• Journal of the Korean Applied Science and Technology
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• v.34 no.2
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• pp.349-356
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• 2017

OH radical generation is one of the common method to evaluate photocatalytic activity. In many of previous studies, only the UV(Ultraviolet) light was applied to test photocatalytic ability of $TiO_2$ nanotubes by studying probe compound(4-Chlorobenzoic acid) concentration change in solution. Also, $TiO_2$ nanotubes were found to show some electrochemical characteristics when the flow of electric current was applied. In this study, the flow of electric current and UV light were applied at the same time to determine whether electrochemical characteristics of $TiO_2$ nanotube plate can give synergetic effect on the photocatalytic activity. $TiO_2$ nanotube was grown on Ti by anodic oxidation to create $TiO_2$ nanotube plate which can be used as a photocatalyst and a electrode that can undergo AOP(Advanced Oxidation Process) for water treatment. Probe compound solution was prepared using 4-chlorobenzoic acid and $H_2O$ as a solvent. NaCl was added to give conductivity to work as electrolyte. As a result, enough level of electric current flow was found to give synergetic photocatalytic effect which can be used for efficient AOP water treatment method.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.785-793
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• 2007

An electrochemical transient response technique was used to study the corrosion of reinforcing steel bar in the concrete. Analysis of the transient electrochemical potential response in a corrosion interface to an applied current has enabled the separate components that make up the measured transient response to be isolated. These components display a range of resistances and capacitances, dependent on the corrosion conditions of the reinforcing steel, which may be attributed to the corrosion process, to effects within the concrete cover or to film effects on the surface of the concrete. In this technique, the corrosion rate was evaluated by summing all of the resistances in the separate components to obtain an aggregated corrosion resistance. However, it is possible that not all resistances identified are associated with the corrosion process. The results obtained show that the corrosion rates are significant dependent on the assignment of the separate components to either corrosion or to other processes. The assignment of resistive components associated with the corrosion rate can be clearly identified by taking a series of the transient measurement at different lateral distances from the corroding reinforcing steel. An inappropriate selection of measurement time however may result in an additional resistance, which is not associated with corrosion, being included or part of the resistance associated with corrosion being left out.

• Journal of Electrochemical Science and Technology
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• v.11 no.2
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• pp.172-179
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• 2020

The impact of effective parameters on the electrodeposition rate optimization of Au-Cu alloy at high thicknesses on the silver substrate was investigated in the present study. After ensuring the formation of gold alloy deposits with the desired and standard percentage of gold with the cartage of 18K and other standard karats that should be observed in the manufacturing of the gold and jewelry artifacts, comparing the rate of gold-copper deposition by direct and pulsed current was done. The rate of deposition with pulse current was significantly higher than direct current. In this process, the duty cycle parameter was effectively optimized by the "one factor at a time" method to achieve maximum deposition rate. Particular parameters in this work were direct and pulse current densities, bath temperature, concentration of gold and cyanide ions in electrolyte, pH, agitation and wetting agent additive. Scanning electron microscopy (SEM) and surface chemical analysis system (EDS) were used to study the effect of deposition on the cross-sections of the formed layers. The results revealed that the Au-Cu alloy layer formed with concentrations of 6gr·L^-1 Au, 55gr·L^-1 Cu, 24 gr·L^-1 KCN and 1 ml·L^-1 Lauryl dimethyl amine oxide (LDAO) in the 0.6 mA·cm^-2 average current density and 30% duty cycle, had 0.841 ㎛·min^-1 Which was the highest deposition rate. The use of electrodeposition of pure and alloy gold thick layers as a production method can reduce the use of gold metal in the production of hallow gold artifacts, create sophisticated and unique models, and diversify production by maintaining standard karats, hardness, thickness and mechanical strength. This will not only make the process economical, it will also provide significant added value to the gold artifacts. By pulsating of currents and increasing the duty cycle means reducing the pulse off-time, and if the pulse off-time becomes too short, the electric double layer would not have sufficient growth time, and its thickness decreases. These results show the effect of pulsed current on increasing the electrodeposition rate of Au-Cu alloy confirming the previous studies on the effect of pulsed current on increasing the deposition rate of Au-Cu alloy.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.3
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• pp.238-244
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• 2017

Plasma ion nitriding has been widely used in various industries to improve the mechanical properties of materials, especially stainless steels by increasing the surface hardness. It has the particular advantages of less distortion compared to that in the case of hardening of steel, gas nitriding, and carburizing; in addition, it allows treatment at low-temperatures, and results in a high surface hardness and improved corrosion resistance. Many researchers have demonstrated that the plasma ion nitriding process should be carried out at temperatures of below $450^{\circ}C$ to improve corrosion resistance via the formation of the expanded austenite phase(S-phase). Most experimentals studied to date have been carried out in chloride solutions like HCl or NaCl. However, the electrochemical characteristics for the chloride solutions and natural seawater differ. Hence, in this work, plasma ion nitriding of 304 stainless steels was performed at various temperatures, and the electrochemical characteristics corresponding to the different process temperatures were analyzed for the samples in natural seawater. Finally the optimum plasma ion nitriding temperature that resulted in the highest corrosion resistance was determined.

• Applied Chemistry for Engineering
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• v.21 no.5
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• pp.590-592
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• 2010

Li-Mn spinel ($LiMn_2O_4$) is prepared by a hydrothermal process with K-Birnessite ($KMnO_4{\cdot}yH_2O$) as a precursor. The K-Birnessite obtained via a hydrothermal process with potassium permanganate [$KMnO_4$] and urea [$CO(NH_2)_2$] as starting materials are converted to Li-Mn spinel nanoparticles reacting with LiOH. The molar ratio of LiOH/K-Birnessite is adjusted in order to find the effect of the ratio on the structural, morphological and electrochemical performances of the Li-Mn spinel. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and thermogravimetry (TG) are used to investigate the crystal structure and morphology of the samples. Galvanostatic charge and discharge are carried out to measure the capacity and rate capability of the Li-Mn spinel. The capacity shows a maximum value of $117\;mAhg^{-1}$ when the molar ratio of LiOH/K-Birnessite is 0.8 and decreases with the increase of the ratio. However the rate capability is improved with the increase of the ratio due to the reduction of the particle size.

• Applied Chemistry for Engineering
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• v.18 no.5
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• pp.522-526
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• 2007

Structural features and electrochemical performances of cokes pyrolized from oxidized cokes were examined, and compared with KOH-activated coke. Needle cokes ($d_{002}=3.5{\AA} $), having a graphene layer structure, were changed to a single phase of graphite oxide after oxidation treatment with an acidic solution having an $NaCLO_3$/needle coke composition ratio of above 7.5, and the inter-layer distance of the oxidized coke was expanded to $6.9{\AA} $ with increasing oxygen content. After heating at $200^{\circ}C$, the oxidized coke was pyrolized to the graphene layer structure with inter-layer distance of $3.6{\AA} $. However, the change of the inter-layer distance of the needle coke was not observed in the KOH activation process. On the other hand, an intercalation of electrolyte ions into the pyrolized coke, observed at first charge, occurred at 1.0 V, in which the value was lower than that of KOH-activation coke. The cell capacitor using pyrolized coke exhibited a lower internal resistance of $0.57{\Omega}$ in 1 kHz, and a larger capacitance per weight and volume of 30.3 F/g and 26.9 F/ml at the two-electrode system in the potential range 0~2.5 V than those of the cell capacitor using KOH-activation of coke. This better electrochemical performance may be associated with structure defects in the graphene layer derived from the process of the inter-layer expansion and shrinkage.

• Applied Chemistry for Engineering
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• v.28 no.5
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• pp.506-512
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• 2017

The transfer reaction characteristics of tetracycline (TC) across a polarized water/1,2-dichloroethane (1,2-DCE) interface was studied via controlling both pH and ionic strength of the aqueous phase in conjunction with cyclic and differential pulse voltammetries. Formal transfer potential values of differently charged TC ionic species at the water/1,2-DCE interface were measured as a function of pH values of the aqueous solution, which led to establishing an ionic partition diagram for TC. As a result, we could identify which TC ionic species are more dominant in the aqueous or organic phase. Thermodynamic properties including the formal transfer potential, partition coefficient and Gibbs transfer energy of TC ionic species at the water/1,2-DCE interface were also estimated. In order to construct an electrochemical sensor for TC, a single microhole supported water/polyvinylchloride-2-nitrophenyloctylether (PVC-NPOE) gel interface was fabricated. A well-defined voltammetric response associated with the TC ion transfer process was achieved at pH 4.0 similar to that of using the water/1,2-DCE interface. Also the measured current increased proportionally with respect to the TC concentration. A $5{\mu}M$ of TC in pH 4.0 buffer solution with a dynamic range from $5{\mu}M$ to $30{\mu}M$ TC concentration could be analyzed when using differential pulse stripping voltammetry.

• Journal of the Korean Electrochemical Society
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• v.2 no.4
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• pp.221-226
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• 1999

Two needle cokes (NC-A and NC-B) that differ in both the texture and impurity content to each other were graphitized at $2000-3000{\circ}C$, and the average particle size, size distribution and surface area were compared after milling. Their anodic properties in Li secondary batteries were also analyzed. Two materials showed a higher degree of graphitization with an increase in the preparation temperature, however, the NC-B series was less graphitized than NC-A due to the presence of impurities and less ordered mosaic texture. The mein particle size of the milled powder was proportional to the degree of graphitization, but the surface area showed the opposite trend. The highly graphitized materials yielded powders of lower uniformity in the size distribution. The discharge capacity of the resulting carbons steadily decreased in the temperature range of 1000 to $2000^{\circ}C$ due to the depletion of carbonaceous interlayers that contain crystal defects. A later increase in the discharge capacity was observed at $>2000^{\circ}C$, which arises from the formation of graphitic interlayers. The milling process gave rise to a sloping discharge curve at >1.0 V, but this was converted to a plateau at <0.25V after a repeated cycling or additional heat-treatment at $1000^{\circ}C$. The discharge at >1.0V likely comes from the disordered surface structure formed during the milling process. The evolution of a plateau at <0.25 V suggests that this disordered structure transforms to a more ordered graphitic one upon a cell cycling or heat-treatment.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.5
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• pp.564-570
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• 2007

This study investigated the treatment of liquid waste containing highly concentrated iron(III)-ethylenediaminetetraaceticacid (Fe(III)-EDTA) of 70,000 mg/L by an underwater electrical discharge process using low voltage and high current. When AC voltage is applied to the discharging electrode with the other electrode grounded, the temperature of the liquid waste around the discharging electrode rapidly increases, and at the same time, hydrogen and oxygen gases are formed at the electrode as a result of electrochemical reactions. Ultimately, gases formed by vaporization of water and electrochemical reactions cover the electrode. Since the liquid waste is electrically conductive, it elongates the ground electrode up to the border of the gas layer, where electrical discharge occurs. Without hydrogen peroxide, electrical discharge was able to remove about 50% of Fe(III)-EDTA. As the concentration of hydrogen peroxide added increased, the removal efficiency of Fe(III)-EDTA increased. When the molar ratio of hydrogen peroxide to the initial Fe(III)-EDTA was higher than 24.7, more than 80 g of Fe(III)-EDTA was removed with an energy of 1 kWh. A comparison between tungsten and steel electrodes showed that electrode material did not affect the Fe(III)-EDTA removal. In the present underwater electrical discharge process, the removal of Fe(III)-EDTA was completed within 30 min at molar ratios of hydrogen peroxide to the initial Fe(III)-EDTA higher than 24.7.

• Korean Chemical Engineering Research
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• v.60 no.2
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• pp.217-222
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• 2022

It is very important to analyze the OCV change behavior during the open circuit potential holding (OCV holding) process, which accelerates the evaluation of the electrochemical durability of the PEMFC membrane. In this study, an empirical formula using the experimental data of three MEAs with different durability was created and compared. The durability evaluation time of the reinforced membrane MEA without radical scavenger inside the membrane was 383 h, and the durability evaluation time of the reinforced membrane MEA with radical scavenger inside the membrane was 1,000 and 1,650 h, respectively. The degradation of the membrane was divided into the reversible degradation that can be recovered by activation and the irreversible degradation that is not recovered. The irreversible degradation of the membrane was indicated by an increase in hydrogen permeability, and the change in hydrogen permeability was similar to the irreversible degradation constant c of all three MEAs. The initiation of irreversible deterioration without recovery is indicated by an increase in hydrogen permeability, and the OCV is not recovered due to an increase in hydrogen permeability, so the slope of the OCV recovery line (ORL) decreases, which can be confirmed by an increase in the constant c value of the empirical formula.