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14. The effect of zirconium on corrosion behavior of NiAl intermetallic compound in molten carbonate salt

Author

Hwang, Gil-Ho, Choi, Jae-Woong, and Kang, Sung-Goon

Abstract

The corrosion of NiAl alloys containing zirconium in molten carbonate salt at 650 °C was studied as a potential coating material on a stainless steel separator. A mixed layer of NiO, ZrO2, and Al2O3was formed on the surface of the NiAl alloy during preoxidation at 1000 °C in air. The Ni2AlZr phase, precipitated along the grain boundaries of NiAl alloys containing zirconium, was the source of the formation of the outermost layer of Al2O3only on the mixed oxide layer during the oxidation. The Al2O3layer inhibited the dissolution of NiO on the NiAl – Zr alloy in molten carbonate salt. Therefore, the oxide layer formed on the NiAl – Zr alloy was more corrosion-resistant than the oxide layer on the NiAl alloy. As the amount of zirconium in NiAl – Zr alloy was increased, the corrosion rate greatly decreased due to an increasing amount of Al2O3at the outermost surface layer oxide. The mixed oxide layer on the NiAl alloy was spalled off the alloy by air cooling after high temperature isothermal oxidation, but the spalling phenomenon of the oxide layer on the NiAl – Zr alloy with more than 0.84 at.% zirconium was greatly reduced by the improvement of the oxide adhesion due to the formation of oxide pegs of Ni2AlZr phase along grain boundaries, which were mechanically anchored to the surface oxide layer.

Published
2022
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15. Synthesis and Phase Transformation Behavior of YAG Powders by a Mechanochemical Solid Reaction

Author

Hwang Gil-Ho, Kang Sung-Goon, Lee Young-Hun, Lim Kwang-Young, and Jung Hyun-Gi

Subjects
Materials science, Metallurgy, chemistry.chemical_element, Yttrium, law.invention, Grinding, chemistry, law, Aluminium, Phase (matter), Reactivity (chemistry), Calcination, Nuclear chemistry, Perovskite (structure), Monoclinic crystal system
Abstract

Yttrium aluminum garnet (YAG) powders were synthesized via mechanochemical solid reaction using with three types of aluminum compounds. reacted mechanochemically with all A1 compounds and formed YAM (yttrium aluminum monoclinic), YAG and YAP (yttrium aluminum perovskite) phases depending on the starting materials. The ground samples containing showed the best reactivity, whereas the ground sample containing A100H, which had the largest surface area, exhibited pure YAG after calcination at . The sample containing Al had the least reactivity, producing YAP along with YAG at . The types and grinding characteristics of the starting materials and grinding time are believed to be important factors in the mechanochemical synthesis of YAG.

Published
2006

22. Effect of Heat Treatment of the Diffusion Barrier for Bus Electrode of Plasma Display by Electroless Ni-B Deposition

Author

Hong Seok Jun, Kang Sung Goon, Choi Jae Woong, and Hwang Gil Ho

Subjects
Materials science, Diffusion barrier, Annealing (metallurgy), Metallurgy, Plasma display, law.invention, Grain growth, Dielectric layer, law, Electrode, Heat treated, General Materials Science, Grain boundary, Composite material
Abstract

Thin Ni-B films, 1 thick, were electrolessly deposited on Cu bus electrode fabricated by electro deposition. The purpose of these films is to encapsulate Cu electrodes for preventing Cu oxidation and to serve as a diffusion barrier against copper contamination of dielectric layer in AC-plasma display panel. The layers were heat treated at (baking temperature of dielectric layer) with and without pre-annealing at ( formation temperature) for 30 minutes. In the layer with pre-annealing, amount of Cu diffusion was lower about 5 times than that in the layer without pre-annealing. The difference of Cu concentration could be attributed to Cu diffusion before formation at grain boundaries. However, the diffusion behavior of the layer with pre-annealing was similar to that of the layer without pre-annealing after formation. With increasing annealing time, Cu concentration of both layers increased due to grain growth.

Published
2004

23. Fabrication and characterization of a Cu seed layer on a 60-nm trench-patterned SiO2 substrate by a self-assembled-monolayer (SAM) process

Author

Han, Won-Kyu, Hwang, Gil-Ho, Hong, Seok-Jun, Yoon, Chong-Seung, Park, Joon-Shik, Cho, Jin-Ki, and Kang, Sung-Goon

Subjects
*ELECTROLESS plating, *COPPER, *SUBSTRATES (Materials science), *SILICA, *MONOMOLECULAR films, *MOLECULAR self-assembly, *X-ray photoelectron spectroscopy
Abstract

Abstract: Continuous electroless deposition of a 10-nm thick layer of Cu was successfully performed on a SiO2/Si substrate coated with a 3-nm Au catalytic layer. The Au catalytic layer was formed by a self-assembled monolayer (SAM) process terminated with NH2 headgroups, upon which negatively charged Au particles were deposited via electrostatic interaction with the positively charged NH2-SAM. The Au and NH2-SAM layers were analyzed by X-ray photoelectron spectroscopy (XPS) and contact angle analysis. Atomic force microscopy, field emission scanning electron microscopy, and XPS revealed that the Cu layer formed by this electroless processes had good step-coverage, small grain size, and excellent adhesion to the substrate. The proposed process is a very promising method for fabrication of a conductive Cu seed layer in a 60-nm trench-pattern. [Copyright &y& Elsevier]

Published
2009
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24. Determination of trace amounts of lead and cadmium using a bismuth/glassy carbon composite electrode

Author

Hwang, Gil-Ho, Han, Won-Kyu, Hong, Seok-Jun, Park, Joon-Shik, and Kang, Sung-Goon

Subjects
*TRACE metals, *CADMIUM, *LEAD, *BISMUTH, *CARBON electrodes, *VOLTAMMETRY, *ELECTROCHEMICAL analysis
Abstract

Abstract: We examined the use of a bismuth–glassy carbon (Bi/C) composite electrode for the determination of trace amounts of lead and cadmium. Incorporated bismuth powder in the composite electrode was electrochemically dissolved in 0.1M acetate buffer (pH 4.5) where nanosized bismuth particles were deposited on the glassy carbon at the reduction potential. The anodic stripping voltammetry on the Bi/C composite electrode exhibited well-defined, sharp and undistorted peaks with a favorable resolution for lead and cadmium. Comparing a non-oxidized Bi/C composite electrode with an in-situ plated bismuth film electrode, the Bi/C composite electrode exhibited superior performance due to its much larger surface area. The limit of detection was 0.41μg/L for lead and 0.49μg/L for cadmium. Based on this study, we are able to conclude that various types of composite electrodes for electroanalytical applications can be developed with a prudent combination of electrode materials. [Copyright &y& Elsevier]

Published
2009
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25. Determination of trace metals by anodic stripping voltammetry using a bismuth-modified carbon nanotube electrode

Author

Hwang, Gil Ho, Han, Won Kyu, Park, Joon Shik, and Kang, Sung Goon

Subjects
*ELECTROLYTIC oxidation, *VOLTAMMETRY, *CARBON nanotubes, *CADMIUM
Abstract

Abstract: A bismuth-modified carbon nanotube electrode (Bi-CNT electrode) was employed for the determination of trace lead, cadmium and zinc. Bismuth film was prepared by in situ plating of bismuth onto the screen-printed CNT electrode. Operational parameters such as preconcentration potential, bismuth concentration, preconcetraion time and rotation speed during preconcentration were optimized for the purpose of determining trace metals in 0.1M acetate buffer solution (pH 4.5). The simultaneous determination of lead, cadmium and zinc was performed by square wave anodic stripping voltammetry. The Bi-CNT electrode presented well-defined, reproducible and sharp stripping signals. The peak current response increased linearly with the metal concentration in a range of 2–100μg/L. The limit of detection was 1.3μg/L for lead, 0.7μg/L for cadmium and 12μg/L for zinc (S/N=3). The Bi-CNT electrode was successfully applicable to analysis of trace metals in real environments. [Copyright &y& Elsevier]

Published
2008
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