• Title/Summary/Keyword: grain-size

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Magnetic Properties and Sintering Behavior of (Nd,Dy)-Fe-B Permanent Magnet by Spark Plasma Sintering (방전 플라즈마 소결을 이용한 (Nd,Dy)-Fe-B 영구자석의 자성 특성 및 소결 거동)

  • Song, Sun-Yong;Kim, Jin-Woo;Kim, Se-Hoon;Kim, Young-Do
    • Journal of Powder Materials
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    • v.19 no.2
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    • pp.105-109
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    • 2012
  • Magnetic properties and the microstructures of magnets prepared by spark plasma sintering were investigated in order to enhance magnetic properties by grain size control. Nd-Fe-B magnets were fabricated by the spark plasma sintering under 30 MPa at various temperatures. The grain size was effectively controlled by the spark plasma sintering and it was possible to make Nd-Fe-B magnets with grain size of 5.9 ${\mu}m$.

Analysis of Ionization Phenomena in Soils under Impulse Voltages (임펄스전압에 의한 토양이온화 현상의 분석)

  • Park, Geon-Hun;Kim, Hoe-Gu;Choi, Jong-Hyuk;Yang, Soon-Man;Lee, Bok-Hee
    • Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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    • 2008.05a
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    • pp.305-308
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    • 2008
  • This paper presents characteristics of soil ionization when high currents such as lightning and switching surge currents are injected into a grounding rod. Soil ionization phenomena are investigated by using both voltage and current signals recorded by oscilloscope. As a result, a critical electric field intensity($E_C$) for ionization is decreased with reduction of grain size. The pre-ionization resistance($R_1$) and post-ionization resistance($R_2$) at the sand with fine grain size are getting lower with increasing current magnitude. Finally, the time to ionization($t_1$) and ionization current peak($t_2$) of fine grain size are significantly shorter than those of medium grain size.

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GEOSTATISTICAL UNCERTAINTY ANALYSIS IN SEDIMENT GRAIN SIZE MAPPING WITH HIGH-RESOLUTION REMOTE SENSING IMAGERY

  • Park, No-Wook;Chi, Kwang-Hoon
    • Proceedings of the KSRS Conference
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    • 2007.10a
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    • pp.225-228
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    • 2007
  • This paper presents a geostatistical methodology to model local uncertainty in spatial estimation of sediment grain size with high-resolution remote sensing imagery. Within a multi-Gaussian framework, the IKONOS imagery is used as local means both to estimate the grain size values and to model local uncertainty at unsample locations. A conditional cumulative distribution function (ccdf) at any locations is defined by mean and variance values which can be estimated by multi-Gaussian kriging with local means. Two ccdf statistics including condition variance and interquartile range are used here as measures of local uncertainty and are compared through a cross validation analysis. In addition to local uncertainty measures, the probabilities of not exceeding or exceeding any grain size value at any locations are retrieved and mapped from the local ccdf models. A case study of Baramarae beach, Korea is carried out to illustrate the potential of geostatistical uncertainty modeling.

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입도분석과 현장수리시험에 의한 수리전도도의 특성 비교

  • Ham Se-Yeong;Jeong Jae-Yeol;Lee Jeong-Hwan;Kim Hyeong-Su;Han Jeong-Sang
    • Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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    • 2005.04a
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    • pp.446-450
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    • 2005
  • Hydraulic conductivity of unconsolidated media can be determined by aquifer tests, laboratory tests and empirical equations based on grain size analysis. Commonly, the different methods give different hydraulic conductivities. Grain size measurements were done to determine hydraulic conductivity, using 184 soil samples collected from eight boreholes in a riverbank filtration area, Daesan-Myeon, Changwon City, Korea, Pumping tests were conducted at the riverbank filtration area. The average hydraulic conductivity by the empirical relations from grain size measurements comes out around $10^{-2}m/s$, 22 to 55 times higher than by the pumping test analyses. The hydraulic conductivity obtained from the empirical equations is interpreted to have a relationship with steady-state condition while that obtained from the pumping tests is interpreted to have a relationship with unsteady-state condition. Thus, hydraulic conductivity obtained from various methods should be critically analyzed for reasonable management of groundwater development.

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The prediction of grain size of Al-5wt%Mg alloy by FEM (유한요소법을 이용한 Al-5wt%Mg합금의 미세조직 크기 예측)

  • 황원주;조종래;배원병
    • Transactions of Materials Processing
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    • v.8 no.6
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    • pp.620-625
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    • 1999
  • A finite element analysis is performed to predict the recrystallized volume fraction and the mean grain size in hot compression of Al-5wt%Mg alloy. In the analysis, a modeling equation of flow stress is assumed as a function of strain, strain rate, and temperature. And the influence of above varibles on flow stress is quantified by using Zener-Hollomon Parameter. In the modeling equation, effects of strain hardening and dynamic recrystallization on microstructure of Al-5wt%Mg alloy are investigated. The predicted results of recrystallized volume fraction and mean grain size are in good agreement with those of microstructures obtained from hot compression tests.

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Influence of Grain Size and Dopant ZnO on the Photoelectrochemical Conversion in TiO2 Ceramic Electrods (TiO2 세라믹 전극의 광전기 화학 변환에 미치는 결정립 크기와 첨가제 ZnO의 영향)

  • 윤기현;장병규;김태희
    • Journal of the Korean Ceramic Society
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    • v.26 no.2
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    • pp.258-266
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    • 1989
  • The effects of grain size and dopant ZnO on the photoelectrochemical conversion in TiO2 ceramic electrodes have been investigated. The photocurrent increases with increasing grain size in the undoped TiO2 ceramic electrode. In ZnO-doped TiO2 electrodes, the photocurrent decreases with increasing ZnO up to 0.4 wt% due to decrease of donor concentration, and then with further addition of ZnO, photocurrent increases according to the formation of second phase. However, the photoresponse appears at wavelength of 420nm, which is very close to the energy band gap of TiO2, regardless of grain size and amount of ZnO.

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Pentacene Thin-Film Transistors with Polyimide/$SiO_2$ Dual Gate Dielectric

  • Imahara, Hirokazu;Kim, Woo-Yeol;Oana, Yasuhisa;Majima, Yutaka
    • 한국정보디스플레이학회:학술대회논문집
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    • 2007.08a
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    • pp.972-973
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    • 2007
  • Relationships between field effect mobility and grain size on pentacene thin-film transistors with $polyimide/SiO_2$ gate dielectrics have been studied. 6 kinds of polyimide were used as surface treatment gate dielectric layer. Grain size of the pentacene thin film were between 5 and $30\;{\mu}m$ and depended on the polyimide. The field effect mobility were also depended on the polyimide and the those values were from 0.027 to $0.69\;cm^2/(Vs)$. The field effect mobility tends to increase with increasing the grain size. Precursor type polyimide containing polyamic acid show better mobility of $0.69\;cm^2/(Vs)$ than soluble type polyimide. Bias stress characteristics in air are discussed in the basis of the grain size.

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Improvement of Strength in ALC using Admixtures and Grain Size (혼합재 및 입도에 따른 경량기포콘크리트의 강도특성 개선)

  • Kim, Young-Yup;Song, Hun;Lee, Jong-Kyu;Chu, Yong-Sik
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2007.11a
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    • pp.79-82
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    • 2007
  • Recently, the use of ALC has became increasingly popular. ALC is a unique building material. Because of its cellular nature, it is lightweight, self-insulating, sound and fireproof, as well as insect and mold resistant. Furthermore, ALC is free of VOCs and various fibers associated with wood and glass wool construction. However, ALC have high water absorption, low compressive strength and popout the origin of the low surface strength in its properties. These properties make troubles under construction such as cracking and popout. Thus, this study is to improve the fundamental strength by controls of increasing of admixtures, and grain size. Admixtures make use of metakaolin, silica fume, sodium silicate and sodium hydroxide. From the test result, the ALC using admixture have a good fundamental properties compared with plain specimen. Compressive strength, specific strength and abrasion's ratio were improved depending on increasing admixtures ratio's, and grain size.

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Engineering Properties of Some Sedimentary Rocks from the Gyeongsang Supergroup (경상계(慶尙系) 퇴적암(堆積岩)의 공학적(工學的) 성질(性質)에 관(關)한 연구(硏究))

  • So, Chil-Sup;Choi, Byoung-Ryol
    • Economic and Environmental Geology
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    • v.8 no.4
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    • pp.203-210
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    • 1975
  • The engineering properties of some Gyeongsang sedimentary rocks with respect to the grain size and the orientation of bedding planes were studied. The suitability of the rocks for civil and architectural construction was also investigated. The porosity of the rocks increases in proportion to the grain size. The ratio of the strain due to stress perpendicular to the bedding planes to the strain resulting from stress parallel to the bedding planes increases as the grain size decreases. The study indicates however, that the ratio of Young's modulus due to stress perpendicular to the bedding planes to Young's modulus resulting from stress parallel to the bedding planes increases in proportion to the grain size. The compressive strength of the sandstones studied is much greater than the strength of the conglomerate or shale. Only the coarse grained sandstone can be used for civil and architectural construction, regardless of the orientation of bedding planes. The relationships between compressive strength and density, elasticity and porosity, and compressive strength and mineral content were also studied.

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Geomorphological Characteristics and OSL Ages of the Moraeul dune in Daechoengdo Island, South Korea (대청도 모래울 사구의 지형 특성과 OSL 연대)

  • Choi, Kwang Hee
    • Journal of The Geomorphological Association of Korea
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    • v.27 no.4
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    • pp.1-11
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    • 2020
  • Coastal dunes play an important role in coastal defense. The Moraeul dune in Daecheongdo Island is representative in this regard. However, there is little knowledge, concerning the morphology, grain size, and formation timing of the dune. This study investigated the geomorphological characteristics of the Moraeul dune using topographic surveys, grain size analyses, and OSL dating. The dune was classified as 'single accreted foredune', which was developed under dense vegetation cover and efficient sand trapping. The dune consisted of fine to medium sand with 1.6Φ of mean grain size, and was covered with pine trees (> 100 years old). The samples from the upper part of the dune yielded quartz OSL ages ranging 0.5 ~ 0.7 ka. Therefore, it is likely that the dune developed at least before the Little Ice Age and became what it is today about one century ago.