• Korean Journal of Materials Research
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• v.27 no.9
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• pp.471-476
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• 2017

In order to improve the high temperature oxidation resistance and lifespan of mat type porous carbon insulation, SiC was coated on carbon insulation by solution coating using polycarbosilane solution, curing in an oxidizing atmosphere at $200^{\circ}C$, and pyrolysis at temperatures up to $1200^{\circ}C$. The SiOC phase formed during the pyrolysis process was converted into SiC crystals as the heat treatment temperature increased, and a SiC coating with a thickness of 10-15 nm was formed at $1600^{\circ}C$. The SiC coated specimen showed a weight reduction of 8.6 % when it was kept in an atmospheric environment of $700^{\circ}C$ for 1 hour. On the other hand, the thermal conductivity was 0.17 W/mK, and no difference between states before and after coating was observed at all.

• Korean Journal of Materials Research
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• v.30 no.2
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• pp.74-80
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• 2020

Synthesis of composite powders for the Fe₂O₃-Zn system by mechanical alloying (MA) has been investigated at room temperature. Optimal milling and heat treatment conditions to obtain soft magnetic composite with fine microstructure were investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that α-Fe/ZnO composite powders in which ZnO is dispersed in α-Fe matrix can be obtained by MA of Fe₂O₃ with Zn for 4 hours. The change in magnetization and coercivity also reflects the details of the solid-state reduction process of hematite by pure metal of Zn during MA. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine at 900 ~ 1,000 ℃ under 60 MPa. Shrinkage change after SPS of sample MA'ed for 5 hrs was significant above 300 ℃ and gradually increased with increasing temperature up to 800 ℃. X-ray diffraction results show that the average grain size of α-Fe in the α-Fe/ZnO composite sintered at 900 ℃ is in the range of 110 nm.

• Journal of Powder Materials
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• v.27 no.3
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• pp.198-202
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• 2020

The effect of sublimable vehicles on the pore structure of Cu fabricated by freeze drying is investigated. The 5 vol% CuO-dispersed slurries with camphene and various camphor-naphthalene compositions are frozen in a Teflon mold at -25℃, followed by sublimation at room temperature. After hydrogen reduction at 300℃ and sintering at 600 ℃, the green bodies of CuO are completely converted to Cu with various pore structures. The sintered samples prepared using CuO/camphene slurries show large pores that are aligned parallel to the sublimable vehicle growth direction. In addition, a dense microstructure is observed in the bottom section of the specimen where the solidification heat was released, owing to the difference in the solidification behavior of the camphene crystals. The porous Cu shows different pore structures, such as dendritic, rod-like, and plate shaped, depending on the composition of the camphornaphthalene system. The change in pore structure is explained by the crystal growth behavior of primary camphor and eutectic and primary naphthalene.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.2
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• pp.256-263
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• 2002

The Boil-Off-Gases(BOG) in the LNG production terminal are continuously generated during the unloading, storage and supply processes by the heat penetration. In order to use these gases as useful fuel, the reliquefaction process should be installed to put the reliquefied BOG in the main LNG supply line before the secondary pump in terminal. The current reliquefaction method of BOG in LNG terminal is the direct contact one between LNG and BOG in the absorption column. But the system has severe disadvantage, which is the 10 times of LNG circulation needed for unit mass of BOG reliquefaction. It causes, therefore, high power consumption of LNG circulation pump and excessive city-gas supply, even if short demand of NG is needed in the summer time. In this paper, the new reliquefaction system of BOG by using LNG cold energy with indirect contact in precooler was suggested and analysed. The result showed new indirect contact method of BOG reliquefaction system between LNG cold energy and BOG is much more effective than the current direct contact one because of only about 1.3 times of LNG circulation needed and higher energy saving by pump power reduction.

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.625-630
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• 2012

Highly porous silicon carbide (SiC) ceramics were fabricated from polysiloxane, SiC and carbon black fillers, AlN-$Y_2O_3$ additives, and poly (ether-co-octene) (PEOc) and expandable microsphere templates. Powder mixtures with a fixed PEOc content (30 wt%) and varying SiC filler contents from 0-21 wt% were compression-molded. During the pyrolysis process, the polysiloxane was converted to SiOC, the PEOc generated a considerable degree of interconnected porosity, and the expandable microspheres generated fine cells. The polysiloxane-derived SiOC and carbon black reacted and synthesized nano-sized SiC with a carbothermal reduction during a heat-treatment. Subsequent sintering of the compacts in a nitrogen atmosphere produced highly porous SiC ceramics with porosities ranging from 78 % to 82 % and a flexura lstrength of up to ~7 MPa.

• Journal of Powder Materials
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• v.10 no.4
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• pp.241-248
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• 2003

Biaxially textured Ni tapes were fabricated by a cold working and recrystallization heat treatment processes from powder compact rods. The processing parameters associated with the cube texture formation in Ni tapes were systematically investigated by using X-ray diffraction and pole-figure analysis. The Ni powder used in this study was 5 $\mu$m in size and 99.99% in purity. To find the optimum sintering temperature, tensile tests were performed for Ni rods sintered at various temperatures. The Ni rods sintered at 100$0^{\circ}C$ showed poor elongation and low fracture strength, while the Wi rods sintered above 100$0^{\circ}C$ revealed good mechanical properties. The higher elongation and fracture strength of the Ni rods sintered at higher temperatures than 100$0^{\circ}C$ are attributed to the full densification of the sintered rods. The sintered Ni rods were cold-rolled with 5% reduction to the final thickness of 100 $\mu$m and then annealed for development of rube texture in rolled Ni tapes. The annealed Ni tapes depicted strong cube texture with FWHM(full-width at half-maximum) of in-plane and out-of-plane in the range of 8$^{\circ}$ to 10$^{\circ}$. The NiO deposited on the Ni tapes by MOCVD process showed good epitaxy with FWHM=10$^{\circ}$, which indicates that the Ni tapes can be used as a substrate for YBCO coated conductors.

• Korean Journal of Materials Research
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• v.29 no.4
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• pp.252-257
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• 2019

Fabrication of soft magnetic composite powders for the $Fe_2O_3-Ca$ system by mechanical alloying(MA) has been investigated at room temperature. It is found that soft magnetic composite powders in which CaO is dispersed in ${\alpha}-Fe$ matrix are obtained by MA of $Fe_2O_3$ with Ca for 5 hours. Changes in magnetization and coercivity also reflect the details of the solidstate reduction process of hematite by pure metal of Ca during MA. The saturation magnetization of MA powders increases with increasing MA time and reaches a maximum value of 65 emu/g after 7 hours of MA. The average grain size of ${\alpha}-Fe$ in MA powders, estimated by diffraction line-width, gradually decreases with increasing MA time and reaches 52 nm after 5 hours of MA. It can also be seen that the coercivity of the 5-hour MA sample is fairly high at 190 Oe, suggesting that the grain refinement of already-produced ${\alpha}-Fe$ tends to clearly occur during MA.

• Transactions of Materials Processing
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• v.30 no.3
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• pp.134-141
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• 2021

In order to improve excessive spring-back behavior as a result of the roll forming process using ultra high strength steel (UHSS) sheet, local softening in region of a partial area expected to be deformed on an initial blank is considered in this study. With SPFC1470 UHSS sheet with initial blank thickness of 1.20mm, the local softening is performed with the following conditions: temperatures of 500℃, 550℃, 600℃ and 650℃, and holding time of 20s, 40s, 80s and 160s. Mechanical properties, such as yield stress and tensile strength, as well as elongation, are evaluated through uniaxial tensile tests, while the microstructural characteristics as a result of local softening are also investigated using the heat-treated specimens. As a result, it is shown that the spring-back behavior of the roll-formed prototype was reduced about by 78.9%, when the local softening at about 500℃ was performed for 160s considering the practical manufacturing condition.

• Journal of Information Technology Services
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• v.20 no.3
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• pp.1-12
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• 2021

Reactor Coolant Pump (RCP) is core part of nuclear power plant to provide the forced circulation of reactor coolant for the removal of core heat. Properly monitoring vibration of RCP is a key activity of a successful predictive maintenance and can lead to a decrease in failure, optimization of machine performance, and a reduction of repair and maintenance costs. Here, we developed real-time RCP Vibration Analysis System (VAS) that web based platform using NoSQL DB (Mongo DB) to handle vibration data of RCP. In this paper, we explain how to implement digital signal process of vibration data from time domain to frequency domain using Fast Fourier transform and how to design NoSQL DB structure, how to implement web service using Java spring framework, JavaScript, High-Chart. We have implement various plot according to standard of the American Society of Mechanical Engineers (ASME) and it can show on web browser based on HTML 5. This data analysis platform shows a upgraded method to real-time analyze vibration data and easily uses without specialist. Furthermore to get better precision we have plan apply to additional machine learning technology.

• Journal of Marine Bioscience and Biotechnology
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• v.16 no.1
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• pp.19-25
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• 2024

To verify the color change in dried laver postproduction during the heating process, chromaticity elements were compared via a spectrophotometer across various heating conditions within the visible light spectrum. In general, the moisture reduction rate increased with rising temperature and time. Surface image comparisons revealed an expanded area of light reflection on the heat-treated dried laver sample due to surface roughening from shrinkage. No statistically significant differences in chromaticity values were observed in the measurements of brightness (L^*), redness (a^*), and yellowness (b^*). Reflectance spectrum measurements in the visible light region confirmed high reflectance under red wavelength conditions. In particular, a significant increase in reflectance at 700 nm compared with untreated samples was noted. The correlation between the increase in 700 nm reflectance of dried laver samples and heating conditions ranged from 0.7471 to 0.7793, suggesting its potential use as an indicator for comparing color changes in dried laver based on heating conditions.