In this study, to improve the performance of a solid oxide fuel cell based on a porous metal support, a fuel cell using a multi-layered anode functional layer was fabricated and electrochemical performance analysis was performed. Surface and cross-sectional microstructures according to particle size control were confirmed through FE-SEM. The pore size of the multi-layer anode functional layer was gradually reduced compared to that of a single-structure anode functional layer. As a result, it was confirmed that the surface roughness was lower than that of the single structure. This led to a reduction in polarization resistance through smooth transmission of gas generated from the electrode. As a result, it was confirmed that electrochemical performance was improved by more than 1.25 times in fuel cells using a multi-layered anode functional layer compared to that with a single structure.
The effectiveness of applying tap water method to reduce the generation of nano-sized wear particles from wheel-rail contacts in the aspect of air quality was investigated. A twin-disk rig was utilized to simulate the generation of airborne wear particles resulting from wheel-rail contacts. Slip rates ranging from 0 to 3% were continuously generated to simulate various railway vehicle dynamics. Dry and tap water application conditions (7 L/min) were tested. The mass concentration of wear particles with sizes below 560 nm generated during tests was measured using a Fast Mobility Particle Sizer (FMPS). Particles measured in the slip zone (0 to 3%) were categorized into PM0.02, PM0.03, PM0.1, and PM0.56 for analysis. Results indicated a significant decrease in mass concentration of particles with sizes above 30 nm, while those with sizes below 30 nm showed an increase. Particle reduction rate was -217.2% for PM0.02, -58.5% for PM0.03, 84.5% for PM0.1, and 90.3% for PM0.56. It should be noted that a negative reduction rate indicates an increase in the amount of particle generation. This study demonstrates that the application of tap water is effective in improving air quality by reducing the generation of nano-sized wear particles overall.
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Measurement and Analysis of Air Quality Improvement Effects of Applying Water Methods at Various Train Velocities Using a Twin-disk Rig HyunWook Lee Journal of the Korean Society for Precision Engineering.2024; 41(10): 753. CrossRef
In this study, a novel size adjustable robot that could overcome an unstructured environment was introduced. To provide the robot with a volume-modifiable function, negative Poisson’s ratio structure with a unique characteristic about deformation of material was applied to the design of the body frame. The robot could simultaneously adjust its width and length with only one directional control with the help of the negative Poisson’s ratio structure. An omni-directional mobile mechanism was adopted to drive its wheels and allow flexible movement in a narrow space. However, during the procedure to adjust the size of the robot, a slip phenomenon occurred, resulting in an unnecessary movement. To solve this problem, the unnecessary offset was measured through repetitive tests and applied to the robot to compensate the position shift. To verify the performance of the robot, a test bed with a narrow space was fabricated. Extensive experiments were conducted to evaluate environmental recognition and size adjustment function by calculating the width of the narrow space and scaling the robot"s body. Results confirmed that the robot sufficiently achieved the motion objective to move in a narrow space with its size adjustment function.
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Auxetic and Holonomic Mobile Robot for Enhanced Navigation in Constrained Terrains Cheonghwa Lee, Jinwon Kim, Hyeongyeong Jeong, Hyunbin Park, Baeksuk Chu Journal of Field Robotics.2025; 42(8): 4414. CrossRef
An electrospray is widely used in the industry due to uniform and continuous droplet generation. Most of the studies on the electrospray modes are conducted in the cone jet mode. The goal of this study is to confirm the spray patterns for each mode of the electrospray by setting various conditions, such as nozzle to substrate, nozzle diameters, fluid properties (Viscosity and Conductivity), and flow rate. As a result, 7 modes were observed by the applied voltage and flow rate. It was confirmed that the smallest droplet size was produced in the cone jet mode and working fluid V (High Conductivity).
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Experimental Investigation of Electrospraying Properties Based on Ring Electrode Modification Ji Yeop Kim, Sang Ji Lee, Mun Hee Lee, Jung Goo Hong ACS Omega.2024; 9(1): 1125. CrossRef
Study on Correlation between Manufacturing Method of Thermal Insulation Fabric and Thermal Insulation Performance for Reducing Rail Temperature in Summer Season Juyeop Park, Donghoon Kang Journal of the Korean Society for Precision Engineering.2024; 41(4): 313. CrossRef
Study of Droplet Characteristics of Electrospray Coating Method as a Function of Ring Electrode Parameters Ji Yeop Kim, Mun Hee Lee, Jun Yeop Kim, Jung Goo Hong Journal of the Korean Society for Precision Engineering.2024; 41(2): 153. CrossRef
Periodicity of Droplet Impact Behavior by Liquid Viscosity on PDMS Surface Dong Kwan Kang, Sangmin Lee Journal of the Korean Society for Precision Engineering.2022; 39(11): 857. CrossRef
Spray Mode and Monodisperse Droplet Properties of an Electrospray Ji Yeop Kim, Sang Ji Lee, Jung Goo Hong ACS Omega.2022; 7(32): 28667. CrossRef
Viscosity Effect on the Electrospray Characteristics of Droplet Size and Distribution Ji Yeop Kim, Sang Ji Lee, Gwang Yeol Baik, Jung Goo Hong ACS Omega.2021; 6(44): 29724. CrossRef
Chemical mechanical planarization (CMP) is a semiconductor process which is necessary for multi-layer interconnection structure. CMP pad is a consumable used in the process and with numerous asperities on the surface that wear out by the load applied from the contact with the wafer. Also, it has a patterned wafer, the step height is gradually removed by contact of the asperities with upper and lower layers. The contact state would be different according to the step height reduction. Likewise, depending on the pattern size at the specific step height, the maximum radius of the asperity curvature differs whether it reaches the down area. In this study, the height distribution of asperities was expressed as a function of time and asperity height taking into account the wear of asperities, and based on the Greenwood-Williamson theory, a mathematical model for material removal rate considering pattern size was derived. The consistency of the novel model is verified with the CMP experiment conducted using oxide patterned wafers, and the experimental data were compared with the residual step height using theoretical removal rate. The root mean square error of the step height reduction was 19.84 nm.
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Precision Engineering and Intelligent Technologies for Predictable CMP Somin Shin, Hyun Jun Ryu, Sanha Kim, Haedo Jeong, Hyunseop Lee International Journal of Precision Engineering and Manufacturing.2025; 26(9): 2121. CrossRef
To study the geometrical scale dependency of thin film solid oxide fuel cells (SOFCs), we fabricated three thin films SOFCs with the same cross-sectional structure but with different electrode areas of 1, 4 and 9 ㎟. Since the activation and ohmic losses of SOFCs depend on their active region, we examined the variations of the power density of the cells with a Pt (anode)/sputtered YSZ/Pt (cathode) structure. We found that a cathode electrode with a low aspect ratio may suffer from high ohmic and activation losses because of the geometrical scale dependency.
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