• Title/Summary/Keyword: Solid state reaction

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Effects of Chemical Inhomogeneity on Phase Coexistence in Pb(Zr, Ti))$O_3$ Ceramics at Morphotropic Tetragonal and Rhombohedral Phase Boundary (정방정상과 능면체상의 경계조성 Pb(Zr, Ti)$O_3$ 세라믹스에서 화학조성의 불균일성이 상공존에 미치는 영향)

  • 천채일;김호기
    • Journal of the Korean Ceramic Society
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    • v.27 no.8
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    • pp.1027-1033
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    • 1990
  • In order to identify the origin of phase coexistence at morphotropic tetragonal and rhombohedral boundary in PZT ceramics, the effect of chemical inhomogeneity on phase coexistence region was investigated. Two kinds of PZT ceramics with different chemical homogeneity were prepared by conventional solid state reaction and co-precipitation method. There was coexistence of tetragonal and rhombohedral phase over a wide composition range in PZT ceramics calcined by solid state reaction, and there was also phase coexistence of which region was reduced considerably in sintered samples. And phase coexistence region was not observed in co-precipitated PZT ceramics(within 1 mole%). Therefore compositional fluctuation is considered to be major origin of the phase coexistence at morphotropic phae boundary in PZT ceramics.

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Superconducting Properties of Ge Substitution for the Bi Site in the 2212 Phase of Bi-Sr-Ca-Cu-O Superconductors (Bi계 산화물 초전도체 2212상에 있어서 Bi 자리에 Ge 치환에 따른 초전도 특성)

  • 신재수;이민수;최봉수;송승용;송기영
    • Journal of the Korean Ceramic Society
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    • v.37 no.8
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    • pp.787-791
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    • 2000
  • Samples with the nominal composition, Bi2-xGexSr2CaCu2O8+$\delta$ (x=0, 0.1, 0.2, 0.3, 0.4, 0.5) were prepared by the solid-state reaction method. We have studied the effect of substitution Ge for Bi and investigated the superconducting properties by changing oxygen content with Ge substitution. It was found that temperature difference, ΔK, between TCon and TCzero was considerably smaller in the samples prepared by the intermediate pressing method than that in the samples by the solid-state reaction method. We found the solubility limit of Ge to the 80 K single phase was around x=0.3. Within the solubility limit, lattice constant c decreased with the increase of x. In the region of the 80K single phase, the onset critical temperature TCon increased and excess oxygen content decreased with increase of x.

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Surface Potential Behavior of Nano $CeO_2$ Particles in Aqueous Media (수계분산매체에서 나노 $CeO_2$ 입자의 계면전위 거동)

  • 이태원;백운규;최성철;이상훈;임형섭;김철진
    • Journal of the Korean Ceramic Society
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    • v.37 no.7
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    • pp.721-725
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    • 2000
  • In this study, the dispersion stability of nano-sized CeO2 particles, synthesized by hydrothermal method in aqueous was evaluated from observing the surface potential behavior of CeO2 particle synthesized by solid state reaction. The isoelectric point(IEP) of nano-sized CeO2 synthesized by hydrothermal synthesis was found to be pH 9 contrary to the isoelectric point of micro-sized CeO2 synthesized by solid state reaction at pH 6.7. IEP was shifted to pH 2.0 as the addition of D-3019 from 0.1 to 1.0 wt%. The surface potential of CeO2 particles synthesized by hydrothermal synthesis was reduced as the addition of B-1001 used as a binder without change of IEP because the absorption of B-1001 polymer on the CeO2 particles shifted the shear plane of CeO2 particles outward away from the surface. This surface potential behavior was well correlated with the dispersion stability of slurry.

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Phase Distribution and Interface Chemistry by Solid State SiC/Ni Reaction

  • Lim, Chang-Sung;Shim, Kwang-Bo;Shin, Dong-Woo;Auh, Keun-Ho
    • The Korean Journal of Ceramics
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    • v.2 no.1
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    • pp.19-24
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    • 1996
  • The phase distribution and interface chemistry by the solid-state reaction between SiC and nickel were studied at temperatures between $550 \;and\; 1250^{\circ}C$ for 0.5-100 h. The reaction with the formation of silicides and carbon was first observed above $650^{\circ}C$. At $750^{\circ}C$, as the reaction proceeded, the initially, formed $Ni_3Si_2$ layer was converted to $Ni_2$Si. The thin nickel film reacted completely with SiC after annealing at $950^{\circ}C$ for 2 h. The thermodynamically stable $Ni_2$Si is the only obsrved silicide in the reaction zone up to $1050^{\circ}C$. The formation of $Ni_2$Si layers with carbon precipitates alternated periodically with the carbon free layers. At temperatures between $950^{\circ}C$ and $1050^{\circ}C$, the typical layer sequences in the reaction zone is determined by quantitative microanalysis to be $SiC/Ni_2$$Si+C/Ni_2$$Si/Ni_2$$Si+C/…Ni_2$Si/Ni(Si)/Ni. The mechanism of the periodic band structure formation with the carbon precipitation behaviour was discussed in terms of reaction kinetics and thermodynamic considerations. The reaction kinetics is proposed to estimate the effective reaction constant from the parabolic growth of the reaction zone.

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Characterization of Poly(vinyl phosphate-b-styrene) by Solid-State $^{31}P$ NMR and Titration

  • Li, Guang-Hua;Kim, Sang-Hun;Cho, Chang-Gi;Park, Tae-Joon;Kim, Yong-Ae
    • Macromolecular Research
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    • v.14 no.5
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    • pp.504-509
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    • 2006
  • Poly(vinyl phosphate-b-styrene) (PVPP-b-PS) block copolymers were synthesized successfully from poly(vinyl alcohol-b-styrene) (PVA-b-PS) by reaction with phosphorus oxychloride and subsequent hydrolysis. The obtained block copolymers were slightly crosslinked, and were characterized by various analytical techniques. The total phosphorus content and the ratio of the differently bound phosphorus were obtained by both solid-state $^{31}P$ NMR and pH titration, but the results differed slightly. Characterization by energy dispersion X-ray analysis (EDS) or Rutherford back scattering (RBS), on the other hand, determined the total phosphorus contents, but the results were quite different from those by solid-state $^{31}P$ NMR.