• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.236.1-236.1
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• 2014

Compounds of Ga, such as gallium oxide (Ga2O3) and gallium nitride (GaN), are of interest due to its unique properties in semiconductor application. In particular, GaN has the potentially application for optoelectronic device such as light-emitting diodes (LEDs) and laser diodes (LDs) [1]. Nanoparticle is an interesting material due to its unique properties compared to the bulk equivalents. In this report, we develop a synthesizing method for gallium nitride nanoparticle using non-thermal plasma. For gallium source, the gallium is heated by thermal conduction of tungsten boat which is heated by eddy current induced from RF current in antenna. Nitrogen source for nanoparticle synthesis are from inductively coupled plasma with N2 gas. The synthesized nano particles are analyzed using field-emission scanning microscope (FESEM), transmission electron microscope (TEM) and x-ray photoelectron spectroscopy (XPS). The synthesized particles are investigated and discussed in wide range of experiment conditions such as flow rate, pressure and RF power.

• Bulletin of the Korean Chemical Society
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• v.30 no.3
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• pp.630-635
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• 2009

For use as a photocatalyst, bismuth tungsten oxide, $Bi_2WO_6$, was successfully synthesized by hydrothermal treatment at pH = 11 and heating at 200 ${^{\circ}C}$ for 24h, and samples were subsequently thermal treated at 400, 600, and 800 ${^{\circ}C}$ to increase crystallinity. TEM results revealed that the initial untreated particles were sheet‐shaped, grain size was below 80 nm, and it increased with treated temperatures. These $Bi_2WO_6$ samples absorbed at around 400 nm in the visible light range and the intensity of absorption was particularly strongest in samples thermal treated at 600 ${^{\circ}C}$. Their photoluminescence abilities, related to the recombination between the excited electrons and holes, were overall small for other general photocatalysts such as TiO2, and the smallest in the case of thermal treatment at 600 ${^{\circ}C}$, as reversible result of UV‐visible absorbance. Methyl orange of 5.0 ppm aqueous solution was almost completely removed after 2 h when treated over the $Bi_2WO_6$ thermal treated at 600 ${^{\circ}C}$.

• Journal of Sensor Science and Technology
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• v.6 no.4
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• pp.274-279
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• 1997

NOx sensors using tungsten oxide films as a base material were prepared and their electrical and sensing characteristics have been investigated. The $WO_{3}$ thick films doped with $SnO_{2}$ or $TiO_{2}$ showed higher sensitivity and better sorption characteristics to NOx gas than the pure $WO_{3}$ films material in air at operating temperature of $400^{\circ}C$. By addition of noble catalysts, such as Ru or Au, to the $TiO_{2}-WO_{3}$ thick films, their sensitivity, recovery and selectivity to NOx gas were found to be more enhanced.

• Journal of Ceramic Processing Research
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• v.19 no.5
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• pp.434-438
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• 2018

The sintering behavior of $BaFe_{12}O_{19}$ with the addition of one and three weight % of $CuWO_4$ as a liquid phase sintering aid is studied. Samples are sintered in the temperature range $900-1250^{\circ}C$ and the effect of $CuWO_4$ addition on density, microstructure, phase composition and magnetic properties is examined. Compared to $BaFe_{12}O_{19}$ with no sintering aid addition, addition of 1 wt % $CuWO_4$ retards densification. Addition of 3 wt % $CuWO_4$ promotes densification at lower sintering temperatures but retards densification at temperatures > $1050^{\circ}C$. Three wt % $CuWO_4$ addition induces the formation of $BaWO_4$ and $Ba_3WFe_2O_9$ secondary phases at temperatures ${\geq}1100^{\circ}C$. Addition of $CuWO_4$ causes a decrease in saturation magnetization, remanent magnetization and coercivity.

• Korean Journal of Metals and Materials
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• v.49 no.5
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• pp.395-399
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• 2011

In this study, micro gas sensors for ammonia gas were prepared by adopting MEMS technology and using a sol-gel process. Three types of sensors were prepared via different synthesis routes starting with W sol and Ru sol mixture. This mixture was deposited on a MEMS platform and the platform was subsegueny heated to a temperature of $350^{\circ}C$. The topography and crystal structure of the sensing film were studied using FE-SEM and XRD. The response of the gas sensor to $NH_3$ gas was examined at various operating temperatures and gas concentrations. The sensor response increased almost linearly with gas concentration and the best sensing response was obtained at $333^{\circ}C$ for 5.0 ppm $NH_3$ for the specimen prepared by coating $WO_3$ powders with the Ru sol mixture.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2860-2866
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• 2020

Oxide dispersion-strengthened materials W-1wt%Pr₂O₃ and W-1wt%La₂O₃ were synthesized by wet chemical method and spark plasma sintering. The field emission scanning electron microscopy (FE-SEM) analysis, XRD and Vickers microhardness measurements were conducted to characterize the samples. The irradiations were carried out with a 5 keV helium ion beam to fluences up to 5.0 × 10²¹ ions/m² under 600 ℃ using the low-energy ion irradiation system. Transmission electron microscopy (TEM) study was performed to investigate the microstructural evolution in W-1wt%Pr₂O₃ and W-1wt%La₂O₃. At 1.0 × 10²⁰ He⁺/m², the average loops size of the W-1wt%Pr₂O₃ was 4.3 nm, much lower than W-1wt% La₂O₃ of 8.5 nm. However, helium bubbles were not observed throughout in both doped W materials. The effects of pre-irradiation with 1.0 × 10²¹ He⁺/m² on trapping of injected deuterium in doped W was studied by thermal desorption spectrometry (TDS) technique using quadrupole mass spectrometer. Compared with the samples without He⁺ pre-irradiation, deuterium (D) retention of doped W materials increased after He⁺ irradiation, whose retention was unsaturated at the damage level of 1.0 × 10²²D₂⁺/m². The present results implied that irradiation effect of He⁺ ions must be taken into account to evaluate the deuterium retention in fusion material applications.

• Applied Chemistry for Engineering
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• v.34 no.4
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• pp.357-364
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• 2023

Selective catalytic reduction (SCR) is the most effective method for reducing nitrogen oxide emissions, but the operating temperature range of V₂O₅-WO₃/TiO₂ catalysts is narrow (300~400℃). In this study, a new catalyst with an operating temperature range of 200~450℃ was developed. The catalyst poison, ammonium bisulfate, generated during the SCR process can be removed by heating above 350℃. To increase the number of active sites and promote the dispersion of active materials, titanium isopropoxide (TTIP) treatment was performed on the TiO₂ support with various TTIP/TiO₂ mass ratios. Among them, the 5 wt% TTIP loaded catalyst showed improved performance due to higher thermal stability caused by high W dispersion and the formation of V⁵⁺. In addition, the 5 wt% TTIP-loaded catalyst prepared by a one-step co-precipitation method showed greater V-OH and W-OH dispersion and enhanced interactions in contrast to conventional methods, resulting in higher catalytic activity at lower temperatures. This review article aims to provide an accessible explanation for researchers investigating how to improve the surface properties of TiO2 catalysts using TTIP.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.235-243
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• 2002

Ni-base superalloys are used extensively in industry, both in aeroengines and land based turbines. About 60% by weight of most modern gas turbine engine structural components are made of Ni-base superalloys. To satisfy practical demands, the efficiency of gas turbine engines has been steadily and systematically increased by design modifications to handle higher turbine inlet or firing temperatures. However, the increase in operating temperatures has lead to a decrease in the life of components and increase in costs of replacement. Moreover, around 80% of the large frame size industrial/utility gas turbines operating in the world today were installed in the mid-sixties to early seventies and are now 25 to 30 years old. Consequently, there are greater opportunities now to repair and refurbish the older models. Basically, there are two major factors influencing the weldability of the cast alloys: strain-age cracking and liquation cracking. Susceptibility to strain-age cracking is due to the total Ti plus AI content of the alloy; Liquation cracking is due either to the presence of low melting constituents or constitutional liquation of constituents. Though Rene 41 superalloy has 4.5wt.% total Ti and Al content and falls just below the safe limit proposed by Prager et al., controlled grain size and special heat treatments are needed to obtain crack-free welds. Varying heat treatments and filler materials were used in a laboratory study, then the actual welding of service parts was carried out to verity the possibility of crack-tree weld of components fabricated from Rene 41 superalloy. The microstructural observations indicated that there were two kinds of carbides in the FCC matrix. MC carbides were located along the grain boundaries, while M$_{23}$C$_{6}$ carbide was located both inter and intra granularly. Two kinds of filler materials, Rene 41 and Hastelloy X were used to gas tungsten arc weld a patch into the sheet metal, along with varying pre-weld heat treatments. The microstructure, hardness and tensile tests were determined. The service distressed parts were categorized into three classes: with large cracks, with medium cracks and with small or no visible cracks. No significant difference in microstructure among the specimens was observed. Specimens were cut from the corner and the straight edge of the patch repair, away from the corner. The only cracks present were found to be associated with inadequate surface preparation to remove oxidation. Guidelines for oxide removal and the welding procedures developed in the research enabled crack-free welds to be produced.d.

• Mineral and Industry
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• v.27
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• pp.8-15
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• 2014

In this study, a proposal for revision of HSK Code was established on legally designated minerals and national stockpile minerals. It is difficult to exactly identify trade balances of minerals, such as lithium ore, rare earth ore, serpentine, kidney stone in legally designated minerals and ingot of indium, ferro-tungsten, ingot of antimony, granule of selenium, gallium, lanthanum oxide, cerium carbonate in national stockpile minerals because HSK Codes of them were not allocated separately. Furthermore, specific use, standard, component, type of products cannot be exactly identified in current HSK Code system. Therefore, it is makes rule to separately manage minerals which were managed by government such as legally designated minerals and national stockpile minerals. However, a proposal for revision of HSK Code system was established to comply with international standard(HS Code) and the items over a certain size(amounts : over 50 mil.$, volumes : over 5000 ton) were selected as revised subjects. Moreover hierarchies between HSK Codes were considered.

• Journal of Preventive Medicine and Public Health
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• v.31 no.3 s.62
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• pp.414-423
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• 1998

Metal fume fever has been known as an occupational disease is induced by intense inhalation of fresh metal fume with a particle size smaller than $0.5{\mu}m\;to\;1{\mu}m$. The fumes originate from heating metals beyond their boiling point, as happens, for example, in welding operations. Oxidation usually accompanies this process. In most cases, this syndrome is due to exposure to zinc oxide fumes; however, other metals like copper, magnesium, cadmium, manganese, and antimony are also reported to produce such reactions. Authors report a case of metal fume fever suspected to be associated with copper fume inhalation. The patient was a 42-year-old male and was a smoker. He conducted inert gas tungsten arc welding on copper-coated materials without safety precautions such as a protective mask and adequate ventilation. Immediately after work, he felt metallic taste in his mouth. A few hours after welding, he developed headache, chilling sensation, and chest discomfort. He also complained of myalgia, arthralgia, feverish sensation, thirst, and general weakness. Symptoms worsened after repeated copper welding on the next day and subsided gradually following two weeks. Laboratory examination showed a transient increase of neutrophil count, eosinophilia, elevated erythrocyte sedimentation rate, and positive C-reactive proteinemia. Blood and urine copper level was also increased compared to his wife. Before this episode, he experienced above complaints several times after welding with copper materials but welding of other metals did not produce any symptoms. It was suggested that copper fume would have induced metal fume fever in this case. Further investigations are needed to clarify their pathogenic mechanisms.