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Page : 435 - 446
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- 화력발전소용 슈퍼 듀플렉스 스테인리스 강(STS 329J4L) 조관 튜브및 핀-튜브재의 부식거동
- Corrosion behaviors of laser-welded super duplex stainless steel (SDSS) tubes after exposure to an actual power plant environment for one year and those of fin-tube welded SDSS were evaluated. Results showed that corrosion damage on the back side of the SDSS tube in the direction of hot air was higher than that on the front side regardless of weldment location. However, corrosion damage showed no difference between weldment and base metal due to recovery of phase fraction in the weldment through post weld heat treatment (PWHT). Nevertheless, the SDSS tube showed severe corrosion damage along grain boundary due to surface phase transformation (δ → γ) and Cr 2 N precipitation caused by PWHT with a high N 2 atmosphere. Corrosion resistance of the SDSS tube was recovered when degraded surface was removed. Corrosion sensitivity of a fin-tube increased significantly due to pre-existing crevice, unbalanced phase fraction, and σ phase precipitation adjacent to the fusion line. Although corrosion resistance was improved by recovered phase fraction and sufficient dissolution of σ phase during PWHT, corrosion reaction was concentrated at the pre-existing crevice. These results suggest that welding conditions for fin-tube steel should be optimized to improve corrosion resistance by removing pre-existing crevice in the weldment.
- KEYWORDs : Super duplex stainless steel, Corrosion, Fin-tube, Heat treatment, Phase transformation
- AUTHORs : 박진성 · 김용현 · 홍승갑 · 김성진†
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Page : 447 - 456
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- 고분자전해질 연료전지용 Ti 분리판을 위한 고분자와 Ti Sol-Gel 탄소코팅의 비교 연구
- In this work, we performed a comparative study examining two coatings on Ti Gr.1 for use in fuel cell bipolar plates. The coatings consisted of carbon black as the conductor along with acrylic polymer and Ti Sol-Gel binder as the binder. Ti Sol-Gel that had precipitated as TiO2 in areas impregnated between carbon black gaps, thereby acting as a binder for carbon black and serving as a polymer coating. Neither of the coatings peeled off during the 90° bend test to check formability. The contact resistance of the TiO2 coating was found to be lower than that of the polymer binder coating. Moreover, due to coating shrinkage (denser) that occurred during the heat treatment process, the TiO2 binder coating showed almost the same level of corrosion resistance, as measured by potentiostatic and EIS tests, despite being thinner than the polymer coating. However, both the polymer binder coating and the TiO2 binder coating had many pores and irregularities internally (around 10 ~ 100 ㎚) and on the surface (0.1 ~ 2 ㎛). We considered that these pores and irregularities contributed to the lower corrosion resistance.
- KEYWORDs : Corrosion, Ti Bipolar plate, Carbon black, Contact resistance, PEMFC
- AUTHORs : 양원석†, 이재호, 노희석, 유주현, 박철민, 이수연, 문성모
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Page : 457 - 465
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- 오스테나이트 스테인리스강 저속인장시험편의 최적 전해연마 특성
- Irradiation-assisted stress corrosion cracking (IASCC) is one of the main degradation mechanisms of austenitic stainless steels, which are used as reactor internal materials. Slow strain rate testing (SSRT) has been widely applied to evaluate the IASCC initiation characteristics of proton-irradiated tensile specimens. Tensile specimens require low surface roughness for micro-crack observation, and electropolishing is the most important specimen pre-treatment process used for this. In this study, optimal electropolishing conditions were examined through analyzing results of polarization experiments and surface roughness measurements after electropolishing. Corrosion cell and electropolishing equipment were fabricated for polarization tests and electropolishing experiments using SSRT specimens. The experimental parameters were electropolishing time, current density, electrolyte temperature, and stirring speed. The optimal electropolishing conditions for SSRT tensile specimens made of type 316 stainless steel were evaluated as a polishing time of 180 seconds, a current density of 0.15 A/cm 2 , an electrolyte temperature of 60 °C, and a stirring speed of 200 RPM.
- KEYWORDs : Electropolishing, Surface roughness, Austenitic stainless steel, SSRT, Polarization
- AUTHORs : 최민재 † · 조은별 · 김동진
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Page : 466 - 477
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- 전고체 리튬 이차전지용 합금계 음극 소재의 연구 동향
- The increasing demand for high-performance energy storage systems has highlighted the limitations of conventional Li-ion batteries (LIBs), particularly regarding safety and energy density. All-solid-state batteries (ASSBs) have emerged as a promising next-generation energy storage system, offering the potential to address these issues. By employing nonflammable solid electrolytes and utilizing high-capacity electrode materials, ASSBs have demonstrated improved safety and energy density. Automotive and energy storage industries, in particular, have recognized the significance of advancing ASSB technology. Although the use of Li metal as ASSB anode is promising due to its high theoretical capacity and the expectation that Li dendrites will not form in solid electrolytes, persistent problems with Li dendrite formation during cycling remain. Therefore, the exploration of novel high-performance anode materials for ASSBs is highly important. Recent research has focused extensively on alloy-based anodes for ASSBs, owing to their advantages of no dendrite formation and high-energy density. This study provides a comprehensive review of the latest advancements and challenges associated with alloy-based anodes for ASSBs.
- KEYWORDs : All-solid-state-battery, Anode materials, Alloy-based anode, Li-ion battery, Solid electrolyte
- AUTHORs : 윤정명 · 박철민†
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Page : 478 - 483
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- 전자 개폐기용 바이메탈 소재(Fe-Ni / Fe-Ni-Mo)의 부식거동
- This study examined the corrosion behavior of bimetal materials composed of Fe-Ni alloy and Fe-Ni-Mo alloy, both suitable for use in electromagnetic switches. Electrochemical polarization and weight loss measurements revealed that, in contrast to Fe-Ni alloy, which exhibited pseudo-passivity behavior, Fe-Ni-Mo alloy had higher anodic current density, displaying only active dissolution and greater weight loss. This indicated a lower corrosion resistance in the Fe-Ni-Mo alloy. Equilibrium calculations for the phase fraction of precipitates suggested that the addition of 1 wt% Mo may lead to the formation of second-phase precipitates, such as Laves and M 6 C, in the γ matrix. These precipitates might degrade the homogeneity of the passive film formed on the surface, leading to localized attacks during the corrosion process. Therefore, considering the differences in corrosion kinetics between these bimetal materials, the early degradation caused by galvanic corrosion should be prevented by designing a new alloy, optimizing heat treatment, or implementing periodic in-service maintenance.
- KEYWORDs : Bimetal, Invar, Electromagnetic switches, Molybdenum, Corrosion
- AUTHORs : 안유정 · 황은혜 · 전재열† · 김성진†
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Page : 1 - 10
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- Methods of Improving Operational Reliability of Oil Well Casing
- Oil well casing leak is caused by contact of casing outer surface with formation electrolyte. It is usually associated with an aquifer with a high salt content or absence of a cement ring behind the casing. The only way to reduce external casing corrosion is through cathodic protection. Through cathodic polarization of casing structure, electron content in crystal lattice and electron density will increase, leading to a potential shift towards the cathodic region. At Tatneft enterprises, cathodic protection is carried out according to cluster and individual schemes. The main criterion for cathodic protection is the size of protective current. For a casing, the protective current is considered sufficient if measurements with a two-contact probe show that the electric current directed to the casing has eliminated all anode sites. To determine the value of required protective current, all methods are considered in this work. In addition, an analysis of all methods used to determine the minimum protective current of the casing is provided. Results show that the method of measuring potential drop along casing is one of the most reliable methods for determining the value of protective current.
- KEYWORDs : Corrosion, Cathodic protection, External casing, Profile of the voltage drop, Distribution of currents along the depth
- AUTHORs : Sergey A. Dolgikh, Irek I. Mukhamatdinov†
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Page : 11 - 19
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- Corrosion Behavior of Fe-Ni Bainitic Steel Through an Inverted Austempering Multi-Step Process for Weathering Steel Applications
- 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 o C for 600 seconds to obtain a partly bainitic transformation. The steel was heated again for 1800 s at 450 o C. 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 ?m. 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.
- KEYWORDs : Inverted austempering multi-step process, Marine environment, Fe-Ni steel, Weathering steel
- AUTHORs : Miftakhur Rohmah†, Gusti Umindya Nur Tajalla, Gilang Ramadhan, Yunita Triana, and Efendi Mabruri
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Page : 20 - 32
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- Comprehensive Analysis of the Corrosion Inhibition Performance of 4-Piperonylideneaminoantipyrine for Mild Steel in HCl Solution: Concentration, Time, Temperature Effects, and Mechanistic Insights
- Metal corrosion in acidic environments is a major issue in various industrial applications. This study evaluates the 4-piperonylideneaminoantipyrine (PPDAA) corrosion inhibition efficiency for mild steel in a hydrochloric acid (HCl) solution. The weight loss method was used to determine the corrosion inhibition efficiency at different concentrations and immersion time periods. Results revealed that the highest inhibition efficiency (94.3%) was achieved at 5 mM concentration after 5 hours of immersion time. To inspect the surface morphology of the inhibitor film on the mild steel surface, scanning electron microscopy (SEM) was used before and after immersion in 1.0 M HCl. Density functional theory (DFT) calculations were performed to investigate the molecular structure and electronic properties of the inhibitor molecule to understand the corrosion inhibition mechanism. Theoretical results showed that the inhibitor molecule can adsorb onto the mild steel surface through its nitrogen and oxygen atoms, forming a protective layer that prevents HCl corrosive attack. These findings highlight the potential of PPDAA as an effective corrosion inhibitor for mild steel in HCl solution. Moreover, combining experimental and theoretical approaches provides insights into the mechanism of corrosion inhibition, which is essential for developing effective strategies to prevent metal corrosion in acidic environments.
- KEYWORDs : Corrosion inhibition, 4-(Piperonylideneamino)antipyrine (PPDAA), Mild steel, Hydrochloric acid (HCl), Density functional theory (DFT)
- AUTHORs : Ahmed Y. I. Rubaye, Sabah M. Beden, Ahmed A. Alamiery†, A. A. H. Kadhum, Waleed K. Al-Azzawi
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Page : 33 - 40
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- The Effect of Mo Addition on Oxygen Vacancies in the Oxide Scale of Ferritic Stainless Steel for SOFC Interconnects
- The concentration and diffusion coefficient of oxide ion vacancies in the oxide scale formed on Fe-22Cr-0.5Mn ferritic stainless steel with and without molybdenum (Mo) was measured at 800 °C by the electrochemical polarization method. After pre-oxidation for 100 h in ambient air at 800 °C, the oxide scale on one side was completely removed with sandpaper. A YSZ plate was placed on the side where the oxide scale remained. Platinum (Pt) meshes were attached on the top of the YSZ plate and the side where the oxide scale was removed. Changes in electrical current were measured after applying an electrical potential through Pt wires welded to the Pt meshes. The results were interpreted by solving the diffusion equation. The diffusion coefficient and concentration of oxide ion vacancy decreased by 30% and 70% in the specimen with Mo, respectively, compared to the specimen without Mo. The oxide ion vacancy concentration of chromia decreased due to the addition of Mo.
- KEYWORDs : Stainless steel, Solid oxide fuel cell, Interconnect, Molybdenum, Oxidation
- AUTHORs : Dae Won Yun†, Hi Won Jeong, Seong Moon Seo, Hyung Soo Lee and Young Soo Yoo
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Page : 41 - 53
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- Nano-engineering of Hybrid Titanium Oxide Structure (TiO2) using Pore-widening Concentration for Enhanced Superhydrophilicity
- Titanium alloy is gaining attention in the medical industry due to its excellent biocompatibility and osteoconductivity. However, the natural oxide film on the titanium surface is insoluble, resulting in inadequate bone adhesion. Therefore, it is necessary to optimize the contact between biological tissues and implant surfaces, and alter the chemical composition and morphological characteristics of the implant surface. In this study, the anodization method was applied to titanium surface treatment to form a uniform and robust oxide film. Subsequently, a chemical process, pore-widening, was employed to change the morphological characteristics of the oxide film. The concentration of the pore-widening solution was varied at 2, 4, 6, and 8 wt% and the process time was set at 30 and 60 minutes. As the concentration of the pore-widening solution increased the pore diameter of the oxide film increased. Notably, at 6 wt% for 60 minutes, the oxide film exhibited a coexistence of pillars and pores. Based on this, it was determined that surface roughness increased with higher concentration and longer process time. Additionally, the presence of pillars and pores structures maximized hydrophilicity. This study provides insights into enhancing the surface properties of titanium for improved performance in medical implants.
- KEYWORDs : Anodization, Pore-widening concentration, Titanium, Hybrid titanium oxide nanostructure, Superhydrophilicity
- AUTHORs : Yeji Choi and Chanyoung Jeong†
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