Search Results

You are looking at 1 - 10 of 12 items for

  • Author: C.K. Lee x
Clear All Modify Search
Open access

C.K. Kim, G.-J. Lee, M.K. Lee and C.K. Rhee

Abstract

In this study, nickel nanoparticles were synthesized in ethanol using portable pulsed wire evaporation, which is a one-step physical method. From transmission electron microscopy images, it was found that the Ni nanoparticles exhibited a spherical shape with an average diameter of 7.3 nm. To prevent aggregation of the nickel nanoparticles, a polymer surfactant was added into the ethanol before the synthesis of nickel nanoparticles, and adsorbed on the freshly synthesized nickel nanoparticles during the wire explosion. The dispersion stability of the prepared nickel nanofluids was investigated by zeta-potential analyzer and Turbiscan optical analyzer. As a result, the optimum concentration of polymer surfactant to be added was suggested for the maximized dispersion stability of the nickel nanofluids.

Open access

J.G. Jang, J.-O. Lee and C.K. Lee

Abstract

Rapid synthesis of gold nanoparticles (AuNPs) by pulsed electrodeposition was investigated in the non-aqueous electrolyte, 1-ethyl-3-methyl-imidazoliumbis(trifluoro-methanesulfonyl)imide ([EMIM]TFSI) with gold trichloride (AuCl3). To aid the dissolution of AuCl3, 1-ethyl-3-methyl-imidazolium chloride ([EMIM]Cl) was used as a supporting electrolyte in [EMIM]TFSI. Cyclic voltammetry experiments revealed a cathodic reaction corresponding to the reduction of gold at −0.4 V vs. Pt-QRE. To confirm the electrodeposition process, potentiostatic electrodeposition of gold in the non-aqueous electrolyte was conducted at −0.4 V for 1 h at room temperature. To synthesize AuNPs, pulsed electrodeposition was conducted with controlled duty factor, pulse duration, and overpotential. The composition, particle-size distribution, and morphology of the AuNPs were confirmed by field-emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). The electrodeposited AuNPs were uniformly distributed on the platinum electrode surface without any impurities arising from the non-aqueous electrolyte. The size distribution of AuNPs could be also controlled by the electrodeposition conditions.

Open access

C.K. Lee and Y.C. Kim

Abstract

The height of the die roll, the distance of the V-ring, and the shear rate were varied with the aim of investigating the effects of the applied changes on the fine blanking line in a cold-rolled and a pickled steel sheet, referred to as SCP-1 and SHP-1, respectively. Both materials consisted primarily of a ferrite phase with small amounts of impurities including F, Mn, and Cr. The distance was found to be a very important factor in controlling the shear of the V-ring in the fine blanking process. When the position of the V-ring was set at distances of 1.5 mm and 2 mm, the die roll height increased with increasing shear speeds from 6.4 m/min to 10 and 16 m/min. Analysis of the influence of the shear rate revealed that low rates resulted in the lowest die roll heights since the flow of material was effectively inhibited.

Open access

C.K. Lee and Y.C. Kim

Abstract

In the drawing process, the roundness of corners in the punch and the die are very important factors in determining the thicknesses of the product. The results clearly revealed that the thickness of a flange was increased and the thickness of body parts reduced when the roundness of the die entrance was small. The material thickness of the top part was decreased when the corner roundness of the punch was large. The smooth inflow of materials was found to have a significant effect on the thickness during the post-process. The compressive strength of STS 304 material exhibited a higher value compared with other processing methods. Moreover, we clearly observed the corner roundness of the punch and the die to be a very important factor for STS 304 materials.

Open access

S.M. Kahar, C.H. Voon, C.C. Lee, U. Hashim, M.K. Md Arshad, B.Y. Lim, S.C.B. Gopinath and W. Rahman

Abstract

Silicon carbide (SiC) is an important ceramics for engineering and industrial applications due to its advantage to withstand in high temperatures. In this article, a demonstration of SiC nanowhiskers synthesis by using microwave heating has been shown. The mixtures of raw materials in the form of pellets were heated, using a laboratory microwave furnace, to 1400 °C for 40 minutes at a heating rate of 20 °C/min. The characterization process proved that the mixture of graphite and silica in the ratio of 1:3 is an ideal composition for synthesizing single phase β-SiC nanowhiskers. Vapor-solid mechanism was suggested to explain the formation of SiC nanowhiskers by the proposed microwave heating.

Open access

K.-A. Lee, Y.-K. Kim, J.-H. Yu, S.-H. Park and M.-C. Kim

Abstract

This study manufactured Ti-6Al-4V alloy using one of the powder bed fusion 3D-printing processes, selective laser melting, and investigated the effect of heat treatment (650°C/3hrs) on microstructure and impact toughness of the material. Initial microstructural observation identified prior-β grain along the building direction before and after heat treatment. In addition, the material formed a fully martensite structure before heat treatment, and after heat treatment, α and β phase were formed simultaneously. Charpy impact tests were conducted. The average impact energy measured as 6.0 J before heat treatment, and after heat treatment, the average impact energy increased by approximately 20% to 7.3 J. Fracture surface observation after the impact test showed that both alloys had brittle characteristics on macro levels, but showed ductile fracture characteristics and dimples at micro levels.

Open access

H. S. Dungey, C. B. Low, J. Lee, M. A. Miller, K. Fleet and A. D. Yanchuk

Abstract

Genetic improvement of Douglas-fir in New Zealand was initiated in 1955 with large provenance trials established in the late 1950’s. These trials illustrated that material from the coast of Oregon and California grew faster than other provenances tested. Further collections were made to evaluate provenance and familylevel performance from these two areas, and in 1996 additional trials were established at four low-altitude sites across New Zealand. Genotype×environment (GxE) interaction among these sites was found to be important for diameter at breast height (DBH), less important for stem straightness and malformation and not important for outerwood acoustic velocity (a surrogate for wood stiffness). Heritabilities were low to moderate for all growth traits, and very low for malformation. Heritability for needle cast due to Swiss needle cast, measured as needle retention on the one site where infection was relatively high, was moderate at 0.37, and was likely a major factor creating GxE interactions for growth among sites. The heritability of wood acoustic velocity was moderate to high at individual sites (0.26-0.74) and across sites (0.49). Individual- trait selection revealed the potential for good genetic gains to be made when selecting the top 20 families for diameter growth (an average of 10.7%), straightness (an average of 11.5%) and acoustic velocity (an average of 7.0%). When we examined predicted genetic gains while selecting for needle retention and/or DBH, we found that selecting for needle cast at the affected site did not compromise DBH gains at that site. Selecting for genotypes with low needle cast at the affected site did, however, reduce gains for DBH estimated across all sites. In order to maximise gains across the current Douglas-fir growing estate, a division of growing sites between those known and predicted to be affected by needle cast and those not affected would seem appropriate. This is particularly relevant given recent climate modelling work suggests that Swiss needle cast will become more important in the South Island, and even more destructive in the North Island of New Zealand. We suggest addressing differences in site through the development of separate deployment populations.

Open access

J.-J. Oak, J.I. Bang, K.-C. Bae, Y.H. Kim, Y.-C. Lee, H.H. Chun and Y.H. Park

Abstract

The proposed sintering process produce porosity and functional graded microstructure in the sinterd titanium powders. Titanium powders with different micro sizes were sintered at the proposed temperature region at 1200 and 1300°C for 2h. The apatite-forming on the graded microstructure is observed by immersion test in Hanks balanced salt soluion at 37°C. Sintering condition of titanium powders is estimated by thermogravitmetry-differential thermal analysis (TG-DTA). The synthersied surface structures and apatite-forming ability were characterized by a field emission scanning electron microscopy (FE-SEM) observation and energy dispersive X-ray spectroscopy (EDS) analysis. As results, these graded microstructure of sintered porous titanium powders reveals apatite-forming ability as osseointegration by calcification in Hanks balanced salt soluion(HBSS) at 37°C.

Open access

K.H. Kang, C.H. Lee, M.K. Jeon, S.Y. Han, G.I. Park and S.-M. Hwang

Abstract

Used cladding hulls from pressurized water reactor (PWR) are characterized to provide useful information for the treatment and disposal of cladding hull wastes. The radioactivity and the mass of gamma emitting nuclides increases with an increase in the fuel burn-up and their removal ratios are found to be more than 99 wt.% except Co-60 and Cs-137. In the result of measuring the concentrations of U and Pu included in the cladding hull wastes, most of the residues are remained on the surface and the removal ratio of U and Pu are revealed to be over 99.98 wt.% for the fuel burn-up of 35,000 MWd/tU. An electron probe micro-analyzer (EPMA) line scanning shows that radioactive fission products are penetrated into the Zr oxide layer, which is proportional to the fuel burn-up. The oxidative decladding process exhibits more efficient removal ratio of radionuclides.

Open access

B. Ali, S.H. Choi, S.J. Seo, D.Y. Maeng, C.G. Lee, T.S. Kim and K.T. Park

Abstract

The water atomization of iron powder with a composition of Fe-3Cr-0.5Mo (wt.%) at 1600°C and 150 bar creates an oxide layer, which in this study was reduced using a mixture of methane (CH4) and argon (Ar) gas. The lowest oxygen content was achieved with a 100 cc/min flow rate of CH4, but this also resulted in a co-deposition of carbon due to the cracking of CH4. This carbon can be used directly to create high-quality, sinter hardenable steel, thereby eliminating the need for an additional mixing step prior to sintering. An exponential relationship was found to exist between the CH4 gas flow rate and carbon content of the powder, meaning that its composition can be easily controlled to suit a variety of different applications.