Papers by Author: Dong Bok Lee

Paper TitlePage

Authors: Dong Bok Lee, S.J. Park, Yun Soo Lim, Jae Chun Lee
Abstract: Carbon nanofibers were reacted with SiO vapor generated from a mixture of Si and SiO2 to produce silicon carbide nanofibers at 1350oC for 2 h under vacuum. The obtained SiC nanofibers with a diameter ranging 100~200 nm had the specific surface area as high as 124 m2/g. The SiC nanofibers were not oxidation resistant, showing nearly complete oxidation at 1000 oC after about 60 h in air, though the oxidation product was amorphous silica which was generally considered to be oxidation resistant. The poor oxidation resistance was attributed to the inherent nanoporous nature of the fibers resulted from the gas-solid reaction.
Authors: Sung Sic Hwang, Sang Whan Park, Seong Jai Cho, Dong Bok Lee
Abstract: The contact fracture behaviors of fine-grained Ti3SiC2 and coarse-grained high purity Ti3SiC2 are examined by the Hertzian indentation and Vickers indentation technique. The Vickers hardness of bulk Ti3SiC2 is as low as 5.3~6.3 Gpa, and the Hertzian contact stress-strain curves for Ti3SiC2 deviate much from linearity, which resembles the fracture behavior of a ductile metal rather than a brittle ceramic. The contact damages by both Vickers indentation and Hertzian indentation reveal a fairly good plastic deformation nature of Ti3SiC2. Un-reacted TiCx in fine-grained Ti3SiC2 may impede the plastic deformation by slip along basal plan inside Ti3SiC2 grain, making Ti3SiC2 less plastic under loading.
Authors: Dong Bok Lee
Abstract: The composite coating that consisted of 50%(Ni-22%Cr-10%Al-1%Y) and 50%(ZrO2-8%Y2O3) was fabricated by air plasma spraying, and corroded at 800 and 900°C for 50 h in Na2SO4 or 75%NaCl-25%Na2SO4 salt. The scales consisted primarily of Cr2O3, NiO and α-Al2O3. However, most of them continuously dissolved off as complex ions into the salt during hot corrosion.
Authors: Yu Ke Shi, Dong Bok Lee
Abstract: Pure Fe3Al and Fe3Al+4%Cr alloys were corroded at 1000 °C for up to 200 h in N2-0.1%H2S-mixed gas in order to study their corrosion behavior in H2S-containing atmosphere. The formed scales consisted primarily of α-Al2O3, FeAl2O4, and Fe2O3. In these oxide scales, hydrogen and sulfur dissolved according to the reaction; H2S→2H+S. Corrosion products of Cr were not identified in the scales from the XRD analysis, indicating that Cr dissolved in the oxide scales. Fe3Al+4%Cr alloy displayed poorer corrosion resistance than Fe3Al alloy, indicating that chromium accelerated the corrosion rates of Fe3Al alloys.
Authors: Poonam Yadav, Sang Hwan Bak, Dong Bok Lee
Abstract: The ASTM T23 steel with a composition of Fe-2.25Cr-1.6W-0.1Mo in wt.% was corroded in the Na2SO4 salt at 800 and at 900°C, and its corrosion behavior was studied. It formed thick, porous oxide scales that consisted primarily of outer Fe-rich oxides and inner (Fe, Cr)-rich oxides. The corrosion of the T23 steel progressed mainly via oxidation.
Authors: Min Jung Kim, Dong Bok Lee
Abstract: Ni-base Inconel 625 alloys with a composition of 58.9Ni-22Cr-9Mo-5Fe 3.5Nb-0.4Si-0.4Mn-0.4Al-0.4Ti (wt.%) corroded at 600, 700 and 800 °C for up to 30 h in 1 atm of N2/H2O/H2S-mixed gases. They corroded fast owing to the formation of sulfides and the presence of hydrogen and water vapor in the gas. Triple layered scales formed. Nickel corroded to NiS to form the outer NiS layer, where Fe was dissolved. Chromium corroded to Cr-sulfides to form the middle layer. Other alloying elements such as Mo, Nb, Si, Mn, Al, and Ti corroded to form the inner layer that consisted primarily of intermixed sulfides and oxides. Since sulfides were present throughout the scale and hydrogen made the scale porous and fragile, Inconel 625 was nonprotective during high-temperature corrosion in N2/H2O/H2S gases.
Authors: Dong Bok Lee, J.H. Ko
Abstract: The Ni-19at.%W coating was electodeposited to protect the stainless steel substrate, and then corroded between 500 and 700oC in Ar-0.2% SO2 atmosphere for 5 hr. The coating effectively protected the substrate from corrosion at 500oC, but failed at 700oC owing to serious corrosion. The corrosion products were mainly NiO, WO3 and NiWO4, together with some NiS, FeS, Fe2O3 and FeWO4. Detailed scale morphologies and corrosion mechanism are presented.
Authors: Min Jung Kim, Dong Bok Lee
Abstract: SUS 310 stainless steels were corroded at 600, 700 and 800°C for up to 30 h in 1 atm of N2/H2O/H2S-mixed gas. The formed scales consisted primarily of (Fe0.5Ni0.5)0.96S, FeNiS2, and FeCr2S4. They were fragile, porous, and susceptible to spallation. During corrosion, Fe, Ni, and Mn diffused outward, while sulfur and a lesser amount of oxygen diffused inward. The diffusion of Cr and Si was not conspicuous. The formation of sulfide scales and the presence of hydrogen and water vapor in the mixed gases made SUS 310 corrode fast.
Authors: Dong Bok Lee
Abstract: The corrosion behavior of the ASTM T92 steel in the Na2SO4 salt was studied at 800 and 900°C. At 800°C, the T92 steel formed thin (Fe, Cr)-rich oxide scales, indicating a good corrosion resistance due to 9%Cr presented in the alloy. However, at 900°C, the T92 steel displayed poor corrosion resistance, because the scales dissolved off rapidly owing to the increased corrosion rate.
Authors: Byeong Soo Lim, Bum Joon Kim, Si Yon Bae, J.W. Kim, Dong Bok Lee
Abstract: New Ti-base alloys were designed to replace conventional expensive elements with low cost elements of iron and silicon. The prepared Ti-4wt%Fe-(0~4)wt%Si alloys were creep tested at 600oC in air, tensile tested at room temperature and 400oC in air, and exposed to hot air for oxidation tests between 700 and 1000oC. When compared to the Ti-6Al-4V alloy, Ti-4wt%Fe-(0.5~2)wt%Si alloys displayed poorer creep resistance, but exhibited good tensile properties and superior oxidation resistance.
Showing 1 to 10 of 52 Paper Titles