• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.6
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• pp.203-209
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• 2023

Cobalt sulfide nanocomposites were synthesized through a simple hydrothermal method as anode materials for sodium ion batteries (SIBs). In this work, a cobalt sulfide nanoparticle (CoS-NF) and a cobalt sulfide nanocomposite integrated with reduced graphene oxide (CoS@G-NC) were fabricated for electrochemical energy storage performance of battery. The as-prepared CoS@G-NC electrode exhibited reversible and stable cycle performance (62 % after 30 cycles at current density of 200 mA g^-1). The improved electrochemical property was attributed to the small grain growth and uniform distribution of cobalt sulfide during synthesis, which maximized the diffusion pathway for sodium ions and effectively suppressed the delamination and volume expansion of cobalt sulfide during the conversion reaction. The results provide promising anode materials for next-generation SIBs.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.8
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• pp.105-114
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• 2018

Membrane fouling in EC-MBR (Electro-Coagulation aided Membrane Bio-Reactor) processes was evaluated according to the operating parameters, such as current density and contact time. In addition, the fouling mechanism was investigated. Compared to the control (i.e., no electro-coagulation), membrane fouling for filtration of the activated sludge suspension after electro-coagulation was reduced significantly. Membrane fouling was improved further when the contact time was doubled under a low current density of $2.5A/m^2$. On the other hand, membrane fouling was not mitigated further, as expected, even though the contact time was doubled from 12 to 24 hr. at a current density of $10A/m^2$. This indicates that the overall decrease in membrane fouling is a function of the product of the current density and contact time. The particle size of the activated sludge flocs after electro-coagulation was changed slightly, which means that the membrane fouling reduction was not attributed to a larger particle size resulting from electro-coagulation. The experimental confirmed that the dynamic membrane made from aluminum hydroxide, Al(OH)3, and/or aluminum phosphate, Al(PO4), which had been formed during the electro-coagulation, played a key role on the reduction of membrane fouling. The dynamic membrane prevents the particles in the feed solution from deposition to the membrane pores and cake layers. Dynamic membrane formation as a result of electro-coagulation plays a critical role in the mitigation of membrane fouling in EC-MBR.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.1
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• pp.49-62
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• 2024

Reckless development of the underground by rapid urbanization causes inspection delay on replacement of existing structure and installation new facilities. However, frequent accidents occur due to deviation in construction design planned by inaccurate location information of underground structure. Meanwhile, the electrical resistivity survey, knowns as non-destructive method, is based on the difference in the electric potential of electrodes to measure the electrical resistance of ground. This method is significantly advanced with multi-electrode and deep learning for analyzing strata. However, there is no study to quantitatively assess change in electrical resistance according to geometric conditions of structures. This study evaluates changes in electrical resistance through geometric parameters of electrodes and structure. Firstly, electrical resistance numerical module is developed using generalized mesh occurring minimal errors between theoretical and numerical resistance values. Then, changes in resistances are quantitatively compared on geometric parameters including burial depth, diameter of structure, and distance electrode and structure under steady current condition. The results show that higher electrical resistance is measured for shallow depth, larger size, and proximity to the electrode. Additionally, electric potential and current density distributions are analyzed to discuss the measured electrical resistance around the terminal electrode and structure.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.357-360
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• 2009

The present study focused on the segmented cell which has the similar performance to unaltered (not segmented) cell in real operating condition. Many literatures have been made the segmented cell to observe the behavior of local current density distribution in the single cell. However, it has been lack of scheme to segment the cell in that the detailed interpretation of segmenting in analytic point of view was insufficient. Hence, the basic idea of segmenting was introduced to determine the component to be segmented in anode side of unit cell. The electrical contact/bulk resistance was measured by using four wire/probe method through each part of cell components including MEA, GDL, Bipolar Plate and Current Collector. Electron transport mechanism was predicted by comparing resistance values which were obtained from the experiment. As a result, this offered a great benefit to segment the cell efficiently. With this method further experiments would be conducted in research areas which require current density distribution at the same operating condition as unaltered cell.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.3
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• pp.317-324
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• 2010

Metal-supported solid oxide fuel cells (SOFCs) have been developed to commercialize SOFCs. This new type of SOFC has high mechanical strength, but its mass transfer rate may be low due to the presence of a contact layer. In this study, the mass transfer characteristics of an anode-supported SOFC and a metal-supported SOFC are studied by performing numerical simulation. Governing equations, electrochemical reactions, and ceramic physical-property models are determined simultaneously; molecular diffusion and Knudsen diffusion are considered in mass transport analysis of porous media. The experimental results are compared with simulation data to validate the results of numerical simulation. The average current density of the metal-supported SOFC is 23% lower than that of the anode-supported SOFC. However, because of the presence of the contact layer, the metal-supported SOFC has a more uniform distribution than the anode-supported SOFC.

• Korean Chemical Engineering Research
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• v.45 no.3
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• pp.242-248
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• 2007

For an optimal design of automotive electric system, it is important to have a reliable modeling tool to predict the charge-discharge behaviors of the automotive battery. In this work, a two-dimensional modeling was carried out to predict the charge-discharge behaviors of a 12-V automotive lead-acid battery. The model accounted for electrochemical kinetics and ionic mass transfer in a battery cell. In order to validate the modeling, modeling results were compared with the experimental data of the charge-discharge behaviors of a lead-acid battery. The discharge behaviors were measured with three different discharge rates of C/5, C/10, and C/20 at operating temperature of $25^{\circ}C$. The batteries were charged with constant current of 30A until the charging voltage reached to a predetermined value of 14.24 V and then the charging voltage was kept constant. The discharge and charge curves from the measurements and modeling were in good agreement. Based on the modeling, the distributions of the electrical potentials of the solid and solution phases, the porosity of the electrodes, and the current density within the electrodes as well as the acid concentration can be predicted as a function of charge and discharge time.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.3
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• pp.81-88
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• 2019

In this study, the effects of graphene oxide (GO) addition on electromigration (EM) lifetime of Sn-3.0Ag-0.5Cu Pb-free solder joint between a ball grid array (BGA) package and printed circuit board (PCB) were investigated. After as-bonded, $(Cu,Ni)_6Sn_5$ intermetallic compound (IMC) was formed at the interface of package side finished with electroplated Ni/Au, while $Cu_6Sn_5$ IMC was formed at the interface of OSP-treated PCB side. Mean time to failure of solder joint without GO solder joint under $130^{\circ}C$ with a current density of $1.0{\times}10^3A/cm^2$ was 189.9 hrs and that with GO was 367.1 hrs. EM open failure was occurred at the interface of PCB side with smaller pad diameter than that of package side due to Cu consumption by electrons flow. Meanwhile, we observed that the added GO was distributed at the interface between $Cu_6Sn_5$ IMC and solder. Therefore, we assumed that EM reliability of solder joint with GO was superior to that of without GO by suppressing the Cu diffusion at current crowding regions.

• Applied Chemistry for Engineering
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• v.9 no.4
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• pp.536-541
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• 1998

The porous size alumina membrane was prepared by anodic oxidation with current method in an aqueous solution of oxalic acid. The aluminum metal plate was pretreated with thermal oxidation, chemical polishing and electropolishing before anodic oxidation. Membrane thickness and pore size distribution were investigated with several anodizing conditions; reaction temperature, cumulative charge, electrolyte concentration and current density. The porous alumina membrane obtained was $55{\sim}75{\mu}m$ thick with straight micropore of 45~100nm. Also, the porous alumina membrane has an uniform pore diameter and pore distribution. It was inorganic ultrafiltration membrane as a kind of the ceramic membrane.

• Journal of the Korean Vacuum Society
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• v.9 no.2
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• pp.136-143
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• 2000

$SrBi_2Ta_2O_9;(SBT)$ films were deposited on p-type Si(100) at room temperature by rf magnetron sputtering method to confirm the possibility of application of $Pt/SBT/Pt/Ti/SiO_2/Si$ structure (MFM) for destructive read out ferroelectric RAM (random access memory). Their structural characteristics with the various annealing times and Ar/$O_2$ gas flow ratios in sputtering were observed by XRD (X-ray diffractometer) and the surface morphologies were observed by FE-SEM (field emission scanning electron microscopy), and their electrical properties were observed by P-V (polarization-voltage measurement) and I-V (current-voltage measurement). The Ar/$O_2$ gas flow ratios of sputtering gas were changed from 1 : 4 to 4 : 1 and SBT thin films were deposited at room temperature. The films show (105), (110) peaks of SBT by XRD measurement. SBT thin films deposited at room temperature were crystallized by furnace annealing at 80$0^{\circ}C$ in oxygen atmosphere during either one hour or two hours. Among their electrical properties, P-V curves showed shaped hysteresis curves, but the SBT thin films showed the asymmetric ferroelectric properties in P-V curves. When Ar/$O_2$ gas flow ratios are 1 : 1, 2: 1, the leakage current density values of SBT thin films are good, those values of 3 V, 5 V, and 7 V are respectively $3.11\times10^{-8} \textrm{A/cm}^2$, $5\times10^{-8}\textrm{A/cm}^2$, $7\times10^{-8}\textrm{A/cm}^2$.After two hours of annealing time, their electrical properties and crystallization are improved.

• Journal of the Korean Electrochemical Society
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• v.5 no.3
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• pp.125-130
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• 2002

An attempt was made for the application of porous reticular metal to a heat dissipation material in semiconductor process. For this aim, the electrodeposition of Fe/Ni alloy on the porous reticular Cu has been performed to minimize the thermal expansion mismatch between Cu skeleton and electronic chip. Preliminary tests for the electrodeposition of Fe/Ni alloy layer were conducted by using standard Hull Cell to examine the effect of current density on the composition of alloy layer. It seemed that mass transfer affected significantly the composition of Fe/Ni layer due to anomalous codeposition in the electrodeposition of Fe/Ni alloy. A paddle type stirring bath, which was employed to control the mass transfer of electrolyte in the work, was found to allow the electrodeposition Fe/Ni with a precise composition. result showed that the thermal expansion of Fe/Ni alloy layer was much lower than that of pure copper. From the tests of heat dissipation by using the apparatus designed in the work the heat dissipation material fabricated in the work showed the excellent heat dissipation capacity, namely, more than two times as compared to that of pure copper plate.