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Page : 412 - 417
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- Autoxidation Core@Anti-Oxidation Shell Structure as a Catalyst Support for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cell
- Proton exchange membrane fuel cells (PEMFCs) provide zero emission power sources for electric vehicles and portable electronic devices. Although significant progresses for the widespread application of electrochemical energy technology have been achieved, some drawbacks such as catalytic activity, durability, and high cost of catalysts still remain. Pt-based catalysts are regarded as the most efficient catalysts for sluggish kinetics of oxygen reduction reaction (ORR). However, their prohibitive cost limits the commercialization of PEMFCs. Therefore, we proposed a NiCo@Au core shell structure as Pt-free ORR electrocatalyst in PEMFCs. NiCo alloy was synthesized as core to introduce ionization tendency and autoxidation reaction. Au as a shell was synthesized to prevent oxidation of core NiCo and increase catalytic activity for ORR. Herein, we report the synthesis, characterization, electrochemical properties, and PEMFCs performance of the novel NiCo@Au core-shell as a catalyst for ORR in PEMFCs application. Based on results of this study, possible mechanism for catalytic of autoxidation core@anti-oxidation shell in PEMFCs is suggested.
- KEYWORDs : Core shell structure, Autoxidation, Catalyst support, Oxygen reduction reaction, Proton exchange
- AUTHORs : Yong-Kang Heo and Seung-Hyo Lee†
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Page : 418 - 421
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- 슬러리 펌프용 고크롬 주철의 교반 가속 부식법
- Stir-accelerated corrosion test of a high chromium cast iron was attempted in 0.1 mol dm-3 H2SO4 + 0.05 mol dm-3 HCl + 10 wt% SiC solution for 48 h at room temperature or at 45 oC. The high chromium cast iron was composed of 2.8 wt% C and 27 wt% Cr and balanced with Fe. The high chromium cast iron was positioned into a 500 mL beaker with stirring of the solution at 1050 rpm using a magnetic hot plate. The corrosion rate was increased by agitating the solution. In addition, the corroded depth of the high chromium cast iron surface was increased by agitating the solution. The surface morphology of the high chromium cast iron after the stir-accelerated corrosion test revealed that a dendritic austenite phase partially remained in the corroded region after agitating the solution, indicating that solution movement during agitating could accelerate the corrosion rate of the high chromium cast iron.
- KEYWORDs : High chromium cast iron, Corrosion, Acidic solution
- AUTHORs : 이준섭† · 이준형 · 이예진 · 오준석 · 김정구 · 이재현
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Page : 423 - 433
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- Corrosion Inhibition of Carbon Steel in Sulfuric Acid Using Cymbopogon citratus as a Green Corrosion Inhibitor
- The objective of this study was to determine whether Cymbopogon citratus extract as a corrosion inhibitor from natural tropical resources could prevent corrosion of carbon steel in sulfuric acid solution. Inhibitory action of this extract was investigated using electrochemical methods such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Those methods revealed corrosion rate, efficiency of inhibition, and adsorptions isotherm values when the extract was added to the sulfuric acid solution at concentration up to 500 ppm with various immersion time at ambient temperature. Results revealed that higher concentration of the extract and longer immersion time decreased the corrosion rate of carbon steel whereas the inhibition efficiency of the extract was increased up to 97.25%. The value of charge transfer resistance was increased significantly by adding the extract at concentration up to 500 ppm with an immersion time of 60 minutes. The type of the extract was a mixed inhibitor. It could inhibit the corrosion process in both anodic and cathodic sides electrochemically. Results of this study suggest that the mechanism of adsorption on the surface of carbon steel is related to Langmuir adsorption isotherm.
- KEYWORDs : Corrosion, Carbon steel, Green corrosion inhibitor, Acid solution, Cymbopogon citratus
- AUTHORs : Gadang Priyotomo†, Tamara Emylia Suci Nurarista, Yanyan Dwiyanti, Bening Nurul Hidayah Kambuna, Arini Nikitasari, Siska Prifiharni, and Sundjono
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Page : 434 - 444
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- Effect of Zn/Al Cation Ratio on Corrosion Inhibition Capabilities of Hydrotalcites Containing Benzoate Against Carbon Steel
- Corrosion inhibitors based on Zn-Al hydrotalcites containing benzoate (ZnAlHB) with different molar ratios of Zn/Al were prepared with a co-precipitation process. Compositions and structures of the resulting hydrotalcites were studied with suitable spectroscopic methods such as inductively coupled plasma mass spectrometry (ICP-MS), ultraviolet-visible spectrophotometry (UV-Vis), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and surface zeta potential measurements, respectively. Results of physico-chemical studies showed that crystallite sizes, compositions of products, and surface electrical properties were significantly changed when the molar ratio of Zn/Al was increased. The release of benzoate from hydrotalcites also differed slightly among samples. Anticorrosion abilities of hydrotalcites intercalated with benzoate at a concentration of 3 g/L on carbon steel were analyzed using electrochemical impedance spectroscopy (EIS), polarization curve, energy-dispersive X-ray spectroscopy (EDX), and SEM. Corrosion inhibition abilities of benzoate modified hydrotalcites in 0.1 M NaCl showed an upward trend with increasing Zn/Al ratio. The reason for the dependence of corrosion resistance on the Zn/Al ratio was discussed, including changes in the microstructure of hydrotalcites such as crystal size, density, uniformity, and formation of ZnO.
- KEYWORDs : Corrosion, Hydrotalcites, Benzoate, Inhibitor
- AUTHORs : Thu Thuy Pham, Anh Son Nguyen, Thu Thuy Thai, Gia Vu Pham, Ngoc Bach Ta, Thuy Duong Nguyen†, and To Thi Xuan Hang†
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Page : 445 - 453
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- Simple Synthesis of SiOx by High-Energy Ball Milling as a Promising Anode Material for Li-Ion Batteries
- SiOx was prepared from a mixture of Si and SiO2 via high-energy ball milling as a negative electrode material for Li-ion batteries. The molar ratio of Si to SiO2 as precursors and the milling time were varied to identify the synthetic condition that could exhibit desirable anode performances. With an appropriate milling time, the material showed a unique microstructure in which amorphous Si nanoparticles were intimately embedded within the SiO2 matrix. The interface between the Si and SiO2 was composed of silicon suboxides with Si oxidation states from 0 to +4 as proven by X-ray photoelectron spectroscopy and electrochemical analysis. With the addition of a conductive carbon (Super P carbon black) as a coating material, the SiOx/C manifested superior specific capacity to a commercial SiOx/C composite without compromising its cycle-life performance. The simple mechanochemical method described in this study will shed light on cost-effective synthesis of high-capacity silicon oxides as promising anode materials.
- KEYWORDs : SiOx, High-energy ball milling, Li-ion batteries
- AUTHORs : Sung Joo Hong and Seunghoon Nam†
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Page : 454 - 465
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- Effects of pH and Chloride Concentration on Corrosion Behavior of Duplex Stainless Steel and Titanium Alloys Ti 6Al 2Nb 1Ta 1Mo at Elevated Temperature for Pump Impeller Applications
- The objective of this study was to determine effects of temperatures and pH of sodium chloride solution with MgCl2 ions on corrosion resistance of duplex stainless-steel X2CrNiMoN22-5-3 (DSS) and Ti 6Al 2Nb1Ta1Mo (Ti). Effects of sodium chloride concentration on corrosion resistance were also studied. Corrosion behavior and pitting morphology of duplex stainless steel (DSS) and Ti alloys were evaluated through potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). It was found that a decrease in pH significantly reduced the corrosion resistance of both alloys. Changes in chloride concentration and temperature had more substantial impact on corrosion behavior of DSS than on Ti alloys. Pitting corrosion was formed on DSS samples under all conditions, whereas crevice corrosion was developed on Ti samples with the presence of magnesium chloride at 90 oC. In conclusion, magnesium chloride ions in an exceedingly strong acidity solution appear to interact with re-passivation process at the surface of these alloys and influence the resulting surface topography.
- KEYWORDs : Corrosion, Duplex stainless steel, Titanium
- AUTHORs : Aymen A. Ahmed†, Ammar Yaseen Burjes, and Marwan Zuhair Elias
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Page : 466 - 475
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- 원전 1차측 수화학 환경에서 수소 농도가 Alloy 600의 표면산화 거동에 미치는 영향
- Surface oxides and intergranular (IG) oxidation phenomena in Alloy 600 depending on hydrogen concentration were characterized to obtain clear insight into the primary water stress corrosion cracking (PWSCC) behavior upon exposure to pressurized water reactor primary water. When hydrogen concentration was between 5 and 30 cm3 H2/kg H2O, NiFe2O4 and NiO type oxides were found on the surface. NiO type oxides were found inside the oxidized grain boundary when hydrogen concentration was 5 cm3 H2/kg H2O. However, only NiFe2O4 spinel on the surface and Ni enrichment were observed when hydrogen concentration was 30 cm3 H2/kg H2O. These results indicate that the oxidation/reduction reaction of Ni in Alloy 600 depending on hydrogen concentration can considerably affect surface oxidation behavior. It appears that the formation of NiO type oxides in a Ni oxidation state and Ni enrichment in a Ni reduction (or metallic) state are common in primary water. It is believed that the above different oxidation/reduction reactions of Ni in Alloy 600 depending on hydrogen concentration can also significantly affect the resistance to PWSCC of Alloy 600.
- KEYWORDs : Alloy 600, Surface oxidation, Hydrogen concentration, Primary water, TEM/EDS
- AUTHORs : 임연수† · 김동진 · 김성우 · 황성식 · 김홍표 · 조성환
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Page : 476 - 486
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- 알루미늄 6061 합금의 표면 나노 구조물 변화에 따른 방빙 특성 연구
- Recently, aluminum 6061 instead of copper alloy is used for cooling heat exchangers used in the internal combustion of engines due to its economic feasibility, lightweight, and excellent thermal conductivity. In this study, aluminum 6061 alloy was anodized with oxalic acid, phosphoric acid, or chromic acid as an anodizing electrolyte at the same concentration of 0.3 M. After the third anodization, FDTS, a material with low surface energy, was coated to compare hydrophobic properties and anti-icing characteristics. Aluminum was converted into an anodization film after anodization on the surface, which was confirmed through Energy Dispersive X-ray Spectroscopy (EDS). Pore distance, interpore distance, anodization film thickness, and solid fraction were measured with a Field Emission Scanning Electron Microscope (FESEM). For anti-icing, hydrophobic surfaces were anodized with oxalic acid, phosphoric acid, or chromic acid solution. The sample anodized in oxalic acid had the lowest solid fraction. It had the highest contact angle for water droplets and the lowest contact hysteresis angle. The anti-icing contact angle showed a tendency to decrease for specimens in all solutions.
- KEYWORDs : Aluminum oxide nanostructure, Anodization, Hydrophilic, Hydrophobic, Anti-icing
- AUTHORs : 김리안 · 정찬영†
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Page : 487 - 494
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- 알루미늄 3003 산화피막 성장 거동에 의한 표면 절연 특성 관찰
- Anodizing is a typical electrochemical surface treatment method that can improve the corrosion and insulating properties of aluminum alloys. The anodization process can obtain a dense structure. It can be used to artificially grow the thickness of an anodization film. Aluminum 3003 alloy used in this study is the most commonly used alloy for batteries due to its high strength and excellent formability as well as its weldability and corrosion resistance. Aluminum 3003 alloy was anodized at 0 oC with 0.3 M oxalic acid at 20 V, 40 V, or 60 V for 1 hour, 6 hours, or 12 hours. As a result of analyzing the composition of each specimen with an Energy Dispersive Spectrometer (EDS), aluminum was converted into an oxide film. The thickness of the formed anodization film increased when the applied voltage and anodization time increased. High corrosion potential values and low corrosion current density values were observed for the thickest oxide layer. The anodization film formed by anodization acted as a protective layer. The electrical resistance increased as the applied voltage and anodization time increased.
- KEYWORDs : Aluminum 3003 alloy, Insulation properties, Anodization processes, Corrosion resistance, Battery
- AUTHORs : 박수빈 · 정찬영†
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Page : 495 - 502
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- 알루미늄 6061 합금 양극산화 후 열처리에 따른 표면 특성 관찰
- Anodization is a representative electrochemical surface treatment method that can improve both heat resistance and corrosion resistance by forming an anodization film on the surface of the aluminum. However, these properties can be changed after an additional heat treatment process. In this study, Al 6061 was subjected to an anodization process at 60 V for 1 hour, 5 hours, or 9 hours. An additional heat treatment process was performed at 500 oC for 30 minutes. Field emission scanning electron microscopy (FE-SEM) analysis revealed that the thickness of the anodized film was increased in proportion to the anodization time. Both pore size and pore diameter of the anodized film was also increased after anodization. After an additional heat treatment process, there were no significant changes in the thickness, pore size, or pore diameter of the anodized film. Heat resistance was confirmed through thermal analysis and chemical resistance was evaluated with a potentiodynamic polarization test.
- KEYWORDs : Anodization, Aluminum 6061 alloy, Heat Treatment, Delta H, Corrosion resistance
- AUTHORs : 이승민 · 정찬영†
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