• 제목/요약/키워드: grain composition

검색결과 823건 처리시간 0.02초

미세구조 관찰에 의한 철제금속유물의 특성화 (Characterization of Ferrous Metal Artifacts by Microstructure Observation)

  • 허우영;이철
    • 분석과학
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    • 제11권4호
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    • pp.316-320
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    • 1998
  • An image analysis was used for the interpretation of microstructures of ferrous metal artifacts. For the purposes, various microstructural features such as average grain size, phase area, shape factor, and composition of the inclusions, were parameterized for the information about manufacturing techniques such as casting, heating and tempering. The carbon content was determined through the evaluation of the amount of pearlite phase. As the amount of pearlite phase increased the shape factor also increased. Grain size was relatively smaller in trans-section than in cross-section. The manufacturing direction was trans-sectional because the orientation of inclusions was elongated lengthwise. All inclusions was of silicate groups and the manufacturing temperature was estimated up to $1450^{\circ}C$.

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질화규소 세라믹스의 미세조직 형성에 미치는 Seed 첨가의 영향 (Effect of Seeding on Microstructural Development of Silicon Nitride Ceramics)

  • 이창주
    • 한국분말재료학회지
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    • 제5권2호
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    • pp.133-138
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    • 1998
  • The effect of $\beta$-$Si_3N_4$ seeding on microstructural development of silicon nitride based materials has been investigated. In particular, to observe more distinctly the abnormal grain growth in pressureless sintering, fine $\alpha$-$Si_3N_4$(mean particle size: 0.26 ${\mu}m$) powder classified by sedimentation method was used. It was possible to prepare silicon nitride with abnormally grown grains under low nitrogen pressure of 1 atm thanks to the heterogeneous nucleation on $Si_3N_4$ seed particles. The size and morphology of silicon nitride grains were strongly influenced by the presence of $\beta$-$Si_3N_4$ seed and overall chemical composition. For specimens with initially low $\beta$-content, the large grains grew without a significant impingement by other large grains. On the contrary, for specimens with initially high $\beta$-content, steric hindrance was effective. The resulting microstructure was less inhomogeneous and characterized by unimodal grain size distribution.

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Nanocrystalline Materials-an Overview

  • Suryanarayana, C.
    • 한국분말재료학회지
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    • 제3권4호
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    • pp.233-245
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    • 1996
  • Nanocrystalline materials, with a grain size of typically <100 nm, are a new class of materials with properties vastly different from and often superior to those of the conventional coarse-grained materials. These materials can be synthesized by a number of different techniques and the grain size, morphology, and composition can be controlled by controlling the process parameters. In comparison to the coarse-grained materials, nanocrystalline materials show higher strength and hardness, enhanced diffusivity, improved ductility/toughness, reduced, density, reduced elastic modulus, higher electrical resistivity, increased specific heat, higher coefficient of thermal expansion, lower thermal conductivity, and superior soft and hard magnetic properties. Limited quantities of these materials are presently produced and marketed in the US, Canada, and elsewhere. Applications for these materials are being actively explored. The present article discusses the synthesis, structure, thermal stability, properties, and potential application of nanocrystalline materials.

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Conduction Mechanism Analysis of Low Voltage ZnO Varistor

  • Jang, Kyung-Uk;Kim, Myung-Ho;Lee, Joon-Ung
    • 한국전기전자재료학회:학술대회논문집
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    • 한국전기전자재료학회 1998년도 추계학술대회 논문집
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    • pp.263-266
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    • 1998
  • ZnO varistors have an excellent non-linearity and a large surge-energy absorption capability. For these reasons, the ZnO varistors are widely used to protect electrical/electronic circuits from an abnormal surge and/or noise signal. In order to obtain the low-voltage varistor with randomly distributed large seed grain within bulk, the ZnO varistors are made by a new three-composition seed grain method. And a conduction mechanism of varistors, which was observed in the temperature range of 30 ∼ 120$^{\circ}C$ and at the current range of 10$\^$-8/∼10$^2$ A/cm$^2$, was classified by the three regions of different mechanism when the current was increased.

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Cu계 스피넬 페라이트의 Cu 함량에 따른 특성 변화 (Properties of Cu-Contained Spinel Ferrites with Various Cu Contents)

  • 남중희;오재희
    • 한국세라믹학회지
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    • 제33권11호
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    • pp.1245-1252
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    • 1996
  • The charcteristics for the copper-contained spinel ferrites such as NiCu-and ZnCu ferrites with various copper content are investigated in this study which can provide a explanation for the behavior of copper in sintering at a low temperatuer. The bulk density and the grain size for these sintered ferrites were increased with the larger amount of copper in compositions. In microstructure of copper-contained spinel ferrites copper exists in the grain boundary which is sintering process. Electrical resistivity and frequency range with maximum Q-facor of NiCu-or ZnCu ferrites were decreased as increasing of copper content in ferrite composition.

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저전압용 바리스터계의 기본조성에 관한 연구 (A Study on the Basic Compositions for Low Voltage ZnO Varistor System)

  • 백수현;마재평;강희창
    • 대한전자공학회논문지
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    • 제24권6호
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    • pp.986-991
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    • 1987
  • To establish the basic composition of low voltage varistor and to find the role of each compont in detail, we investigated the electrical properties and the microstructures. As a result, ZnO 1.0m/oBi2O3-1.0m/oCo2kO3-0.2m/oMnO2 system was optimum for low voltage varisor. We found that Bi2o3 promotes grain growth of ZnO and that Co2O3 doped in ZnO grain lowers the nonlinear resistance and MnO2 mainly existed near the ZnO grainboundary elevates nonlinear resistance.

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Fe-Ni 합금 극박재 제조를 위한 전주성형기술 및 극박재 특성 (Electroforming and Properties of Fe-Ni Alloy Thin Foils)

  • 임태홍;이흥렬
    • 소성∙가공
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    • 제14권2호
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    • pp.121-125
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    • 2005
  • Electroforming is a process that employs technology similar to that used for electroplating but which is used for manufacturing metallic articles, rather than as a means of producing surface coatings. Electroforming provides a cost-effective means of producing alloys and fully dense nanocrystalline metals as foils, sheets and complex shapes. Fe-Ni nanocrystalline alloy foils with composition in the $36\~80wt\%$ Ni range were fabricated by electroforming. The thickness of electroformed foils was in the range of $5\~30{\mu}m$. TEM and XRD analysis was applied for measuring the grain size. Very fine grain size$(\~10nm)$ was obtained in alloy foils. The yield and tensile strength of electroformed Fe-Ni alloy were 2000-2800 MPa and 2500-3300 MPa respectively. The magnetic permeability at high frequency of electroformed Fe-Ni foil was higher than that of thicker foils.

전기도금법으로 제조한 Ni-Fe 나노박막의 스트레스와 자기적 특성에 미치는 용액의 조건 및 전류밀도의 영향 (Effect of Bath Conditions and Current Density on Stress and Magnetic Properties of Ni-Fe Nano Thin Films Synthesized by Electrodeposition Methods)

  • 구본급
    • 한국표면공학회지
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    • 제44권4호
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    • pp.137-143
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    • 2011
  • The internal stress and magnetic properties (coercivity and squareness) of Ni-Fe nano thin film synthesized by electrodeposition method were studied as a function of acidic chloride bath conditions (composition and temperature) and current density. Fe deposition patterns were different depending on the temperature of the solution, the stress of film decreased with increasing the solution temperature, and the depending on the amount of Fe deposition showed a parabolic shape. The grain size of film was inversely proportional to stress of thin film. The internal stress of thin film and magnetic properties were deeply relevant, and the stress of thin film had a relationship with bath conditions and grain size of the thin film surface.

용융염법으로 합성한 Ba-ferrite의 $SiO_2$ 및 Seed 첨가 효과 (Effects of $SiO_2$ and Seed on Ba-ferrite Synthesized by Molten Salt)

  • 김영근;이승관;김현식;오영우
    • 한국전기전자재료학회:학술대회논문집
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    • 한국전기전자재료학회 1996년도 추계학술대회 논문집
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    • pp.326-329
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    • 1996
  • In order to synthesize Ba-ferrite fine particles by molten salt method and inhibit the abnormal grain growth of sintered specimen, KCI anti NaCl were added to basic composition to 50% by weight, and added 1 male% of $SiO_2$ to control the shape of Ba-ferrite particles. $H_{c}$ and $M_{r}$ were decreased when F $e^{3+}$ was substituted with $Co_{2+}$ and $Ti_{4+}$ from x=0 to x=1.0 in $BaFe_{12-2x}$ $Ti_{x}$ $Co_{x}$ $O_{19}$ , and 1 mole% $SiO_2$ increased the size but shortened c-axis of hexagonal ferrite. Seeds added in Ba-ferrite particle effected inhibition of abnormal grain growth during sintering.ing.g.

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$Zr(Y,Ce)O_2$ TZP의 수열분위기 시효후의 기계적 성질 (Mechanical Properties of $Zr(Y,Ce)O_2$ TZP After Aging in Hydrothermal Conditon)

  • 손영국;박홍채
    • 한국세라믹학회지
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    • 제36권12호
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    • pp.1390-1395
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    • 1999
  • Zr(Y,Ce)O2 TZP ceramics were prepared by sintering compacts of 3 mol% Y2O3-TZP(3Y-TZP) powders with different amount of 12 mol% CeO2-TZP(12Ce-TZP) in air at 140$0^{\circ}C$ for 2 h. The phase changes microstructure and mechanical properties of Zr(Y. Ce)O2 TZP after hydrothermal aging(20$0^{\circ}C$ 5h) were investigated. Although an addition of 12Ce-TZP accelerated the grain growth of Zr(Y, Ce)O2 TZP it restrained the transformation of tetragonal to the monoclinic phase during aging. The degradation in mechanical properties of sintered bodies was governed by the formed monoclinic phase and chemical composition. Induced Vickers indentation crack was propagated intergranually. From SEM observation of the fracture surfaces the pull-out of individual grain was confirmed.

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