• Journal of the Korean Electrochemical Society
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• v.18 no.4
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• pp.143-149
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• 2015

Carbon-coated $Li_2MnSiO_4$ powders as the active materials for the cathode were synthesized by planetary ball milling and solid-state reaction, and their phase formation behavior and charge-discharge properties were investigated. Calcination temperature and atmosphere were controlled in order to obtain the ${\beta}-Li_2MnSiO_4$ phase, which was active electrochemically, and the carbon-coated $Li_2MnSiO_4$ active material powders with near single phase ${\beta}-Li_2MnSiO_4$ could be fabricated. The particles of the synthesized powders were secondary particles composed of primary ones of about 100 nm size. The carbon incorporation was essential to enable the Li ions to be inserted and extracted from $Li_2MnSiO_4$ active materials, and the initial capacity of 192 mAh/g could be obtained in the $Li_2MnSiO_4$ active materials with 4.8 wt% of carbon.

• Journal of the Korean Electrochemical Society
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• v.17 no.4
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• pp.229-236
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• 2014

In this study, the method to improve the electrochemical performance of $LiFePO_4$ by carbon coating and morphology control into porous structure was studied. The synthesis of $LiFePO_4$ was done by coprecipitation method by two step procedure. In the first step $FePO_4$ precursor was synthesized by coprecipitation method, followed by impregnation of lithium into the precursor at $750^{\circ}C$. The carbon coating was done by both physical and chemical coating processes. Using the physical coating process, the amount of coating layer was 6% and the capacity achieved was 125 mAh/g. In case of chemical coating process, the active material delivered 130~140 mAh/g, which is about 40% improvement of delivered capacity compared to uncoated $LiFePO_4$. For the morphology control into porous structure, we added nano particles of $Al_2O_3$ or $SiO_2$ into the active materials and formed the nanocomposite of ($Al_2O_3$ or $SiO_2$)/$LiFePO_4$. Between them, $SiO_2/LiFePO_4$ porous nanocomposite showed larger capacity of 132 mAh/g.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.2
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• pp.49-53
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• 2017

We study on the change of electrical properties of two-dimensional (2D) $SnSe_2$ materials with respect to Cl doping as $SnSe_{1.994}Cl_{0.006}$ under a high temperature condition. (300~450 K) By the simple solid-state reaction method, non-and Cl-doped 2D $SnSe_2$ materials are successfully synthesized with negligible impurities as confirmed by X-ray diffraction. From the temperature dependence of resistivity, it is observed that the conduction mechanism is changed from hopping to degenerate conduction with Cl doping. By Hall effect measurement, an increase on electron carrier concentration from ${\sim}7{\times}10^{16}$ to ${\sim}3{\times}10^{18}cm^{-3}$ with Cl doping verifies that Cl is an effective electron donor which results in the encouraged carrier concentration. Detailed analysis for temperature dependent Hall mobility reveals that the electrical transports in high temperature regime are governed by the grain boundary-controlled mechanism for non-doped $SnSe_2$, which is effectively suppressed by Cl-doping as entering metallic transport regime.

• Journal of the Korean Geographical Society
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• v.39 no.2
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• pp.269-282
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• 2004

Luminescence dating of a coastal dune from the Shindu dunefield on the T'aean Peninsula shows that deposition of the dune structure began about 500-600 years ago. The lower section of the dune has remained stable since then but the upper part yields an age of about 30 years, suggesting reactivation or additional deposition since the 1970's. The two samples that were collected from the lower part of the dune at depths of 3.5 m and 2.0 m below the surface differ by an age interval of about 50-70 years. This indicates a net depositional rate of around 2.5 cm a year which is relatively slow for a coastal dune. Whilst only one dune structure has been dated for the time being and even though the dunefield was probably established much earlier in the Holocene, the OSL ages obtained demonstrate that some dunes in the area could be younger than 1000 years. Such chronologies point to a dynamic environment where the dune structures are not permanently fixed. Sedimentological properties of the dune sands are consistent with those of particles initially deposited under subaqueous conditions and then later transported by wind.

• Membrane Journal
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• v.31 no.2
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• pp.101-119
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• 2021

The demand for clean water is virtually present in all modern human societies even as our society has developed increasingly more advanced and sophisticated technologies to improve human life. However, as global climate change begins to show more dramatic effects in many regions in the world, the demand for a cheap, effective way to treat wastewater or to remove harmful bacteria, microbes, viruses, and other solvents detrimental to human health has continued to remain present and remains as important as ever. Well-established synthetic membranes composed of polyaniline (PANI), polyvinylidene fluoride (PVDF), and others have been extensively studied to gather information regarding the characteristics and performance of the membrane, but recent studies have shown that making these synthetic membranes conductive to electrical current by doping the membrane with another material or incorporating conductive materials onto the surface of the membrane, such as allotropes of carbon, have shown to increase the performance of these membranes by allowing the adjustability of pore size, improving antifouling and making the antibacterial property better. In this review, modern electrically conductive membranes are compared to conventional membranes and their performance improvements under electric fields are discussed, as well as their potential in water filtration and wastewater treatment applications.

• 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 the Korean Crystal Growth and Crystal Technology
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• v.29 no.5
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• pp.187-191
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• 2019

Perovskite-type oxides have consistently attracted considerable attention for their applications in high-temperature electrochemical devices, such as electrolytes and electrodes of solid oxide fuel cells, oxygen permeating membranes and sensors etc. Among them, the electrical conductivity of 10 % Sr and 10 % Mg doped $LaAlO_3$ (LSAM9191) was measured using impedance spectroscopy and 4-probe d.c. method. Below $550^{\circ}C$, the grain boundary resistance mostly determined the overall conductivity; however, it nearly disappeared above $800^{\circ}C$. Using the defect model and curve fitting, the ionic and electronic conductivity contributions were also separated. In the temperature region where the sample resistance is mostly determined by the grain volume property, LSAM9191 was an oxygen ion conductor at low $Po_2$ and a mixed conductor at high $Po_2$. With increasing temperature, the ionic conduction region only slightly increased. Thus, LSAM9191 is a promising material as an oxygen ion conductor at high temperature and in low $Po_2$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.12
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• pp.938-943
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• 2018

Thin nano-sized fibres were prepared by an electrospinning method. The spinning appratus consisted of pump for polymer injection, nozzle and nozzle rotus, and an aluminum plate collected the polymer fibers. Its surface was chemically modified for selective improved adsorption of carbon monoxide at indoor level. The chemical activation enabled to form the fibres 250-350 nm in thickness with pore sizes distributed between 0.6 and 0.7 nm and an average specific surface area of $569m^2/g$. The adsorption capacities of pure (100%) and indoor (0.3%) $CO_2$, of which level frequently appears, at the ambient condition were improved from 1.08 and 0.013 to 2.2 and 0.144 mmol/g, respectively. It was found that the adsorption amount of $CO_2$ adsorbed by the chemically activated carbon nanofiber prepared through chemical activation would vary depending on the ratio of specific surface area and micropores. In particular, chemical interaction between adsorbent surface and gas molecules could enhance the selective capture of weak acidic $CO_2$.

• 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.4
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• pp.159-165
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• 2021

The fiber composites have been investigated as lightweight structure material platforms for aerospace applications because their strength can be enhanced by adding reinforcement without a significant increase in weight. In this study, the fabrication and characterization of carbon nanotube (CNT) reinforced glass fiber composites are demonstrated to enhance the tensile strength of longitudinal direction along the glass fibers. Due to the reinforcement of CNT in epoxy layers, the yield strength of fiber/epoxy composites is enhanced by about 10 %. Furthermore, using scanning electron microscopy, analysis of fracture surfaces shows that mixed CNT in epoxy layers acts as necking agents between fractured surfaces of fiber/epoxy; thereby, initiation and evolution of crack across fiber composite can be suppressed by CNT necking between fractured surfaces.