• Journal of the Korean Ceramic Society
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• v.31 no.7
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• pp.772-776
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• 1994

Using two kinds of ZrO2 powder stabilized by 8 mol% and 3 mol% of Y2O3 several microstructures were designed; two single composition specimens of 8 mol% Y2O3-ZrO3 and 3 mol% Y2O3-ZrO2 and five mixture specimens with multi-layered structure and particulate mixture structure at a mixing ratio of 1:1 by weight. Electrical conductivities were measured from 250 to 75$0^{\circ}C$ in air using an impedance analyser, and fracture toughness at room temperature using the indentation method. Making the mixture structures was more effective in enhancing fracture toughness than electrical conductivity. At low temperatures 3 mol% Y2O3-ZrO2 showed the highest values in both electrical conductivity and fracture toughness, while at high temperature the specimens of alternately stacked planar and coarse granulated structure were most favorable.

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1439-1442
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• 1997

We investigated the electrical and CO sensing properties of ZnO-$TiO_2$ composite ceramics. The electrical conductivities and relative dielectric constants of $TiO_2$ added ZnO increased with increasing $TiO_2$ content in air. The calculated dielectric constants of 3mol%, 5mol%, and 7mol% $TiO_2$ added ZnO were 7, 13, and 120, respectively. The measured CO sensivities were $1{\sim}6.42$ in the temperature range from $100^{\circ}C$ to $400^{\circ}C$.

• Carbon letters
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• v.16 no.1
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• pp.34-40
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• 2015

In this study, in order to improve the thermal and electrical properties of epoxy/graphene nanoplatelets (GNPs), surface modifications of GNPs are conducted using silane coupling agents. Three silane coupling agents, i.e. 2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane (ETMOS), 3-glycidoxypropyltriethoxysilane (GPTS), and 3-glycidoxypropyltrimethoxysilane (GPTMS), were used. Among theses, GPTMS exhibits the best modification performance for fabricating GNP-incorporated epoxy composites. The effect of the silanization is evaluated using transmission electron microscopy (TEM), scanning electron microscopy, thermogravimetric analysis, and energy dispersive X-ray spectroscopy. The electrical and thermal conductivities are characterized. The epoxy/silanized GNPs exhibits higher thermal and electrical properties than the epoxy/raw GNPs due to the improved dispersion state of the GNPs in the epoxy matrix. The TEM microphotographs and Turbiscan data demonstrate that the silane molecules grafted onto the GNP surface improve the GNP dispersion in the epoxy.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1992.05a
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• pp.77-81
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• 1992

$C_{22}$-Quinolium-TCNQ LB films were deposited on the glass substrates by Langmuir-Blodgett technique at room temperature. Transfer ratios and UV-visible absorption spectra were studied for X, Y and Z-Types. Absorption in Z-Type was higher than X and Y-Types, which indicates a better arrangement in this type. We have also investigated dc electrical conductivities and ac responses along the horizontal and vertical direction to the film surface. As a result, we are able to determine the capacitance of film and the measured horizontal conductivity was about $10^{-7}$~$10^{-8}$ S/cm.

• The Korean Journal of Ceramics
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• v.4 no.2
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• pp.146-150
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• 1998

The total conductivity and oxygen permeation in (Ce1-xZrxO2)0.9(CaO)0.1 solid solutions were measure das a function of temperature and oxygen partial pressure. Empirically, σ at given x and T was expressed essentially by σ=σo2+σeo Po2-1/4, where σo2 and σeo are constant. Applying a standard defect model in which major defects are Cace", Cece' and Vo in ideal solution, we can assign σo2 as the oxide ion conductivity decreases while the electronic conductivity increases with the increase in Zr content. Using the oxide ion and electronic conductivities thus determined, the oxygen permeation flux was calculated for respective Po2 and T conditions at which the measurements were made. The calculated values were found to agree with the observed ones.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.9
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• pp.2181-2193
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• 1995

The effective elasticity and conduction of composite materials containing arbitrarily oriented multiple phases has been analyzed using the concept of orientation-dependent average fields and concentration factors. The analysis provided closed form expressions for the effective stiffnesses and conductivities. Under the prescribed boundary conditions, the concentration factors were evaluated by the equivalent inclusion principle, through which the interaction between various phases is approximated by the Mori-Tanaka mean-field approximation. SiC particulate(SiC$_{p}$) reinforce aluminum(Al) matrix composites were fabricated and their elastic constants and electrical conductivities were measured together with a careful study of their microstructure. The measured properties showed a systematic anisotropy and this behavior could be attributed to the preferred orientation of SiC$_{p}$. The theoretical model developed was applied to the computation of the anisotropic properties of these composites. Both two-phase and three-phase composites were considered based on the microstructural information. The SiC$_{p}$ was modeled as an ellipsoid with planar random orientation distribution in the extruded Al/SiC$_{p}$ composites. The effect of extraneous phase such as intermetallic compounds was also investigated.tigated.

• Journal of Powder Materials
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• v.25 no.5
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• pp.435-440
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• 2018

In the present study, we develop a conductive copper/carbon nanomaterial additive and investigate the effects of the morphologies of the carbon nanomaterials on the conductivities of composites containing the additive. The conductive additive is prepared by mechanically milling copper powder with carbon nanomaterials, namely, multi-walled carbon nanotubes (MWCNTs) and/or few-layer graphene (FLG). During the milling process, the carbon nanomaterials are partially embedded in the surfaces of the copper powder, such that electrically conductive pathways are formed when the powder is used in an epoxy-based composite. The conductivities of the composites increase with the volume of the carbon nanomaterial. For a constant volume of carbon nanomaterial, the FLG is observed to provide more conducting pathways than the MWCNTs, although the optimum conductivity is obtained when a mixture of FLG and MWCNTs is used.

• Proceedings of the KIEE Conference
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• summer
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• pp.581-583
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• 2004

This paper analysed the induced current density characteristics inside human body by extremely low frequency magnetic fields according to varying conductivities of human model. Human model was composed of several organs and other parts of 곳 human body, whose shapes were spheroids or cylinders. Organs taken into account were the brain, heart, lungs, liver and intestines. Applying the boundary element method to the human model, effects of the organ conductivity difference to the induced current distribution were estimated.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.48-51
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• 2002

This paper predicted the thermal conductivity of spun carbon/phenolic composites by the thermal resistance method. This method uses the analogy between the diffusion of heat and electrical charge. To verify the theoretical predictions, the thermal conductivity of spun carbon/phenolic composites was examined experimentally. The reported thermal conductivities of graphite/epoxy composite of a eight harness satin laminate was used of the comparison with the prediction values of the model and it was noticed that a good agreement has been found.

• Journal of Soil and Groundwater Environment
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• v.11 no.2
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• pp.56-67
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• 2006

Trends of variation in groundwater levels, electrical conductivities and water temperatures obtained from the national groundwater monitoring stations (95 shallow and 169 deep wells) of Korea were evaluated. For the analysis, both parametric (linear regression) and non-parametric (Mann-Kendall test, Sen's test) methods were adopted. Results of linear regression analysis indicated that about 50% of the monitoring wells showed increasing trends of groundwater levels, electrical conductivities, and water temperatures and the others showed decreasing trends. However, the non-parametric analyses with monthly median values revealed that $14.8{\sim}20.0%$ of water levels were decreased, $24.2{\sim}36.9%$ of electrical conductivities were increased, and $27.4{\sim}32.5%$ of water temperatures were increased at a confidence level of 99%. Highly proportions of increasing or decreasing trends were unexpected and they resulted from the relatively short term of data collection (maximum 6 years). Meanwhile, the investigation of groundwater around the national groundwater monitoring stations showed that the decreasing or increasing trends of water levels, electrical conductivities, themselves, didn't indicate directly groundwater hazards such as groundwater depletion or groundwater contamination. Both the values and variation rates (slopes) of water level, electrical conductivity and temperature in the longer period are considered simultaneously. This study is the first comprehensive work in analyzing trends of groundwater data obtained from the national groundwater monitoring stations. Based on this study, the periodical and regular analysis of groundwater data is essentially required to grasp the overall variational trend of groundwater resources in the country.