like reverse design, reverse setting and margin for thermal shrinkage. These efforts are a quite effective in fabrication stages, but not in erection stages. If a ship block which consists of common steel is exposed to directional solar radiation, its dimensional accuracy will change high as time by its thermal expansion coefficient. Therefore, the measuring work would be often done at dawn or evening even with having a very accurate device. In this study, an FE analysis method is developed to solve this problem. It can change measured data affected by solar thermal distortion to ones not, even though ship-block is measured at an arbitrary time. It will use the time when measuring, the direction of block and the weather record by satellites. It is confirmed by a comparison between measured data of a ship-block and the result by suggested analysis method. Furthermore, a pre-processing system is also developed for fast application of the suggested analysis method.

• Progress in Superconductivity and Cryogenics
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• v.1 no.1
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• pp.7-14
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• 1999

Wekk oriented $Bi_{2} Sr_{2} CaCu_{2} O_{8}$ suppercondcting thick films were fabricared on copper tape by LiReac-PreCu (liquid reaction between a Cu-free precousor and Cu tape) method. Cu-free precursor power which is composed of $Bi_{2}Sr_{2}Ca_{5}$ was printed on a copper tape by screen printing and was heat-treated. The speciment were partially in a molten state at the heat treatment temperature (85$0^{\circ}C$~87$0^{\circ}C$). The heat heat treatments for the reaction were performed in air or low oxygen pressure in several stages. XRD analyses of the resulting Bi2Sr2CaCu2O8 superconducting tapes show that the $Bi_{2} Sr_{2} CaCu_{2} O_{8}$ phase is dominant and a small amount of $Bi_{2} Sr_{2} Cu_{2} O_{6}$ phase is detected. Both phases are aligned in the c-axis direction.

• Journal of the Korean Institute of Telematics and Electronics
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• v.12 no.5
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• pp.12-18
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• 1975

Triac phase controlled pre-regulator를 이용한 직류안정화전원에서 제어소자 전력소모를 촤소로 줄이기 위하여, 부하전류의 증가에 따라 제어소자 양단전압을 낮추어 주는 회로를 고안하여 부가하였다. 이렇게 하므로써 제어소자의 전력소모가 약 40%정도 감소되어 방열장치가 간단해지거나 전력용량을 증가할 수 있게 되었으며 열발산이 곤란한 monolithic I.C.화에 유용하도록 하였다. A method on minimizing the power dissipation in the control element of a series D.C. voltage regutator is devised. An additional control circuit which reduces the average voltage drop across the control element according to increasing the load current is attached :o the trial phase controlled pre-regulator system. It is verified that the power dissipation in the control element is reduced up to 40% by this. circuit arrangement. The heat sink system can be simplified and the capacity of tile handling power is also increased. It is expected that this circuit arrangement can be applied to I.C. fabrication.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.329-334
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• 2002

Preflex beam is a method of construction to hold the Pre-compressive stresses over the concrete pier by the Preflexion load. During the fabrication of the girder, welding causes the welding residual stresses. The welding residual stresses must be relieved to generate the accurate compressive pre-stresses that is designed. On this study, to find out the thermal distribution characteristics on the girder by welding, both the three-dimensional finite element analysis and the two-dimensional finite element analysis in a quasi-steady state is carried out. After comparing with each result between the three-dimensional analysis and the two-dimensional analysis, finite element analysis is carried out against the actual girder and analyze welding thermal distribution characteristic over the preflex beam and obtain the input data for the analysis of the welding residual stresses.

• Progress in Superconductivity and Cryogenics
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• v.21 no.3
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• pp.27-31
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• 2019

Large grain YBCO bulk superconductors are fabricated by the top-seeded melt growth (TSMG) or top-seeded infiltration growth (TSIG) method. Both growth methods use at least one of $YBa_2Cu_3O_{7-{\delta}}$, $Y_2BaCuO_5$, $BaCuO_3$ pre-reacted precursor powders. However, the synthesis of the pre-reacted powders includes multiple calcination runs which are cost-bearing and time-consuming. In this work, we report the successful growth of single-domain YBCO bulk superconductors directly by using the powder compact that has been pressed from the mixture of $Y_2O_3$, $BaCuO_3$ and CuO powders without any intermediate grinding step. Single-domain YBCO bulk superconductor has been also prepared by using $Y_2O_3$, $BaO_2$ and CuO powders without intermediate grinding step. Investigations on the trapped magnetic field and microstructure of the melt-processed specimen show that the elimination of the repeated processes of calcinations and pulverization has hardly affected on the crystal growth and the magnetic properties of the grown YBCO bulk superconductors. However, it is thought that the presence of residual carbon affects on the size of Y211 particles in melt-processed YBCO bulk superconductor.