• Journal of the Korean Chemical Society
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• v.58 no.5
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• pp.437-444
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• 2014

The electrochemical corrosion and passivation of Co-RDE in borate buffer solution was studied by Potentiodynamic and electrochemical impedance spectroscopy. The mechanisms of both the active dissolution and passivation of cobalt and the hydrogen evolution in reduction reaction were hypothetically established while utilizing the Tafel slope, the rotation speed of Co-RDE, impedance data and the pH dependence of corrosion potential. Based on the EIS data, an equivalent circuit was suggested. In addition, the electrochemical parameters for specific anodic dissolution regions were carefully measured. An induction loop in Nyquist plot measured at the open-circuit potential was observed in the low frequency, and this could be attributed to the adsorption-desorption behavior in the corrosion process.

• Journal of Surface Science and Engineering
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• v.37 no.2
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• pp.110-118
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• 2004

The corrosion of pure titanium (CP- Ti Grade 2) and titanium alloy (Ti6Al4V ELI) were studied under various conditions of simulated body fluids. The static immersion test and the electrochemical test were performed in accordance with ISO 10271 : 2001. For the electrochemical test, the open circuit potential was monitored as a function of time, and the cyclic polarization curve was recorded. The corrosion resistance was evaluated from the values of corrosion potential, passivation current density, breakdown potential, and the shape of hysteresis etc. The effects of alloy type, surface condition, temperature, oxygen, and constituents in the fluids such as acid, chloride were estimated. Both specimens had extremely low dissolution rate in the static immersion test. They showed strong passivation characteristics in the electrochemical test. They maintained negligible current density throughout the wide anodic potential range. The passive layer was not broken up to 2.0 V (vs. SCE). The hysteresis and the shift of passivation potential toward the anodic direction was observed during the reversed scan. The passivation process appeared to be accelerated by oxygen in air or that dissolved in the fluids. The passivation also proceeded without oxygen by the reaction of constituents in the fluids. Acid or chloride in the fluids, specially later weakened the passive layer, and then induced higher passivation current density and less shift of passivation potential in the reversed scan. CP-Ti Grade 2 was more reactive than Ti6Al4V ELI in the fluids containing acid or chloride, but thicker layer produced on its surface provided higher corrosion resistance.

• Journal of the Korean Electrochemical Society
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• v.1 no.1
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• pp.8-13
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• 1998

This work presents the way how to evaluate the degree of reversibility of the discharging process undergone by the nickel hydroxide film cathodically deposited on pure nickel as a positive electrode for electrochemical capacitor using the combined cyclic voltammetry and potential drop method, supplemented by galvanostatic discharge and open-circuit potential transient methods. The time interval necessary just to establish the current reversal of anodic to cathodic direction from the moment just after applying the potential inversion of anodic to cathodic direction, was obtained on cyclic voltammogram. The cathodic charge density passed upon dropping the applied potential, was calculated on potentiostatic current density-time curve. Both the time interval and the cathodic charge density in magnitude can be regarded as being measures of the degree of reversibility of the discharging process undergone by the positive active material for supercapacitor, i.e. , the longer the time interval is, the lower is the degree of reversibility and the greater the cathodic charge density is, the higher is the degree of reversibility. From the applied potential dependences of the time interval and cathodic charge density, discharge at $0.42 V_{SCE}$ was determined to be the most reversible.

• Proceedings of the KIEE Conference
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• 2002.07a
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• pp.541-543
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• 2002

This paper describes the analysis resulates on the P.T ferroresonance at 154kV GIS(Gas Insulated Substation) by EMTP(Electromagnetic transient program). We had simulated the PT ferroresonance between a potential transformer(PT) and open circuit braker's grading capacitance. The ferroresonance leads to very large power frequency overvoltage on PT bus and subsequent insulation failure. The damping circuit connected on the secondary winding were considered in the model. The actual countermeasure include a saturable inductor and a resistor series mounted, but the 2 ohms of damping resistance was used in the computational model.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.727-728
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• 2008

This paper deals with characteristic analysis of permanent magnet synchronous motor with full-ring magnet. The modeling of magnetic circuit is performed analytically. And then, analytical solution for open-circuit field distribution due to permanent magnet, back-EMF and torque are derived in terms of magnetic vector potential and two-dimensional polar coordinate system. The analytical results are validated extensively by finite element analyses. Finally, we performed experiments of permanent magnet synchronous motor with full-ring magnet.

• Journal of the Korea Institute of Building Construction
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• v.19 no.6
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• pp.511-520
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• 2019

The critical chloride content of rebar embedded in concrete was experimentally evaluated according to the admixture replacement ratio and admixture type. Four types of reinforced concrete were mixed OPC 100%, OPC 70% + GGBFS 30%, OPC 40% + GGBFS 60%, and OPC 40% + GGBFS 40% + FA 20%. NaCl solution was supplied to the specimens, and the open circuit potential of the embedded rebar was monitored. The specimens determined to initiate corrosion were cut at intervals of 5mm from the NaCl solution supply surface and conducted to chlorine ion profile. Corrosion initiation time of rebar embedded in concrete was delayed as the admixture replacement ratio increased. Looking at the critical chloride content of the types of reinforced concrete, it was highest in OPC 1.46kg/㎥, followed in order by S30 0.98kg/㎥, TBC 0.74kg/㎥, and S60 0.71kg/㎥.

• Journal of Electrochemical Science and Technology
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• v.14 no.4
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• pp.311-319
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• 2023

This work was performed to characterize the electrochemical behavior of AZ31 Mg alloy in neutral aqueous solutions where Cl^-, SO₄^2-, PO₄^3-, and F^- ions were present and pH was adjusted to 6 to exclude the contribution of H⁺ and OH^- ions. Open-circuit potential (OCP) transient, electrochemical impedance spectroscopy (EIS) and potnetiodynamic polarization curves were employed. The OCP value appeared to decrease in the order of F^- > Cl^- > SO₄^2- > PO₄^3- ions while corrosion current density increased in the same order. Electrochemical impedance spectroscopy (EIS) data showed two capacitive arcs in all the solutions and one more inductive arc appeared in PO₄^3--containing solution. By fitting of two capacitive arcs, capacitance of dense film (C_df), resistance of porous film (R_pf) and double layer capacitance (C_dl) and charge transfer resistance (R_ct) beneath the porous films were obtained. A simplified model in which various thicknesses and coverages of dense and porous films are assumed to be present on the AZ31 Mg alloy surface, is suggested to explain the effects of four different anions on the electrochemical behavior of AZ31 Mg alloy.

• Bulletin of the Korean Chemical Society
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• v.18 no.4
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• pp.385-389
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• 1997

We report on the development of a new method to control the coverage of a metal film prepared with immersion method. An Sb species in solution adsorbed irreversibly at an open circuit potential (∼0.2 V) as an oxygenous Sb(Ⅲ) on a clean Au electrode, and the adsorbates showed voltammetric features in the potential range from 0.1 V to - 0.4 V. The full coverage of the Sb adsorbates was ∼0.45. On the contrary, the Sb species in solution did not adsorb at all on iodine-covered Au electrode surfaces, when the iodine coverages were more than 0.25. As the iodine coverage decreased below 0.25, however, the irreversible adsorption of Sb took place and the coverage of Sb increased accordingly. This electrochemical behavior has been interpreted as the penetration of the adsorbing Sb species in solution through open spaces among the iodine adlattices of coverages less than 0.25. With the manipulation of the iodine coverage, the controllable range of Sb coverage was from 0 to 0.45, i.e. the full coverage of Sb. In addition, the reversible deposition of Sb on an iodine-saturated Au electrode with voltammetric scan has been observed, which is contrasted with the adsorptive behavior of Sb on the clean Au electrode.

• Korean Journal of Materials Research
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• v.33 no.6
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• pp.236-241
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• 2023

Solar cells based on p-conjugated donor-acceptor (D-A) organic molecular systems are a promising alternative to conventional electrical energy generation. D-A molecular systems, which have a triphenylamine (TPA) moiety linked with a benzothiadiazole (BTD) moiety, open the potential development of new small molecule donors for bulk heterojunction (BHJ) solar cells. Here, a series of donor-acceptor-π-acceptor (D-A-π-A) small molecule donors (SMD) derived from triphenylamine (TPA) donor and benzothiadiazole (BTD) acceptor building blocks, were designed for BHJ organic solar cells. The small molecule donors SMD1-4 were studied using density functional theory (DFT) and time dependent-DFT (TDDFT) methods, to understand the effect of cyano and fluorine group functionalization on their properties. The effect of structure alteration by cyano and fluorine group functionalization on the optoelectronic properties, the calculated highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) and the HOMO-LUMO gaps were theoretically explored. The V_oc (open-circuit photovoltage) and fill factor (FF) for SMD1-4 were obtained with a PC₇₁BM acceptor, which showed that these organic small molecules are potential small molecule donors for organic bulk heterojunction solar cells.

• Tribology and Lubricants
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• v.18 no.4
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• pp.299-304
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• 2002

This paper reports the studies on the wear-corrosion behavior of ductile cast iron in the acidic environment. In atmosphere and variety of pH solution, specific wear rate and wear-corrosion characteristics of GCD 60 with various sliding speed and distance were investigated. And electrochemical polarization test of GCD 60 was examined in the environment of various pH values. The main results are as following : As the contact pressure increases, the critical velocity of specific wear rate becomes transient at low sliding speed. As pH value becomes low, wear-corrosion loss increases in the aqueous solution. As the corrosion environment is acidified, corrosion potential of GCD 60 becomes noble and corrosion current density increases.