• Composites Research
• /
• v.33 no.2
• /
• pp.68-75
• /
• 2020

Recently, the use of TiO₂ as a phtocatalyst has been diversely investigated due to its excellent durability performance and high photocatalytic reaction efficiency. Active researches have particularly focused on the development of TiO₂-incorporated cementitious composites in order to remove the atmospheric pollutants. Furthermore, the potential utilization of TiO₂-incorporated cementitious composites as road accessories such as tunnels, road median separators and soundproof walls in the form of tiles, blocks and structural components has been widely examined. In this regard, a thorough understanding on the material characteristics of TiO₂-incorporated cementitious composites should be preceded. The present overview article, therefore, revisits previous studies of TiO₂-incorporated cementitious composites and summarizes their various physicochemical properties and atmospheric pollutants removal performance.

• Membrane Journal
• /
• v.21 no.4
• /
• pp.389-397
• /
• 2011

In this study, polymer composite membranes based on sulfonated poly(arylene ether sulfone) (SPAES) were prepared using a solution casting method with different amount of vermiculite (VMT) content. The dispersion of VMT particles in the SPAES matrix was confirmed by means of a scanning electron microscopy observation. The composite membrane containing less than 1 wt% of VMT has a smooth skin on the top and bottom, which means there is a good dispersion of VMT in the matrix. The water uptake of the composite membranes gradually increases as the temperature increases, and the results confirm that all the adsorbed water is bound water because VMT has a strong water affinity on account of its high cation exchange value. A composite membrane with a VMT content of less than 1 wt% increases the proton conductivity and reduces the methanol permeability. Of all the composite membranes, the membrane SPAES/VMT 1.0 has the best fuel cell performance in terms of membrane selectivity. The performance value of SPAES/VMT 1.0 is double that of Nafion 112, which suggests that SPAES/VMT1.0 could be an excellent candidate for direct methanol fuel cells.

• Journal of the Korean Electrochemical Society
• /
• v.16 no.3
• /
• pp.151-156
• /
• 2013

As the cathode material for li-ion battery, $LiNi_{0.5}Mn_{0.3}Co_{0.2}O_2$ were synthesized by supercritical hydrothermal method and calcined $850^{\circ}C$ and $900^{\circ}C$ for 10hrs in air. The effect of temperature in the heat treatment on the powder and its performance were studied of xray diffraction pattern, SEM-image, physical properties and electrochemical behaviors. As a result, calcined at $900^{\circ}C$ material particle size more increase than calcined at $850^{\circ}C$ material, especially shows excellent electrochemical performance with initial reversible specific capacity of 163.84 mAh/g (0.1C/2.0-4.3V), 186.87 mAh/g (0.1C/2.0-4.5V) and good capacity retention of 91.49% (0.2C/2.0-4.3V) and 90.36% (0.2C/2.0-4.5V) after 50th charge/discharge cycle.

• Journal of Biomedical Engineering Research
• /
• v.25 no.6
• /
• pp.439-445
• /
• 2004

Diffusion tensor image(DTI) exploits the random diffusional motion of water molecules. This method is useful for the characterization of the architecture of tissues. In some tissues, such as muscle or cerebral white matter, cellular arrangement shows a strongly preferred direction of water diffusion, i.e., the diffusion is anisotropic. The degree of anisotropy is often represented using diffusion anisotropy indices (relative anisotropy(RA), fractional anisotropy(FA), volume ratio(VR)). In this study, FA images were obtained using different gradient schemes(N=6, 11, 23, 35. 47). Mean values and the standard deviations of FA were then measured at several anatomic locations for each scheme. The results showed that both mean values and the standard deviations of FA were decreased as the number of gradient directions were increased. Also, the standard error of ADC measurement decreased as the number of diffusion gradient directions increased. In conclusion, different gradient schemes showed a significantly different noise performance and the schem with more gradient directions clearly improved the quality of the FA images. But considering acquisition time of image and standard deviation of FA, 23 gradient directions is clinically optimal.

• Journal of the Microelectronics and Packaging Society
• /
• v.16 no.2
• /
• pp.33-42
• /
• 2009

A polymer-based flexible neural probe was fabricated for monitoring of neural activities from a brain. To improve the insertion stiffness, a 5 ${\mu}m$ thick biocompatible Au layer was electroplated between the top and bottom polymer layers. The developed neural probe penetrated a gel whose elastic modulus is similar to that of a live brain tissue without any fracture, To minimize mechanical residual stress and bending from the probe, two new methods were employed: (1) use of a thermal annealing process after completing the device and (2) incorporation of multiple different layers to compensate the residual stress between top and bottom layers. Mechanical bending around the probe tip was clearly removed after employing the two processes. In electrical test, the developed probe showed a proper impedance value to record neural signals from a brain and the result remained the same for 72 hours. In simple in-vitro probe characterization, the probe showed a great removal of residual stress and an excellent recording performance. The in-vitro recording results did not change even after 1 week, suggesting that this electrode has the potential for great recording from neuron firing and long-term implant performance.

• Nuclear Engineering and Technology
• /
• v.49 no.5
• /
• pp.1044-1062
• /
• 2017

The construction project of the Kijang research reactor (KJRR), which is the second research reactor in Korea, has been launched. The KJRR was designed to use, for the first time, U-Mo fuel. Plate-type U-7 wt.% Mo/Al-5 wt.% Si, referred to as U-7Mo/Ale5Si, dispersion fuel with a uranium loading of $8.0gU/cm^3$, was selected to achieve higher fuel efficiency and performance than are possible when using $U_3Si_2/Al$ dispersion fuel. To qualify the U-Mo fuel in terms of plate geometry, the first miniplates [HANARO Miniplate (HAMP-1)], containing U-7Mo/Al-5Si dispersion fuel ($8gU/cm^3$), were fabricated at the Korea Atomic Energy Research Institute and recently irradiated at HANARO. The PIE (Post-irradiation Examination) results of the HAMP-1 irradiation test were analyzed in depth in order to verify the safe in-pile performance of the U-7Mo/Al-5Si dispersion fuel under the KJRR irradiation conditions. Nondestructive analyses included visual inspection, gamma spectrometric mapping, and two-dimensional measurements of the plate thickness and oxide thickness. Destructive PIE work was also carried out, focusing on characterization of the microstructural behavior using optical microscopy and scanning electron microscopy. Electron probe microanalysis was also used to measure the elemental concentrations in the interaction layer formed between the U-Mo kernels and the matrix. A blistering threshold test and a bending test were performed on the irradiated HAMP-1 miniplates that were saved from the destructive tests. Swelling evaluation of the U-Mo fuel was also conducted using two methods: plate thickness measurement and meat thickness measurement.

• Journal of the Korean Electrochemical Society
• /
• v.22 no.1
• /
• pp.43-52
• /
• 2019

As the application area of lithium secondary batteries becomes wider, performance characterization becomes difficult as well as diverse. To address this issue, battery manufacturers have to evaluate many batteries for a longer period, recruit many researchers and continuously introduce expensive equipment. Simulation techniques based on battery modeling are being introduced to solve such difficulties. Various lithium secondary battery modeling techniques have been reported so far and optimal techniques have been selected and utilized according to their purpose. In this review, the electrochemical modeling based on the Newman model is described in detail. Particularly, we will explain the physical meaning of each equation included in the model; the Butler-Volmer equation, which represents the rate of electrode reaction, the material and charge balance equations for each phase (solid and liquid), and the energy balance. Moreover, simple modeling processes and results based on COMSOL Multiphysics 5.3a will be provided and discussed.

• The Journal of Advanced Prosthodontics
• /
• v.13 no.6
• /
• pp.385-395
• /
• 2021

PURPOSE. To characterize the microstructure of three yttria partially stabilized zirconia ceramics and to compare their hardness, indentation fracture resistance (IFR), biaxial flexural strength (BFS), and fatigue flexural strength. MATERIALS AND METHODS. Disc-shaped specimens were obtained from 3Y-TZP (Vita YZ HT), 4Y-PSZ (Vita YZ ST) and 5Y-PSZ (Vita YZ XT), following the ISO 6872/2015 guidelines for BFS testing (final dimensions of 12 mm in diameter, 0.7 and 1.2 ± 0.1 mm in thicknesses). Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed, and mechanical properties were assessed by Vickers hardness, IFR, quasi-static BFS and fatigue tests. RESULTS. All ceramics showed similar chemical compositions, but mainly differed in the amount of yttria, which was higher as the amount of cubic phase in the diffractogram (5Y-PSZ > 4Y-PSZ > 3Y-TZP). The 4Y- and 5Y-PSZ specimens showed surface defects under SEM, while 3Y-TZP exhibited greater grain uniformity on the surface. 5Y-PSZ and 3Y-TZP presented the highest hardness values, while 3Y-TZP was higher than 4Y- and 5Y-PSZ with regard to the IFR. The 5Y-PSZ specimen (0.7 and 1.2 mm) showed the worst mechanical performance (fatigue BFS and cycles until failure), while 3Y-TZP and 4Y-PSZ presented statistically similar values, higher than 5Y-PSZ for both thicknesses (0.7 and 1.2 mm). Moreover, 3Y-TZP showed the highest (1.2 mm group) and the lowest (0.7 mm group) degradation percentage, and 5Y-PSZ had higher strength degradation than 4Y-PSZ group. CONCLUSION. Despite the microstructural differences, 4Y-PSZ and 3Y-TZP had similar fatigue behavior regardless of thickness. 5Y-PSZ had the lowest mechanical performance.

• Journal of Powder Materials
• /
• v.29 no.5
• /
• pp.411-417
• /
• 2022

Environmental issues such as global warming due to fossil fuel use are now major worldwide concerns, and interest in renewable and clean energy is growing. Of the various types of renewable energy, green hydrogen energy has recently attracted attention because of its eco-friendly and high-energy density. Electrochemical water splitting is considered a pollution-free means of producing clean hydrogen and oxygen and in large quantities. The development of non-noble electrocatalysts with low cost and high performance in water splitting has also attracted considerable attention. In this study, we successfully synthesized a NiCo₂O₄/NF electrode for an oxygen evolution reaction in alkaline water splitting using a hydrothermal method, which was followed by post-heat treatment. The effects of heat treatment on the electrochemical performance of the electrodes were evaluated under different heat-treatment conditions. The optimized NCO/NF-300 electrode showed an overpotential of 416 mV at a high current density of 50 mA/cm² and a low Tafel slope (49.06 mV dec^-1). It also showed excellent stability (due to the large surface area) and the lowest charge transfer resistance (12.59 Ω). The results suggested that our noble-metal free electrodes have great potential for use in developing alkaline electrolysis systems.

• Korean Chemical Engineering Research
• /
• v.61 no.3
• /
• pp.479-486
• /
• 2023

In this study, we investigated the effect of the Ce_xZr_1-xO₂ (CZ) addition onto Ni/Al₂O₃ catalysts on the catalytic performance in methane steam reforming. In the reaction results, the CZ-added Ni/Al₂O₃ catalyst showed higher CH₄ conversion and H₂ yield under the same reaction conditions than Ni/Al₂O₃. From the characterization data, the two catalysts had similar support porosity and Ni dispersion, confirming that the two properties could not determine the catalytic performance. However, the oxygen vacancy over the CZ-added Ni/Al₂O₃ catalyst induced an efficient steam activation at low reaction temperatures, resulting in an increase in the catalytic activity and H₂ yield.