• Geophysics and Geophysical Exploration
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• v.18 no.4
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• pp.171-180
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• 2015

Electrical resistivity of 23 core samples from Ulleung Island at dry or saturated condition has been measured along with dry density and effective porosity, and the relations between the properties has also been discussed. Upper and lower bounds of electrical resistivity at room temperature can be provided by the dry- and saturated-resistivity, respectively. Injecting nitrogen gas to the pore space at the very end of drying process can prevent humid air from getting into the pore space, so that measurement of dry-resistivity can be less affected by humidity in the air. Dry density and porosity have very close correlation; the ratio between increase of porosity and the decrease of density showed distinct relation to the rock types, such that basaltic rocks showed higher ratio while trachytic rocks showed lower. Saturated resistivity showed close correlation to density and effective porosity of the rock sample, while dry resistivity didn't.

• Geophysics and Geophysical Exploration
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• v.18 no.3
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• pp.105-114
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• 2015

A long-term resistivity monitoring system has been developed for saturated cores in room temperature and humidity condition. A 3-channel water-pump continuously drops the water onto the top of saturated core sample surrounded by shrinkable tube as well as on the paper filters of the electrodes at both sides of the core sample, by which one can monitor the resistivity changes with maintaining full saturation of the rock core for a week or longer. Monitoring the resistivity changes has been performed with 3 kinds of rock samples including biotite gneiss, andesitic tuff, and shale for 9 days using the system. Consequently, it is proposed two hypothesis that conversion speed of temperature coefficient has close relation to the thermal properties of the rock sample and that the ratio of resistance between dry and saturated conditions for a rock sample can be related to the effective porosity of the sample. The ratio between dry and saturated resistance for the three rock types are 48, 705, and 2, while effective porosity was 3.7%, 3.3%, and 13.0%, respectively.

• 한국지구물리탐사학회:학술대회논문집
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• 2009.10a
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• pp.93-98
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• 2009

Comprehension of physical properties distribution of underground cavity must be made primarily to show the clear image of the state of the cavity. A physical scale model experiment is executed assuming that underground cavity in filled with air or water of different ratio. The state of cavity wall is considered wet. Cavity model is made of agar. As a experimental result, even if the cavity wall is wet, high air and water ratio cavity shows high anomaly.

• Geophysics and Geophysical Exploration
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• v.12 no.2
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• pp.215-220
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• 2009

Cement based mortars are widely used to improve the soft ground of a dam site, highway construction, and karst voids. The mechanical properties of the mortar are well documented in literature, however very limited work is done on their physical properties such as electrical resistivity which is considered as one of the most important physical property known while improving the soft grounds. In this paper, electrical resistivity of the Portland cement mortars is examined by employing the Wenner technique. Cylindrical specimens with various water/cement ratios (w/c) ranges from 0.35, 0.45, 0.50 and 0.65 were cast and tested. The test results showed that the electrical resistivity of the mortar increases with increasing curing time and decreases with increasing water content and w/c. A reasonable, good relation was found between electrical resistivity and compressive strength of mortar.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.5
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• pp.591-610
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• 2020

Concrete with activated carbon and titanium dioxide (TiO₂) has been used to reduce the particulate matter (PM) in underground structures (e.g., tunnels) due to the high performance of nitrogen oxides (NOx) abatement. Damage (e.g. crack, spalling, or detachment) can be caused by the environmental and ageing effects on the surface of the particulate matter reduction concrete, installed on the tunnel lining. Therefore, it is important to evaluate the existence of spalling on the concrete surface for maintaining performance of NOx reduction. In this study, a basic research was performed for feasibility of spalling evaluation using electrical resistivity characteristics. Given the test results, the electrical resistivity was decreased as the ratios of activated carbon (0~15%) and TiO₂ (0~25%) were increased for specimens. Under a dry condition, electrical resistivity of cement specimens, mixed with activated carbon and TiO₂, was decreased up to 2.3 times, compared with the normal cement specimen. In addition, under saturation conditions (degree of saturation: 85~98%), electrical resistivity of cement specimens with activated carbon, was decreased up to 3.5 times, compared with the normal cement specimen. Regardless of the condition (dry or saturated), the difference of electrical resistivity values shows the range of 2.3~2.8 times between the mixing specimen (with activated carbon (15%) and TiO₂ (25%)) and the normal cement specimen. This study can help to provide basic knowledge for spalling evaluation using the electrical resistivity on the surface of the particulate matter reduction concrete in tunnels.

• Journal of the Korean Geotechnical Society
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• v.40 no.3
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• pp.55-63
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• 2024

Xanthan gum biopolymer is an ecofriendly ground stabilizer that maintains stability in a wide range of temperatures and pH values. The binding effect of sandy soil particles realized by injecting xanthan gum biopolymer is dependent on the xanthan gum matrix, which is formed during the drying process; thus a study on the effects of the drying process of the xanthan gum solution on the changes in stiffness characteristics of sandy soil is required. In this study, shear wave velocity and electrical resistivity were monitored in sandy soil specimens saturated with biopolymer solutions of different gravimetric concentrations to investigate the improvement effects of biopolymer-treated sandy soils with the drying process. The experimental results reveal that both shear wave velocity and electrical resistivity increase during drying process. The results demonstrate the stiffness improvement effects of biopolymer-treated sandy soils. In addition, a higher stiffness improvement effect was monitored in the biopolymer-treated sandy soils with a higher gravimetric concentration. The results of this study may be used to estimate the stiffness improvement effects of sandy soils treated with biopolymer solutions with the drying process.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.82-92
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• 2022

This study aims to investigate the effect of total electrochemical cell resistance (TECR) on electrochemical impedance (EI) measurements of reinforced concrete (RC) by electrochemical impedance spectroscopy (EIS) using a three-electrode system. A series of experimental study is performed to measure electrochemical behavior of a steel bar embedded in a concrete cube specimen, with a side length of 200 mm, in various experimental conditions. Main variables include concrete dry conditions, coupling resistance between sensing electrodes and concrete surface, and area of the counter electrode. It is demonstrated that EI values remains stable when the compliant voltage of a measuring device is sufficiently great compared to the potential drop caused by TECR of concrete specimens. It is confirmed that the effect of the coupling resistance of TECR is far more influential than other two factors (concrete dry conditions and area of the counter electrode). The results in this study can be used as a fundamental basis for development of a surface-mount sensor for corrosion monitoring of reinforced concrete structures exposed to wet-and-dry cycles under marine environment.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2012.03a
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• pp.63-63
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• 2012

전자제품 패키지에 요구되는 쿠션성과 정전방전 기능을 갖는 폴리우레탄 발포 필름의 제조기술을 확립하게 되면 IT산업용에 적용 가능한 필름제품이 개발되어 ESD(정전방전, Electrostatic Dissipation) 성능을 발휘하게 됨으로서 정전기 쇼크에 의한 각종 전자제품의 오작동이나 파손 방지가 가능하게 되어 포장재, 자동차 전자제품의 하우징 등으로 사용될 수 있게 된다. 전도성 고분자인 Polyaniline (PANI)은 다른 여러 고분자와 비교하여 볼 때 다른 유형의 전도성 고분자보다 합성하기가 쉽고 높은 전기전도도를 보임은 물론 열적 및 대기 안정성이 우수하며 가격이 저렴한 장점을 가지고 있다. 본연구는 CNT 나노기술을 응용한 IT산업용 적층간지용 ESD PU발포필름의 제조 가공기술 및 상품화 개발을 수행하고자 방수, 투습방수성을 가지는 유연재료인 폴리우레탄(PU)의 1액형 PU와 DMF에 PANI의 함량을 5, 10, 15, 20, 25, 30wt%로 변화시켜 제조한 PANI/DMF 분산용액과 IPA/MWNT 3wt% 분산용액의 혼용비에 변화를 주어 $120^{\circ}C$에서 2분 건조시켜 그라운드 필름을 제조하였다. 그리고 2액형 PU와 IPA/MWNT 3wt% 분산용액과 발포제를 사용하여 발포온도 $150^{\circ}C$에서 5분간 건조시켜 발포필름을 제조하였으며 이들의 전기적 특성과 역학적 특성을 조사하였다. 제조된 필름의 전기전도성은 전기저항측정기 KEITHLEY 8009를 사용하여 부피저항과, 표면저항을 각각 측정하여 확인하였으며, 필름의 마찰 대전압은 E.S.T-7 마찰 대전압 시험기를 이용하여 표면 마찰 대전압을 측정하여 확인하고, 필름의 물리적 특성은 인장시험기를 이용하여 breaking stress, breaking strain을 측정하였다. 필름단면의 CNT 발포특성은 주사전자현미경(SEM)을 사용하여 측정하여 발포특성과 물성과의 연관성을 확인하였다. 그 결과 필름의 전기적 특성은 PANI가 30% 함량일 때 전반적으로 낮은 저항값이 측정되었으며, 마찰대전압을 측정한 결과 대부분의 시료가 0에 가까운 낮은 값을 가졌다. 필름의 물리적 인장특성은 PANI가 10wt%의 함량일 때 가장 높은 절단강도를 가졌으며 분산용액의 혼용비에 따른 경향성은 나타나지 않았다. 필름의 단면형상을 확인하여 발포특성을 분석한 결과 PANI의 함량에 따라 발포 cell의 크기는 뚜렷한 경향성을 보이지 않았으나 30wt%의 PANI/DMF 분산용액 20part(gr)와 3wt% IPA/MWNT 분산용액 40part(gr)로 제조한 시료의 cell이 가장 균일하고 고르게 발포되었으며, 3.90E+06ohm으로 가장 낮은 표면저항 값으로 측정되어 가장 좋은 전기전도성을 가짐을 확인하였다.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.452-453
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• 2006

저압 개폐기는 에어컨, 냉동기, 쇼케이스, 산업용 청소기, 전기 온수기, 건조기, 공조기, 펌프, 콤프레셔 등의 모터제어 및 히터와 조명기기의 개폐 등에 광범위하게 이용되는 개폐장치이다. 저압 전자개폐기는 수 천회에서 수백만회까지 빈번한 개폐사용조건으로 인해 시험규격에서는 개폐시험을 통해 수명을 검증하도록 되어 있다. 이 개폐시험 회로는 규정된 전압, 전류, 역률 조건을 맞추기 위해 저항과 리액터를 직렬 연결하여 구성한다. 또한 모터와 같은 리액터 부하를 개폐하는 개폐기의 경우는 전류차단 순간 과도회복전압의 피크비와 주파수를 규정하여 적용하고 있다. IEC60947-1에서는 과도회복전압의 피크비와 주파수에 대한 규정값을 제시하고 있으며 제시된 값을 제어하기 위한 회로를 제시하고 있다. 과도회복전압의 피크비와 주파수는 개폐기 접점의 절연성능과 밀접한 관계가 있으며 수명에 치명적인 영향을 미친다. 본 연구에서는 LS산전(주) 부하개폐시험 회로의 과도회복전압 조건과 영향을 설명하고 제어하기 위한 저항과 커패시터를 적용하는 방법을 제안하고자 한다.

• Journal of the Korean Electrochemical Society
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• v.27 no.1
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• pp.40-46
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• 2024

Among the electrode manufacturing processes for lithium-ion batteries, the drying process is crucial for production speed and process cost. Particularly, as the loading level of the electrode increases to enhance the energy density of the battery, optimizing process conditions for electrode drying becomes more critical. In this study, we compared the drying time and electrochemical performance of the positive electrode prepared at different drying temperatures. LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) was used as the active material and manufactured under various drying temperature conditions ranging from 120 ℃ to 210 ℃ at loading levels of 2.5 and 4.5 mAh cm^-2. The physical and electrochemical properties of the electrodes were compared. As the loading level of the electrode increases, the drying time of the electrode also increases, but this time can be reduced by increasing the drying temperature. The drying temperature used in manufacturing the NCM622 positive electrode does not significantly affect the electrochemical performance but drying above 210 ℃ resulted in an increase in the volume resistivity of the electrode and a decrease in electrochemical performance. Accordingly, in the manufacture of high-loading electrodes, the drying temperature was increased to 190 ℃ to shorten the electrode manufacturing time without a loss of performance.