• Tribology and Lubricants
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• v.38 no.6
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• pp.255-260
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• 2022

This research presents tetrahedral amorphous (ta-C) coating on the artificial tooth for improving the durability and functionality (esthtics, foreign body of tooth) by filtered cathodic vacuum arc (FCVA). A differentiated coating method is required for a ta-C coating on polymer owing to the low melting point of the polymer, inter-facial adhesion, low friction, and non-conductivity. Herein, ta-C coating is applied below 50℃, and the potential difference of the carbon plasma drawn to the substrate was controlled by applying a positive duct bias voltage without using a substrate bias voltage. Consequently, the ta-C coating with a thickness of 70nm using the duct bias condition of 20V with the highest plasma intensity satisfies the esthetics of the artificial tooth and had a 5B level of inter-facial adhesion. In addition, the composite hardness of ta-C/polymer is 380 MPa, and correlations with esthetics, sp³ bonding, and mechanical properties. The friction coefficient (CoF) of the ta-C coating in a water-lubricated environment is 0.07, showing a six-fold reduction in CoF compared with that of a polymer.

• Journal of Electrochemical Science and Technology
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• v.13 no.2
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• pp.213-226
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• 2022

In the present study, the corrosion behavior of aluminum Al-7075 tempered (T-6 condition) alloy was evaluated by immersion testing and electrochemical testing in 1.75% and 3.5% NaCl environment at acidic, neutral and basic pH. The data obtained by both immersion tests and electrochemical corrosion tests (potentiodynamic polarization and electrochemical impedance spectroscopy tests) present that the corrosion rate of the alloy specimens is minimum for the pH=7 condition of the solution due to the formation of dense and well adherent thin protective oxide layer. Whereas the solutions with acidic and alkaline pH cause shift in the corrosion behavior of aluminum alloy to more active domains aggravated by the constant flux of acidic and alkaline ions (Cl^- and OH^-) in the media which anodically dissolve the Al matrix in comparison to precipitated intermetallic phases (cathodic in nature) formed due to T6 treatment. Consequently, the pitting behavior of the alloy, as observed by cyclic polarization tests, shifts to more active regions when pH of the solutions changes from neutral to alkaline environment due to localized dissolution of the matrix in alkaline environment that ingress by diffusion through the pores in the oxide film. Microscopic analysis also strengthens the results obtained by immersion corrosion testing and electrochemical corrosion testing as the study examines the corrosion behavior of this alloy under a systematic evaluation in marine environment.

• Corrosion Science and Technology
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• v.22 no.2
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• pp.123-130
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• 2023

This study aimed to evaluate corrosion resistance of steel coated with GI and Zn-Al-Mg alloy using cyclic corrosion test (CCT) with electrochemical polarization and impedance measurements. Results showed that the Zn-Al-Mg alloy coated steel had a much higher corrosion rate than GI coated steel in early stages of corrosion. With prolonged immersion, however, the corrosion rate of the Zn-Al-Mg alloy coated steel greatly decreased, mainly owing to a significant decrease in the cathodic reduction reaction and an increase in polarization resistance at the surface. This was closely associated with the formation of protective corrosion products including Zn₅(OH)₈Cl₂·H₂O and Zn₆Al₂(OH)₁₆CO₃. Moreover, when the steel substrate was locally exposed due to mechanical damage, the kinetics of anodic dissolution from the coating layer and the formation of protective corrosion products on the surface of the Zn-Al-Mg alloy coated steel became much faster compared to the case of GI coated steel. This could provide a longer-lasting corrosion inhibition function for Zn-Al-Mg alloy coated steel used in plant farms.

• Journal of Electrochemical Science and Technology
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• v.15 no.1
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• pp.198-206
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• 2024

Given the high theoretical capacity (1,675 mAh g^-1) and the inherent affordability and ubiquity of elemental sulfur, it stands out as a prominent cathode material for advanced lithium metal batteries. Traditionally, sulfur was sequestered within conductive porous carbons, rooted in the understanding that their inherent conductivity could offset sulfur's non-conductive nature. This study, however, pivots toward a transformative approach by utilizing diatom shell (DS, diatomite)-a naturally abundant and economically viable siliceous mineral-as a sulfur host. This approach enabled the development of a sulfurlayered diatomite/S composite (DS/S) for cathodic applications. Even in the face of the insulating nature of both diatomite and sulfur, the DS/S composite displayed vigorous participation in the electrochemical conversion process. Furthermore, this composite substantially curbed the loss of soluble polysulfides and minimized structural wear during cycling. As a testament to its efficacy, our Li-S battery, integrating this composite, exhibited an excellent cycling performance: a specific capacity of 732 mAh g^-1 after 100 cycles and a robust 77% capacity retention. These findings challenge the erstwhile conviction of requiring a conductive host for sulfur. Owing to diatomite's hierarchical porous architecture, eco-friendliness, and accessibility, the DS/S electrode boasts optimal sulfur utilization, elevated specific capacity, enhanced rate capabilities at intensified C rates, and steadfast cycling stability that underscore its vast commercial promise.

• Journal of Electrochemical Science and Technology
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• v.15 no.3
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• pp.405-413
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• 2024

Several techniques for determining the reverse peak current from a cyclic voltammogram (CV) for a reversible system are described in the literature: CV itself as a baseline with long switching potential (E_λ) that serves as a baseline for other CVs, Nicholson equation that uses CV parameters to calculation reverse peak current and linear extrapolation of the current obtained at the switching potential. All methods either present experimental difficulties or large errors in the peak current determination. The paper demonstrates, both theoretically and experimentally, that trapezoidal cyclic voltammetry (TCV) can be used as a baseline to determine anodic peak current (i_ap) with high accuracy and with a switching potential shorter than that used by CV, as long as E_λ is at least 130 mV away from the cathodic peak. Beyond this value of switching potential the electroactive specie is completely depleted from the electrode surface. Using TCV with E_λ = 0.34 V and a switching time (t_λ) of 240 s as a baseline, the determination of the reverse peak current presents a deviation from the expected value of less than 1% for most of the CVs studied (except cases when E_λ is close to the direct potential peak). This result presents better accuracy than the Nicholson equation and the linear extrapolation of the current measured at the switching potential, in addition to presenting a smaller error than that obtained in the acquisition of the experimental current. Furthermore, determining the reverse peak current by extrapolating the linear fit of i_ap vs. ${\sqrt[1/]{t_{\lambda}}}$ to infinite time gave a reasonable approximation to the expected value. Experiments with aqueous potassium hexacyanoferrate (II) and ferrocene in acetonitrile confirmed the theoretical predictions.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.10
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• pp.591-598
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• 2017

Power overshoot phenomenon was observed in microbial fuel cells (MFCs) used non-catalyzed graphite felt as cathode. Voltage loss in MFCs was mainly caused by cathode potential loss. Cheap stainless steel scrubber, which has high conductivity, and Pt/C coated graphite felt as cathode were used for overcoming power overshoot and reducing the cathode potential loss in MFCs. The MFCs used stainless steel scrubber showed no power overshoot even slow catholyte flow rate and produced 29% enhanced maximum current density ($23.9A/m^3$) than MFCs used non-catalyzed graphite felt while the power overshoot phenomenon was existed in Pt/C coated MFCs. Increasing catholyte flow rate resulted in disappearing power overshoot of MFCs used non-catalyzed graphite felt. In addition, maximum power density and current density of both MFCs used non-catalyzed graphite felt and stainless steel scrubber increased by 2-3.5 times. Cathode potential losses in all region of activation loss, ohmic loss, and mass transport loss were reduced according to increase of catholyte flow rate. Therefore, stainless steel scrubber has advantages that are economical materials as electrode and prevents power overshoot, leading to enhance electricity generation. In addition, increasing catholyte flux is one of great solution when power overshoot caused by cathodic overpotential is observed in MFCs.

• Korean Journal of Materials Research
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• v.7 no.2
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• pp.114-120
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• 1997

Perovskite $BaTiO_3$ thin films on stainless steel substrate were prepared by using electrochemical reduction method in solution of $TiCl_4\;and\;Ba(N0_3)_2$. According to current density and electrolysis time. the morphology and thickness of film were varied. Ra/'Ti atomic ratio in $BaTiO_3$ film was controlled by Ha/Ti atomic ratio in solution. Although the excess $TiO_2{\cdot}nH_2O$ film was coated in initial stage of electrolysis. UiilTi atomic ratio in film was nearly constant in later stage. $BaTiO_3$ film precursor was obtained under the condition of $1OmA/cm^2$ current density and Smin electrolysis time. $BaTiO_2$ thin films with perovskite phase were formed 11,. the heat treatment above $500^{\circ}$.

• Journal of the Korean Chemical Society
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• v.37 no.5
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• pp.483-490
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• 1993

Voltammetric behavior of heavy lanthanide ions has been investigated by the DC, DPP and CV in acetonitrile solution. The reduction of $Gd^{3+}, Tb^{3+}, Dy^{3+}, Ho^{3+}, Er^{3+}, Tm^{3+} 및 Lu^{3+} proceed by three-electron change to the metallic state with totally irreversibility in 0.1M tetraethylammonium perchlorate. However, the reduction of Yb(Ⅲ) proceeds in two steps $(Yb^{3+} ＋ e^- \Leftrightarrow Yb^{2+} and Yb^{2+} ＋ 2e^- → Yb^0)$. The first reduction of Yb(Ⅲ) showed quasi reversible behavior, but the second reduction was irreversible in cyclic voltammetry. The cathodic peak current showed adsorptive properties in high concentration with lower sweep rate. The electroreduction of heavy lanthanides in water-acetonitrile mixture has been studied. In water-acetonitrile mixture, the negative shift of the peak potential and the decrease peak current were observed increasing water concentration. Also the Yb(Ⅲ) reduction to Yb(Ⅲ) has been deviated from quasi-reversible character with increase water amount. These results drive from the high solvation abilities of water which has high donor number.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.6
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• pp.569-576
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• 2012

In general, aluminum alloys forms the passive film($Al_2O_3$, $Al_2O_3{\cdot}3H_2O$) in neutral solution. However, the passive film created on the surface will be destroyed by chloride ions contained in sea water so the corrosion will occur. In this study, in order to solve the problem of corrosion under a seawater environment, potentiostatic protection techniques were applied to Al-4.5%Mg-0.6%Mn aluminum alloy in seawater. At polarization experiments, active state were observed at anodic polarization and concentration polarization by reduction of dissolves oxygen and activation polarization were found at anodic polarization. As a results of potentiostatic experiment, calcareous deposit were created much more as applying time increase from the turning point of the concentration polarization and activation polarization and crevice corrosion was partially observed between calcareous deposit and surface of base metal. Overall potentiostatic anodic polarization experiment was difficult to apply potentiostatic corrosion protection technology by occurrence of active state, whereas potentiostatic cathodic polarization experiment examined optimum corrosion protection condition of -1.1 V~-0.75 V within the range of concentration polarization considered various applying time.

• Journal of the Korean Institute of Gas
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• v.20 no.5
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• pp.64-71
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• 2016

According to the urban gas business law, electrical corrosion prevention measures shall be installed to the buried gas pipelines and the pipe-to-soil potentials should be measured at the test box at least once a year. Most of the test boxes installed in urban area are usually located on the road where the vehicle travels, therefore, it is difficult to measure the CP potentials at the test boxes. That is, we need traffic control when carrying out the measurement of the CP potentials on daytime when the traffic is heavy, or we have to measure the potentials in the late night when the traffic is light. To solve these difficulties, we have studied remotely CP potential measuring method by using the patrol car. We have installed solid reference electrodes and data loggers under the test boxes on the site and received the CP potentials from the data loggers when the vehicle moves. It was difficult to send and receive the data because the data logger was located under the ground. We have applied 3 different method including 2 antenna systems to achieve best effective way in receiving the data. We have found the remote CP measuring method by using a car can save more 20 times of measuring time than conventional measuring methods.