• Korean Journal of Materials Research
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• v.15 no.2
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• pp.93-96
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• 2005

The arc melting was employed to prepare undoped $CoSb_3$ compounds and their thermoelectric properties were investigated. Specimen annealed at $400^{\circ}C$ for 24 hrs showed sound microstructure. However, considerable voids and cracks were found after annealing at above $500^{\circ}C$. It seems to be attributed to the phase dissociation and thermal expansion due to phase transitions during annealing and cooling. Single phase $\delta-CoSb_3$ was successfully obtained by annealing at $400^{\circ}C$ for 24 hrs. In the case of increasing annealing temperature, phase decompositions occurred. Undoped $CoSb_3$ showed p-type conduction and intrinsic semiconducting behavior at all temperatures examined. Thermoelectric properties were remarkably improved by annealing and they were closely related to phase transitions.

• Polymer(Korea)
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• v.28 no.3
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• pp.253-262
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• 2004

Poly(vinyl alcohol)(PVA)/chitosan blend films with non-toxicity, biodegradability, and biocom-patibility were prepared by solution casting. Variation of the physicochemical properties of the blend films was investigated through to several analysis methods. Examination of antibacterial properties revealed that bacterio-static ratios of all blend samples containing chitosan more than 10 wt％ were greater than 99.9％. Moisture regain was increased with increasing chitosan content but the degree of swelling was decreased. Up to chitosan content 15 wt％t, the melting and crystallization temperature of blend films was increased with chitosan content. The blends containing chitosan content 10 and 15 wt％ gave melting temperature 229 and 228$^{\circ}C$, respectively. However, the melting temperature was decreased if chitosan content exceeded 20 wt％. The mechanical properties of the blend films were increased with increasing chitosan content in both dry and wet states. The blend film including 15 wt％ chitosan exhibited unusually high tensile strength.

• Ocean and Polar Research
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• v.41 no.2
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• pp.63-77
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• 2019

In order to investigate the behavior and seasonal variability of Mn as one of the bio-essential metals in the Amundsen sea, which is known as the most biologically productive coastal area around the Antartica, seawaters were collected using a clean sampling system for 10 stations (96 ea) in 2014 (ANA04B) and for 12 stations (139 ea) in 2016 (ANA06B) surveys of RV ARAON. Dissolved and particulate Mn concentration varied in the range of 0.15-4.43 nmol/kg and <0.01 to 2.42 nM in 2014 and in the range of 0.25-4.15 nmol/kg and 0.01-2.64 nM in 2016, respectively. From the sectional distribution of dissolved and particulate Mn, it might be suggested that dissolved/particulate Mn was provided from iceberg melting and diffusion/resuspension from sediments, respectively. Although this sea is highly productive, there was little evidence regarding the biological origin of dissolved Mn, but particulate Mn only in sea ice and offshore areas could be explained as originating from organic matters, e.g. phytoplanktons. And it could be suggested that the subsurface maximum of dissolved Mn was formed by isopycnal transport of melting materials from ice wall to offshore. Compared to early (2014) summer, temperature, salinity, biomass, dissolved and particulate Mn in late (2016) summer indicated that temporal variations might be resulted from the reduction of ice melting and mCDW flow, which induced a reduction in resuspension. In addition, in the late summer, particles including biomass were reduced, which brought about a reduction in the removal rate of dissolved Mn.

• Korean Journal of Metals and Materials
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• v.50 no.10
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• pp.753-761
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• 2012

The reduction behavior of low level oxides such as (T.Fe), (MnO) and ($P_2O_5$) in molten EAF slag was investigated using commercial reductants. In an air atmosphere, the slag volume increased and the reduction rate of the slag was very low due to the oxidation loss of reductants by oxygen in the air. The reduction rate of the slag was also low when a commercial reductant was used alone in an Ar gas atmosphere. The reason is probably because the material transfer through the interface between the slag and reductant is difficult due to the formation of high melting point oxide. When reductants were mixed with burnt lime in order to form low melting point reaction products, the reduction rate of the slag increased up to the range of 45-70%. By using the mixtures of reductants and burnt lime so as to form a low melting point slag at the reaction end, the reduction rate of the slag was improved up to 60-85%.

• Korean Journal of Materials Research
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• v.32 no.3
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• pp.132-138
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• 2022

Zintl phase Mg₃Sb₂ is a promising thermoelectric material in medium to high temperature range due to its low band gap energy and characteristic electron-crystal phonon-glass behavior. P-type Mg₃Sb₂ has conventionally exhibited lower thermoelectric properties compared to its n-type counterparts, which have poor electrical conductivity. To address these problems, a small amount of Sn doping was considered in this alloy system. P-type Mg₃Sb₂ was synthesized by controlled melting, pulverizing, and subsequent vacuum hot pressing (VHP) method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate phases and microstructure development during the process. Single phase Mg₃Sb₂ was successfully formed when 16 at.% of Mg was excessively added to the system. Nominal compositions of Mg_3.8Sb_2-xSn_x (0 ≤ x ≤ 0.008) were considered in this study. Thermoelectric properties were evaluated in terms of Seebeck coefficient, electrical conductivity, and thermal conductivity. A peak ZT value ≈ 0.32 was found for the specimen Mg_3.8Sb_1.994Sn_0.006 at 873 K, showing an improved ZT value compared to intrinsic one. Transport properties were also evaluated and discussed.

• Food Science of Animal Resources
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• v.44 no.4
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• pp.790-804
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• 2024

This study compared the physicochemical properties of edible insect oils from silkworm (Bombyx mori) pupa (SP), sago palm weevil (Rhynchophorus ferrugineus) larva (PW), and bamboo caterpillar (Omphisa fuscidentalis; BC) to oils from chicken skin (CK), beef back fat (BF), pork back fat (PF), salmon belly (SB), sea bass belly (BB), coconut (C), and peanut (P). The fatty acid profiles and thermal behaviors (crystallization and melting) of the extracted oils were evaluated. PW and BC oils had more saturated fatty acids (SFAs) than CK, PF, SB, BB, and P oils. SP oil had equivalent SFA content to CK and BB oils. Insect oils exhibited similar monounsaturated fatty acid concentrations in all samples, except C oils. PW and BC oils exhibited a higher content of palmitoleic acid than the other oils. SP oils contained polyunsaturated fatty acids similar to those in SB and BB oils, which were higher than those in PW, BC, CK, BF, and PF oils. SP oil also exhibited the highest concentration of α-linolenic acid (C18:3 n-3). Arachidonic acid (0.01-0.02 g/100 g) in all insect oils was lower level compared to CK, BF, PF, SB, and BB oils. SP oil (0.03 g/100 g) exhibited a slightly higher level of eicosapentaenoic acid compared to PW (0.01 g/100 g) and BC (0.01 g/100 g) oils. The insect oils were liquid at ambient temperature, solid below -15℃, and required less energy (∆H_m-max) for melting than other samples. This study indicated that insects, particularly SP, could serve as an alternative source of fat to meet its growing demand.

• International Journal of Korean Welding Society
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• v.4 no.1
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• pp.15-22
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• 2004

Metal transfer behavior of three shielded metal arc welding electrodes, AWS El1018, E6013 and E6010, were investigated through the characterization of size distribution of droplets and measurement of arc voltage signals. Of the three electrodes, Ell018 electrode showed the largest droplet size with the smallest amount of spatter, while E6010 electrode showed the smallest droplet size with the largest amount of spatter. Even though Ell0l8 electrode showed a good agreement between the frequencies of voltage drop in FFT processed voltage signals and the transfer rate of droplets, E6013 and E6010 electrodes showed weaker correlation because of their dominant explosive transfer behavior. The type of cathode used and electrode baking time also influenced the metal transfer behavior. Compared to bead-on-plate welding using steel plate as a cathode, welding on a water-cooled copper pipe showed less short-circuiting and higher melting rate in all electrodes because of higher arc potential and/or anode drop. When baked for a long time, E6010 electrode showed much more stable arc with less short-circuiting and explosion due to the loss of gas formation ingredients.

• Corrosion Science and Technology
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• v.11 no.5
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• pp.191-195
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• 2012

The aim of this study was to investigate effects of hafnium content on the corrosion behavior of Ti alloys in electrolyte containing chloride ion. For this study, Ti-Hf binary alloys contained 10 wt%, 20 wt% and 30 wt% Hf were manufactured in a vacuum arc-melting furnace and subjected to heat treatment for 12h at $1000^{\circ}C$ in an argon atmosphere. The pitting corrosion behavior of the specimens was examined through potentiodynamic and potentiostatic tests in 0.9 wt% NaCl electrolyte at $36.5{\pm}1^{\circ}C$. The corrosion morphology of Ti-xHf alloys was investigated using optical microscopy (OM) and X-ray diffractometer (XRD). From the optical microstructures and XRD results, needle-like martensite ($\alpha$') phases of the Ti-xHf alloys increased with an increase of Hf addition. Corrosion current density $(I_{corr})$ and current density $(I_{300mV})$ in passive region decreased, whereas, corrosion potential increased with Hf content. At the constant potential ($300mV_{SCE}$), current density decreased as time increased.

• Journal of Korea Foundry Society
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• v.42 no.6
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• pp.347-357
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• 2022

In this study, 3D visualization of the packing behavior of the charge material in a foundry was attempted. It was simulated based on the practical conditions of the charge material and the melting furnace. It was confirmed whether the 3D visual simulation realistically implements the packing behavior of the manufacturing site. The realistic packing state by the 3D visual simulation was compared with the ideal packing state. It was analyzed in which case the difference between the two packing states occurred. The advantages of applying the 3D visual simulation to the manufacturing process were investigated, and various application plans in the casting industry were proposed.

• Journal of the Korean Ceramic Society
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• v.48 no.4
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• pp.293-297
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• 2011

The thermodynamic behavior of phenolic resin was investigated to verify the relation between the properties of porous ceramics with $ZrO_2$-C system for submerged entry nozzle and the characteristics of phenolic resin with various relative humidity. The green and the sintered density were decreased between 25% and 50% relative humidity, whereas they were gradually enhanced above 50% relative humidity. The highest value of apparent porosity was 20.1% and the minimum compressive strength was 69MPa in the specimen using the powder exposed to 50% relative humidity. As a result of thermal analysis for phenolic resin, the shift of endothermic peak to low temperature and the reduction of exothermic peak were observed, and the peaks corresponded to melting and curing of phenolic resin, respectively. The melting and the curing of phenolic resin generate the change of green density, and it can affect the properties of submerged entry nozzle.