• Korean Journal of Materials Research
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• v.25 no.1
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• pp.43-47
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• 2015

$Zn(BH_4)_2$ was prepared by milling $ZnCl_2$ and $NaBH_4$ in a planetary ball mill in an Ar atmosphere, and XRD analysis, SEM observation, FT-IR analysis, DTA, and TGA were performed for synthesized $Zn(BH_4)_2$ samples. 90 wt% $MgH_2$+1.67 wt% $Zn(BH_4)_2(+NaCl)$+5 wt% Ni+1.67 wt% Ti+1.67 wt% Fe (named $90MgH_2+1.67Zn(BH_4)_2(+NaCl)$+5Ni+1.67Ti+1.67Fe) samples were also prepared by milling in a planetary ball mill in an $H_2$ atmosphere. The gas absorption and release properties of the $Zn(BH_4)_2(+NaCl)$ and $90MgH_2+1.67Zn(BH_4)_2(+NaCl)_2(+NaCl)$+5Ni+1.67Ti+1.67Fe samples were investigated. An FT-IR analysis showed that $Zn(BH_4)_2$ formed in the $Zn(BH_4)_2(+NaCl)$ samples prepared by milling $ZnCl_2$ and $NaBH_4$. At the first cycle at $320^{\circ}C$, $90MgH_2+1.67Zn(BH_4)_2(+NaCl)$+5Ni+1.67Ti+1.67Fe absorbed 2.95 wt% H for 2.5 min and 4.93 wt% H for 60 min under 12 bar $H_2$, and released 1.46 wt% H for 10 min and 4.57 wt% H for 60 min under 1.0 bar $H_2$.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.37-37
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• 2010

Silicate-silsesquioxane or siloxane-silsesquioxane hybrid thin films are strong candidates as matrix materials for ultra low dielectric constant (low-k) thin films. We synthesized the silicate-silsesquioxane hybrid resins from tetraethoxyorthosilicate (TEOS) and methyltrimethoxysilane (MTMS) through hydrolysis and condensation polymerization by changing their molar ratios ([TEOS]:[MTMS] = 7:3, 5:5, and 3:7), spin-coating on Si(100) wafers. In the case of [TEOS]:[MTMS] 7:3, the dielectric permittivity value of the resultant thin film was measured at 4.30, exceeding that of the thermal oxide (3.9). This high value was thought to be due to Si-OH groups inside the film and more extensive studies were performed in terms of electronic, ionic, and orientational polarizations using Debye equation. The relationship between the mechanical properties and the synthetic conditions of the silicate-silsesquioxane precursors was also investigated. The synthetic conditions of the low-k films have to be chosen to meet both the low orientational polarization and high mechanical properties requirements. In addition, we have investigated a new solution-based approach to the synthesis of semiconducting chalcogenide films for use in thin-film transistor (TFT) devices, in an attempt to develop a simple and robust solution process for the synthesis of inorganic semiconductors. Our material design strategy is to use a sol-gel reaction to carry out the deposition of a spin-coated CdS film, which can then be converted to a xerogel material. These devices were found to exhibit n-channel TFT characteristics with an excellent field-effect mobility (a saturation mobility of ${\sim}\;48\;cm^2V^{-1}s^{-1}$) and low voltage operation (< 5 V). These results show that these semiconducting thin film materials can be used in low-cost and high-performance printable electronics.

• Composites Research
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• v.32 no.4
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• pp.177-184
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• 2019

If what the mechanical properties according to a layer have was found out by analyzing the already fabricated composite, it could be possible to develop the composite of the better performance than the existing products. In this study, we tried to calculate the mechanical properties of the inner prepreg lamina by applying the reverse design technique to the composite structure made by laminating prepregs. When the physical quantities obtained by the simple tensile test are used alone and the physical quantities obtained by the tensile test and the mode analysis are used at the same time, the results of this study show that the accuracy of the latter is higher Finally, the maximum error of $E_1$ predicted was 0.09% and the maximum error of predicted $E_2$ was 7%.

• Current Applied Physics
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• v.18 no.12
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• pp.1564-1570
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• 2018

Charge transport dynamics in ZnO based inverted organic solar cell (IOSC) has been characterized with transient photocurrent spectroscopy and localised photocurrent mapping-atomic force microscopy. The value of maximum exciton generation rate was found to vary from $2.6{\times}10^{27}m^{-3}s^{-1}$ ($J_{sat}=79.7A\;m^{-2}$) to $2.9{\times}10^{27}m^{-3}s^{-1}$ ($J_{sat}=90.8A\;m^{-2}$) for devices with power conversion efficiency ranging from 2.03 to 2.51%. These results suggest that nanorods served as an excellent electron transporting layer that provides efficient charge transport and enhances IOSC device performance. The photovoltaic performance of OSCs with various growth times of ZnO nanorods have been analysed for a comparison between AM1.5G spectrum and local solar spectrum. The simulated PCE of all devices operating under local spectrum exhibited extensive improvement with the gain of 13.3-3.7% in which the ZnO nanorods grown at 15 min possess the highest PCE under local solar with the value of 2.82%.

• Composites Research
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• v.34 no.3
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• pp.148-154
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• 2021

Carbon/epoxy composite bipolar plate (BP) is a BP that is likely to replace existing graphite bipolar plate of vanadium redox flow cell (VRFB) due to its high mechanical properties and productivity. Multi-functional carbon/epoxy composite BP requires graphite coating or additional surface treatment to reduce interfacial contact resistance (ICR). However, the expanded graphite coating has the disadvantage of having low durability under VRFB operating conditions, and the surface treatments incur additional costs. In this work, an excessive resin absorption method is developed, which uniformly removes the resin rich area on the surface of the BP to expose carbon fibers by applying polyester fabric. This method not only reduces ICR by exposing carbon fibers to BP surfaces, but also forms a unique ditch pattern that can effectively hold carbon felt electrodes in place. The acidic environmental durability, mechanical properties, and gas permeability of the developed carbon/epoxy composite BP are experimentally verified.

• Composites Research
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• v.34 no.6
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• pp.406-411
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• 2021

PEM (proton exchange membrane) fuel cells generate only water as a by-product, and thus are in the spotlight as an eco-friendly energy source. Among the various components composing the stack of the fuel cell, research on the bipolar plate that determines the efficiency of the fuel cell is being actively conducted. The composite bipolar plate has high strength, rigidity and corrosion resistance, but has the disadvantage of having a relatively low electrical conductivity. In this study, to overcome these shortcomings, a gas diffusion layer (GDL)-composite bipolar plate assembly was developed and its performance was experimentally verified. The graphite foil coating method developed in the previous study was applied to reduce the contact resistance between the bipolar plate and the GDL. In addition, in order to improve electron path in the stack and minimize the contact resistance between the GDL and the bipolar plate, a GDL-bipolar plate assembly was fabricated using a thin metal foil. As a result of the experiment, it was confirmed that the developed GDL-bipolar plate assembly had 98% lower electrical resistance compared to the conventional composite bipolar plate.

• Journal of Surface Science and Engineering
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• v.55 no.4
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• pp.222-230
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• 2022

The electroplating for copper foils has many advantages in economics. During the electroplating, the selection of appropriate additives is needed to manufacture copper foils with various properties. Therefore, it is investigated the initial plating voltage and the properties of copper foil electroplated in the electrolyte with benzothiazole as additives. The addition of benzothiazole without any additives decreased effectively the initial plating voltage. However, the initial voltage increased when the additives was used in combination with an inhibitor and a leveler along with benzothiazole. Moreover, the voltage tends to increase with the concentration of benzothiazole except for 40 ppm group. The mixed additives could change not only the initial voltage but also the morphology of crystals on the surface. When benzothiazole is added at 20 ppm or less, it was observed that the clustered crystals existed on the surface, which result in ununiform surface and high roughness value. In addition, the grain size increased with the amount of benzothiazole, but the resistivity decreased. However, when the leveler was added in 20 ppm, the grain size was decreased with the amount of benzothiazole. The size of the crystals could be influenced by the mixing ratio of additives. Therefore, it is necessary to study on the effect of concentration ratio of additives in the future.

• Composites Research
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• v.36 no.6
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• pp.422-428
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• 2023

The electrical contact resistance between the bipolar plate (BP) and the carbon felt electrode (CFE), which are in contact by the stack clamping pressure, has a great impact on the stack efficiency because of the relatively low clamping pressure of the vanadium redox flow battery (VRFB) stack. In this study, a polyethylene (PE) composite-CFE hybrid bipolar plate structure is developed through a local heat welding process to reduce such contact resistance and improve cell performance. The PE matrix of the carbon fiber composite BP is locally melted to create a direct contact structure between the carbon fibers of CFE and the carbon fibers of BP, thereby reducing the electrical contact resistance. Area specific resistance (ASR) and gas permeability are measured to evaluate the performance of the PE composite-CFE hybrid bipolar plate. In addition, an acid aging test is performed to measure stack reliability. Finally, a VFRB unit cell charge/discharge test is performed to compare and analyze the performance of the developed PE composite-CFE hybrid BP and the conventional BP.

• Journal of Ceramic Processing Research
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• v.22 no.2
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• pp.169-178
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• 2021

In this work, in-flight synthesis route of Ga doped ZnO (GZO) nano-powders was investigated experimentally and numerically, using Radio-Frequency (RF) induction plasmas. For experimental study, mixture of micron-sized ZnO and Ga₂O₃ powders were treated by RF induction plasmas, then, the as-treated powders were retrieved from reactor bottom and filtration for characterization. For numerical study, single particle model was combined with two-dimensional simulation code of RF induction plasma to predict the particle behaviors of ZnO and Ga₂O₃ depending on their sizes. First, experimental results showed that filtration-retrieved powders were characterized as GZO nano-powders although gallium content can be decreased due to Ga₂O₃ decomposition into sub-oxides at the elevated temperatures. From reactor bottom, however, spherical structures consisting of Ga₂O₃ and ZnO particles were observed in sub-millimeter sizes. Numerical results predicted that micron-sized (≤ 10 ㎛) ZnO and Ga₂O₃ particles can vaporize easily during the flight of plasma, while particles with the sizes of 25~100 um were simulated to be partially evaporated or unevaporated. Comparing these experimental and numerical results indicates that GZO nano-powders can be synthesized from vapor species of ZnO and Ga₂O₃, which are primarily produced by in-flight treatment of micron-sized ZnO and Ga₂O₃ powders in RF induction plasmas.

• Journal of Surface Science and Engineering
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• v.57 no.4
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• pp.274-284
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• 2024

In this study, copper foil was electroplated under high current density conditions. We used Polyethylene Glycol (PEG), known for its thermal stability and low decomposition rate, as an inhibitor to form a stable and smooth copper layer on the titanium cathode. The electrolyte was composed of 50 g/L CuSO₄ and 100 g/L H₂SO₄, MPSA as an accelerator, JGB as a leveler, and PEG as a suppressor, and HCl was added as chloride ions for improving plating efficiency. The copper foil electroplated in the electrolyte added PEG which induced to inhibit the growth of rough crystals. As a result, the surface roughness value was reduced, and a uniform surface was formed over a large area. Moreover, the addition of PEG led to priority growth to the (111) plane and the formation of polygonal crystals through horizontal and vertical growth of crystals onto the cathode. In addition, the grains became fine when more than 30 ppm of PEG was added. As the microcrystalline structure changed, mechanical and electrical properties were altered. With the addition of PEG, the tensile strength increased due to grain refinement, and the elongation was improved due to the uniform surface. However, as the amount of PEG added increased, the corrosion rate and resistivity increased due to grain refinement. Finally, it was possible to manufacture a copper foil with excellent electrical and mechanical properties and the best surface properties when electroplating was carried out under the condition of additives with Cl-20 ppm, MPSA 10 ppm, JGB 5 ppm, and PEG 10 ppm.