• Fire Science and Engineering
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• v.31 no.6
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• pp.91-98
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• 2017

The present paper is a study on the tracking characteristics depending on accelerated degradation of PVC insulation material. In order to insulation degradation of PVC insulation material, the Arrhenius equation, a type of accelerated degradation test formula, was used to conduct accelerated degradation experiments with experiment samples prepared at the following age equivalents: 0, 10, 20, 30 and 40 years. Afterwards, a tracking experiment was conducted on the accelerated experiment samples as part of the KS C IEC 60112 criteria. When measuring the PVC tracking features according to the accelerated aging, the results showed that when 0.1% of ammonium chloride was added to the PVC insulating material, but no tracking occurred. However, depending on the age equivalent, The results of analyzing the current waveform and voltage waveform of the tracking propagation process showed the age equivalent from 0 years to 40 years displayed a break down in insulation resistance and even the BDB(before dielectric breakdown) sections did not maintain the same functionality of the original material. Based on a criterion of an age equivalent of 0 years, material with an age equivalent of 10 years posed a 1.4 times greater risk, material with an age equivalent of 20 years posed a 2 times greater risk, material with an age equivalent of 30 years posed a 4.6 times greater risk, and material with an age equivalent of 40 years posed a 7 times greater risk.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.27-27
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• 2011

For the design of real applicable molecular devices, current-voltage properties through molecular nanostructures such as metal-molecule-metal junctions (molecular junctions) have been studied extensively. In thiolate monolayers on the gold electrode, the chemical bonding of sulfur to gold and the van der Waals interactions between the alkyl chains of neighboring molecules are important factors in the formation of well-defined monolayers and in the control of the electron transport rate. Charge transport through the molecular junctions depends significantly on the energy levels of molecules relative to the Fermi levels of the contacts and the electronic structure of the molecule. It is important to understand the interfacial electron transport in accordance with the increased film thickness of alkyl chains that are known as an insulating layer, but are required for molecular device fabrication. Thiol-tethered RuII terpyridine complexes were synthesized for a voltage-driven molecular switch and used to understand the switch-on mechanism of the molecular switches of single metal complexes in the solid-state molecular junction in a vacuum. Electrochemical voltammetry and current-voltage (I-V) characteristics are measured to elucidate electron transport processes in the bistable conducting states of single molecular junctions of a molecular switch, Ru(II) terpyridine complexes. (1) On the basis of the Ru-centered electrochemical reaction data, the electron transport rate increases in the mixed self-assembled monolayer (SAM) of Ru(II) terpyridine complexes, indicating strong electronic coupling between the redox center and the substrate, along the molecules. (2) In a low-conducting state before switch-on, I-V characteristics are fitted to a direct tunneling model, and the estimated tunneling decay constant across the Ru(II) terpyridine complex is found to be smaller than that of alkanethiol. (3) The threshold voltages for the switch-on from low- to high-conducting states are identical, corresponding to the electron affinity of the molecules. (4) A high-conducting state after switch-on remains in the reverse voltage sweep, and a linear relationship of the current to the voltage is obtained. These results reveal electron transport paths via the redox centers of the Ru(II) terpyridine complexes, a molecular switch.

• Applied Chemistry for Engineering
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• v.27 no.5
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• pp.495-501
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• 2016

Mineral oil has been widely used as an insulating oil for electrical transformers for a long time, but the necessity of employing new insulation oil such as vegetable oil has been increased due to urgent needs for the biodegradability when it leaks and also for the thermal stability at a higher operation temperature. Although specific periods are required between the production and consumption, there are still short of the data to prove the insulation oils' storage stability depending upon various circumstances and their resources. Thus, this paper demonstrates the insulation oils' oxidation characteristics of both mineral and vegetable oils when each was exposed to different environments for 12 weeks. From this test, some properties including total acid number, water content and dielectric breakdown were changed under specific conditions and resources. Vegetable oils showed higher hydrophilicity and water saturation than those of mineral oils due to their molecular compositions. Under sunlight exposure condition, all insulation oils oxidized and changed their properties when exposing to the direct light, regardless of the resource used.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.293-294
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• 2011

It is known that semiconductor quantum-dot (QD) heterostructures have superior zero-dimensional quantum confinement, and they have been successfully applied to semiconductor laser diodes (QDLDs) for optical communication and infrared photodetectors (QDIPs) for thermal images [1]. The self-assembled QDs are normally formed at Stranski-Krastanov (S-K) growth mode utilizing the accumulated strain due to lattice-mismatch existing at heterointerfaces between QDs and cap layers. In order to increase the areal density and the number of stacks of QDs, recently, sub-monolayer (SML)-thick QDs (SQDs) with reduced strain were tried by equivalent thicknesses thinner than a wetting layer (WL) existing in conventional QDs (CQDs) by S-K mode. Despite that it is very different from CQDs with a well-defined WL, the SQD structure has been successfully applied to QDIP[2]. In this study, optical characteristics are investigated by using photoluminescence (PL) spectra taken from self-assembled InAs/GaAs QDs whose coverage are changing from submonolayer to a few monolayers. The QD structures were grown by using molecular beam epitaxy (MBE) on semi-insulating GaAs (100) substrates, and formed at a substrate temperature of 480$^{\circ}C$ followed by covering GaAs cap layer at 590$^{\circ}C$. We prepared six 10-period-stacked QD samples with different InAs coverages and thicknesses of GaAs spacer layers. In the QD coverage below WL thickness (~1.7 ML), the majority of SQDs with no WL coexisted with a small amount of CQDs with a WL, and multi-peak spectra changed to a single peak profile. A transition from SQDs to CQDs was found before and after a WL formation, and the sublevel of SQDs peaking at (1.32${\pm}$0.1) eV was much closer to the GaAs bandedge than that of CQDs (~1.2 eV). These revealed that QDs with no WL could be formed by near-ML coverage in InAs/GaAs system, and single-mode SQDs could be achieved by 1.5 ML just below WL that a strain field was entirely uniform.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.2
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• pp.97-106
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• 2009

self-loading, various problems related to construction can be solved as well as the save of construction cost. Thus, this study has an aim of applying foam concrete to structural purpose by adding bottom ash as a reinforcing material like fine aggregate, in contrast to conventional non-structural usage such as soundproofing or insulating materials. In addition, it was evaluated in terms of unit volume weight, flow value, air void, water absorption and dosage of foam agent wether replacement of cement by granulated blast furnace slag or fly-ash has an effect on the material characteristics of foam concrete. As results of experiments, it can be found that the increase of fine aggregate ratio, that is to say, the increase of bottom ash results in the increase of unit volume weight, while decreasing air void and flow value. But, appropriate addition of bottom ash to foam concrete makes it easy to control a homogeneous and uniform quality in foam concrete due to less sensitive to bubbles. As the replacement ratio of mineral admixtures such as granulated blast furnace slag and fly-ash increases, as unit volume weight tends to decrease. In the meanwhile, serious effects were shown on fluidity of foam concrete when more than limit of replacement ratio was applied.

• Journal of Sensor Science and Technology
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• v.25 no.6
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• pp.440-446
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• 2016

This study introduces the characteristics of current-voltage (I-V) and impedance variance for $ZnO-Zn_2BiVO_6-Co_3O_4$ (ZZCo), which is sintered at $900^{\circ}C$, according to temperature changes. ZZCo varistor demonstrates dramatic improvement of non-linear coefficient, ${\alpha}=66$, with lower leakage current and higher insulating resistivity than those of ZZ ($ZnO-Zn_2BiVO_6$) from the aspect of I-V curves. While both systems are thermally stable up to $125^{\circ}C$, ZZCo represents a higher grain boundary activation energy with 1.05 eV and 0.94 eV of J-E-T and from IS & MS, respectively, than that of ZZ with 0.73 eV and 0.82 eV of J-E-T and from IS & MS, respectively, in the region above $180^{\circ}C$. It could be attributed to the formation of $V^*_o$(0.41~0.47 eV) as dominant defect in two systems, as well as the defect-induced capacitance increase from 781 pF to 1 nF in accordance with increasing temperature. On the other hand, both the grain boundary capacitances of ZZ and ZZCo are shown to decrease to 357 pF and 349 pF, respectively, while the resistances systems decreased exponentially, in accordance with increasing temperature. So, this paper suggests that the application of newly formed liquid phases as sintering additives in both $Zn_2BiVO_6$ and the ZZCo-based varistors would be helpful in developing commercialized devices such as chips, disk-type ZnO varistors in the future.

• Korean Journal of Soil Science and Fertilizer
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• v.33 no.1
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• pp.15-23
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• 2000

RC oscillation method was applied to study the condenser characteristics of two metal sticks insulated by vinyl tube and used in the dielectric constant determinations of most soils. Its capacitance as influenced by the contacted ambient materials was measured as relative capacitance of the sensor sticks compared with the standard one on the RC oscillation circuit. According to the equivalent circuit of the sensor stick set, the measured capacitance was composed of a basic capacitance connected in parallel with sensor stick capacitance, which was composed of lineally connected vinyl tube capacitances and the sensing part capacitance. The dielectric constant (U) of the contacted ambient moist soil located in the sensing part around the sticks interrelated with the other parameters as following equation. $$\frac{1}{C-B}=\frac{k}{U}+Z$$ where C is the output total relative capacitance, B is the hidden and fixed basic relative capacitance, k is a constant related with U, and Z is a constant for the insulating vinyl tube capacitances determined by its thickness and dielectric constant. The constant k is determined by the spacing and length of sensor sticks. The Z value is theoretically an invariable constant, but it may become considerably bigger than the determined in lab if air tube is formed on the surface of sensor sticks by some shocks on them after their installation in soil. Due to the unstability of lab Z value, it may be better to revise it after sensor stick's installation in soil and no shaking shocks should be applied on them.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.286-286
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• 2016

Hexagonal boron nitride (hBN) is a dielectric insulator with a two-dimensional (2D) layered structure. It is an appealing substrate dielectric for many applications due to its favorable properties, such as a wide band gap energy, chemical inertness and high thermal conductivity[1]. Furthermore, its remarkable mechanical strength renders few-layered hBN a flexible and transparent substrate, ideal for next-generation electronics and optoelectronics in applications. However, the difficulty of preparing high quality large-area hBN films has hindered their widespread use. Generally, large-area hBN layers prepared by chemical vapor deposition (CVD) usually exhibit polycrystalline structures with a typical average grain size of several microns. It has been reported that grain boundaries or dislocations in hBN can degrade its electronic or mechanical properties. Accordingly, large-area single crystalline hBN layers are desired to fully realize the potential advantages of hBN in device applications. In this presentation, we report the growth and transfer of centimeter-sized, nearly single crystal hexagonal boron nitride (hBN) few-layer films using Ni(111) single crystal substrates. The hBN films were grown on Ni(111) substrates using atmospheric pressure chemical vapor deposition (APCVD). The grown films were transferred to arbitrary substrates via an electrochemical delamination technique, and remaining Ni(111) substrates were repeatedly re-used. The crystallinity of the grown films from the atomic to centimeter scale was confirmed based on transmission electron microscopy (TEM) and reflection high energy electron diffraction (RHEED). Careful study of the growth parameters was also carried out. Moreover, various characterizations confirmed that the grown films exhibited typical characteristics of hexagonal boron nitride layers over the entire area. Our results suggest that hBN can be widely used in various applications where large-area, high quality, and single crystalline 2D insulating layers are required.

• Journal of the Korean Electrochemical Society
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• v.18 no.1
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• pp.17-23
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• 2015

$Li_4Ti_5O_{12}$ (LTO) have attracted much attention of researchers in the field of energy storage, because of their excellent stability for electric vehicle application. A main drawback of LTO is however their insulating nature due to the wide bandgap, which should be addressed to enhance the battery performance. In this study, we investigated the effect of water solubility of dopant precursor on the electrochemical characteristics of conducting LTO prepared by doping with $Cr^{3+}$ ions with the well-known wet-mixing method. The solubility of dopant precursor directly affected the morphology and the phase of doped LTO, and therefore their battery performance. In the case of employing the most soluble dopant precursor, $Cr(NO_3)_2$, the doped LTO demonstrated a markedly enhanced discharge capacity at high C-rate (130mAh/g @ 10C), which is about 2 times higher value than that of bare LTO.

• Korean Journal of Materials Research
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• v.21 no.5
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• pp.277-282
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• 2011

Negative temperature coefficient (NTC) materials have been widely studied for industrial applications, such as sensors and temperature compensation devices. NTC thermistor thick films of $Ni_{1+x}Mn_{2-x}O_{4+{\delta}}$ (x = 0.05, 0, -0.05) were fabricated on a glass substrate using the aerosol deposition method at room temperature. Resistance verse temperature (R-T) characteristics of the as-deposited films showed that the B constant ranged from 3900 to 4200 K between $25^{\circ}C$ and $85^{\circ}C$ without heat treatment. When the film was annealed at $600^{\circ}C$ 1h, the resistivity of the film gradually decreased due to crystallization and grain growth. The resistivity and the activation energy of films annealed at $600^{\circ}C$ for 1 h were 5.203, 5.95, and 4.772 $K{\Omega}{\cdot}cm$ and 351, 326, and 299 meV for $Ni_{0.95}Mn_{2.05}O_{4+{\delta}}$, $NiMn_2O_4$, and $Ni_{1.05}Mn_{1.95}O_{4+{\delta}}$, respectively. The annealing process induced insulating $Mn_2O_3$ in the Ni deficient $Ni_{0.95}Mn_{2.05}O_{4+{\delta}}$ composition resulting in large resistivity and activation energy. Meanwhile, excess Ni in $Ni_{1.05}Mn_{1.95}O_{4+{\delta}}$ suppressed the abnormal grain growth and changed $Mn^{3+}$ to $Mn^{4+}$, giving lower resistivity and activation energy.