• 한국표면공학회지
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• 제30권4호
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• pp.285-297
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• 1997

Finned segment, with which are lined inner wall of the turbine combustors, are subject to severe degradation when they are exposed to a hostile environmment at elevated temperature. To protect the finned segment from this environment and to maintain good mechanical properties of components at high temperature, they are preferred to be coated. The most governing factor for the durability of coatings used in the high temperature is the microstructure of coatings; these are splat from, distibution of microcacks, size and distribution of pores, thickness of coating layer, adhesion between coating layer, and oxidation of band coating. In this study, based on the evaluation of the imported finned segment, new finned segment segment was manufactured with optimum plasma spraying parameters, and their properties were examined. Using $ZrO_2(8wt$Y_2O_3)$,/TEX> powder for ceramic coating and 67Ni-22Cr-10Al-0.5Y mixing powder for bond coating, thickness of ceramic and bond coating layer were varied in order to find optimum condition, the results showed that B2T4(bond coating : 100~250$\mu\textrm{m}$, ceramic coating : 250~300$\mu\textrm{m}$) was the best among the specimens tested. Compared to the imported finned segment, B2T4 has better bond strength, hardness, and isothermal and cyclic oxidation resistance.

• Corrosion Science and Technology
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• 제5권4호
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• pp.149-152
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• 2006

$BaTiO_3$ coatings were prepared by micro arc oxidation (MAO) method. Only $Ba(OH)_2$ was dissolved in the electrolyte and process time was less than 30 min. Commercial purity $Ba(OH)_2$ (97%) containing $BaCO_3$ as impurity was used in preparing the electrolyte. XRD showed that the coating was composed of largely $BaTiO_3$, and in some process conditions, small quantity of impurity, $BaCO_3$, was characterized in the coating layer. The quantity of $BaCO_3$ could be controlled to negligible quantity by regulating the applied voltage and duration time of the MAO process.

• 한국분말재료학회지
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• 제28권5호
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• pp.396-402
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• 2021

Stainless steel, a type of steel used for high-temperature parts, may cause damage when exposed to high temperatures, requiring additional coatings. In particular, the Cr₂O₃ product layer is unstable at 1000℃ and higher temperatures; therefore, it is necessary to improve the oxidation resistance. In this study, an aluminide (Fe₂Al₅ and FeAl₃) coating layer was formed on the surface of STS 630 specimens through Al diffusion coatings from 500℃ to 700℃ for up to 25 h. Because the coating layers of Fe₂Al₅ and FeAl₃ could not withstand temperatures above 1200℃, an Al₂O₃ coating layer is deposited on the surface through static oxidation treatment at 500℃ for 10 h. To confirm the ablation resistance of the resulting coating layer, dynamic flame exposure tests were conducted at 1350℃ for 5-15 min. Excellent oxidation resistance is observed in the coated base material beneath the aluminide layer. The conditions of the flame tests and coating are discussed in terms of microstructural variations.

• 한국표면공학회지
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• 제50권6호
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• pp.432-438
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• 2017

AZ91D casting alloy requires an advanced plasma anodizing processing because large amount of defects are liable to generate during anodization. In this study, plasma electrolytic oxidation (PEO) of AZ91D Mg alloy was conducted by the application of either constant voltage or current using a pulse mode and its effects on pore formation, surface roughness and corrosion resistance were investigated. The PEO films showed a three-layer structure. The PEO film thickness was found to increase linearly with voltage. The surface roughness, Ra, ranged between $0.2{\mu}m$ and $0.3{\mu}m$. The corrosion resistance increased from RN 3.5 to 9.5 by the PEO treatment when evaluated according to the 72 hour salt spray test. The PEO-treated surface exhibited higher pitting potential than the raw material.

• 한국태양에너지학회 논문집
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• 제31권4호
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• pp.48-56
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• 2011

Black cobalt solar selective coatings were prepared by thermal oxidation of electroplated cobalt metal on copper and nickel substrates. The optical properties and structure of the black cobalt selective coating for solar energy utilizations were characterized by glow discharge spectrometry (GDS), ultraviolet-visible-near infrared (UV-VIS-NIR) spectrometer, atom force microscopy(AFM) and X-ray photoelectron spectroscopy(XPS). The optical properties of optimum black cobalt selective coating prepared on copper substrate were a solar absorptance of 0.82 and a thermal emittance of 0.01. From the GDS depth profile analysis of these coatings, the concentration of cobalt particles near the interface was higher than at the surface, but oxygen concentration at the surface was higher than at the interface. These results suggest that the selective absorption was dominated by this chemical composition variation in the coating. The surface of this film exhibited morphology with root-mean-square(rms) roughness of about 144.3nm. XPS measurements data showed that several phases of Co coexist($Co_3O_4$,CoO) in the film.

• 한국세라믹학회지
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• 제46권3호
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• pp.295-300
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• 2009

The crystal structure of surface coatings on Al1050 alloy by PEO (Plasma Electrolytic Oxidation), were investigated. The electrolyte for PEO was Na-Si-P system solution. The main crystalline phase were $\gamma$-alumina and $\alpha$-alumina. Crystallinity was increased with applied voltage and applied time. The dominant crystalline phase were affected not only chemical composition of Al alloy substrate and electrolyte, but also the +/- ratio of applied voltage.

• 한국태양에너지학회 논문집
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• 제33권4호
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• pp.31-38
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• 2013

The chemical composition of the black Cr solar selective coatings electrodeposited were investigated for property analysis by using a XPS(X-ray photoelectron spectroscopy) before and after annealing in air at $300^{\circ}C{\sim}500^{\circ}C$ for 120 hours. Black Cr selective coating exposed by solar radiation for 5 months was compared with annealed sample. In addition, The Cu solar selective coatings were prepared by thermal oxidation method for low temperature application. The samples obtained were characterized by using the optical reflectance measurements by using a spectrometer. Optical properties of oxidized Cu solar coatings were solar absorptance $({\alpha}){\simeq}0.62$ and thermal emittance $({\epsilon}){\simeq}0.41(100^{\circ}C)$. In the as-prepared Cr black selective coating, the surface of the coating was found to have Cr hydroxide and Cr. The Cr hydroxide of the major component was converted to $Cr_2O_3$ or $CrO_3$ form after annealing at $500^{\circ}C$ with the desorption of water molecules. The black Cr selective coating was degraded significantly at temperature of $500^{\circ}C$. The main optical degradation modes of this coating were diffusion of Cu substrate materials.

• Journal of Welding and Joining
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• 제26권4호
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• pp.50-54
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• 2008

In this research, anode for SOFC has been manufactured from two different kinds of feedstock materials through thermal spraying process and the properties of the coatings were characterized and compared. One kind of feedstock was manufactured from spray drying method which includes nano-components of NiO, YSZ (300 nm) and graphite. And the other is manufactured by blending the micron size NiO coated graphite, YSZ and graphite powders as feedstock materials. Microstructure, mechanical properties and electrical conductivity of the coatings as-sprayed, after oxidation and after hydrogen reduction containing nano composite which is prepared from spray-dried powders were evaluated and compared with the same properties of the coatings prepared from blended powder feedstock. The coatings prepared from the spray dried powders has better properties as they provide larger triple phase boundaries for hydrogen oxidation reaction and is expected to have lower polarization loss for SOFC anode applications than that of the coatings prepared from blended feedstock. A maximum electrical conductivity of 651 S/cm at $800^{\circ}C$ was achieved for the coatings from spray dried powders which much more than that of the average value.

• 한국세라믹학회지
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• 제50권2호
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• pp.108-115
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• 2013

Oxide coatings were prepared on Al-1050 substrates by an environment-friendly plasma electrolytic oxidation (PEO) process using an electrolytic solution of $Na_2SiO_3$ (8 g/L) and NaOH (3 g/L). The effects of three different duty cycles (20%, 40%, and 60%) and frequencies (50 Hz, 200 Hz, and 800 Hz) on the structure and micro-hardness of the oxide coatings were investigated. XRD analysis revealed that the oxides were mainly composed of ${\alpha}-Al_2O_3$, ${\gamma}-Al_2O_3$, and mullite. The proportion of each crystalline phase depended on various electrical parameters, such as duty cycle and frequency. SEM images indicated that the oxide coatings formed at a 60% duty cycle exhibited relatively coarser surfaces with larger pore sizes and sintering particles. However, the oxides prepared at a 20% duty cycle showed relatively smooth surfaces. The PEO treatment also resulted in a strong adhesion between the oxide coating and the substrate. The oxide coatings were found to improve the micro-hardness with the increase of duty cycle. The structural and physical properties of the oxide coatings were affected by the duty cycles.

• 한국표면공학회지
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• 제20권3호
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• pp.95-105
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• 1987

For the purpose of improving the hot corrosion resistance of Ni-base superalloy, Inconel 600, aluminide and chromium-aluminide coatings by pack cementation process were studied. The morphology of these coatings is dependent on the type of process employed. And their overall composition depends on the composition of the base alloy and on the nature of the cement. Therefore the different aluminide and chromium-aluminide coatings obtained on a superalloy do not possess the same resistance to oxidation and hot corrosion. The mechanisms governing the formation of the coatings and the composition of the coating were varied by pack composition and temperature, and cyclic hot corrosion resistance of the auluminide coating formed by one-step process was inferior to that of the coating formed by two-step process. and Cr-Al composite coating showed good resistance for cyclic hot corrosion.