• Title/Summary/Keyword: Hot pressing

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Preparation of a Li7La3Zr1.5Nb0.5O12 Garnet Solid Electrolyte Ceramic by using Sol-gel Powder Synthesis and Hot Pressing and Its Characterization

  • Lee, Hee Chul;Oh, Nu Ri;Yoo, Ae Ri;Kim, Yunsung;Sakamoto, Jeff
    • Journal of the Korean Physical Society
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    • v.73 no.10
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    • pp.1535-1540
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    • 2018
  • In this study, we prepared and characterized Nb-doped $Li_7La_3Zr_{2-x}O_{12}$ (LLZNO) powder and pellets with a cubic garnet structure by using a modified sol-gel synthesis and hot pressing. LLZNO powder with a very small grain size and cubic structure without secondary phases could be obtained by using a synthesis method in which Li and La sources in a propanol solvent were mixed together with Zr and Nb sources in 2-methoxy ethanol. A pure cubic phase LLZNO pellet could be fabricated from the prepared LLZNO and an additional 6-wt% of $Li_2CO_3$ powder by hot pressing at $1050^{\circ}C$ and 15.8 MPa. The hot-pressed LLZNO pellet with a relative density of 99% exhibited a very dense surface morphology. The total Li ionic conductivity of the hot-pressed LLZNO was $7.4{\times}10^{-4}S/cm$ at room temperature, which is very high level compared to other reported values. The activation energy for ionic conduction was estimated to be 0.40 eV.

Effects of Y2O3 and Al2O3 Addition on the Properties of Hot Pressed AlN Ceramics (AlN 세라믹의 hot pressing에 사용되는 Y2O3 및 Al2O3 소결조제의 효과)

  • Kong, Man-Sik;Hong, Hyun-Seon;Lee, Sung-Kyu;Seo, Min-Hye;Jung, Hang-Chul
    • Korean Journal of Materials Research
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    • v.17 no.10
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    • pp.560-566
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    • 2007
  • AlN plates were fabricated by hot pressing at $1700-1900^{\circ}C$ using yttria and alumina (3 and $10\;{\mu}m$ particle size) powders as additives and characterized: density, thermal conductivity, transverse rupture strength, and grain size measurement by SEM and EDS. Density values of $3.31-3.34\;g/cm^3$ are largely attributed to hot pressing of powder mixtures in carbon mold under $N_2$ atmosphere which caused effective degree of oxygen removal from yttrium-aluminate phase expected to form at $1100^{\circ}C$. The grain size of hot pressed AlN was almost homogeneous, with size approximately from 3.2 to $4.0\;{\mu}m$ after hot pressing. $Al_2O_3$ powder of $3\;{\mu}m$ particle size resulted in better transverse rupture strength and finer grain size compared to $10\;{\mu}m$ $Al_2O_3$ powder. The thermal conductivity of AlN ranged between $83-92.7\;W/m{\cdot}K$ and decreased with $Al_2O_3$ addition. Fine grain size is preferred for better mechanical properties and thermal conductivity.

Thermoelectric Property and p-n Transition Mechanism of Hot Pressed Bi4/3Sb2/3Te3 ($Bi_{4/3}Sb_{2/3}Te_3$ 가압소결체의 열전특성과 p-n 전이기구)

  • 박태호;유한일;심재동
    • Journal of the Korean Ceramic Society
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    • v.29 no.11
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    • pp.855-862
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    • 1992
  • Thermoelectric power, electrical conductivity and Hall effect were measured, as functions of temperature in the range of 100 to 600 K, on polycrystalline Bi4/3Sb2/3Te3 which had been prepared via uniaxial hot-pressing at different temperatures in the range of 373 K to 773 K, aiming at searching a profitable processing route to a polycrystalline thermoelectric material, a promising, viable alternative to a single crystalline one. It was found that, with increasing temperature of pressing under a fixed pressure, the material, normally a p-type prior to being hot-pressed, underwent a transition to n-type. This transition was confirmed to be due to plastic deformation during hot-pressing and interpreted as being attributed to the change of the major ionic defect BiTe' into TeBi˙at temperature high enough for structure elements mobility. Thermoelectric figure-of-merit of the hot-pressed material was discussed in connection with the p-n transition in addition to microstructure.

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Thermoelectric Properties of Half-Heusler ZrNiSn1-xSbx Synthesized by Mechanical Alloying Process and Vacuum Hot Pressing

  • Ur, Soon-Chul
    • Journal of Powder Materials
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    • v.18 no.5
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    • pp.401-405
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    • 2011
  • Half-heusler phase ZrNiSn is one of the potential thermoelectric materials for high temperature application. In an attempt to investigate the effect of Sb doping on thermoelectric properties, half-heusler phase $ZrNiSn_{1-x}Sb_x$ ($0{\leq}x{\leq}0.08$) was synthesized by mechanical alloying of stoichiometric elemental powder compositions, and consolidated by vacuum hot pressing. Phase transformations during mechanical alloying and hot consolidation were investigated using XRD. Sb doped ZrNiSn was successfully produced in all doping ranges by vacuum hot pressing using as-milled powders without subsequent annealing. Thermoelectric properties as functions of temperature and Sb contents were evaluated for the hot pressed specimens. Sb doping up to x=0.04 in $ZrNiSn_{1-x}Sb_x$ was shown to be effective on thermoelectric properties and the figure of merit (ZT) was shown to reach to the maximum at x=0.02 in this study.

Effects of Hot Pressing Condition on the Properties of SiCf/SiC Composites (SiCf/SiC 복합체의 특성에 미치는 열간가압소결 조건의 영향)

  • Noviyanto, Alfian;Yoon, Dang-Hyok
    • Journal of the Korean Ceramic Society
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    • v.48 no.5
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    • pp.335-341
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    • 2011
  • Continuous SiC fiber-reinforced SiC-matrix composites ($SiC_f$/SiC) had been fabricated by electrophoretic infiltration combined with ultrasonication. Nano-sized ${\beta}$-SiC added with 12 wt% of $Al_2O_3-Y_2O_3$ additive and Tyranno$^{TM}$-SA3 fabric were used as a matrix phase and fiber reinforcement, respectively. After hot pressing at 5 different conditions, the density, microstructure and mechanical properties of $SiC_f$/SiC were characterized. Hot pressing at relatively severe conditions, such as $1750^{\circ}C$ for 1 and 2 h, resulted in a brittle fracture behavior due to the strong fiber-matrix interface in spite of their high flexural strength. On the other hand, toughened $SiC_f$/SiC composite could be achieved by hot pressing at milder condition because of the formation of weak interface in spite of the decreased flexural strength. These results proposed the importance of weak fiber-matrix interface in the fabrication of ductile $SiC_f$/SiC composite.

Effect of Ceramic Ball Inclusion on Densification of Metal Powder Compact (삽입된 세라믹 볼이 금속분말성형체의 치밀화에 미치는 영향)

  • Park, Hwan;Yu, Yo-Han;Kim, Gi-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.1 s.173
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    • pp.29-37
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    • 2000
  • The effect of a ceramic ball inclusion on densification behavior of a metal powder compact was investigated under cold isostatic pressing, pressureless sintering and hot isostatic pressing. To simulate those processes, proper constitutive models were implemented into a finite element program (ABAQUS). Measured density distributions of metal powder compacts were also compared with finite element results and showed the same trend with simulated results. Residual stress distributions were calculated by finite element analysis to study the effect of ceramic ball inclusions with different thermal expansion coefficients. The higher residual stress was observed in a metal powder compact when the difference between thermal expansion coefficients for a ceramic ball and metal powder became larger. Samples produced by Wing showed more uniform density distributions and lower residual stresses compared to those by sintering after cold isostatic pressing. For various sizes of ceramic ball inclusions, densification and deformation of powder compacts were also studied during hot isostatic pressing.