• Title/Summary/Keyword: Crystal grain size

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Effect of $U_3O_8$-seed on the grain growth of uranium dioxide ($U_3O_8$ 종자가 $UO_2$ 핵연료 소결체의 입자성장에 미치는 영향)

  • Rhee, Young-Woo;Kim, Dong-Joo;Kim, Keon-Sik
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.17 no.2
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    • pp.75-81
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    • 2007
  • Densification and grain growth have been investigated in 5 wt% $U_3O_8$ seeded $UO_2$ and compared with those of the common $UO_2$ pellet. $UO_2$ compacts and $U_3O_8$ seeded $UO_2$ compacts were sintered at $1300{\sim}1700^{\circ}C$ for 0 h to 4 h. Density and grain size of the sintered pellets were measured by the water immersion method and the image analyzer, respectively. The seeded pellet has a slightly lower density during the intermediate sintering stage. However, the difference of density between two pellets decreases to about 0.5%TD with increasing the sintering temperature. The grain size of the two pellets is similar until $1600^{\circ}C$ but that of the seeded pellet rapidly increases with increasing the sintering temperature.

Study on the emulsion and its physical properties (전자현미경(電子顯微鏡) 건판(乾板)의 제작(製作) 및 그 특성(特性) 조사(調査) 연구(硏究))

  • Kim, Hyun-Chang;Pak, Kyoo-Eun
    • Applied Microscopy
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    • v.1 no.1
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    • pp.3-10
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    • 1969
  • By the use of electron microscope, the study has beek made on the grain size in photo graphic emulsions, which are made at different temperature. It is found that ,the optimum temperature is $60^{\circ}C$, at which the average grain size obtained is the biggest. Also electron micrographs show NaCl-type crystal structure of AgBr and AgCl, as we expected.

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Investigation of aluminum-induced crystallization of amorphous silicon and crystal properties of the silicon film for polycrystalline silicon solar cell fabrication (다결정 실리콘 태양전지 제조를 위한 비정절 실리콘의 알루미늄 유도 결정화 공정 및 결정특성 연구)

  • Jeong, Hye-Jeong;Lee, Jong-Ho;Boo, Seong-Jae
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.20 no.6
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    • pp.254-261
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    • 2010
  • Polycrystalline silicon (pc-Si) films are fabricated and characterized for application to pc-Si thin film solar cells as a seed layer. The amorphous silicon films are crystallized by the aluminum-induced layer exchange (ALILE) process with a structure of glass/Al/$Al_2O_3$/a-Si using various thicknesses of $Al_2O_3$ layers. In order to investigate the effects of the oxide layer on the crystallization of the amorphous silicon films, such as the crystalline film detects and the crystal grain size, the $Al_2O_3$ layer thickness arc varied from native oxide to 50 nm. As the results, the defects of the poly crystalline films are increased with the increase of $Al_2O_3$ layer thickness, whereas the grain size and crystallinity are decreased. In this experiments, obtained the average pc-Si sub-grain size was about $10\;{\mu}m$ at relatively thin $Al_2O_3$ layer thickness (${\leq}$ 16 nm). The preferential orientation of pc-Si sub-grain was <111>.

Computer aided simulation of spark plasma sintering process (Part 2 : analysis) (스파크 플라스마 소결공정의 전산모사(2부 : 해석))

  • Keum Y.T.;Jung S.C.;Jean J.H.
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.16 no.1
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    • pp.43-48
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    • 2006
  • In this Part 2, the grain growth processes of $Al_2O_3$ ceramics is numerically simulated using Monte Carlo method (MCM) and finite element method (FEM) and the pore sizes are analyzed. As the green ceramics whose thermal conductivities in high temperatures are generally low are sintered by the plasma heat and are rapidly cooled, the grain growth of the sintered body in the center is different from that in the outer. Also, even in the same sintering temperature, the pore size differs according to the pressing pressure. In order to prove the difference, the temperature distribution of the sintered body was analyzed using the finite element method and then the grain growth process associated with pressing pressures and relative densities was simulated using Monte Carlo method.

Fabrication and Magnetic Properties of Nanostructured Fe-Co Alloy Powder (나노 구조 Fe-Co 합금분말의 제조 및 자성특성)

  • 이백희;안봉수;김대건;김영도
    • Journal of Powder Materials
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    • v.9 no.3
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    • pp.182-188
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    • 2002
  • Conventional Fe-Co alloys are important soft magnetic materials that have been widely used in industry. Compared to its polycrystalline counterpart, the nanostructured materials have showed superior magnetic properties, such as higher permeability and lower coercivity due to the single domain configuration. However, magnetic properties of nanostructured materials are affected in complicated manner by their microstructure such as grain size, internal strain and crystal structure. Thus, studies on synthesis of nanostructured materials with controlled microstructure are necessary for a significant improvement in magnetic properties. In the present work, starting with two powder mixtures of Fe and Co produced by mechanical alloying (MA) and hydrogen reduction process (HRP), differences in the preparation process and in the resulting microstructural characteristics will be described for the nano-sized Fe-Co alloy particles. Moreover, we discuss the effect of the microstructure such as crystal structure and grain size of Fe-Co alloys on the magnetic properties.

Characteristics of CdS thin film depending on annealing temperature (열처리온도에 따른 CdS박막 특성)

  • 김성구;박계춘;유용택
    • Electrical & Electronic Materials
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    • v.7 no.1
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    • pp.49-56
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    • 1994
  • Polycrystalline CdS thin films were deposited by using EBE method and its crystal structure, surface morphology, electrical and optical properties as a function of annealing temperature were investigated. It was found that optimum growth conditions were substrate temperature annealing temperature 300[.deg. C]. The films were hexagonal structure preferred(002) plane and maximum grain size was 421[.angs.]. As the results, resistivity and optical transmittance of CdS thin films were $8.3{\times}{10^3}$[.ohm.cm] and 89[%] respectively.

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APPLICATION OF IMPEDANCE SPECTROSCOPY TO POLYCRYSTALLINE SI PREPARED BY EXCIMER LASER ANNEALING (임피던스 측정법을 이용한 엑시머 레이져 열처리 Poly-Si의 특성 분석)

  • 황진하;김성문;김은석;류승욱
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2003.11a
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    • pp.200-200
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    • 2003
  • Polycrystalline Si(polysilicon) TFTs have opened a way for the next generation of display devices, due to their higher mobility of charge carriers relative to a-Si TFTs. The polysilicon W applications extend from the current Liquid Crystal Displays to the next generation Organic Light Emitting Diodes (OLED) displays. In particular, the OLED devices require a stricter control of properties of gate oxide layer, polysilicon layer, and their interface. The polysilicon layer is generally obtained by annealing thin film a-Si layer using techniques such as solid phase crystallization and excimer laser annealing. Typically laser-crystallized Si films have grain sizes of less than 1 micron, and their electrical/dielectric properties are strongly affected by the presence of grain boundaries. Impedance spectroscopy allows the frequency-dependent measurement of impedance and can be applied to inteface-controlled materials, resolving the respective contributions of grain boundaries, interfaces, and/or surface. Impedance spectroscopy was applied to laser-annealed Si thin films, using the electrodes which are designed specially for thin films. In order to understand the effect of grain size on physical properties, the amorphous Si was exposed to different laser energy densities, thereby varying the grain size of the resulting films. The microstructural characterization was carried out to accompany the electrical/dielectric properties obtained using the impedance spectroscopy, The correlation will be made between Si grain size and the corresponding electrical/dielectric properties. The ramifications will be discussed in conjunction with active-matrix thin film transistors for Active Matrix OLED.

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Transformation Behavior on Heat Treatment Condition in Grain-Refined Cu-Zn-Al Shape Memory Alloy (결정립 미세화된 Cu-Zn-Al 형상기억합금의 열처리 조건에 따른 변태거동)

  • Kang, J.W.;Jang, W.Y.;Yang, G.S.
    • Journal of the Korean Society for Heat Treatment
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    • v.4 no.4
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    • pp.34-43
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    • 1991
  • A small amount of misch metal and/or Zr was added as a dopant to 70.5wt----Cu-26wt----Zn-3.5wt----Al shape memory alloy in order to study the effect of grain refinement and heat treatments on the transformation behavior, stabilization of martensite, and shape memory ability. It was found that the addition of misch metal and Zr was very effective for reducing the grain size. The fracture mode has been changed from intergranular brittle fracture to ductile fracture with void formation and coalescence by the addition of misch metal and Zr. Aging of the ${\beta}$-phase decreases the $M_s$ temperature, but that of the martensite phase increases the $A_s$ temperature. The hysteresis of transformation temperature ${\Delta}T(A_s-M_s)$ has an increasing tendancy by grain refinement. The crystal structure of martensite was identified as monoclinic structure. As the grain size decreased, martensite stabilization more easily occured and the shape, memory ability has been reduced by the grain size refined.

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Effect of Na2CO3 Addition on Grain Growth Behavior and Solid-state Single Crystal Growth in the Na0.5Bi0.5TiO3-BaTiO3 System (Na0.5Bi0.5TiO3-BaTiO3 계에서 입자성장 및 고상단결정성장에 미치는 Na2CO3 첨가 효과)

  • Moon, Kyoung-Seok
    • Journal of Powder Materials
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    • v.25 no.2
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    • pp.104-108
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    • 2018
  • Grain-growth behavior in the $95Na_{1/2}Bi_{1/2}TiO_3-5BaTiO_3$ (mole fraction, NBT-5BT) system has been investigated with the addition of $Na_2CO_3$. When $Na_2CO_3$ is added to NBT-5BT, the growth rate is higher than desired and grains are already impinging each other during the initial stage of sintering. The grain size decreases as the sintering temperature increases. With the addition of $Na_2CO_3$, a liquid phase infiltrates the interfaces between grains during sintering. The interface structure can be changed to be more faceted and the interface migration rate can increase due to fast material transport through the liquid phase. As the sintering temperature increases, the impingement of abnormal grains increases because the number of abnormal grains increases. Therefore, the average grain size of abnormal grains can be decreased as the temperature increases. The phenomenon can provide evidence that grain coarsening in NBT-5BT with addition of $Na_2CO_3$ is governed by the growth of facet planes, which would occur via mixed control.

Sintering Behavior, Dielectric and Pyroelectric Properties of $(Pb, La)TiO_3$ Ceramics ($(Pb, La)TiO_3$ 세라믹스의 소결 거동 및 유전.초전 특성)

  • 최동구;최시경
    • Journal of the Korean Ceramic Society
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    • v.31 no.8
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    • pp.841-848
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    • 1994
  • The sintering behavior of La-modified PbTiO3 ceramics was investigated in order to improve the poor sinterability of PbTiO3. Addition of La improved the sinterability. It was confirmed that this improvement was due to the decrease in tetragonality ratio c/a of crystal lattice. The variations of dielectric constant and pyroelectric coefficient were measured with temperature. It was observed that with the increase of La content, Curie temperature decreased and dielectric constant at room temperature increased. La-modified PbTiO3 ceramics had smaller pyroelectric figure of merits than those of pyroelectric materials in use. The effects of grain size on dielectric and pyroelectric properties were also investigated. The change of grain size had effect on maximum dielectric constant and pyroelectric coefficient, but is had little effect on pyroelectric figure of merit at room temperature. The closer examination near ferro-paraelectric phase transition temperature revealed that the behavior of phase transition approached a more relaxor character with the increase of La content and the decrease of grain size.

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