• Journal of Powder Materials
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• v.29 no.4
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• pp.320-324
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• 2022

Lightweight steel is a crucial material that is being actively studied because of increased carbon emissions, tightening regulations regarding fuel efficiency, and the emergence of UAM, all of which have been recently labeled as global issues. Hence, new strategies concerning the thickness and size reduction of steel are required. In this study, we manufacture lightweight steel of the Fe-Mn-Al-C system, which has been recently studied using the DED process. By using 2.8 wt.% low-Mn lightweight steel, we attempt to solve the challenge of joining steel parts with a large amount of Mn. Among the various process variables, the laser scan power is set at 600 and 800 W, and the laser scan speed is fixed at 16.67 mm/s before the experiments. Several pores and cracks are observed under both conditions, and negligibly small pores of approximately 0.5 ㎛ are observed.

• Carbon letters
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• v.19
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• pp.72-78
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• 2016

Spinnable pitches and carbon fibers were successfully prepared from petroleum or coal pyrolysis residues. After pyrolysis fuel oil (PFO), slurry oil, and coal tar were simply filtered to eliminate the solid impurities, the characteristics of the raw materials were evaluated by elemental analysis, ¹³C nuclear magnetic resonance spectrometer, matrix-assisted laser desorption/ionization time-of-flight mass spectrometer (MALDI-TOF-MS), and so on. Spinnable pitches were prepared for melt-spinning carbon fiber through a simple distillation under strong nitrogen flow, and further vacuum distillation to obtain a high softening point. Carbon fibers were produced from the above pitches by single-hole melt spinning and additional heat treatment, for oxidization and carbonization. Even though spinnable pitches and carbon fibers were processed under the same conditions, the melt-spinning and properties of the carbon fiber were different depending on the raw materials. A fine carbon fiber could not be prepared from slurry oil, and the different diameter carbon fibers were produced from the PFO and coal tar pitch. These results seem to be closely correlated with the initial characteristics of the raw materials, under this simple processing condition.

• Journal of Microbiology and Biotechnology
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• v.26 no.9
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• pp.1570-1578
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• 2016

Commercial application of laccase is often hampered by insufficient enzyme stocks, with very low yields obtained from natural sources. This study aimed to improve laccase production by mutation of a Coriolopsis gallica strain and to determine the biological properties of the mutant. The high-yield laccase strain C. gallica TCK was treated with N-methyl-N-nitro-N-nitrosoguanidine and ultraviolet light. Among the mutants isolated, T906 was found to be a high-production strain of laccases. The mutant strain T906 was stabilized via dozens of passages, and the selected ones were further processed for optimization of metallic ion, inducers, and nutritional requirements, which resulted in the optimized liquid fermentation medium MF9. The incubation temperature and pH were optimized to be 30℃ and 4.5, respectively. The mutant strain T906 showed 3-times higher laccase activity than the original strain TCK under optimized conditions, and the maximum laccase production (303 U/ml) was accomplished after 13 days. The extracellular laccase isoenzyme 1 was purified and characterized from the two strains, respectively, and their cDNA sequence was determined. Of note, the laccase isoenzyme 1 transcription levels were overtly increased in T906 mycelia compared with values obtained for strain TCK. These findings provide a basis for C. gallica modification for the production of high laccase amounts.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2005.11a
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• pp.221-228
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• 2005

The objectives of this paper are to present the general features of the current IAEA programs and their future prospects in the fields of the nuclear fuel cycle and the related materials technologies thus responding to a need to achieve a consolidated understanding of the Agency's programs for an effect ive implementation of the respective national R&D projects in Korea. During the development of the Agency's programs for 2005-2007 in the aforementioned fields. it is foreseen that an considerable attention will be attributed to the concepts, models and opportunities for optimizing the fuel cycle, mining the raw materials, re-using the materials and reducing the waste arisings (e.g. through Partitioning and transmutation), all of which, will Include an enhanced consideration for proliferation and security concerns.

• Particle and aerosol research
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• v.9 no.3
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• pp.139-147
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• 2013

The performances of indoor air cleaners including particle cleaning capacity and collection efficiency are usually tested at the condition of the maximum air flow rate of the air cleaners. However, the power consumption of the air cleaners is highly dependent on the air flow rate of the individual air cleaners. Therefore, there seems to be an optimized air flow rate for the air cleaning capacity considering power consumption. In this study, clean air delivery rate(or standard useful area as suggested room size) and power consumption have been investigated for different maximum air flow rates of 15 air cleaners and then compared those for different air flow rate modes of the individual 5 air cleaners selected from the 15 cleaners. For the maximum air flow rate conditions of 15 air cleansers, the power consumption per unit area was less related to the maximum air flow rate. However, for the different air flow rate modes of the selected 5 air cleaners, the lower power consumption per unit area was corresponding to the lower air flow rate mode of the individual air cleaners. When considering the operation time to the desired particle concentrations, there was an optimized one in the medium air flow rate modes for the individual air cleaners. Therefore, not only the maximum air flow rate but also lower air flow rates of individual air cleaners should be considered for estimating air cleaning capacity based on energy consumption per unit area.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.1
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• pp.105-110
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• 2018

The flow boiling heat transfer of water was experimentally investigated on plain and sintered microporous surfaces in a mini-channel. The effects of microporous coating on flow boiling heat transfer of subcooled water were investigated in a 300 mm long mini-channel with a cross section of $20{\times}10mm^2$. The test section has sufficiently long entrance length of 300 mm which provides a fully-developed flow before the channel inlet. The bottom side of the channel was heated by a copper block assembled with a high-density cartridge heater and other sides of the channel were insulated. The microporous surface was fabricated by sintering copper particles with the average particle size of $50{\mu}m$ on the top side of the copper block. Heat transfer measurement was conducted at the mass flux of $208kg/m^2s$ and the heat flux up to $500kW/m^2$. Microporous coated surface showed an earlier boiling incipience compared with plain surface regardless of the mass flux. Microporous coating were significantly attributed to local wall temperature and local heat transfer coefficient for flow boiling.

• Ceramist
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• v.23 no.2
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• pp.184-199
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• 2020

The solid oxide fuel cells (SOFCs) are the one of the most promising energy conversion devices which can directly convert chemical energy into electric power with high efficiency and low emission. The lowering operating temperature below 800 ℃ has been considered as the mostly considerable research and development for commercialization. The major issue is to maintain reasonably high performance of SOFCs at reduced temperatures due to increment of polarization resistance of electrodes and electrolyte. Thus, the alternative materials with high catalytic activities and fast oxygen ion conductivity are required. For recent advances in electrolyte materials and technology, newly designed, highly conductive electrolyte materials and structural engineering of them provide a new path for further reduction in ohmic polarization resistance from electrolytes. Here, a powerful strategy of the bilayer concept with various oxide electrolytes of SOFCs are briefly reviewed. These recent developments also highlight the need for electrolytes with greater conductivity to achieve a high performance, thus providing a useful guidance for the rational design of cell structures for SOFCs. Moreover, cell design, materials compatibility, processing methods, are discussed, along with their role in determining cell performance. Results from state-of-the-art SOFCs are presented, and future prospects are discussed.

• Composites Research
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• v.32 no.1
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• pp.45-49
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• 2019

Fiber reinforced composites fabricated by the resin film infusion (RFI) process, which is one of the outof-autoclave process, have the advantage of significantly reducing the processing cost in large structures while having excellent mechanical properties and uniform impregnation of the resin. In this study, we applied RFI carbon fiber composites to unmanned aerial vehicle structures to improve structural safety and achieve weight reduction. The tensile test results showed that the strength was 46% higher than that of generic T300 grade plain weave carbon fiber composites. As a result of the layup design and finite element analysis of the composite wing structure using the above material properties, the wing tip deflection is decreased by 31%, the structural safety factor is increased by 28% and the weight of the entire structure can be reduced by more than 10% compared to the reference model using glass fiber composite material.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.1
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• pp.8-18
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• 2022

With rapid industrialization and population growth, fossil fuel use has increased, which has a significant impact on the environment. Hydrogen does not cause contamination in the energy production process, so it seems to be a solution, but it is essential to find an appropriate storage method due to its low efficiency. In this study, Mg-based alloys capable of ensuring safety and high volume and hydrogen storage density per weight was studied, and Mg₂NiH_x synthesized with Ni capable of improving hydrogenation kinetics. In addition, in order to improve thermal stability, a hydrogen storage composite material synthesized with CaO was synthesized to analyze the change in hydrogenation reaction. In order to analyze the changes in the metallurgical properties of the materials through the process, XRD, SEM, BET, etc. were conducted, and hydrogenation behavior was confirmed by TGA and hydrogenation kinetics analysis. In addition, in order to evaluate the impact of the process on the environment, the environmental impact was evaluated through "Material Life Cycle Assessments" based on CML 2001 and EI99' methodologies, and compared and analyzed with previous studies. As a result, the synthesis of CaO caused additional power consumption, which had a significant impact on global warming, and further research is required to improve this.

• Transactions of the Korean hydrogen and new energy society
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• v.35 no.2
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• pp.240-248
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• 2024

The purpose of this study is to investigate the freezing phenomena in printed circuit heat exchanger (PCHE) for cryogenic liquid hydrogen vaporizer. Local freezing phenomena in hot channels should be avoided in designing PCHE for cryogenic liquid hydrogen vaporizer. Hence, the flow and thermal characteristics of PCHE is experimentally investigated to figure out the conditions under when freezing occurs. To conduct lab-scale PCHE experiment, liquid nitrogen is used as a working fluid in cold channels instead of using liquid hydrogen. Glycol water is used as a working fluid in hot channels. Based on the experimental data, ratio between mass flow rates of cold channels and that of hot channels is proposed as contour map to avoid the freezing phenomena in PCHE.