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Page : 257 - 164
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- 플라즈마 전해 산화처리된 Ti-6Al-4V합금의 표면특성에 미치는 울라스토나이트 코팅효과
- Ti-6Al-4V alloys are mainly used as dental materials due to their excellent biocompatibility, corrosion resistance, and chemical stability. However, they have a low bioactivity with bioinertness in the body. Therefore, they could not directly bond with human bone. To improve their applications, their bone bonding ability and bone formation capacity should be improved. Thus, the objective of this study was to improve the bioinert surface of titanium alloy substrate to show bioactive characteristics by performing surface modification using wollastonite powder. Commercial bioactive wollastonite powder was successfully deposited onto Ti-6Al-4V alloy using a room temperature spray process. It was found that wollastonite-coated layer showed homogeneous microstructure and uniform thickness. Corrosion resistance of Ti-6Al-4V alloy was also improved by plasma electrolytic oxidation treatment. Its wettability and bioactivity were also greatly increased by wollastonite coating. Results of this study indicate that both plasma electrolytic oxidation treatment and wollastonite coating by room temperature spray process could be used to improve surface bioactivity of Ti-6Al-4V alloy substrate.
- KEYWORDs : Biocompatibility, Corrosion resistance, Wollastonite coatings, Plasma electrolytic oxidation, Room temperature spray process
- AUTHORs : 고재은 · 이종국† · 최한철†
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Page : 265 - 272
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- 원전 고온 1차수 환경에서 응력부식균열의 실시간 마이크로 스케일 관찰 방법 개발
- The aim of this study was to develop a new in-situ observation method and instrument in micro-scale to investigate the mechanism of stress corrosion cracking (SCC) initiation of Ni-base alloys in a high temperature water environment of pressurized water reactors (PWRs). A laser confocal microscope (LCM), an autoclave with diamond window view port, and a slow strain-rate tester with primary water circulation loop system were components of the instrument. Diamond window, one of the core components of the instrument, was selected based on its optical, chemical, and mechanical properties. LCM was used to observe the specimen in micro-scale, considering the experimental condition of a high-temperature primary water environment. Using in-situ method and instrument, it is possible to observe oxidation and deformation of specimen surface in micro-scale through the diamond window in a high-temperature primary water in real-time. The in-situ method and instrument developed in this work can be utilized to investigate effects of various factors on SCC initiation in a high-temperature water environment.
- KEYWORDs : Alloy 600, In-situ observation, Laser confocal microscope, Primary water environment, Stress corrosion cracking
- AUTHORs : 신정호 · 이종연 · 김성우†
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Page : 273 - 286
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- Corrosion of Steel Rebar in Concrete: A Review
- Rebar is embedded in concrete to create reinforced concrete (RC). Rebar carries most of the tensile stress and gives compressively loaded concrete fracture resistance. However, embedded steel corrosion is a significant cause of concern for RC composite structures worldwide. It is one of the biggest threats to concrete structures\' longevity. Due to environmental factors, concrete decays and reinforced concrete buildings fail. The type and surface arrangement of the rebar, the cement used in the mortar, the dosing frequency of the concrete, its penetrability, gaps and cracks, humidity, and, most importantly, pollutants and aggressive species all affect rebar corrosion. Either carbonation or chlorides typically cause steel corrosion in concrete. Carbonation occurs when carbon dioxide in the atmosphere combines with calcium within the concrete. This indicates that the pH of the medium is falling, and the steel rebar is corroding. When chlorides pass through concrete to steel, corrosion rates skyrocket. Consideration must be given to concrete moisture. Owing to its excellent resistance, dry concrete has a low steel corrosion rate, whereas extremely wet concrete has a low rate owing to delayed O 2 transfer to steel surfaces. This paper examines rebar corrosion causes and mechanisms and describes corrosion evaluation and mitigation methods.
- KEYWORDs : Reinforced concrete (RC), Steel Rebar, Carbonation Corrosion, Chloride Corrosion, Corrosion Monitoring
- AUTHORs : Akib Jabed, Md Mahamud Hasan Tusher † , Md. Shahidul Islam Shuvo, and Alisan Imam
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Page : 287 - 296
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- 리튬금속과 고체전해질의 계면 반응
- Li-ion batteries have been gaining increasing importance, driven by the growing utilization of renewable energy and the expansion of electric vehicles. To meet market demands, it is essential to ensure high energy density and battery safety. All-solid-state batteries (ASSBs) have attracted significant attention as a potential solution. Among the advantages, they operate with an ion-conductive solid electrolyte instead of a liquid electrolyte therefore significantly reducing the risk of fire. In addition, by using high-capacity alternative electrode materials, ASSBs offer a promising opportunity to enhance energy density, making them highly desirable in the automotive and secondary battery industries. In ASSBs, Li metal can be used as the anode, providing a high theoretical capacity (3860 mAh/g). However, challenges related to the high interfacial resistance between Li metal and solid electrolytes and those concerning material degradation during charge-discharge cycles need to be addressed for the successful commercialization of ASSBs. This review introduces and discusses the interfacial reactions between Li metal and solid electrolytes, along with research cases aiming to improve these interactions. Additionally, future development directions in this field are explored.
- KEYWORDs : Interfacial reaction, Li metal, Solid electrolyte, All-solid-state battery
- AUTHORs : 김재헌†
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Page : 297 - 303
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- 소성인장변형 몇 아연도금된 Fe-Mn-C계 TWIP 강의 전기화학적 수소투과거동
- This study aimed to evaluate hydrogen permeation behaviors of pre-strained twinning-induced plasticity steel with or without Zn coating using electrochemical permeation technique. In contrast to un-strained and 30% strained samples, permeation current density was measured in the 60% strained sample. Tensile prestraining at 60% involved microstructural modifications, including a high level of dislocation density and stacking fault with a semi-coherent twin boundary, which might provide a high diffusion path for hydrogen atoms. However, reproducibility of measurements of hydrogen permeation current was low due to nonuniform deformation and localized stress concentration. On the other hand, the permeation current was not measured in pre-strained TWIP steel with Zn coating. Instead, numerous blisters with some cracks were observed on the surface of the coating layer. In locally damaged Zn coating under tensile straining, hydrogen atoms could relatively easily permeate through the coating layer. However, they were trapped at the interface between the coating layer and the substrate, which might delay hydrogen penetration into the steel substrate.
- KEYWORDs : Tensile strain, TWIP steel, Hot-dip galvanizing, Hydrogen permeation
- AUTHORs : 김성진 †
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Page : 305 - 313
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- Effects of Corrosion Inhibitor on Corrosion of Al-based Alloys in Ethylene Glycol-Water Coolant Environment
- The objective of this study was to investigate the effectiveness of sodium dodecyl benzene sulfonate (SDBS) as a corrosion inhibitor on the pitting corrosion behavior of aluminum alloys used in electric vehicle battery cooling systems within a mixture of ethylene glycol and water (EG-W) coolant. Potentiodynamic polarization testing revealed unstable passive film formation on the aluminum alloys in the absence of SDBS. However, the addition of SDBS resulted in a robust passive film, enhancing the pitting corrosion resistance across all examined alloys. Pitting corrosion was predominantly observed near intermetallic compounds in the presence of Cl? ions, which was attributed to galvanic interactions. Among tested alloys, A1040 demonstrated superior resistance due to its lower areal fraction of precipitates and donor density. The incorporation of SDBS inhibitors mitigated the overall pitting corrosion process by hindering Cl? ion penetration. These findings suggest that SDBS can significantly improve pitting corrosion resistance in aluminum alloys employed in battery coolant environments.
- KEYWORDs : Battery cooling system, Aluminum alloys, Corrosion inhibitor, Intermetallic compounds, Pitting corrosion
- AUTHORs : Gwang-Soo Choi, Young-Man Kim† , and Chan-Jin Park†
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Page : 314 - 321
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- Evaluation of Inhibition Efficiency of Thymus Extract as a Corrosion Inhibitor of Aluminum Alloy 5083 in an Ethylene Glycol/NaCl Corrosive Medium
- The aim of the present study was to investigate the effect of thymus extract on corrosion inhibition of aluminum 5083 alloy in a 0.1 M NaCl medium prepared using a mixture of ethylene glycol and water using potentiodynamic and electrochemical impedance spectroscopy (EIS) techniques. The potentiodynamic electrochemical technique showed an increase in corrosion inhibition efficiency starting from 49.63% at a concentration of 0.25 g/L to 92.71% at a maximum concentration of 1.25 g/L of the extract. These results were consistent with those obtained via EIS analysis. Spectral characterization of the tested plant extract using the Fourier-transform infrared spectroscopy (FTIR) technique confirmed the presence of organic compounds having different oxygen and aromatic functionalities in the extract that could help enhance the adsorption of these compounds on the aluminum surface. This study reveals possible adsorption isotherm of the thymus extract on the aluminum surface, supporting a Langmuir isotherm for the adsorption of inhibitor molecules on this surface.
- KEYWORDs : Thymus extract, Inhibition efficiency, Aluminum alloy, Ethylene glycol, Electrochemical impedance
- AUTHORs : H. Hachelef, R. Mehdaoui, K. Hachama, M. Amara, A. Khelifa, A. Benmoussat, M. Hadj Meliani†, and Rami K. Suleiman†
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Page : 322 - 329
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- Galvanic Corrosion Between Component Parts of Aluminum Alloys for Heat Exchanger of Automobile
- There are a variety of heat exchangers used in automobiles, such as shell and tube heat exchangers, double tube heat exchangers, and plate heat exchangers. Most of them are water-cooled to prevent engine overheating. There have been reports of corrosion damage to these heat exchangers due to continuous wetting caused by external temperature differences, road pollutants, and snow removal. In addition, galvanic corrosion, which occurs when two dissimilar materials come into contact, has been identified as a major cause. In this study, corrosion characteristics and galvanic corrosion behavior of Al alloy (AA3003, AA4045 and AA7072) used in automobile heat exchangers were analyzed. Effective clad materials for heat exchanger tubes and fins were also evaluated. It was found that AA7072 should be applied as the cladding material for fin AA3003 and that AA4045 was suitable as a cladding material for tube AA3003 because this clad materials application was the most effective clad design to delay the occurrence of pinhole in the tube. Main factors influencing galvanic corrosion dissolution were found to be galvanic corrosion potential difference and galvanic corrosion current density.
- KEYWORDs : Heat exchanger, Aluminum alloys, Galvanic corrosion, Clad materials, Sacrificial anode
- AUTHORs : Y. R. Yoo, D. H. Kim, G. B. Kim, S. Y. Won, S. H. Choi, and Y. S. Kim†
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Page : 330 - 340
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- Relationship Between Properties Degradation and Critical Aging Time of Super Austenitic and Duplex Stainless Steels
- The objective of this study was to analyze effects of aging time on property degradation of super austenitic stainless steel of PRE 52.8 and super duplex stainless steel of PRE 48.7. To analyze corrosion properties based on aging time, a critical pitting temperature test was performed in a solution of 6% FeCl 3 + 1% HCl
and an anodic polarization test was performed in deaerated 0.5N HCl + 1N NaCl solution at a temperature of 50 o C. Surface hardness was measured to analyze mechanical properties. It was found that corrosion properties and mechanical properties deteriorated rapidly as aging time increased. Critical pitting temperature had the most effect on critical aging time at which property changes occurred rapidly, followed by pitting potential and hardness. This trend was found to be closely related to the fraction of sigma phase. Rate of sigma phase formation was found to be significantly faster in duplex stainless steel than in austenitic stainless steel. - KEYWORDs : Critical aging time, CPT, Pitting potential, Hardness, Sigma fraction
- AUTHORs : S. H. Choi, Y. R. Yoo†, S. Y. Won, G. B. Kim, and Y. S. Kim†
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Page : 341 - 350
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- Zn-Flash 코팅 처리가 전기아연도금 시 초고강도 강재의 수소 발생, 유입 및 취화 거동에 미치는 영향
- In the present study, effects of a thin Zn-flash coating on hydrogen evolution, infusion, and embrittlement of advanced high strength steel during electro-galvanizing were examined. The electrochemical permeation technique in conjunction with impedance spectroscopy was employed under applied cathodic polarization. Moreover, a slow-strain rate test was conducted to evaluate loss of elongation (i.e., indicative of hydrogen embrittlement (HE)) and examine fracture surfaces. Results showed that the presence of a thin Zn-flash coating, even when it was not distributed uniformly, reduced hydrogen evolution rate and substantially impeded infusion of hydrogen into the steel substrate. This was primarily due to a hydrogen overvoltage on Zn coating and trapping of hydrogen at the interface of Zn coating/flash coating/steel substrate. Consequently, the sample with flash coating had a smaller HE index than the sample without flash coating. These results suggest that a thin Zn-flash coating could be an effective technical strategy for mitigating HE in advanced high-strength steels.
- KEYWORDs : Advanced high strength steel, Zn-flash coating, Electro-galvanizing, Hydrogen evolution, Hydrogen embrittlement
- AUTHORs : 방혜린 · 김상헌 · 김성진†
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