• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.3
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• pp.443-450
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• 2021

After selecting a PES substrate with excellent thermal stability and optical properties among plastic substrates, a SiO₂ thin film was deposited as a buffer layer to a thickness of 20nm by plasma-enhanced chemical vapor deposition to compensate for the high moisture absorption. Then, the ITZO thin film was deposited by a RF magnetron sputtering method to investigate electrical and optical properties according to RF power. The ITZO thin film deposited at 50W showed the best electrical properties such as a resistivity of 8.02×10^-4 Ω-cm and a sheet resistance of 50.13Ω/sq.. The average transmittance of the ITZO thin film in the visible light region(400-800nm) was relatively high as 80% or more when the RF power was 40 and 50W. Figure of Merits (Φ_TC and FOM) showed the largest values of 23.90×10^-4 Ω^-1 and 5883 Ω^-1cm^-1, respectively, in the ITZO thin film deposited at 50W.

• Membrane Journal
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• v.31 no.6
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• pp.434-442
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• 2021

Poly(vinylidene fluoride) (PVDF) membrane has a good membrane durability because of its high mechanical resistance, thermal and chemical stability. However, the strong hydrophobic property of PVDF membrane can induce a low water permeability and easy fouling by proteins and organic matters. In order to improve the anti-fouling properties of PVDF membrane, the PVDF mixed matrix asymmetric membranes impregnated with biofunctional material 𝛽-cyclodextrin (𝛽-CD) in the membrane structure were prepared by phase inversion method. The membrane filtration experiments of pure water and BSA solution were performed using the PVDF/𝛽-CD mixed matrix asymmetric membranes prepared according to the 𝛽-CD contents. The experiments showed that the introduction of 𝛽-CD into the PVDF polymer matrix contributed to increase in the hydrophilic property of the PVDF membranes, and this led to the reduction of contact angles and improvement of anti-fouling properties. The PVDF/𝛽-CD membrane which was prepared using the dope solution with a 2 wt% 𝛽-CD content represented 64 L/m²·h of pure water flux, 95% of BSA rejection and maximum 80% of flux enhancements compared to flux results of the pristine PVDF membrane.

• Economic and Environmental Geology
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• v.55 no.3
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• pp.219-229
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• 2022

Bentonite is being considered as a candidate for buffer material in geological disposal systems for high-level radioactive wastes. In this study, the effect of cement-bentonite interactions on bentonite alteration was investigated by reviewing the literature on studies of cement-bentonite interactions. The major bentonite alteration by hyperalkaline fluids produced by the interaction of cementitious materials with groundwater includes cation exchange, montmorillonite dissolution, secondary mineral precipitation, and illitization. When the hyperalkaline leachate from the reaction of the cementitious material with the groundwater comes into contact with bentonite, montmorillonite, the main component of bentonite, is dissolved and a small amount of secondary minerals such as zeolite, calcium silicate hydrate, and calcite is produced. When montmorillonite is continuously dissolved, the physicochemical properties of bentonite may change, which may ultimately causes changes in bentonite performance as a buffer material such as adsorption capacity, swelling capacity, and hydraulic conductivity. In addition, the bentonite alteration is affected by various factors such as temperature, reaction period, pressure, composition of pore water, bentonite constituent minerals, chemical composition of montmorillonite, and types of interlayer cations. This study can be used as basic information for the long-term stability verification study of the buffer material in the geological disposal system for high-level radioactive wastes.

• Korean Journal of Optics and Photonics
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• v.33 no.5
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• pp.218-229
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• 2022

We have investigated reliable inspection methods for finding the defects generated during the manufacturing process of lightweight, large-aperture satellite telescope mirrors using silicon carbide, and we have measured the basic physical properties of the mirrors. We applied the advanced ceramic material (ACM) method, a combined method using liquid-silicon penetration sintering and chemical vapor deposition for the carbon molded body, to manufacture four SiC mirrors of different sizes and shapes. We have provided the defect standards for the reflectors systematically by classifying the defects according to the size and shape of the mirrors, and have suggested effective nondestructive methods for mirror surface inspection and internal defect detection. In addition, we have analyzed the measurements of 14 physical parameters (including density, modulus of elasticity, specific heat, and heat-transfer coefficient) that are required to design the mirrors and to predict the mechanical and thermal stability of the final products. In particular, we have studied the detailed measurement methods and results for the elastic modulus, thermal expansion coefficient, and flexural strength to improve the reliability of mechanical property tests.

• Journal of the Korean Electrochemical Society
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• v.25 no.4
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• pp.184-190
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• 2022

Spinel LiMn₂O₄ (LMO) and layered LiNi_0.5Co_0.2Mn_0.3O₂ (NCM) are widely used as positive electrode materials for lithium-ion batteries. LMO and NCM positive electrode materials have a complementary properties. LMO has low cost and high safety and NCM materials show a relatively high specific capacity and better cycle life even at elevated temperature. Therefore, the LMO and NCM active materials are blended and used as a positive electrode in large-size batteries for electric vehicles (xEV). In this study, the cycle performance of a blended electrode prepared by simply mixing LMO and NCM and a bi-layer electrode in which two electrode layers aree sequentially coated are compared. The bi-layer electrode prepared by composing the same ratio of both active materials has similar capacity and cycle performance to the blend electrode. However, the LN electrode coated with LMO first and then NCM is the best in the full cell cycle performance at elevated temperature, and the NL electrode, in which NCM is first coated with LMO has a faster capacity degradation than the blended electrode because LMO is mainly located on the top of the electrode adjacent to electrolyte and graphite negative electrode. Also, the LSTA (linear sweep thermmametry) analysis results show that the LN bi-layer electrode in which the LMO is located inside the electrode has good thermal stability.

• Membrane Journal
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• v.32 no.6
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• pp.427-441
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• 2022

Polymer electrolyte membrane (PEM) serving as a separator that can prevent the permeation of unreacted fuels as well as an electrolyte that selectively transports protons from the anode to the cathode has been considered a key component of polymer electrolyte membrane fuel cell (PEMFC). The perfluorinated sulfonic acid-based PEMs, represented by Nafion®, have been commercialized in PEMFC systems due to their high proton conductivity and chemical stability. Nevertheless, these PEMs have several inherent drawbacks including high manufacturing costs by the complex synthetic processes and environmental problems caused by producing the toxic gases. Although numerous studies are underway to address these drawbacks including the development of sulfonated hydrocarbon polymer-based PEMs (SHP-PEMs), which can easily control the polymer structures, further improvement of PEM performances and durability is necessary for practical PEMFC applications. Therefore, this study focused on the various strategies for the development of SHP-PEMs with outstanding performance and durability by 1) introducing cross-linked structures, 2) incorporating organic/inorganic composites, and 3) fabricating reinforced-composite membranes using porous substrates.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.5
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• pp.555-566
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• 2023

In this study, a composite phase change material (CPCM) produced using the SOL-GEL technique was developed as a thermal energy storage medium for low-temperature applications. Tetradecane and activated carbon (AC) were used as the core and supporting materials, respectively. The tetradecane phase change material (PCM) was impregnated into the porous structure of AC using the vacuum impregnation method, and a thin layer of silica gel was coated on the prepared composite using the SOL-GEL process, where tetraethyl orthosilicate (TEOS) was used as the silica source. The thermal performance of the CPCM was analysed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC results showed that the pure tetradecane PCM had melting and freezing temperatures of 6.4℃ and 1.3℃ and corresponding enthalpies 226 J/g and 223.8 J/g, respectively. The CPCM exhibited enthalpy of 32.98 J/g and 27.7 J/g during the melting and freezing processes at 7.1℃ and 2.4℃, respectively. TGA test results revealed that the AC is thermally stable up to 500℃, which is much higher than the decomposition temperature of the pure tetradecane, which is around 120℃. Moreover, in the case of AC-PCM and CPCM thermal degradation started at 80℃ and 100℃, respectively. The chemical stability of the CPCM was studied using Fourier-transform infrared (FT-IR) spectroscopy, and the results confirmed that the developed composite is chemically stable. Finally, the surface morphology of the AC and CPCM was analysed using scanning electron microscopy (SEM), which confirmed the presence of a thin layer of silica gel on the AC surface after the SOL-GEL process.

• Analytical Science and Technology
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• v.19 no.5
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• pp.369-375
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• 2006

Calibration gas mixtures were prepared using dynamic volumetric method according to ISO 6145-5 and the uncertainty was evaluated. Ten identical capillaries with 0.25 mm in inner diameter and 50 cm in length were applied in this system. Dilution ratio of parent gas was determined by the number of capillaries that passes parent gas and that passes balance gas through. Capillaries were made of Teflon which had good chemical stability against adsorption of gaseous substances. Mechanical valves were introduced in this system in order to minimize the thermal effect of solenoid valves. Concentration of prepared gases were compared with master grade standard gases in cylinders made by RiGAS Co. and calibration of the instrument were completed using comparison method according to ISO 6143. Experimental results showed that the coefficient of variance of diluted oxygen standard gases showed less then 0.2% in most dilution range, that of diluted hydrogen sulfide standard gases showed less then 1.0%. Therefore, it is proven that the standard gases prepared by this system are appropriate to be used as a calibration standards in ambient monitoring, etc.

• Economic and Environmental Geology
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• v.56 no.5
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• pp.581-588
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• 2023

This study reports depth-dependent elemental distribution and mineral abundance of the oceanic sediment sample (WP21GPC04) near the Mariana Trench collected during the WP21 expedition in 2021. The elemental distribution determined by μ-XRF shows no significant differences with varying depth, with an average SiO₂ 53.91 wt%, FeO 4.48 wt%, Al₂O₃ 16.56 wt%, MgO 2.56 wt%, CaO 4.79 wt%, Na₂O 3.52 wt%, K₂O 5.48 wt%, similar to the average chemical composition of global subducting sediments (GLOSS). The mineral abundances analyzed using synchrotron XRD, however, vary with depth. While quartz, mica, and plagioclase were identified at all depths, chlorite was found at shallow depths, and zeolite group minerals, phillipsite and heulandite, showed a gradual change in phase fraction with depth. This suggests a change in sedimentation and alteration environments in the region, or the potential for coexistence emerges due to similar sediment stability. Overall, this study will provide a basis for the future investigations on the evolution of sedimentary environment near the Mariana Trench in the western Pacific Ocean and the phase distribution and the behavior of subducting oceanic sediments, which will affect the lithological and geochemical characteristics of the Mariana susduction system.

• Applied Chemistry for Engineering
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• v.34 no.6
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• pp.603-607
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• 2023

Aqueous film forming foam (AFFF) is a critical fire suppression agent used in combating hydrocarbon fires. This type of fire suppressant is highly effective due to its ability to form a protective film, dissipate heat, inhibit combustion, and utilize a blend of chemical substances to extinguish fires. While these properties offer significant advantages in responding to hydrocarbon fires, AFFF is distinct in its deployment as it is dispensed in the form of foam. Therefore, the rheological analysis of AFFF foam using a rheometer plays a crucial role in predicting the spray characteristics of AFFF for combating hydrocarbon fires, and this is closely associated with effective fire suppression. In this study, we conducted rheometer experiments to confirm the non-Newtonian behavior (shear-thinning) of AFFF foam and obtained data on the form's stability. These experimental data are expected to contribute to enhancing the efficiency of fire suppression systems utilizing AFFF.