• Journal of the Korean institute of surface engineering
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• v.56 no.4
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• pp.250-258
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• 2023

Ceramic oxide layer was formed on the surface of high silicon aluminum alloy by using PEO (plasma electrolytic oxidation) process. The microstructure of the oxide layer was analyzed using scanning electron microscopy (SEM) and x-ray diffraction patterns (XRD). The high silicon aluminum alloy prior to PEO process consists of Al, Si and Al₂Cu phases in XRD analysis, whereas Al₂Cu phase selectively disappeared after PEO treatment. Considerable decrease of relative intensity in most of peaks in XRD results of the high silicon aluminum alloy treated by PEO process was observed. It may be attributed to the formation of amorphous phases after PEO treatment. The corrosion behavior of the high silicon aluminum alloy treated by PEO process was investigated using electrochemical impedance spectroscopy (EIS) and other electrochemical techniques (i.e., open circuit potential and polarization curve). Electroanalytical studies indicated that the high silicon aluminum alloy treated by PEO process shows greater corrosion resistance than that untreated by PEO process.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.81-82
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• 2022

Al and Zn are used to protect the steel structures from corrosion. In the present studies, 15Al-85Zn alloy wires has been used for the deposition of coating by arc thermal spray process. Moreover, this process of coating exhibited severe defects formation, therefore, this coating was post-treated with different concentrations i.e. 0.05, 0.1 and 0.5M sodium hexa meta phosphate (Na6[(PO3)6]: SHMP) to fill to defects of deposited coatings and assessed their corrosion resistance in 3.5 wt.% NaCl solution with exposure periods. After the treatment, the porosity of the coating reduced significantly by formation of composite oxide films onto the coating surface. Initially, 0.5 M SHMP treated coating exhibited highest in total impedance due to significant reduction of porosity but once the exposure periods are extended, the composite oxides are dissolved, thus, total impedance is decreased.

• Korean Journal of Materials Research
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• v.32 no.12
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• pp.533-537
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• 2022

Flexible zinc-air batteries have many merits, including low cost, high safety, environmentally friendliness applicability, etc. One of the key factors to improve the performance of flexible zinc-air batteries is to use a gel electrolyte. In this study, gel electrolytes were synthesized from potato, sweet potato, and corn starch. In a comparison of each starch, the corn starch-based gel electrolyte showed the highest discharge capacity of 12.41 mAh/cm² in 20 mA and 6.47 mAh/cm² in 30 mA. It also delivered a higher specific discharge capacity of 7.06 mAh/cm² than the other materials after 100° bending. In addition, the electrochemical impedance spectroscopy (EIS) was analyzed to calculate the ionic conductivity. The potato, sweet potato, and corn starch-based gel electrolytes showed electrolyte resistances (Re) of 0.306, 0.298, and 0.207 Ω, respectively. In addition, the corn starch-based gel electrolyte delivered the highest ionic conductivity of 0.121 S cm^-1 among the other gel electrolytes. Thus, the corn starch-based gel electrolyte was verified to improve the performance of flexible zinc-air batteries.

• Nuclear Engineering and Technology
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• v.55 no.4
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• pp.1518-1527
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• 2023

A method was proposed for in-situ evaluating the thickness and resistivity of the oxide/hydroxide film formed on the surface of aluminum alloy exposed to sump water formed in the containment after a loss-of-coolant accident. The evaluation entailed fitting a model for the film impedance, which has film thickness and other variables describing the resistivity profile of the film along its thickness direction as fitting parameters, to the practically measured electrochemical impedance data. The obtained resistivity profiles implied that the films formed at pHs_25℃ 7, 8, 9, 10, and 11 all had a duplex structure; compared to the outer layer in contact with the solution, the inner layer of the film had a much higher resistivity and was inferred to be denser and provide most of the protectiveness of the film. Both the thickness and the total resistance of the film decreased with the increasing solution pH_25℃, suggesting that the films formed in more alkaline solutions had less protectiveness against corrosion, consistent with the increasing aluminum alloy corrosion rates previously identified.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.04a
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• pp.101-102
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• 2022

A new hydrazone derivatives namely (E)-N'-(4-(dimethylamino)benzylidene)-2-(5-methoxy-2-methyl-1H-indol-3-yl)acetohydrazide (HIND) has been confirmed for mitigating the corrosion of the steel rebar exposed to chloride contaminated synthetic concrete pore solution (ClSCPS). The mitigation of corrosion properties has been characterized by weight loss and electrochemical methods (Electrochemical impedance, Potentiodynamic polarization studies) as well as surface observations. The presence of HIND in the ClSCPS decreased the corrosion of steel rebar by adsorption of HIND molecules on the surface of the steel rebar. The optimal HIND concentration was 0.5 mmol/L, corresponding to an inhibition efficiency of 88.4%. The use of HIND enables the corrosion process to have a higher energy barrier. X-ray photo electron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD) spectroscopy interpretations confirmed that HIND mitigates the corrosion attack on the surface steel rebar.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.2
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• pp.78-82
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• 2023

The oxygen evolution reaction (OER) is the primary challenge in renewable energy storage technologies, specifically electrochemical water splitting for hydrogen generation. We report effects of Mo doping into Ni layered double hydroxide (Ni-LDH) microcrystal on electrocatalytic activities. In this study, Mo doped Ni-LDH were grown on three-dimensional porous nicekl foam (NF) by a facile solvothermal method. Homogeneous LDH structure on the NF was clearly observed. However, the surface microstructure of the nickel foam began to be irregular and collapsed when Mo precursor is doped. Electrocatalytic OER properties were analyzed by Linear sweep voltammetry (LSV) and Electrochemical impedance spectroscopy (EIS). The amount of Mo doping used in the electrocatalytic reaction was found to play a crucial role in improving catalytic activity. The optimum Mo amount introduced into the Ni LDH was discussed with respect to their OER performance.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.59-60
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• 2023

The corrosion of steel rebar embedded in the coastal areas is corroding once the chloride ions ingress through the pores of the concrete. Therefore, in the present study, a 100 ㎛ thick Al and Zn coating was deposited by an arc thermal spray process onto the steel. The corrosion studies of these deposited coatings were assessed in 3.5 wt.% NaCl contaminated concrete pore (CP) solution with immersion periods. The results show that the Al coating is more corrosion resistance compared to the Zn coating attributed to the formation of gibbsite (γ-Al(OH)₃) whereas Zn coating exhibits Zn(OH)₂ onto the coating surface as passive layer. The Zn(OH)₂ is readily soluble in an alkaline solution. Alternatively, γ-Al(OH)₃ on the Al coating surface is less solubility in the alkaline pH, which further provides barrier protection against corrosion.

• Journal of the Korean Applied Science and Technology
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• v.40 no.6
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• pp.1191-1200
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• 2023

The lithium ion battery has applied to various fields of energy storage systems such as electric vehicle and potable electronic devices in terms of high energy density and long-life cycle. Despite of various research on the electrode and electrolyte materials, there is a lack of research for investigating of the binding materials to replace polymer based binder. In this study, we have investigated petroleum pitch/polymer composite with various ratios between petroleum pitch and polymer in order to optimize the electrochemical and physical performance of the lithium-ion battery based on petroleum pitch/polymer composite binder. The electrochemical and physical performances of the petroleum pitch/polymer composite binder based lithium-ion battery were evaluated by using a charge/discharge test, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and universal testing machine (UTM). As a result, the petroleum pitch(MP-50)/polymer(PVDF) composite (5:5 wt % ratio) binder based lithium-ion battery showed 1.29 gf mm^-1 of adhesion strength with 144 mAh g^-1 of specific dis-charge capacity and 93.1 % of initial coulombic efficiency(ICE) value.

• Corrosion Science and Technology
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• v.23 no.1
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• pp.11-19
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• 2024

A Fe-Ni Bainitic steel as a weathering steel application was developed by combining its excellent mechanical properties and corrosion resistance in maritime environments. Nickel concentration (0.4-3 wt%) and inverted austempering multi-step (IAM) process were primary determinants of the microstructure of the Fe-Ni Bainitic steel. The initial austempering steel was performed at 300 ℃ for 600 seconds to obtain a partly bainitic transformation. The steel was heated again for 1800 s at 450 ℃. The microstructure was comprised of ferrite, a blocky martensite/austenite island, and a homogeneous lath-shape bainite structure with widths ranging from 4.67 to 6.89 ㎛. The maximum strength, 1480 MPa, was obtained with 3 wt% nickel. In this study, corrosion behavior was investigated utilizing potentiodynamic and electrochemical impedance spectroscopy (EIS) tests. A higher nickel content in Fe-Ni Bainitic steel refined the grain size, improved the bainite fraction, lowered the corrosion rate to 0.0257 mmpy, and increased the charge transfer of film resistance to 1369 Ω.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2021-2025
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• 2007

Performance of single cell at solid oxide fuel cell (SOFC) system is largely affected by electrocatalytic and thermal properties of cathode. Samarium-based perovskite oxide material is recently recognized as promising cathode material for intermediate temperature-operating SOFC due to its high electrocatalytic property. Perovskite structured $Sm_{0.5}Sr_{0.5}CoO_{3-\delta}$ and its composite material, $Sm_{0.5}Sr_{0.5}CoO_{3-\delta}/Sm_{0.2}Ce_{0.8}O_{1.9}$ were investigated in terms of area specific resistance (ASR), thermal expansion coefficient (TEC), thermal cycling and long term performance. $Sm_{0.2}Ce_{0.8}O_{1.9}$ was used as electrolyte material. Electrochemical ac impedance spectroscopy (EIS) and dilatometer were used to measure the cathodic properties. Composite cathode ($Sm_{0.5}Sr_{0.5}CoO_{3-\delta}$: $Sm_{0.2}Ce_{0.8}O_{1.9}$ = 6:4) showed a good ASR of 0.13${\Omega}$ $cm^2$ at 650$^{\circ}C$ and its TEC value was 12.3${\times}$10-6/K at 600$^{\circ}C$ which is similar to the value of ceria-based electrolyte of 11.9${\times}$10-6/K. Performance of composite cathode was maintained with no degradation even after 13 times thermal cycle test.