• Korean Journal of Metals and Materials
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• v.48 no.12
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• pp.1056-1063
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• 2010

We present a new joining method for Pd-Cu membrane foils used as permeation tubes to collect $CO_2$. Since foils have poor mechanical strength, joining should be done at low temperatures to reduce residual stresses and without joining pressure. This contradicts the well known conditions for good contact between base materials that determines joint qualities. We selected Sn-Ag-Cu alloys that are highly reactive with Pd and Cu as a filler metal. As the filler melts at joining temperatures as low as $220{\sim}280^{\circ}C$, Pd and Cu are dissolved into the melt and react with the filler elements, which raises the melting temperature of the filler based on eutectic structures among the elements. Then, isothermal solidification progresses for the rest of the joining time. Intermetallic compounds (IMC) in the joints, one of the main factors for brittle joints, are inevitably formed. However, by optimizing both joining time and temperature, we balanced the wettability with IMC. Sealing test results confirmed that the joints are mechanically reliable during operation.

• Fire Science and Engineering
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• v.30 no.3
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• pp.104-109
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• 2016

Candle fires do not occur frequently, but can easily result in death. In this study, the thermal characteristics of candles and conditions and debris of candle fires were investigated to determine the causes of candle fires. The rates of decrease in weight of 10 candles were measured and found to be between 2.6 g/h and 6.7 g/h. Most candle fires are caused by the ignitiong of combustible materials close to them. The temperature near a candle ranges from about $200^{\circ}C$ to $400^{\circ}C$ at a distance of 1 cm and low ignition temperature materials such as papers can easily catch fire. The melting temperature of candles ranges between $50^{\circ}C$ and $70^{\circ}C$ and their major chemical components are fatty acids and normal hydrocarbons (over C20). Using pretreatment conditions involving the use of activated charcoal strips at $150^{\circ}C$ for 16 hours, the fire debris including candle residues were analyzed using a Gas-chromatograph/Mass-spectrometer (GC/MS).

• Journal of Korea Water Resources Association
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• v.33 no.2
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• pp.229-235
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• 2000

Characteristics of hail occurred during 1989-1998 is studied. Hail is observed mainly at west coast, southwest inland, and Taegwallyong. Average diameter of hailstone is 0.6 cm, and 70% of the occurrence frequency of hail is observed at west coast. During winter and spring, the wet -bulb zero height (WBZ) is low enough to prevent the melting process of hail. But the lack of available low-level moisture (mean mixing ratio in lowest 100 hPa) makes the size of hail small. As a result, smaller size hail is observed frequently over west coast. On the contrary, WBZ is higher during summer, it means that hail is melted before it reaches ground, but the size of hail is bigger. Thus the larger hail is observed mainly Taegwallyong during summer. Hail is observed from 1100 LST to 1500 LST over west coast and around 1800 LST over Taegwallyong. It suggest that thermally driven mesoscale circulations such as land-sea breeze and mountain ridge-valley circulation aid in the formation of hail. Upper and surface air temperature is related to formation of hailstorm. Before formation of hailstorm in November 1998, the upper air temperature decreases. And hails is observed in the spot of strong temperature and dew point temperature gradient coincidently.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.3
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• pp.508-512
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• 1998

The NTC thermistors were sintered by using microwave hybrid heating method at $1100^{\circ}C$~$1300^{\circ}C$ and those electrical properties were investigated. The obtained $B_{25^{\circ}C/85^{\circ}C}$ values from temperature dependence of electrical resisitivity were around 3100~3200 K which were almost the same values as conventionally sintered ones. Compared with conventional sintering process, this process could complete whole sintering process within 20 minutes. This the processing time and energy consumption could be reduced through this rapid heating by using microwave hybrid heating.t there were showed only two peaks, glycolide melting peak and lower molecular weight melting peak without lauryl alcohol. Conversion increased slowly with the reaction time up to 50 minutes, and then gave a sudden increase above that. The reaction time to disappear in glycolide melting peak during polymerization was shortened with the increase of lauryl alcohol content. Zero-shear viscosity of polyglycolic acid decreased with the increase of free acid content in glycolide.ssional energy and bending hysteresis increased. \circled3 Surface characteristics such as friction coefficient and thickness variation of highly shrinkage fabrics became relatively roughened state. \circled4 Since stiffened and roughened characteristics of highly shrinkage fabrics, drapabilities of them were significantly lowered. Additionally thermal insulation property of high shrinkage fabric was higher than that of low shrinkage fabric due to bulky and thickened feature. From the results, it is considered that the silk fabrics with high filling shrinkage have the good bulkiness and heat keeping properties and thus they have the suitable characteristics for high quality men's and women's formal garments.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.3 no.1
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• pp.32-43
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• 1995

Ni-Ti alloy has excellent corrosion resistance, biocompatibility, shape memory effect and superelasticity, so it has been used widely in biomedical fields. But it has difficulty in casting due to its high melting temperature and oxygen affinity at high temperature. Recently it has been attempted to cast Ni-Ti alloy using new casting machine and investment. The purpose of this study was to examine the superelastic behavior of cast shape memory Ni-Ti alloy and to compare the mechanical properties of the cast shape memory alloy with those of commercial alloys for removable partial denture framework. Ni-Ti alloy(Ni 50.25%, Ti 49.75% : atomic ratio) was cast with dental argon-arc pressure casting machine and Type IV gold alloy, Co-Cr alloy, Ni-Cr alloy, pure titanium were cast as reference. Experimental cast Ni-Ti alloy was treated with heat($500{\pm}2^{\circ}C$) in muffle furnace for 1 hour. Transformation temperature range of cast Ni-Ti alloy was measured with differential scanning calorimetry. The superelastic behavior and mechanical properties of cat Ni-Ti alloy were observed and evaluated by three point bending test, ultimate tensile test, Vickers microhardness test and scanning electron microscope. The results were as follows : 1. Cast Ni-Ti alloy(Ni 50.25%, Ti 49.75% : atomic ratio) was found to have superelastic behavior. 2. Stiffness of cast Ni-Ti alloy was considerably lesser than that of commercial alloys for removable partial denture. 3. Permanent deformation was observed in commercial alloys for removable partial denture framework at three point bending test over proportional limit(1.5mm deflection), but was not nearly observed in cast Ni-Ti alloy. 4. On the mechanical properties of ultimate tensile strength, elongation and Vickers microhardness number, cast Ni-Ti alloy was similiar to Type IV gold alloy, Co-Cr alloy, Ni-Cr alloy and pure titanium. With these results, cast Ni-Ti alloy had superelastic behavior and low stiffness. Therefore, it is suggested that cast Ni-Ti alloy may be applicated to base metal alloy for removable partial denture framework.

• Macromolecular Research
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• v.17 no.12
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• pp.1015-1020
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• 2009

The role of the water structure present in hydrogels from nutlets of three species of salvias, S. miltiorrhiza (SM), S. sclarea (SS) and S. viridis (SV), was analyzed by differential scanning calorimetry (DSC). The sharp endothermic peaks that appeared at $5.9^{\circ}C$ (SM), $2.8^{\circ}C$ DC (SS) and $1.8^{\circ}C$ (SV) in each 1.0% hydrogel of 10.4-15.8% were not affected by addition of 0.1 M urea and alkali-metal salts. The order-disorder portions in the network were slightly affected by the distribution of freezable and non-freezable water in the hydrogel networks. The SV hydrogel was further used to investigate the effects of additives (0.1-8.0 M urea and 0.1-5.0 M NaCl) on its melting behavior. At 0.5-4.0 M urea and 1.0-3.0 M NaCl, two endothermic peaks appeared, corresponding to unbound (high temperature) and bound (low temperature) water in the gel networks, and eventually merged into one endothermic peak at 5.0-8.0 M urea and 4.0-4.5 M NaCl. After this merger, the endothermic peak shifted to 3.7, 4.0 and $5.6^{\circ}C$ at 5.0, 6.0 and 8.0 M urea, respectively. In the case of NaCl, a combination of peaks that occurred at 4.0-4.5 M were accompanied by a shift to lower temperature (-14.4 and $15.3^{\circ}C$) and the endothermic peak finally disappeared at 5.0 M NaCl due to the strong binding of water in the gel networks.

• Journal of the Korean Ceramic Society
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• v.52 no.6
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• pp.462-466
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• 2015

This paper reports the microstructure of hot-pressed $ZrB_2$-SiC ceramics with added $B_4C$ as characterized by transmission electron microscopy. $ZrB_2$ has a melting point of $3245^{\circ}C$, a relatively low density of $6.1g/cm^3$, and specific mechanical properties at an elevated temperature, making it a candidate for application to environments with ultra-high temperatures which exceed $2000^{\circ}C$. Due to the non-sinterability of $ZrB_2$-based ceramics, research on sintering aids such as $B_4C$ or $MoSi_2$ has become prominent recently. From TEM investigations, an amorphous layer with contaminant oxide is observed in the vicinity of $B_4C$ grains remaining in hot-pressed $ZrB_2$-SiC ceramics with $B_4C$ as an additive. The effect of a $B_4C$ addition on the microstructure of this system is also discussed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.3
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• pp.315-324
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• 1994

The effects of impurities of the quartz raw materials on the trasformation of quartz to cristobalite were investigated. As the increase of impurities content, the amount of cristobalite crystal increased, whereas the fusion temperature of quartz and the formation temperature of cristobalite decreased. And the courses of the transformation of quartz to cristobalite were examined. The course of quartz $\rightarrow$ transitional noncrystalline phase $\rightarrow$ melt (T) and quartz $\rightarrow$ transitional noncrystalline phase $\rightarrow$ cristobalite $\rightarrow$ melt (C) were always coexisted on the transformation of quartz. In the case of high purity quartz raw material, the T course was predominant, while in low purity quartz raw material, the C course was predominant. And the calculated density of heat treated sand by the quantitative analysis of quartz and cristobalite phase by XRD is well agreed with the measured density by pycnometer. On the melting proces of quartz glass, the volume expansion of sand at a certain temperature can be estimated with the calculated density data.

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.393-397
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• 2001

The innovatory process, that is the direct separation and recovery of the iron and zinc metals contained in the high temperature exhaust gas generated from the electric arc furnace fer the inn scrap melting and/or the dust treatment, has been proposed. This proposed process consists of the moving coke bed filter that is directly connected to the electric furnace, and the following heavy metal condenser. The exhaust gas passes through the filter and the condenser right after exhausting from the electric furnace. The moving coke bed filter is being controlled at about 1000℃ and collects iron and slag components contained in the high temperature exhaust gas. Heavy metals such as zinc and lead pass through the filter as vapor. Based on the thermodynamic considerations, the iron oxide and the zinc oxide are reduced in the filter. The solution loss reaction rate is comparatively low at about 1000℃ in the coke bed filter by the analysis using the mathematical simulation model. The heavy metal condenser is installed in the position after the coke bed filter, and rapidly cools the gas from about 1000℃ to 450℃ by a full of the cooling medium like the solid ceramic ball in addition to the cooling from the wall. The zinc and lead vapor condense and separate f개m the gas in a liquid state. The investigation of the characteristics of the exhaust gas of the commercial electric arc furnace, the fundamental experiments of the laboratory scale and the bench scale ensured the formation of this proposed process. A small-scale pilot plant examination is carrying out at present to confirm the formation of the process. It is certain that the dust generation of the electric arc furnace is extremely decreased, and it can save the energy consumption of usual dust treatment processes by the realization of this process.

• Korean Journal of Materials Research
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• v.26 no.1
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• pp.22-28
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• 2016

In this study, we fabricated high quality color conversion component with green/red phosphor and low melting glass frit. The color conversion component was prepared by placing the green and red phosphor layer on slide glass via screen printing process. The properties of color conversion component could be controlled by changing coating sequence, layer thickness and heat treatment temperature. We discovered that optical properties of color conversion component were generally determined by the lowest layer. On the other hand, the heat treatment temperature also affected to correlated color temperature (CCT) and color rending index (CRI). The color conversion component with a green (lower) - red (upper) layer which was sintered at $550^{\circ}C$ showed the best optical properties: CCT, CRI and luminance efficacy were 3340 K, 78, and 56.5 lm/w, respectively.