• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.46-46
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• 2010

In this paper, we studied the volume resistivity and the electrical conductivity properties of nano composites to investigate the electrical properties of epoxy composites added nano MgO. The specimens were produced by classifying to 1.0, 3.0, 5.0, 10[wt%] and virgin specimen according to the addition amount of MgO. We measured the volume resistivity of nano filler using the High Resistance Meter(4329A) at the measuring temperature changed to 25, 50, 80, 100, and [$120^{\circ}C$]. As the result, it is confirmed that the volume resistivity was the highest stability and volume resistivity value is $2.6{\times}10^{17}\;[\Omega{\cdot}cm]$ at 3.0[wt%]. And it is confirmed that the electrical conductivity property is sharply increased at low electric filed region and the conductivity current density is rapidly increased at high electric filed region.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.3
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• pp.89-96
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• 2005

To improve the mean-life and reliability of power cables, we have investigated the volume resistivity and thermal properties demonstrated by changing the content of carbon black, an additive of the semiconductive shield for underground power transmission. Nine specimens were made of sheet form for measurement. Volume resistivity of the specimens was measured by a volume resistivity meter after 10 minutes in a preheated oven at temperatures of both 25$\pm$1[$^{\circ}C$] and 90$\pm$ 1[$^{\circ}C$]. As well, specific heat (Cp) and thermal conductivity were measured by Nano Flash Diffusivity and DSC (Differential Scanning Calorimetry). The ranges of measurement temperature were from 0[$^{\circ}C$] to 200[$^{\circ}C$], and heating temperature was 4[$^{\circ}C$/min]. From these experimental results, volume resistivity was high according to an increase of the content of carbon black. Specific heat was decreased, while thermal conductivity was increased according to a rise in the content of carbon black. Furthermore, both specific heat and thermal conductivity were increased by heating temperature because the volume of materials was expanded according to a rise in temperature.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.11
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• pp.477-482
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• 2005

We have investigated volume resistivity and thermal properties showed by changing the content of carbon black which is the component parts of semiconducting shield in underground power transmission cable. Specimens were made of sheet form with the nine of specimens for measurement. Volume resistivity of specimens was measured by volume resistivity meter after 10 minutes in the preheated oven of both 25$\pm$1[$^{\circ}C$] and 90$\pm$1[$^{\circ}C$]. And specific heat (Cp) and thermal conductivity were measured by Nano Flash Diffusivity and DSC (Differential Scanning Calorimetry). The measurement temperature ranges of specific heat using the BSC was from 20[$^{\circ}C$] to 60[$^{\circ}C$], and the heating rate was 1[$^{\circ}C$/min]. And the measurement temperatures of thermal conductivity using Nano Flash Diffusivity were both 25[$^{\circ}C$] and 55[$^{\circ}C$]. Volume resistivity was high according to an increment of the content of carbon black from these experimental results. And specific heat was decreased, while thermal conductivity was increased by an increment of the content of carbon black. And both specific heat and thermal conductivity were increased by heating rate because volume of materials was expanded according to rise in temperature.

• International Journal of Concrete Structures and Materials
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• v.9 no.1
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• pp.119-132
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• 2015

Electrical resistivity is an important physical property of portland cement concrete which is directly related to chloride induced corrosion process. This study examined the electrical surface resistivity (SR) and bulk electrical resistivity (BR) of concrete cylinders for various binary and ternary based high-performance concrete (HPC) mixtures from 7 to 161 days. Two different types of instruments were utilized for this investigation and they were 4 point Wenner probe meter for SR and Merlin conductivity tester for bulk resistivity measurements. Chronological development of electrical resistivity as well as correlation between two types of resistivity on several days was established for all concrete mixtures. The ratio of experimental surface resistance to bulk resistance and corresponding resistivity was computed and compared with theoretical values. Results depicted that bulk and SR are well correlated for different groups of HPC mixtures and these mixtures have attained higher range of electrical resistivity for both types of measurements. In addition, this study presents distribution of surface and bulk resistivity in different permeability classes as proposed by Florida Department of Transportation (FDOT) specification from 7 to 161 days. Furthermore, electrical resistivity data for several HPC mixtures and testing procedure provide multiple promising options for long lasting bridge decks against chloride induced corrosion due to its ease of implementation, repeatability, non-destructive nature, and low cost.

• Korean Journal of Materials Research
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• v.20 no.5
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• pp.271-277
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• 2010

In this paper two aspects of the percolation and conductivity of carbon black-filled polyethylene matrix composites will be discussed. Firstly, the percolation behavior, the critical exponent of conductivity of these composites, are discussed based on studying the whole change of resistivity, the relationship between frequency and relative permittivity or ac conductivity. There are two transitions of resistivity for carbon black filling. Below the first transition, resistivity shows an ohmic behavior and its value is almost the same as that of the matrix. Between the first and second transition, the change in resistivity is very sharp, and a non-ohmic electric field dependence of current has been observed. Secondly, the electrical conduction property of the carbon black-filled polyethylene matrix composites below the percolation threshold is discussed with the hopping conduction model. This study investigates the electrical conduction property of the composites below the percolation threshold based on the frequency dependence of conductivity in the range of 20 Hz to 1 MHz. There are two components for the observed ac loss current. One is independent of frequency that becomes prevalent in low frequencies just below the percolation threshold and under a high electrical field. The other is proportional to the frequency of the applied ac voltage in high frequencies and its origin is not clear. These results support the conclusion that the electrical conduction mechanism below the percolation threshold is tunneling.

• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.369-376
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• 2007

Electrical resistivity tomography was carried out at seawater intrusion monitoring wells located at watershed in coastal areas. It is difficult to identify the characteristics of resistivity near monitoring well in case of using high signalto-noise ratio array due to the high conductivity condition in coastal aquifer although electrical resistivity survey is well adopted to delineate hydrogeological characteristics with the distribution of electrical resistivity. To improve the quality of electrical resistivity survey for two sites with seawater intrusion monitoring wells, inversion with the results of holeto-surface electrical resistivity tomography using single well was executed. The results of inversion for aquifer near wells were verified with the results of drilling log with the informations of fracture, electrical conductivity logging and normal resistivity logging. The inversion for aquifer near one of two wells was also performed at low and high tide with the same electrodes, respectively. From the inversion result, it is possible to obtain the resistivity images with high resolution and to identify the characteristics of aquifer related to seawater intrusion with tidal fluctuation. From this study, it was demonstrated that the hole-to-surface electrical resistivity tomography method accompanied with drilling log, electrical conductivity logging and normal resistivity logging would be useful to delineate the hydrogeological structures near monitoring wells in coastal areas.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.4
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• pp.51-56
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• 2014

After the preparation of low-cost conductive paste containing Ag-coated Cu flakes, thermal conductivity and electrical resistivity of the paste were measured with different curing conditions. Under air-curing conditions, the thermal conductivity of the cured sample increased with an increase of curing time from 30 to 60 min. After identical curing time of 60 min, the sample cured under nitrogen indicated more enhanced thermal conductivity than that cured under air, approaching that of paste containing pure Ag flakes. Under air-curing conditions, meanwhile, the electrical resistivity of the cured sample increased with an increase of curing time from 30 to 60 min. After identical curing time of 60 min, however, the sample cured under nitrogen indicated extremely enhanced electrical resistivity ($7.59{\times}10^{-5}{\Omega}{\cdot}cm$) in comparison with that cured under air.

• Economic and Environmental Geology
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• v.46 no.3
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• pp.215-220
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• 2013

We estimated the hydraulic conductivity of the sediments using constant-head permeability tests and electrical resistivity measurements with Jumoonjin standard sand of a uniform size and glass beads of different grain sizes. In this study, we determined the variations of the porosity, the hydraulic conductivity, and the resistivity in case 1 (changing the packing of the Jumoonjin standard sand) and in case 2 (varying the size of the glass beads). The results of case 1 showed that the hydraulic conductivity decreased with an increase in the electrical resistivity. This occurred because the sand grain while packing became rhombohedral with the a decrease of both the pore size and porosity. The results of the case 2 showed that the hydraulic conductivity increased due to the increase in the pore size as caused by the increased glass bead size. In addition, the porosity decreased and the electrical resistivity increased. Therefore, the relationship between the hydraulic conductivity and the electrical resistivity is negatively proportional as regards the grain packing with a change from cubic to rhombohedral whereas this relationship is positively proportional to the increase in the grain size.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.134-135
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• 2005

To improve mean-life and reliability of power cable, we have investigated volume resistivity and thermal conductivity showed by changing the content of acetylene black which is the component parts of semiconductive shield in underground power transmission cable. The sheets were primarily kneaded in their pellet form material samples for 5 minutes on rollers ranging between 70[$^{\circ}C$] and 100[$^{\circ}C$]. Then they were produced as sheets after pressing for 20 minutes at 180[$^{\circ}C$] with a pressure of 200[kg/cm]. The content of conductive acetylene black was the variable, and their contents were 20, 30 and 40[wt%], respectively. Volume resistivity of specimens was measured by volume resistivity meter after 10 minutes in the preheated oven of both $25\pm1[^{\circ}C]$ and $90\pm1[^{\circ}C]$. Thermal conductivity was measured by Nano Flash Diffusivity. The measurement temperatures of thermal conductivity using Nano Flash Diffusivity were both 25[$^{\circ}C$] and 55[$^{\circ}C$]. From these experimental results, volume resistivity was high according to an increase of the content of acetylene black. And thermal conductivity was increased to an increase of the content of acetylene black. And thermal conductivity were increased by heating rate because volume of materials was expanded according to rise in temperature.

• The Journal of Engineering Geology
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• v.12 no.1
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• pp.63-73
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• 2002

To evaluate reinforced region of dike by cement grouting, we investigated both the electrical resistivity and the strength of cement grout having various water-cement ratio with curing time. These investigation results showed that the electric conductivity of grout is much higher than that of water and that the apparent resistivity of grouted region is much lower than that of unoccupied region by grout. It was founded that electrical resistivity survey might be quite effective to detect grout region in dike. As the results of electrical resistivity sounding at three dikes, apparent resistivities after grouting showed several tens to several hundreds of ohm-m which were lower than those of pre-grouting and showed stabilizing trend with curing time. From these results, we could estimate that this behavior of apparent resistivity is due to increasing strength with curing time.