• Title, Summary, Keyword: conductivity

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Electrical Conductivity, Flammable Gas Response and Humidity Effect of Pporous ZnO (다공질 ZnO의 전기적 특성, 환원성 가스 감응 특성 및 습도의 영향)

  • 윤당혁;최경만
    • Journal of the Korean Ceramic Society
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    • v.32 no.11
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    • pp.1283-1291
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    • 1995
  • The electrical conductivity, flammable gas response and their humidity effect of porous ZnO, added with 5wt% corn starch as the fugitive phase, were examined. Porous ZnO showed different conductivity curves during increasing and decreasing temperature, and its electrical conductivity decreased rapidly by desorption of OH- between 20$0^{\circ}C$ and 35$0^{\circ}C$ when the temperature increased in dry air. The CO gas sensitivity of starchadded ZnO samples was higher than that of ZnO without starch addition. The sensitivity of porous, starchadded ZnO to 200ppm CO gas was much less in humid atmosphere than in dry atmosphere since water vapor increased the conductivity of porous ZnO in air, but decreased the conductivity in CO. Maximum sensitivity to 200 ppm CO gas balanced by air was about 100 in dry atmosphere and about 15 in RH 23% atmosphere.

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Thermal Conductivity Enhancement of Bentonite Grout Using Silica Sands (실리카샌드 첨가에 의한 벤토나이트 그라우트의 열전도도 증가)

  • Sohn, Byong-Hu
    • Proceedings of the SAREK Conference
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    • pp.713-718
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    • 2006
  • This paper concerns the measurement of thermal conductivity of grouting materials for ground loop heat exchanger. A thermal conductivity meter, QTM-500 based on modified transient hot wire method was used to measure the thermal conductivity of neat bentonite and mixtures of bentonite and various additives. Relative to the total mixture mass, as the percent additive was increased the mixture thermal conductivity increased. For the bentonite-silica sand mixtures, the higher density of the sand particles resulted in much higher mixture thermal conductivity.

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Electrical Conductivity of Chemically Reduced Graphene Powders under Compression

  • Rani, Adila;Nam, Seung-Woong;Oh, Kyoung-Ah;Park, Min
    • Carbon letters
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    • v.11 no.2
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    • pp.90-95
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    • 2010
  • Carbon materials such as graphite and graphene exhibit high electrical conductivity. We examined the electrical conductivity of synthetic and natural graphene powders after the chemical reduction of synthetic and natural graphite oxide from synthetic and natural graphite. The trend of electrical conductivity of both graphene (synthetic and natural) was compared with different graphite materials (synthetic, natural, and expanded) and carbon nanotubes (CNTs) under compression from 0.3 to 60 MPa. We found that synthetic graphene showed a marked increment in electrical conductivity compared to natural graphene. Interestingly, the total increment in electrical conductivity was greater for denser graphite; however, an opposite behavior was observed in nanocarbon materials such as graphene and CNTs, probably due to the differing layer arrangement of nanocarbon materials.

Estimation of Empirical Equation on Thermal Conductivity (열전도계수 경험식의 국내 적용성에 관한 평가)

  • Kim, Hak-Seung;Lee, Jang-Guen;Kim, Young-Seok;Kang, Jae-Mo;Hong, Seung-Seo
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.1151-1155
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    • 2010
  • Frost depth is one of important factors to design roadway structure, and it can be estimated with numerical simulation on thermal distribution through subgrade soils. Thermal conductivity is a key parameter for accurate prediction on thermal distribution, but there are few studies on thermal conductivity of subgrade soils in Korea. Thermal conductivity can be affected by several factors such as dry density, moisture content, and saturation degree based on previous researches. Two empirical equations to estimate thermal conductivity are applied to access the accuracy of these equations with experimental data. Results indicate that the equation can be used to estimate thermal conductivity with proper quartz fraction.

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Estimation of Thermal Conductivity at Liquid and Vapor Interface by Molecular Dynamics Simulation (분자동역학을 이용한 액상과 기상계면에서의 열전도율 예측)

  • Koo, Jin-Oh;Choi, Young-Ki;Lee, Joon-Sik;Park, Seung-Ho
    • Proceedings of the KSME Conference
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    • pp.1558-1563
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    • 2004
  • This work applies the nonequilibrium molecular dynamics simulation method to study a Lennard-Jones liquid thin film suspended in the vapor and calculates the thermal conductivity by linear response function. As a preliminary test, the thermal conductivity of pure argon fluid are calculated by nonequilibrium molecular dynamics simulation. It is found that the thermal conductivity decrease with decreasing the density. When both argon liquid and vapor phase are present, the effects of the system temperature on the thermal conductivity are investigated. It can be seen that the thermal conductivity of liquid-vapor interface is constant with increasing the temperature

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Influence of P and Mg Additions on the Mechanical Properties and Electrical Conductivity of Cu-Sn Based Alloys (Cu-Sn계 합금의 기계적 성질과 전기전도도에 미치는 P 및 Mg 첨가의 영향)

  • Kim, Jeong-Min;Park, Joon-Sik;Kim, Ki-Tae
    • Journal of the Korean Society for Heat Treatment
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    • v.20 no.6
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    • pp.318-322
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    • 2007
  • The high electrical conductivity Cu-0.15% Sn alloys containing various P contents, and the high conductivity and high strength Cu-0.1% Sn-0.1%Ag alloys with various Mg/P additions were fabricated and their mechanical properties and electrical conductivity were investigated. The electrical conductivity was generally decreased as the P content was increased where as the hardness and strength was shown to increase. When Mg was added to P-containing Cu alloys, the detrimental effect of P on the conductivity was significantly reduced, and TEM observations indicated that the formation of $Mg_3P_2$ phase is responsible for this result.

Thermal conductivity of PLA-bamboo fiber composites

  • Takagi, Hitoshi;Kako, Shuhei;Kusano, Koji;Ousaka, Akiharu
    • Advanced Composite Materials
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    • v.16 no.4
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    • pp.377-384
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    • 2007
  • 'Green' composites were fabricated from poly lactic acid (PLA) and bamboo fibers by using a conventional hot pressing method. The insulating properties of the PLA-bamboo fiber 'green' composites were evaluated by determination of the thermal conductivity, which was measured using a hot-wire method. The thermal conductivity values were compared with theoretical estimations. It was demonstrated that thermal conductivity of PLA-bamboo fiber 'green' composites is smaller than that of conventional composites, such as glass fiber reinforced plastics (GFRPs) and carbon fiber reinforced plastics (CFRPs). The thermal conductivity of PLA-bamboo fiber 'green' composites was significantly influenced by their density, and was in fair agreement with theoretical predictions based on Russell's model. The PLA-bamboo fiber composites have low thermal conductivity comparable with that of woods.

Measurement of Thermal Conductivity of Foods in Liquid and Solid Phase Using a Thermal Probe

  • Hong, Ji-Hyang;Han, Young-Joe;Chung, Jong-Hoon
    • Food Science and Biotechnology
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    • v.14 no.3
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    • pp.334-339
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    • 2005
  • An instrument using thermal probe method was designed to measure thermal conductivity of liquid and solid foods. Thermal conductivity probe was designed with diameter to length ratio of 100 and diameter of 0.51 mm to minimize axial flow effect on thermal conductivity measurement. Thermal conductivities of distilled/deionized water, glycerin, and beef frankfurter meat were measured at $20-80^{\circ}C$. Mean thermal conductivity values of water showed less than 2.0% difference from several reference values without using time correction factor or probe calibration constant. For glycerin, difference was less than 0.7% from reference values at $20-50^{\circ}C$. Mean values of thermal conductivity for beef frankfurter meat ranged from 0.389 to $0.350\;W/m{\cdot}K$ at $20-80^{\circ}C$.

Development of Conductivity Standards for Metals using the van der Pauw Method (van der Pauw method를 이용한 금속도전율 표준시편 개발)

  • Kang, Jeon-Hong;Yu, Kwang-Min;Lee, Sang-Hwa
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.62 no.11
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    • pp.1617-1620
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    • 2013
  • The widely-used measurement methods for conductivity of non-magnetic metals are van der Pauw method, Two Point Probe method and Eddy Current method. Among them a more simpler and easier method is the Eddy Current method and an instrument using the method is a Conductivity Meter which can measure a conductivity by contacting its probe on a sample surface. However, conductivity standards are essentially needed to confirm the meter's performance or to calibrate it. In this study, six kinds of the standards which are made of Cu, Al-1, Al-2, brass, Zn and SUS-316 are developed and conductivity ranges for the standards are 2.27 %IACS ~ 101.6 %IACS with measurement uncertainty of less than 0.3 %.

Thick Graphene Embedded Metal Heat Spreader with Enhanced Thermal Conductivity

  • Park, Minsoo;Chun, Kukjin
    • Journal of Sensor Science and Technology
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    • v.23 no.4
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    • pp.234-237
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    • 2014
  • In this paper, a copper foil-thick grapheme (thin graphite sheet)-copper foil structure is reported to achieve mechanically strong and high thermal conductive layer suitable for heat spreading components. Since graphene provides much higher thermal conductivity than copper, thick graphene embedded copper layer can achieve higher effective thermal conductivity which is proportional to graphene/copper thickness ratio. Since copper is nonreactive with carbon material which is graphene, chromium is used as adhesion layer to achieve copper-thick graphene-copper bonding for graphene embedded copper layer. Both sides of thick graphene were coated with chromium as an adhesion layer followed by copper by sputtering. The copper foil was bonded to sputtered copper layer on thick graphene. Angstrom's method was used to measure the thermal conductivity of fabricated copper-thick graphene-copper structure. The thermal conductivity of the copper-thick graphene-copper structures is measured as $686W/m{\cdot}K$ which is 1.6 times higher than thermal conductivity of pure copper.