• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.128-130
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• 2017

$NaBH_4$ was added to improve the water reactivity of aluminum powder as a solid propellant for underwater propulsion. Aluminum powders showed different combustion characteristics depending on the amount of $NaBH_4$ added. When $NaBH_4$ was added, it was burned by reaction with water even at a temperature much lower than the boiling point. In this study, it was confirmed that $NaBH_4$ is an effective additive to accelerate the vapor reaction with Al powder.

• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.1022-1028
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• 2024

A neutronics study of a supercritical CO₂-cooled fast reactor core for nuclear propulsion has been performed in this work. The thermal power of the reactor core is 30 MWth and a ceramic UO₂ fuel can be used to achieve a 20-year lifetime without refueling. In order to make a compact core with inherent safety features, the drum-type reactivity control system and folding-type shutdown system are adopted. In addition, we suggest a cold shutdown system using gadolinium as a spectral shift absorber (SSA) against flooding. Although there is a penalty of U-235 enrichment for the core embedded with the cold shutdown system, it effectively mitigates the increment of reactivity at the flooding of seawater. In this study, the neutronics analyses have been performed by using the continuous energy Monte Carlo Serpent 2 code with the evaluated nuclear data file ENDF/B-VII.1 Library. The supercritical CO₂-cooled fast reactor core is characterized in view of important safety parameters such as the reactivity worth of reactivity control systems, fuel temperature coefficient (FTC), coolant temperature coefficient (CTC), and coolant temperature-density coefficient (CTDC). We can say that the suggested core has inherent safety features and enough flexibility for load-following operation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.3
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• pp.223-228
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• 2019

We fabricated a printed Ag:CNT film as a liquid sensor for the detection of HNS (hazardous and noxious substances) in seawater. The paste required for printing was prepared using Ag powder, MWCNTs (multi-walled carbon nanotubes), and an organic binder. The heat treatment process for binder removal was optimized. In order to confirm that the sensor was operational, the resistance change characteristics in brine (3.5%) and methanol (99.8%) were assessed at $20^{\circ}C$. EDL (electrical double layer) formation and redox reactivity were confirmed as the most important reactions affect each electrical property of sensor in brine and methanol. From these results, it was determined that printed Ag:CNT film can be applied as a sensor to detect HNS in seawater.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.4
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• pp.578-584
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• 2021

This study comparatively analyzed the properties of hydration reaction and strength development of four types of pond ash(PA) and fly ash(FA), aiming for the effective use of PA. The PA whose chlorine content was highest due to the seawater movement method had a faster setting time, higher cumulative heat, and greater initial strength development than those of FA due to the acceleration of the cement hydration reaction. However, the activity factor increase rate decreased after seven days of curing due to the rapid generation of early hydrates. The PA that contained impurities, such as a large amount of unburned carbon, had a delayed setting time due to the lower hydration reaction. Moreover, the strength was degraded in all curing ages. The PA whose chlorine content was lower due to the freshwater movement method and the amorphous content exhibited similar hydration reactivity and strength development characteristics compared to that of FA. The thermogravimetric analysis results verified that it had a similar level of Ca(OH)₂ consumption and pozzolanic reactivity with that of FA. Conclusively, it is necessary to expand the application of the freshwater movement method and manage the ignition loss to raise PA's usability.

• Bulletin of the Korean Chemical Society
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• v.28 no.3
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• pp.432-438
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• 2007

Environmentally important phthalic esters have been analyzed by GC-MS in terms of individual phthalic esters or total phthalic esters directly or after derivatization. Derivatization improves the chromatographic characteristics of the highly polar phthalic esters. This study focused on the GC-MS determination of the total phthalic esters and the individual phthalic esters simultaneously. The phthalic esters were hydrolyzed to phthalate and corresponding alcohols in 1 M NaOH solution at 90 oC for 30 min followed by extraction with ethyl acetate after acidifcation. The phthalic acid and alcohols were simultaneously silyl derivatized using bis(trimethylsilyl)trifluoroacetamide (BSTFA) to their corresponding silyl ester and ethers in the mixture of 60% acetone and 40% ethyl acetate at room temperature within 30 min. Because of the high reactivity of BSTFA with the phthalic acid and alcohols effective silyl derivatization was possible simultaneously. GC-MS analysis of the silyl derivatives of phthalic acid and alcohols was performed. The total phthalic ester content was estimated from the analytical result of phthalic silyl ester, while the individual phthalic ester was quantified from the analytical results of alcoholic silyl ethers. This technique was applied to spiked tab water and real seawater samples from the Lake Shihwa in Korea. The results were checked against the results from the direct GC-MS analysis of the phthalic esters and reasonable recoveries with high sensitivity were achieved. The recoveries were higher than 75% with low relative standard deviation (below 10%).