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Page : 351 - 358
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- 발전소 공기예열기 소재의 배기가스 농도 및 온도에 따른 내식성 및 노점 분석
- Although many thermal power plants use heat recovery systems, high exhaust gas temperatures are maintained due to corrosion at dew points and ash deposits caused by condensate formation. The dew point of exhaust gas is primarily determined by the concentration of SO 3 and steam, and various experiments and cal-culation equations have been employed to estimate it. However, these methods are known to be less suitable for exhaust gases with low SO 3 concentrations. Therefore, in this study, since the temperature of the exhaust gas is expected to decrease due to the low-load operation of the coal-fired power plant, sulfuric acid condensation and low-temperature corrosion are anticipated. We aimed to conduct a quantitative evaluation to propose ways to prevent damage by limiting operating conditions and improving facilities. The experimental results showed that the corrosion rate increased linearly with rising temperatures at a certain sulfuric acid concentration. Furthermore, variations in sulfuric acid concentrations generated during the current power plant operation process did not significantly affect the dew point, and the dew point of sulfuric acid under these conditions was observed to be between 120 - 130o C.
- KEYWORDs : Corrosion, Dew point, SO 2 , Air preheater, S-Ten2
- AUTHORs : 이승준†
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Page : 359 - 367
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- Inconel 718의 국부 부식 저항성에 미치는 용체화 열처리의 영향
- The localized corrosion resistance of the Ni-based Inconel 718 alloy after solution heat treatment was evaluated using electrochemical techniques in a solution of 25 wt% NaCl and 0.5 wt% acetic acid. Solution heat treatment at 1050o C for 2.5 hours resulted in an increased average grain diameter. Both Ti carbides (10 ?m diameter) and Nb-Mo carbides (1 ? 9 ?m diameter) were distributed throughout the material.
Despite heat treatment, the shape and composition of these carbides remained consistent. An increase in solution temperature led to a decrease in pitting potential value. However, the pitting potential value of solution heat-treated Inconel 718 was consistently higher than that of as-received Inconel 718 at all tested temperatures. Localized corrosion initiation occurred at 0.4 V SSE in a temperature environment of 80 o C for both as-received and solution heat-treated Inconel 718 alloys. X-ray photoelectron spectroscopic analysis indicated that the composition of the passive film formed on specimen surfaces remained largely unchanged after solution heat treatment, with O1s, Cr2p 3/2 , Fe2p 3/2 , and Ni2p 3/2 present. The difference in localized corrosion resistance between as-received and solution heat-treated Inconel 718 alloys was attributable to microstructural changes induced by the heat treatment process. - KEYWORDs : Inconel, Heat treatment, Passivity, Corrosion, Acidic chloride
- AUTHORs : 이윤화 · 이준섭† · 권순일 · 신정호 · 이재현
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Page : 368 - 376
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- 치과용 Ni-Ti파일의 표면특성에 미치는 ta-C코팅효과
- Dental Ni-Ti files must ensure stability and resistance to fatigue fracture. DLC and ta-C were coated to remove defects on the surface and ensure stability, and the surface characteristics were investigated. When coated with DLC, it was black, and in case of ta-C coating, it was blue-black. Scratches, which are defects caused by mechanical processing, were formed on the surface of the un-coated Ni-Ti file from the end of the file along the direction of processing, with the Pro-file appearing in the vertical direction and the K-file appearing in the file direction. Scratches were reduced on the coated surface, and the surface roughness was greatly reduced after coating compared to before coating. The un-coated Ni-Ti file had the lowest hardness, the DLC-coated file had the highest hardness, and ta-C showed relatively high hardness. The elastic modulus of the DLC coating film was high, and the ta-C elastic modulus was low. The adhesion of the DLC coating film tended to be higher than that of ta-C, and the wear loss amount of DLC coating of taC was lower. The corrosion potential of the ta-C coating increased significantly, and the corrosion current density decreased.
- KEYWORDs : Ni-Ti file, DLC, ta-C, Corrosion resistance, Mechanisal properties
- AUTHORs : 박순균 · 최한철†
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Page : 377 - 386
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- 인공신경망과 대기부식환경 모니터링 데이터를 이용한 항공기 세척주기 결정 알고리즘
- Aircraft washing is performed periodically for corrosion control. Currently, the aircraft washing interval is qualitatively set according to the geographical conditions of each base. We developed a washing interval determination algorithm based on atmospheric corrosion environment monitoring data at the Republic of Korea Air Force (ROKAF) bases and United States Air Force (USAF) bases to determine the optimal interval. The main factors of the washing interval decision algorithm were identified through hierarchical clustering, sensitivity analysis, and analysis of variance, and criteria were derived. To improve the classification accuracy, we developed a washing interval decision model based on an artificial neural network (ANN). The ANN model was calibrated and validated using the atmospheric corrosion environment monitoring data and washing intervals of the USAF bases. The new algorithm returned a three-level washing interval, depending on the corrosion rate of steel and the results of the ANN model. A new base-specific aircraft washing interval was proposed by inputting the atmospheric corrosion environment monitoring results of the ROKAF bases into the algorithm.
- KEYWORDs : Atmospheric corrosion, Artificial neural network (ANN), Aircraft wash interval
- AUTHORs : 권혁준 · 이두열†
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Page : 387 - 392
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- 일상 생활용수 내 Zn-Al-Mg계 합금도금강재의 부식거동
- The objective of this study was to evaluate corrosion resistance of Zn-Al-Mg alloy coated steel in residential water with trace quantities of Cl - . Comparative evaluations were performed using two commercial coated steel products, GI and Galvalume, as reference samples. Examination of corrosion morphology and measurement of weight loss revealed that the Zn-Al-Mg alloy coated steel exhibited higher corrosion resistance than reference samples. This finding suggests that the alloy coated steel possesses long-term corrosion resistance not only in highly Cl - concentrated environments such as seawater, but also in environments with extremely low levels of Cl - found in residential water. The primary factor contributing to the superior corrosion resistance of the Zn-Al-Mg alloy coated steel in residential water is the formation of an inhibiting corrosion product composed primarily of two phases: Zn 5 (OH) 6 (CO 3 ) 2 and Zn 5 (OH) 8 Cl 2 ·H 2 O. The preferential dissolution of Mg from the corroded coating layer can increase alkalinity, which might
enhance the thermodynamical stability of Zn 5 (OH) 6 (CO 3 ) 2. - KEYWORDs : Zn-Al-Mg alloy coated steel, Corrosion, Tap water, Residential water, Corrosion product
- AUTHORs : 이재원 · 김성진†
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Page : 393 - 398
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- Microstructures and Mechanical Properties of HfN Coatings Deposited by DC, Mid-Frequency, and ICP Magnetron Sputtering
- Properties of hafnium nitride (HfN) coatings are affected by deposition conditions, most often by the sputtering technique. Appropriate use of different magnetron sputtering modes allows control of the structural development of the film, thereby enabling adjustment of its properties. This study compared properties of HfN coatings deposited by direct current magnetron sputtering (dcMS), mid-frequency direct current magnetron sputtering (mfMS), and inductively coupled plasma-assisted magnetron sputtering (ICPMS) systems. The microstructure, crystalline, and mechanical properties of these HfN coatings were investigated by field emission electron microscopy, X-ray diffraction, atomic force microscopy, and nanoindentation measurements. HfN coatings deposited using ICPMS showed smooth and highly dense microstructures, whereas those deposited by dcMS showed rough and columnar structures. Crystalline structures of HfN coatings deposited using ICPMS showed a single δ-HfN phase, whereas those deposited using dcMS and mfMS showed a mixed δ-HfN and HfN 0.4 phases. Their performance were increased in the order of dcMS < mfMS < ICPMS, with ICPMS achieving a value of 47.0 GPa, surpassing previously reported results.
- KEYWORDs : Direct current magnetron sputtering, Mid-frequency magnetron sputtering, Inductively coupled plasma-assisted magnetron sputtering, HfN, Coatings
- AUTHORs : Sung-Yong Chun†
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Page : 399 - 407
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- Investigation of Functional 6061 Aluminum Alloy Oxide Film with Anodization Voltage and its Corrosion Resistance
- This study investigated the formation of oxide films on 6061 aluminum (Al) alloy and their impacts on corrosion resistance efficiency by regulating anodization voltage. Despite advantageous properties inherent to Al alloys, their susceptibility to corrosion remains a significant limitation. Thus, enhancing corrosion resistance through developing protective oxide films on alloy surfaces is paramount. The first anodization was performed for 6 h with an applied voltage of 30, 50, or 70 V on the 6061 Al alloy. The second anodization was performed for 0.5 h by applying 40 V after removing the existing oxide film. Resulting oxide film’s shape and roughness were analyzed using field emission?scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Wettability and corrosion resistance were compared before and after a self-assembled monolayer (SAM) using an FDTS (1H, 1H, 2H, 2H-Perfluorodecyltrichlorosilane) solution. As the first anodization voltage increased, the final oxide film’s thickness and pore diameter also increased, resulting in higher surface roughness. Consequently, all samples exhibited superhydrophilic behavior before coating. However, contact angle after coating increased as the first anodization voltage increased. Notably, the sample anodized at 70 V with superhydrophobic characteristics after coating demonstrated the highest corrosion resistance performance.
- KEYWORDs : Aluminum 6061 alloy, Anodization voltage variation, Corrosion resistance, Superhydrophilicity, Superhydrophobicity
- AUTHORs : Jisoo Kim, Chanyoung Jeong†
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Page : 408 - 418
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- Effect of Al and Nb Doping on the Electrochemical Characteristics of Garnet-type Li7 La3 Zr2 O12 Solid Electrolytes
- In this study, we synthesized and characterized garnet-type Li 7-x Al x La 3 Zr 2-(5/4)y NbyO 12 (LALZN) solid elec-trolytes for all-solid-state battery applications. Our novel approach focused on enhancing ionic conduc-tivity, which is crucial for battery efficiency. A systematic examination found that co-doping with Al and
Nb significantly improved this conductivity. Al 3+ and Nb 5+ ions were incorporated at Li + and Zr 4+ sites, respectively. This doping resulted in LALZN electrolytes with optimized properties, most notably enhanced ionic conductivity. An optimized mixture with 0.25 mol each of Al and Nb dopants achieved a peak conductivity of 1.32 × 10 -4 S cm -1 . We fabricated symmetric cells using these electrolytes and observed excellent charge-discharge profiles and remarkable cycling longevity, demonstrating the potential for long-term application in battery systems. The garnet-type LALZN solid electrolytes, with their high ionic conductivity and stability, show great potential for enhancing the performance of all-solid-state batteries. This study not only advances the understanding of effective doping strategies but also underscores
the practical applicability of the LALZN system in modern energy storage solutions. - KEYWORDs : Solid electrolyte, Garnet, Doping, Ionic conductivity, Solid-state batteries
- AUTHORs : Ahmed Tarif and Chan-Jin Park †
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Page : 419 - 428
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- 해수배관 내부 에폭시 코팅재의 캐비테이션 및 침지 열화에 따른 압입인장특성
- Seawater has been used to cool devices in nuclear power plants. However, the pipes used to transport seawater are vulnerable to corrosion; hence, the inner side of pipelines is coated with an epoxy layer as prevention. Upon coating damage, the pipe becomes exposed, and corrosion progresses. The major cause is widely known as cavitation corrosion, causing the degradation of mechanical properties. In this study, corroded specimens were prepared using cavitation and immersion methods to clarify the degradation trend of mechanical properties with corrosion. Three different types of epoxy coatings were used, and accelerated cavitation procedures were composed of amplitudes of 15 ?m, 50 ?m, and 85 ?m for 2 h, 4 h, and 6 h. The immersion periods were 3 and 6 weeks. We conducted instrumented indentation tests on all degradation samples to measure mechanical properties. The results showed that higher cavitation amplitudes and longer cavitation or immersion times led to more degradation in the samples, which, in turn, decreased the yield strength. Of the three samples, the C coating had the highest resistance to cavitation and immersion degradation.
- KEYWORDs : Cavitation, Epoxy coating, Degradation, Indentation, Stress analysis
- AUTHORs : 정민재 · 김수현 · 전종모 · 김영식 · 김영천†
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Page : 429 - 434
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- UNS G41400 강의 인산염 표면 처리에 따른 국부 부식 저항성
- This study investigated the localized corrosion behavior of a UNS G41400 steel surface treated with manganese phosphate. The phosphate coating, primarily composed of oxygen (O), phosphorus (P), and manganese (Mn) elements, had an approximate thickness of 6 ?m. The particles comprising the coating varied in size by several micrometers; smaller particles were mainly composed of O, P, Mn, and iron (Fe) elements, indicating incomplete formation of the manganese phosphate film. Potentiodynamic polarization curves revealed a decrease in anodic current after surface treatment and a shift in corrosion potential toward the noble direction after treatment. After immersion in a 3.5 wt% NaCl solution for 96 hours, localized corrosion was observed, with some regions retaining residual phosphate film. Even though localized corrosion occurred on the treated surface, it was less severe than that on the untreated UNS G41400 steel surface. These findings suggest that manganese phosphate coating improved resistance to localized corrosion.
- KEYWORDs : Phosphate coating, Corrosion, Steel, Chloride
- AUTHORs : 이준섭† · 박시욱
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