• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.13-16
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• 2008

Solid oxide fuel cell(SOFC) is an electrochemical energy conversion system with high efficiency and low-emission of pollution. In order to reduce the operating temperature of SOFC system under $800^{\circ}C$, the thickness reduction of YSZ electrolyte to be as thin as possible, e.g., less than 10 ${\mu}m$ are considered with the microstructure control and optimum design of unit cell. Methods for reducing the thickness of YSZ electrolyte have been investigated in coin cell. Moreover, a large unit cell($8cm{\times}8cm$) for SOFC was fabricated using an anode-supported electrolyte assembly with a thinner electrolyte layer, which was prepared by a tape casting method with a co-sintering technique. we studied the design factors such as active layer, electrolyte thickness, cathode composition, etc,. by the coin type of unit cell ahead of the fabrication process of a large unit cell and also reviewed about the evaluation technique of a large size unit cell such as interconnect design, sealing materials and current collector and so forth. Electrochemical evaluations of the unit cells, including measurements such as power density and impedance, were performed and analyzed. Maximum power density and polarization impedance of coin cell were 0.34W/$cm^2$ and $0.45{\Omega}cm^2$ at $800^{\circ}C$, respectively. However, Maxium power density of a large unit cell($5cm{\times}5cm$) decreased to 0.21W/$cm^2$ at $800^{\circ}C$ due to the increase of ohmic resistance. However, It was found that the potential value of a large unit cell loaded by 0.22A/$cm^2$ showed 0.76V at 100hrs without the degradation of unit cell.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.4
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• pp.425-432
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• 2014

Necessity of compact X-band solid-state weather radar is required to provide weather data, which generate locally in a lot of Korea's mountainous area, rather than tube-type radar. Solid State Power Amplifier (SSPA) for using Dual-polarization method in weather radar is able to obtain desired high output by combining many low output power devices in parallel. Thus, Power combiner applying to high-output power amplifier has disadvantages such as path loss, ballast resistance problem by high frequency and high power, heat release. Therefore, In this paper we demonstrated the excellence of isolation, which is the result from modified Gysel power combiner. As a result, we designed X-band 250W solid state power amplifier with peak power 54dBm, 25% power efficiency for weather radar.

• Journal of Hydrogen and New Energy
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• v.21 no.1
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• pp.19-25
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• 2010

Composites of LSCF($La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_{3-\delta}$) and CGO (gadolinium doped ceria)-based ceramics are logical candidate cathode materials with CGO electrolytes. LSCF with perovskite structure was synthesized and investigated by Solid State Reaction (SSR) method used as cathode materials for SOFC (solid oxide fuel cell). The optimized temperature was $1100^{\circ}C$ to synthesize $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_{3-\delta}$ with rhombohedral structure. The polarization resistance of the LSCF/CGO (50:50 wt.%) was smaller than that of other composite cathodes. The analysis of the EIS data of LSCF/CGO suggests that the diffusion and adsorption-desorption of oxygen can be the key process in the cathodic reaction.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.37 no.2
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• pp.147-152
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• 2001

Corrosion damage of boiler, factory equipment and so forth occur quickly due to using of the polluted water, resulting in increasing leak accident. Especially, working life of hot water boiler using the polluted water becomes more short, and energy loss increases. The cathodic protection method is the most economical and reliable one to prevent corrosion damage of steel structures. Mg-base alloys galvanic anode protection of cathodic protection methode is suitable for the application of hot water boiler using water with high specific resistance such as tap water. This paper is studied on the cathodic protection characteristics of hot water boiler. In tap water solution, the measurement of cathodic protection potential according to the time elapsed is carried out, and behavior of cathodic polarization with current change is investigated. The main results obtained are as follows. In hot water boiler shell, the open circuit potential of base metal become less noble than that of weld Bone, and the current density of base metal becomes low than that of weld zone. The further distance from Mg-alloy galvanic anode, the higher cathodic protection potential of hot water boiler appears. And protective potential becomes high according to pass cathodic protection time and after 6∼10 days become stable.

• Corrosion Science and Technology
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• v.16 no.4
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• pp.175-182
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• 2017

Galvanic current measurement, polarization curves, electrochemical impedance spectroscopy and weight loss test were used to study the corrosion behavior of carbon steel before and after carbon fibers coupling to the carbon steel in simulated concrete pore solutions, and the film composition on the steel surface was analyzed using XPS method. The results indicate that passive film on steel surface had excellent protective property in pore solutions with different pH values (13.3, 12.5 and 11.6). After coupling with carbon fibers (the area ratio of carbon steel to carbon fiber was 12.31), charge transfer resistance $R_{ct}$ of the steel surface decreased and the $Fe^{3+}/Fe^{2+}$ value in passive film decreased. As a result, stability of the film decreased and the corrosion rate of steel increased. Decreasing of the area ratio of steel to carbon fiber from 12.3 to 6.15 resulted in the decrease in $R_{ct}$ and the increase in corrosion rate. Especially in the pore solution with pH 11.6, the coupling leads the carbon steel to corrode easily.

• Korean Journal of Materials Research
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• v.20 no.3
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• pp.125-131
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• 2010

In this study, Ti powders were fabricated from Ti scrap by the Hydrogenation-Dehydrogenation (HDH) method. The Ti powders were prepared from the spark plasma sintering (SPS) and their microstructure was investigated. Hydrogenation reactions of Ti scrap occurred at near $450^{\circ}C$ with a sudden increase in the reaction temperature and the decreasing pressure of hydrogen gas during the hydrogenation process in the furnace. The dehydrogenation process was also carried out at $750^{\circ}C$ for 2 hrs in a vacuum of $10^{-4}$ torr. After the HDH process, deoxidation treatment was carried out with the Ca (purity: 99.5%) at $700^{\circ}C$ for 2 hrs in the vacuum system. It was found that the oxidation content of Ti powder that was deoxidized with Ca showed noticeably lower values, compared to the content obtained by the HDH process. In order to fabricate the Ti compacts, Ti powder was sintered under an applied uniaxial punch pressure of 40 MPa in the range of $900-1200^{\circ}C$ for 5 min under a vacuum of $10^{-4}$ torr. The relative density of the compact was 99.5% at $1100^{\circ}C$ and the tensile strength decreased with increasing sintering temperature. After sintering, all of the Ti compacts showed brittle fracture behavior, which occurred in an elastic range with short plastic yielding up to a peak stress. Ti improved the corrosion resistance of the Ti compacts, and the Pd powders were mixed with the HDH Ti powders.

• Journal of Electrochemical Science and Technology
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• v.12 no.2
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• pp.246-256
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• 2021

Mo,Cu-doped CeO₂ (CMCuO) nanopowders were synthesized by the nitrate-fuel combustion method aiming to improve the electrical and electrochemical properties of its Mo-doped CeO₂ (CMO) parent by the addition of copper. An electrical conductivity of ca. 1.22·10^-2 S cm^-1 was measured in air at 800℃ for CMCuO, which is nearly 10 times higher than that reported for CMO. This increase was associated with the inclusion of copper into the crystal lattice of ceria and the presence of Cu and Cu₂O as secondary phases in the CMCuO structure, which also could explain the increase in the charge transfer activities of the CMCuO based anode for the hydrogen and carbon monoxide electro-oxidation processes compared to the CMO based anode. A maximum power density of ca. 120 mW cm^-2 was measured using a CMCuO based anode in a solid oxide fuel cell (SOFC) with YSZ electrolyte and LSM-YSZ cathode operating at 800℃ with humidified syngas as fuel, which is comparable to the power output reported for other SOFCs with anodes containing copper. An increase in the area specific resistance of the SOFC was observed after ca. 10 hours of operation under cycling open circuit voltage and polarization conditions, which was attributed to the anode delamination caused by the reduction of the Cu₂O secondary phase contained in its microstructure. Therefore, the addition of a more electroactive phase for hydrogen oxidation is suggested to confer long-term stability to the CMCuO based anode.

• Journal of Electrochemical Science and Technology
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• v.14 no.2
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• pp.162-173
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• 2023

Aqueous zinc-ion batteries are considered as promising alternatives to lithium-ion batteries for energy storage owing to their safety and cost efficiency. However, their lifespan is limited by the irreversibility of Zn anodes because of Zn dendrite growth and side reactions such as the hydrogen evolution reaction and corrosion during cycling. Herein, we present a strategy to restrict direct contact between the Zn anode and aqueous electrolyte by fabricating a protective layer on the surface of Zn foil via phosphidation method. The Zn₃(PO₄)₂ protective layer effectively suppresses Zn dendrite growth and side reactions in aqueous electrolytes. The electrochemical properties of the Zn₃(PO₄)₂@Zn anode, such as the overpotential, linear polarization resistance, and hydrogen generation reaction, indicate that the protective layer can suppress interfacial corrosion and improve the electrochemical stability compared to that of bare Zn by preventing direct contact between the electrolyte and the active sites of Zn. Remarkably, MnO₂ Zn₃(PO₄)₂@Zn exhibited enhanced reversibility owing to the formation a stable porous layer, which effectively inhibited vertical dendrite growth by inducing the uniform plating of Zn²⁺ ions underneath the formed layer.

• Korean Journal of Materials Research
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• v.34 no.8
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• pp.377-386
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• 2024

The surface of titanium (Ti) dental implants was modified by applying a zinc (Zn)-doped titanium dioxide (TiO₂) coating. Initially, the Ti surfaces were etched with NaOH, followed by a hydrolysis co-condensation using tetrabutyl titanate (TBT, Ti(OC₄H₉)₄) and zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O), with ammonia water (NH₃·H₂O) acting as a hydroxide anion source. The morphology and chemical composition of the Zn-doped TiO₂-coated Ti plates were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and scanning electron microscopy (SEM). Synthesis temperatures were carefully adjusted to produce anatase Zn-doped TiO₂ nanoparticles with a bipyramidal structure and approximate sizes of 100 nm. Wettability tests and cell viability assays demonstrated the biomedical potential of these modified surfaces, which showed high biocompatibility with a survival rate of over 95 % (p < 0.05) and improved wettability. Corrosion resistance tests using potentiodynamic polarization reveal that Zn-TiO₂-treated samples with an anatase crystal structure exhibited a lower corrosion current density and more noble corrosion potential compared to samples coated with a rutile structure. This method offers a scalable approach that could be adapted by the biomaterial industry to improve the functionality and longevity of various biomedical implants.

• Journal of Surface Science and Engineering
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• v.41 no.5
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• pp.181-188
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• 2008

A.C. impedance properties of HA/Ti compound layer coated Ti-30Ta-($3{\sim}15$)Nb alloys have been studied by electrochemical method. Ti-30Ta binary alloys contained 3, 7, 10 and 15 wt% Nb were manufactured by the vacuum furnace system. And then specimen was homogenized at $1000^{\circ}C$ for 24 hrs. The sample was cut and polished for corrosion test and coating. It was coated with HA/Ti compound layer by magnetron sputter. The non-coated and coated morphology of Ti alloy were analyzed by X-ray diffractometer (XRD), energy X-ray dispersive spectroscopy (EDX) and filed emission scanning electron microscope (FE-SEM). The corrosion behaviors were investigated using A.C. impedance test (PARSTAT 2273, USA) in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. Ti-30Ta-($3{\sim}15\;wt%$)Nb alloys showed the ${\alpha}+{\beta}$ phase, and $\beta$ phase peak was predominantly appeared in the case of increasingly Nb contents. The microstructures of Ti alloy were transformed from needle-like structure to equiaxed structure as Nb content increased. From the analysis of coating surface, HA/Ti composite surface uniformed coating layer with 750 nm thickness. The growth directions of film were (211), (112), (300) and (202) for HA/Ti composite coating on the surface after heat treatment at $550^{\circ}C$, whereas, the growth direction of film was (110) for Ti coating. The polarization resistance ($R_p$) of HA/Ti composite coated Ti-alloys were higher than those of the Ti and HA coated samples in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. Especially, corrosion resistance of Ti-Ta-Nb system increased as Nb content increased.