• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.263-263
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• 2013

This work examines the dynamic properties of ice surfaces in vacuum for the temperature range of 140~180 K, which extends over the onset temperatures for ice sublimation and the phase transition from amorphous to crystallization ice. In particular, the study focuses on the transport processes of excess protons and chloride ions in ice and their segregative behavior to the ice surface. These phenomena were studied by conducting experiments with a relatively thick (~100 BL) ice film constructed with a bottom $H_2O$ layer and an upper $D_2O$ layer, with excess hydronium and chloride ions trapped at the $H_2O$/$D_2O$ interface as they were generated by the ionization of hydrogen chloride. The migration of protons, chloride ions, and water molecules to the ice film surface and their H/D exchange reactions were measured as a function of temperature using the methods of low energy sputtering (LES) and Cs+ reactive ion scattering (RIS). Temperature programmed desorption (TPD) experiments monitored the desorption of water and hydrogen chloride from the surface. Our observations indicated that both hydronium and chloride ions migrated from the interfacial layer to segregate to the surface at high temperature. Hydrogen chloride gas desorbs via recombination reaction of hydronium and chloride ions floating on the surface. Surface segregation of these species is driven by thermodynamic potential gradient present near the ice surface, whereas in the bulk, their transport is facilitated by thermal diffusion process. The finding suggests that chlorine activation reactions of hydrogen chloride for polar stratospheric ice particles occur at the surface of ice within a depth of at most a few molecular layers, rather than in the bulk phase.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.2
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• pp.15-21
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• 2007

The aim of this paper is controlling ignition timing and load in homogeneous charge compression ignition (HCCI) combustion with low cetane number fuel, hydrogen. Homogeneous charge compression ignition (HCCI) combustion is an advanced combustion technology that achieves higher thermal efficiency and lower $NO_x$ emissions than that of conventional combustion system. Dimethyl ether (DME), which has been researched widely as the most attractive alternative fuel of diesel, is attractive for HCCI combustion because of the easy evaporation. In this study, the single cylinder DME engine operated with a direct injection system has been used to investigate combustion processes and emissions of DME HCCI with a premixed hydrogen supply. The experiment was carried out under various engine speed and fraction rates of hydrogen. As a result, the increase of fraction rates of hydrogen retard the DME ignition timing and eliminated the knocking during high engine speed condition. IMEP was increased with increase of fraction rates of hydrogen by 30%. 40% of the fraction rates of hydrogen resulted in misfiring. The $NO_x$ emission was reduced by increasing the fraction rates of hydrogen, but HC emission was increased.

• Journal of Biomedical Engineering Research
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• v.37 no.5
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• pp.168-177
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• 2016

In this paper we present an implantable pressure sensor to measure real-time blood pressure by monitoring mechanical movement of artery. Sensor is composed of inductors (L) and capacitors (C) which are formed by microfabrication and direct bonding on two biocompatible substrates (quartz). When electrical potential is applied to the sensor, the inductors and capacitors generates a LC resonance circuit and produce characteristic resonant frequencies. Real-time variation of the resonant frequency is monitored by an external measurement system using inductive coupling. Structural and electrical simulation was performed by Computer Aided Engineering (CAE) programs, ANSYS and HFSS, to optimize geometry of sensor. Ultrafast laser (femto-second) cutting and MEMS process were executed as sensor fabrication methods with consideration of brittleness of the substrate and small radial artery size. After whole fabrication processes, we got sensors of $3mm{\times}15mm{\times}0.5mm$. Resonant frequency of the sensor was around 90 MHz at atmosphere (760 mmHg), and the sensor has good linearity without any hysteresis. Longterm (5 years) stability of the sensor was verified by thermal acceleration testing with Arrhenius model. Moreover, in-vitro cytotoxicity test was done to show biocompatiblity of the sensor and validation of real-time blood pressure measurement was verified with animal test by implant of the sensor. By integration with development of external interrogation system, the proposed sensor system will be a promising method to measure real-time blood pressure.

• Journal of Powder Materials
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• v.11 no.1
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• pp.28-33
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• 2004

In the present study, the focus is on the analysis of carbothermal reduction of the titanium-cobalt-oxygen based oxide powder by solid carbon for the optimizing synthesis process of ultra fined TiC/Co composite powder. The titanium-cobalt-oxygen based oxide powder was prepared by the combination of the spray drying and desalting processes using the titanium dioxide powder and cobalt nitrate as the raw materials. The titanium-cobalt-oxygen based oxide powder was mixed with carbon black, and then this mixture was carbothermally reduced under a flowing argon atmosphere. The changes in the phase structure and thermal gravity of the mixture during carbothermal reduction were analysed using XRD and TGA. The synthesized titanium-cobalt-oxygen based oxide powder has a mixture of $TiO_2$ and $CoTiO_3$. This oxide powder was transformed to a mixed state of titanium car-bide and cobalt by solid carbon through four steps of carbothermal reduction steps with increasing temperature; reduction of $CoTiO_3$ to $TiO_2$ and Co, reduction of $TiO_2$, to the magneli phase($Ti_nO_{2n-1}$, n>3), reduction of the mag-neli phase($Ti_nO_{2n-1}$, n>3) to the $Ti_nO_{2n-1}$(2$\leq$n$\leq$3) phases, and reduction and carburization of the $Ti_nO_{2n-1}$(2$\leq$n$\leq$3) phases to titanium carbide.

• Journal of Powder Materials
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• v.12 no.6 s.53
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• pp.406-412
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• 2005

This work is to present a new synthesis of metallic glass (MG)/metallic glass (MG) composites using gas atomization and spark plasma sintering (SPS) processes. The MG powders of $Cu_{54}Ni_6Zr_{22}Ti_{18}$ (CuA) and $Ni_{59}Zr_{15}Ti_{13}Nb_7Si_3Sn_2Al_1$(NiA) as atomized consist of fully amorphous phases and present a different thermal behavior; $T_g$ (glass transition temperature) and $T_x$ (crystallization temperature) are 716K and 765K for the Cu base powder, but 836K and 890K for the Ni base ones, respectively. SPS process was used to consolidate the mixture of each amorphous powder, being $CuA/10\%NiA\;and\;NiA/10\%CuA$ in weight. The resultant phases were Cu crystalline dispersed NiA matrix composites as well as NiA phase dispersed CuA matrix composites, depending on the SPS temperatures. Effect of the second phases embedded in the MG matrix was discussed on the micro-structure and mechanical properties.

• Journal of Powder Materials
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• v.18 no.6
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• pp.532-537
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• 2011

Thermally stable $TiO_2$/Pt/$SiO_2$ core-shell nanocatalyst has been synthesized by chemical processes. Citrated capped Pt nanoparticles were deposited on amine functionalized silica produced by Stober process. Ultrathin layer of titania was coated on Pt/$SiO_2$ for preventing sintering of the metal nanoparticles at high temperatures. Thermal stability of the metal-oxide hybrid catalyst was demonstrated heating the sample up to $600^{\circ}C$ in air and by investigating the morphology and integrity of the structure by transmission electron spectroscopy. The surface analysis of the constituent elements was performed by X-ray photoemission spectroscopy. The catalytic activity of the hybrid catalysts was investigated by CO oxidation reaction with oxygen as a model reaction.

• Journal of the Korean Society for Railway
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• v.12 no.6
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• pp.1059-1066
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• 2009

Recently, the amount of thermosetting plastic wastes has increased with the production of reinforced plastic composites and causes serious environmental problems. The epoxy resins, one of the versatile thermosetting plastics with excellent properties, cannot be melted down and remolded as what is done in the thermoplastic industry. In this research, a series of experiments that decompose epoxy resin and recover carbon fibers from carbon fiber reinforced epoxy composites applied to railway vehicles was performed. We experimentally examined various decomposition processes and compared their decomposition efficiencies and mechanical property of recovered carbon fibers. For the prevention of tangle of recovered carbon fibers, each composites specimen was fixed with a Teflon supporter and no mechanical mixing was applied. Decomposition products were analyzed by scanning electron microscope (SEM), gas chromatography mass spectrometer (GC-MS), and universal testing machine (UTM). Carbon fibers could be completely recovered from decomposition process using nitric acid aqueous solution, liquid-phase thermal cracking and pyrolysis. The tensile strength losses of the recovered carbon fibers were less than 4%.

• Korean Journal of Remote Sensing
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• v.33 no.2
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• pp.159-169
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• 2017

The Satellite Electro-Optic Payload System needsspecial requirements with the conditions of limited power consumption and the space environment of solar radiation. The acquired image quality should be mainly depend on the GSD (Ground Sampled Distance), SNR (Signal to Noise Ratio), and MTF (Modulation Transfer Function). On the well-manufactured sensor level, the thermal noise is removed on ASP (Analog Signal Processing) using the CDS (Corrective Double Sampling); the noise signal from the image sensor can be reduced from the offset signals based on the pre-pixels and the dark-pixels. The non-uniformity shall be corrected with gain, offset, and correction parameter of the image sensor pixel characteristic on the sensor control system. This paper describes the SNR enhancement method of the satellite EOS payload using the mentioned noise remove processes on the system design and operation, which is verified by tests and simulations.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.59-64
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• 2002

Effects of the aging treatments on the microstructure and strength of heat affected zone(HAZ) in the welds of a age-hardened Al-Mg-Si alloy, 5N01-T5, were investigated. The base metal aging treatments before MIG welding were conducted at 423K to 473K for 28.8ks Post weld heat treatment(PWHT) to recover the HAZ strength was performed at 448K for 28.8ks. Microstructure observations, hardness measurements and tensile tests were conducted to study properties of the MIG weld joints. The position of the softest region in HAZ where the hardness insufficiently recovered after natural aging and PWHT was at a distance of approximately 15mm from the center of the fusion zone. Hardness of the softest regions after natural aging and PWHT decreased with increase in the base metal aging temperature. TEM observation clarified that strengthening ${\beta}$"(Mg$_2$Si) precipitates and coarse ${\beta}$′ precipitates affected the hardnes of HAZ. Incomplete recover of hardness in HAZ after PWHT was caused by the precipitating of non-hardening ${\beta}$′ phase during the weld thermal cycle. In order to examine the effects of weldheat input and welding speed, the laser weld joints were also investigated and compared with the MIG weld ones. Laser welding had the narrower width of the softened regions in HAZ compared with MIG welding. The hardness of the softest regions of the laser welds after PWHT was higher than that of the MIG welds. Quantitative relations between hardness of the softest region and base metal aging temperature were obtained for both welding processes. Accordingly, the equations to estimate the strength of the weld joints after PWHT with varying base metal temperatures were proposed for MIG welding and laser welding.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.4
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• pp.57-62
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• 2014

Using flexible bismaleimide-triazine co-polymer as a substrate, inkjet-printed Cu films were also investigated for low-cost and process feasibility of flexible electronics. After annealing at $200^{\circ}C$ for 1 h under various reducing ambient, surface color was changed to red and electrical resistivity was decreased to the level of conductor under formic acid ambient. However, its resistivity was much higher than conventional copper films due to surface crack. In order to reduce the residual film stress after annealing, additional isothermal treatment was inserted before anneal hiring the stress relaxation applied in processes of amorphous materials. As a result, no surface crack was observed and electrical resistivity of $3.4{\mu}{\Omega}cm$ was measured after annealing at $230^{\circ}C$ with stress relaxation while electrical resistivity of $7.4{\mu}{\Omega}cm$ was observed after normal annealing without relaxation. The effect of stress relaxation was also confirmed by observing surface crack after decreasing the relaxation time to 0 min.