• Title, Summary, Keyword: Final Stage Densification

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Constitutive Models for Final Stage Densification of Powder Compacts with Power-Law Creep Deformation (Power-law 크리프 변형을 따르는 분말 성형체의 말기 치밀화 모델)

  • Yang, Hoon-Chul;Kim, Ki-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.7
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    • pp.930-939
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    • 2004
  • Constitutive models for final stage densification of metal powder compacts with power-law creep deformation were investigated. The constitutive models were implemented into a finite element program (ABAQUS) by using user subroutine CREEP and, from FEM results, useful densification curves were obtained when hydrostatic and uniaxial stress were applied to the powder compacts at various pressures and temperatures. Because the densification behavior varied as the constitutive models, the equivalent stress surface on each constitutive equation was investigated to analyze the difference of densification behavior.

Effect of Sintering Atmosphere on the Densification and Grain Growth of Uranium Dioxide at the Final-Stage Sintering (소결 분위기에 따른 이산화 우라늄의 치밀화 및 입자성장)

  • 이영우
    • Journal of Korean Powder Metallurgy Institute
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    • v.4 no.3
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    • pp.214-221
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    • 1997
  • The densification and grain growth mechanisms of $UO_{2+x}$ in $H_2$ and in $CO_2$ have been investigated. Uranium dioxide powder compacts were sintered at 1$700^{\circ}C$ in $H_2$ or at 110$0^{\circ}C$ in $CO_2$ for various times from 0.5 h to 16 h. The grain size and density of the specimens were measured. From the measured data, the mechanisms of the densification and grain growth were determined by use of available kinetic equations which express the relations between densification and grain growth. In both atmospheres, it has been found that the densification was controlled by the lattice diffusion and the grain growth by the surface diffusion of atoms around pores. It appears that the surface diffusivity as well as the lattice diffusivity increase considerably with the increase in O/U ratio in the specimen.

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Particle Agglomerate Effect on Intermediate/Final Microstructure (입자 응집이 중기/말기 미구조에 미치는 영향)

  • 손영돈;전병세
    • Journal of the Korean Ceramic Society
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    • v.29 no.11
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    • pp.843-850
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    • 1992
  • The purpose of this study was to describe the heterogeneity effects on Intermediate/Final microstructure in isothermal liquid phase sintering. Several kinds of pore shapes were made by the different in the heterogeneity stress level during Intermediate/Final stage. Specimen with 48% green density especially showed that the local regions of a sintered compact were subject to more rapid shrinkage than the surroundings. This densification limiting factors generally inhibited sintering and made the large isolated crack-like pore in heterogeneous microstructures.

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A Study on the Initial Stage of Sintering and the Grain Growth of ZnO in ZnO-Bi2O3 System (ZnO-Bi2O3계의 소결초기단계와 입자성장에 관한 연구)

  • 성건용;강을손;김종희
    • Journal of the Korean Ceramic Society
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    • v.26 no.4
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    • pp.505-513
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    • 1989
  • The sintering behavior and grain growth of ZnO in 99.0mol% ZnO-1.0mol% Bi2O3 which are the basic compositions of ZnO varistor were studied. The microstructrual observation confirmed that the final sintered density was mainly determined at the initial stage of sintering, i.e. grain rearrangement and grain growth which were induced by the penetration of eutectic melts formed at eutectic temperature(74$0^{\circ}C$). But when the liquid penetration was terminated, the grain growth did not promote further densification. Activation energy of the grain growth of ZnO in the system of 99.0mol% ZnO-1.0mol% Bi2O3 was 44.8$\pm$1.8Kcal/mol.

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Sintering and Grain Growth of Rare Earth-Doped Ceria Particles

  • Sameshima, Soichiro;Higashi, Kenji;Hirata, Yoshihiro
    • Proceedings of the Korea Association of Crystal Growth Conference
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    • pp.65-86
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    • 2000
  • Rare earth-doped ceria powders with a composition of Ce0.8R0.2O1.9(R=Yb, Y, Gd, Sm, Nd and La) were prepared by heating the oxalate coprecipitate. The green compacts began to shrink at 600$^{\circ}$-700$^{\circ}C$. The relative density after the sintering at 1200$^{\circ}$ and 1400$^{\circ}C$ became higher for the higher green density. The samples were densified above 98% relative density by the sintering ant 1600$^{\circ}C$ for 4 h and the grain sizes (4.7-7.6$\mu\textrm{m}$) showed a tendency to become larger with increasing ionic radius of doped-rare earth element. In the intial stag of sintering at 700$^{\circ}$-800$^{\circ}C$, the dominant mass transport process changed from lattice diffusion to grain boundary diffusion to grain boundary diffusion with heating time. The porosity during the intermediated and final stage of the sintering at 1200$^{\circ}$ and 1400$^{\circ}C$ decreased by the mass transport through lattice diffusion with grain growth.

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The Characteristic of Agglomerate and Sintering of Y-PSZ Powders Prepared by Different Processes (제조방법에 따른 Y-PSZ 분말의 응집 및 소결특성)

  • Lee, Jong-Kook;Kim, Hwan;Hwang, Kyu-Hong
    • Journal of the Korean Ceramic Society
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    • v.22 no.5
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    • pp.9-16
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    • 1985
  • Agglomeration of Y-PSZ and its related properties were studied. The ultrafine $ZrO_2$ powder containg 3 mol% $Y_2O_3$ was prepared by 1) coprecipitation method b) hot petroleum drying method c) sol-gel method and the characteristics of calcined powders and the microstructures of sintered body were observed. Powder prepared by the coprecipitation method was about 125$\AA$ in crystallite size and 0.1~1.0${\mu}{\textrm}{m}$ of intra-agglomerate pore size when calcined at $600^{\circ}C$ for 1 hour. because of small crystallite size and weak agglo merate strength resultant densification of sintered body was high. But above the temperature of 130$0^{\circ}C$ efflorescent phenomena due to anions attached to powder surface was observed. Powder prepared by hot petroleum drying method was 65$\AA$ in crystallite size and 1~10${\mu}{\textrm}{m}$ of intraagglome-rate pore size and it was observed that the agglemerates were formed during the calcining process. In this case despite of small crystallite size the rate of sintering was slow and the existing lenticular interagglomerate pore was not eliminated to the final stage of sintering. Powder prepared by sol-gel method showed solid agglomertes due to rapi dhydrolysis reaction. In this powder which involves strong solid agglomerates overall sintering rate was determined by the sintering between the agglomerates and therefore sinterability of powders made by sol-gel method was very poor.

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