• Korean Chemical Engineering Research
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• v.56 no.6
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• pp.819-825
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• 2018

Porous nanofibers comprising hollow ${\alpha}-Fe_2O_3$ nanospheres were prepared by applying both template method and Kirkendall diffusion effect to electrospinning process. During heat-treatment processes, the solid Fe nano-metals formed by initial heat-treatment in the carbon matrix were converted into the hollow structured ${\alpha}-Fe_2O_3$ nanospheres. In particular, PS nanobeads added in the spinning solution were decomposed and formed numerous channels in the composite, which served as a good pathway for Kirkendall diffusion gas. The resulting porous nanofibers comprising hollow ${\alpha}-Fe_2O_3$ nanospheres were applied as an anode material for lithium-ion batteries. The discharge capacities of the nanofibers for the 30th cycle at a high current density of $1.0A\;g^{-1}$ was $776mA\;h\;g^{-1}$. The good lithium ion storage property was attributed to the synergetic effects of the hollow ${\alpha}-Fe_2O_3$ nanospheres and the interstitial nanovoids between the nanospheres. The synthetic method proposed in this study could be applied to the preparation of porous nanofibers comprising hollow nanospheres with various composition for various applications, including energy storage.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.31 no.3
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• pp.226-236
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• 2021

Objectives: Concerns have been raised about the possible health effects of radon on both workers and consumers with the spread of social attention to the impact of radon exposure. Thus, an entire raw material handling workshop was investigated, and standards for radon levels in the workplace were newly established at 600 Bq/m³. However, regulations on the management of workers exposed to radon are still insufficiently developed. Therefore, by comparative analysis of overseas and domestic radon-related regulations for workplaces, this study aims to suggest improvement plans of protection regulations under the Occupational Safety and Health Act (OSH Act) for the prevention of health disorders of radon-exposed workers. Methods: For overseas case studies, we consulted radon-related laws and reports officially published on the websites of the European Union (EU), the United States (U.S.) and the United Kingdom (UK) government agencies. Domestic law studies were conducted mainly on the Act on Protective Action Guidelines against Radiation in the Natural Environment and the OSH Act. Results: In Europe, the basic safety standards for protection against risks arising from radon (Council Directive 2013/59/EURATOM of 5 December 2013) was established by the EU. They recommend that the Member States manage radon level in workplaces based on this criterion. In the U.S., the standards for workplaces are controlled by the Occupational Safety and Health Administration (OSHA) and the Mine Safety and Health Administration (MSHA). Action on radon in the UK is specified in "Radon in the workplace" published by the Health and Safety Executive (HSE). Conclusions: The Act on Protective Action Guidelines against Radiation in the Natural Environment mainly refers to the management of workplaces that use or handle raw materials but does not have any provisions in terms of protecting naturally exposed workers. In the OSH Act, it is necessary to define whether radon is included in radiation for that reason that its current regulations have limitations in ensuring the safety workers who may be exposed to naturally occurring radon. The management standards are needed for workplaces that do not directly deal with radon but are likely to be exposed to radon. We propose that this could be specified in the regulations for the prevention of health damage caused by radiation, not in Article 125 of the OSH Act.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.1
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• pp.37-42
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• 2021

The effect of chemical composition on the structural and thermal properties of TiZrN thin films was studied. As the Zr fraction in the deposited TixZr1-xN (x = 0.87, 0.82, 0.7, 0.6, and 0.28) increased, microstructural changes consisted of reduction in the grain size and a gradual transition from columnar structure to granular structure were observed. In addition, it was also confirmed that a gradual crystal phase transition from TiN to TiZrN has occurred as the Zr fraction increased up to 0.4. After heat treatment at 900℃, Ti0.82Zr0.18N and Ti0.7Zr0.3N layers were converted to a form in which rutile phase TiO2 and TiZrO4 oxides coexist, while Ti0.6Zr0.4N layer was converted to TiZrO4 oxide. Among the five compositions of TiZrN films, the Ti0.6Zr0.4N showed the best high temperature stability and produced a significant enhancement in the thermal oxidation resistance of Inconel 617 through suppressing the surface diffusion of Cr caused by thermal oxidation of the Inconel 617 substrate.

• Applied Chemistry for Engineering
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• v.22 no.6
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• pp.672-678
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• 2011

In this work, carbon fibers were electrolessly Ni-plated in order to investigate the effect of metal plating on the electromagnetic shielding effectiveness (EMI-SE) of Ni-coated carbon fibers-reinforced epoxy matrix composites. The surfaces of carbon fibers were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Electric resistance of the composites was tested using a 4-point-probe electric resistivity tester. The EMI-SE of the composites was evaluated by means of the reflection and adsorption methods. From the results, it was found that the EMI-SE of the composites enhanced with increasing Ni plating time and content. In high frequency region, the EMI-SE didn't show further increasing with high Ni content (Ni-CF 10 min) compared to the Ni-CF 5 min sample. In conclusion, Ni content on the carbon fibers can be a key factor to determine the EMI-SE of the composites, but there can be an optimized metal content at a specific electromagnetic frequency region in this system.

• Journal of Industrial Convergence
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• v.20 no.10
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• pp.33-38
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• 2022

In this paper, a simple method of forming a solution-based carbon nanotube (CNT) for use as a conductive material for electronic devices was studied. The CNT thin film coating was performed on the glass by applying the spin coating method and the argon atmospheric pressure plasma process. In order to observe changes in electrical and physical properties according to the number of coatings, samples formed in the same manner from times 1 to 5 were prepared, and surface shape, reflectance, transmittance, absorbance, and sheet resistance were measured for each sample. As the number of coatings increased, the transmittance decreased, and the reflectance and absorptivity increased in the entire measurement wavelength range. Also, as the wavelength decreases, the transmittance decreases, and the reflectance and absorption increase. In the case of electrical properties, it was confirmed that the conductivity was significantly improved when the second coating was applied. In conclusion, in order to replace CNT with a transparent electrode, it is necessary to consider the number of coatings in consideration of reflectivity and electrical conductivity together, and it can be seen that 2 times is optimal.

• Journal of the Korea Organic Resources Recycling Association
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• v.30 no.3
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• pp.5-12
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• 2022

This study suggests the effective recycling method of sludge waste from various industrial fields to synthesize uniform colloidal silica nanoparticles. In detail, polymers are removed from the sludge waste to attain sludge-extracted silica (s-SiO₂) micron-sized particles, and ammonia assisted sonication is applied to s-SiO₂, which has effectively extracted the silanol precursor. The nano-sized silica (n-SiO₂) particles are successfully synthesized by a typical sol-gel method using silanol precursor. Also, the yield amounts of n-SiO₂ are determined by the function of s-SiO₂ etching time. Finally, n-SiO₂-based slurry is synthesized for the practical CMP application. As a result, rough-surfaced semiconductor chip is successfully polished by the n-SiO₂-based slurry to exhibit the mirror-like clean surface. In this regard, sludge wastes are successfully prepared as valuable semicondutor grade materials.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.3
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• pp.293-299
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• 2022

Recently, various stakeholder are interested in microplastic to cause pollution of the marine's ecosystem and effort to conduct study of product's life cycle to reduce pollution of marine's ecosystem. The micorplastic refer to materials of the nano- to micro- sized units and it can be classified into primary and secondary. The primary microplastic mean the manufactured for use in the specific field such as the microbead of the cosmetic or cleanser. also, secondary mean the unintentionally generated during use of the product such as the textile crumb by the doing the laundry. Tire and Road Wear Particles(TRWPs) are also defined as secondary microplastic. Typically, TRWPs are created by friction between the tread compound's rubber of the tire and the surface of the road du ring the driving cars. Most of the generated TRWPs exist on the roadside and some of them were carried to marine by the rainwater. In this study, we perform the quantitative analysis of the TRWPs existed in fine dust at the roadside. So, we collected the dust from the roadside in Chungcheongnam-do's C site with a movement of 1,300 cars per the hour. The collected samples were separated according to size and density. And shape analysis was performed using the Scanning Electron Microscope(SEM). We were possible to discover a lot of TRWPs at the fine dust of the 100 ± 20 ㎛. And we analysis it u sing the Thermo Gravimetric Analysis(TGA) and Gas Chromatography/Mass Spectrometer(GC/MS) for the quantitative components from the tire. As a result, it was confirmed that TRWPs generated from the roadside fine dust were included the 0.21 %, and the tire and road components in the generated TRWPs consisted of the 3:7 ratio.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.6
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• pp.787-792
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• 2022

In winter, the excessive use of deicing salt deteriorates concrete pavement durability. To reduce the amount of deicing salt used, phase-change materials (PCMs) potentially offer an alternative way to melt snow through their latent heat storage characteristics. In this research, thermal energy storage concrete was developed by using PCM-impregnated expanded clay as 50 % replacement to normal aggregate by volume. In addition, to improve the thermal efficiency of PCM lightweight aggregate (PCM-LWA)-incorporated concrete, multi-walled carbon nanotubes (MWCNTs) were incorporated in proportions of 0.10 %, 0.15 %, and 0.20 % by binder weight. Compressive strength testing and programmed thermal cycling were performed to evaluate the mechanical and thermal responses of the PCM-LWA concrete. Results showed a significant strength reduction of 54 % due to the PCM-LWA; however, the thermal performance of the PCM-LWA concrete was greatly improved with the addition of MWCNTs. Thermal test results showed that 0.10 % MWCNT-incorporated concrete had high thermal fatigue resistance as well as uniform heat flow, whereas specimens with 0.15 % and 0.20 % MWCNT content had a reduced thermal response due to supercooling when the ambient temperature was varied between -5℃ and 10℃.

• Nutrition Research and Practice
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• v.16 no.sup1
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• pp.134-146
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• 2022

BACKGROUND/OBJECTIVES: Accumulating evidence has shown the beneficial effects of isoflavone on health. There is limited information on the usual isoflavone intake for Koreans. This study examined the usual intake of total isoflavone and its major food sources in Koreans according to age and gender. SUBJECTS/METHODS: The dietary intake data of 21,271 participants aged 1 yrs and older from the Korea National Health and Nutrition Examination Survey (KNHANES) VII 2016-2018 were analyzed. The average isoflavone intake was estimated based on the 24-h dietary recall data in KNHANES and the isoflavone database from the Korea Rural Development Administration (RDA) and literatures. The usual isoflavone intake was estimated by applying the ratio of within- and between-participant variance estimated from the 2009 KNHANES data to the 7th KNHANES (2016-2018) data. The variance of the isoflavone intake was calculated using MIXTRAN macro with intake data for two days in the 2009 KNHANES. Complex sample analysis with stratified variables and integrated weights was conducted. RESULTS: The mean total isoflavone intake in the Korean population aged 1 yrs and older (n = 21,271) was 139.27 mg/d, which was higher than the usual intake of 47.44mg/d. Legumes were a major contributing food group (91%), with arrowroot being a major individual contributor to the isoflavone intake (67.2%), followed by 21.3% of soybean, 5.4% of bean sprouts, and 2.1% of tofu. The usual isoflavone intake was highest in the participants aged 50 to 64 yrs old and increased with age until 50 to 64 yrs and then decreased with further increases in age. The usual isoflavone intake of participants aged 65 yrs and older was higher for men than for women, showing gender differences. CONCLUSIONS: The usual dietary intake of isoflavone varied according to age and gender in the Korean population. This study showed that the usual isoflavone intake was lower than the average isoflavone intake. The difference between percentiles of the usual isoflavone intake was similarly smaller than the average intake. An estimation of average intake can be hindered by the occasional consumption of foods high in isoflavones, suggesting that the usual intake estimation method can be more appropriate. Further research will be needed to establish isoflavone dietary guidelines regarding the effects of isoflavone intake on health outcomes.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.1
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• pp.1-16
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• 2023

A non-rare earth-based strontium-aluminate red light emitting phosphor was synthesized by a solid-state reaction method and the effect of synthesis temperature and Mn⁴⁺ activator concentration on the photoluminescence characteristics of the phosphor was studied. The synthesized SrAl₂O₄:Mn⁴⁺ phosphor showed broad band absorption characteristics in the near-ultraviolet and blue regions with peaks at wavelengths of near 330 and 460 nm, and a triple band deep red emission consisted of three peaks at near 644, 658, and 673 nm. The SrAl₂O₄:Mn⁴⁺ phosphor synthesized at a temperature 1600℃ and a Mn⁴⁺ activator concentration of 0.5 mol% showed the strongest PL emission intensity, and concentration quenching was observed at concentrations higher than 0.7 mol%. FE-SEM and DLS particle size distribution analysis showed that the synthesized SrAl₂O₄:Mn⁴⁺ phosphor had a particle size distribution of 2~6.4 ㎛ and an irregular spherical shape with an average particle size of ~4 ㎛.