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저널/프로시딩 상세정보

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H : 소장처정보

T : 목차정보

Journal of the European Ceramic Society 12건

  1. [해외논문]   Kinetics and morphology of electrochemical vapour deposited thin zirconia/yttria layers on porous substrates  

    Brinkman, H.W. ; Meijerink, J. ; de Vries, K.J. ; Burggraaf, A.J.
    Journal of the European Ceramic Society v.16 no.6 ,pp. 587 - 600 , 1996 , 0955-2219 ,

    초록

    Abstract By means of electrochemical vapour deposition (EVD), it is possible to grow thin (0.5–5 μm), dense zirconia/yttria layers on porous ceramic substrates. Kinetics of the EVD process, morphology and oxygen permeation properties of the grown layers are investigated. Very thin (~ 0.5 μm) layers are grown at relatively low temperatures (700–800 °C). Water vapour as reactant enhances the surface reaction rate at the solid oxide/oxygen source reactant interface. A transition occurs from pore diffusion (above 1000 °C) to bulk electrochemical diffusion (below 900 °C) as rate-limiting step for layer growth. The zirconia/yttria solid solution is mainly deposited in the cubic phase; the layers grow in a typical columnar way and are polycrystalline. Oxygen permeation measurements show that the oxygen permeation flux through the zirconia/yttria layers is influenced by the layer thickness, morphology, presence of water vapour and the oxygen pressure gradient over the layer.

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  2. [해외논문]   Enhanced mechanical properties by grain boundary strengthening in ultra-fine-grained TZP ceramics  

    He, Y.J. ; Winnubst, A.J.A. ; Sagel-Ransijn, C.D. ; Burggraaf, A.J. ; Verweij, H.
    Journal of the European Ceramic Society v.16 no.6 ,pp. 601 - 612 , 1996 , 0955-2219 ,

    초록

    Abstract The mechanical properties of ceramics with the compositions of 5 mol% YO 1.5 -TZP (ZY5) and 4 mol% YO 1.5 -4 mol% CeO 2 -TZP (ZY4Ce4) were investigated. Nanocrystalline powders of both TZPs were synthesized by a gel precipitation technique. Powder compacts were made by cold isostatic pressing, and were then pressureless sintered or sinter-forged to dense TZP ceramics (density: 96–99%) with grain sizes of 180 nm. Shear deformation during sinter-forging was found to favourably affect densification and microstructure. The mechanical properties of both types of ultrafinegrained TZP ceramics were examined up to 760 °C. The results point towards an improved grain boundary structure and the elimination of residual flaws obtained by the sinter-forging technique. The sinter-forged samples exhibited a higher Vicker hardness compared to that of pressureless sintered specimens. After sinter-forging the fracture energy value was found to be 325 J/m 2 and the fracture toughness to be 10 MPa m 12 . A Weibull modulus of 21 was obtained for the sinter-forged samples which was significantly higher than the value of 8 for the pressureless sintered specimens. The enhancement of reliability is obviously connected to a decrease in the average size and concentration of flaws caused by inhomogeneous powder particle packing due to the presence of irregular agglomerates.

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  3. [해외논문]   Ageing of zirconia-toughened alumina ceramics under different hydrothermal conditions  

    Basu, D. ; Gupta, A.Das ; Basu, M.K. ; Sarkar, B.K.
    Journal of the European Ceramic Society v.16 no.6 ,pp. 613 - 617 , 1996 , 0955-2219 ,

    초록

    Abstract Changes in the crystalline phases of ZrO 2 in different zirconia-toughened alumina (ZTA) compositions were studied at lower temperature (150–250 °C) by exposing them in a stream of humid air for a period of 24 h. Fresh samples of these compositions were also aged in an autoclave with superheated water for 2.5 h in the same temperature range, and the degree of phase transformation was compared with data from the previous samples to establish the effect of pressure on this phenomenon. It was observed for all the ZTA compositions that phase transformation increased monotonically with ageing time, temperature and pressure, although for the compositions with a lower percentage (15 vol%) of zirconia (3 mol% Y 2 O 3 ), ageing in an autoclave was more detrimental particularly at lower temperature. As the ageing temperature increased in the composition with 15 vol% ZrO 2 (3 mol% Y 2 O 3 ), the influence of ageing duration on phase transformation of ZrO 2 increased and the effect for 24 h of exposure time was found to be even more catastrophic than that of autoclave pressure at 250 °C. On the other hand, for the ZTA compositions containing more than 15 vol% zirconia (3 mol% Y 2 O 3 ), the damaging effect of ageing in the autoclave was greater and this difference increased with increase in temperature.

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  4. [해외논문]   Characterisation of sol-gel derived alumina-silica matrices for continuous fibre reinforced composites  

    Wu, J. ; Chen, M. ; Jones, F.R. ; James, P.F.
    Journal of the European Ceramic Society v.16 no.6 ,pp. 619 - 626 , 1996 , 0955-2219 ,

    초록

    Abstract Bulk gels corresponding to an oxide composition of 3Al 2 O 3 ·2SiO 2 , prepared from a sol with a high solids yield using submicron alumina powder and colloidal silica sol as precursors, were sintered to over 99% of theoretical density after 2 h at 1300 °C. Densification occurred by viscous flow of the amorphous silica matrix containing well dispersed alumina particles. After 2 h at 1600 °C almost complete crystallisation to mullite occurred. Uniform unidirectional carbon fibre reinforced composites were produced by a single stage infiltration of fibres, using the above sol, and hot-pressing either at 1300 or at 1400 °C to 98 and 97% of the theoretical density respectively. The composites, with a matrix predominantly of silica glass and dispersed alumina particles, exhibited non-brittle failure with mean flexural strengths of 720 and 766 MPa for hot-pressing at 1300 and 1400 °C respectively. Extensive fibre pull-out during testing indicated a relatively weak bond between the fibres and the matrix, and transmission electron microscopy revealed no evidence of chemical interactions at the interface.

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  5. [해외논문]   Sintering behaviour of precursor mullite powders and resultant microstructures  

    Kara, F. ; Little, J.A.
    Journal of the European Ceramic Society v.16 no.6 ,pp. 627 - 635 , 1996 , 0955-2219 ,

    초록

    Abstract Crystallization and sintering behaviour of two structurally different diphasic precursor mullite powders were studied. Powder derived from boehmite and colloidal silica formed mullite at around 1250 °C and could be sintered to high density at this temperature by viscous flow sintering. Calcination of the powder up to 1000 °C did not affect its sinterability but the weight loss decreased from 20% for the uncalcined powder to 5% for the 1000 °C calcined powder. In contrast, powder derived from aluminium sulfate and colloidal silica formed mullite at around 1200 °C and did not sinter much by the viscous flow, but showed enhanced solid-state sintering behaviour compared with crystalline mullite powders. Calcination of the powder at temperatures below mullite formation temperature did not affect its sinterability. Microstructural examinations revealed that dense mullite obtained by sintering of powder derived from aluminium sulfate-colloidal silica had much finer grain size (~135 nm) than that obtained from the boehmite-colloidal silica mixture (~1500 nm) and the fine grain size of the mullite was stable up to 1300 °C upon long heat treatments (120 h).

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  6. [해외논문]   Phase equilibria and crystal chemistry in the system Sr-Ca-Cu-O under high oxygen pressure  

    Robertson, A.D. ; Sastry, P.V.P.S.S. ; West, A.R.
    Journal of the European Ceramic Society v.16 no.6 ,pp. 637 - 643 , 1996 , 0955-2219 ,

    초록

    Abstract Phase equilibria in the system SrO-CaO-CuO have been studied under high oxygen pressures. The recently discovered non-superconducting binary phase, Sr 0.74(3) CuO 2 , which is stable only under high oxygen pressure, forms a complete range of solid solutions with the structurally related phase, Ca 0.81(1) CuO 2 . These materials have complicated superstructures and may form a family of Vernier phases, such as was found in Sr 0.74(3) CuO 2 . Stabilities and oxygen stoichiometries of tetragonal Sr 2−2 x Ca 2 x CuO 3+δ (0.0 ≤ x ≤ 0.1) and Sr 14−14 x Ca 14 x Cu 24 O 38+δ (0.0 ≤ x ≤ 0.5) solid solutions under high oxygen pressures are also discussed.

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  7. [해외논문]   Threshold stress intensity factor in soda-lime silicate glass by interrupted static fatigue test  

    Sglavo, Vincenzo M. ; Green, David J.
    Journal of the European Ceramic Society v.16 no.6 ,pp. 645 - 651 , 1996 , 0955-2219 ,

    초록

    Abstract The measurement of the threshold stress intensity factor K th for sub-critical crack growth of soda-lime glass in a water environment was performed using the interrupted static fatigue test. The experimental procedures suggested in a previous paper by the current authors were followed. In the first approach, K th was calculated as the stress intensity factor at which half of the specimens fail during the constant stress phase of the test. In the second approach, the fatigue limit was determined from the stress intensity factor applied to the weakest surviving sample during the stress hold. For both cases, values of the stress intensity factor were obtained for increasing hold times, which ranged from 1 hour to 20 days. The estimated K th values decrease with holding time but are expected to reach a limiting value, equivalent to the true threshold at long times. For holding times of 20 days, values of 0.16 and 0.15 M Pa m 12 were obtained by using the two different approaches. For the current test, the necessary limit in the estimated K th values was not obtained, suggesting that if a threshold exists, it must be equal to or less than these values. These values are significantly lower than previous K th estimates that were obtained by extrapolation from crack velocity and time-to-failure measurements (0.2 – 0.4 M Pa m 12 ).

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  8. [해외논문]   Microstructural instability and the resultant strength of SiCO (Nicalon) and SiNCO (HPZ) fibres  

    Bodet, R. ; Jia, N. ; Tressler, R.E.
    Journal of the European Ceramic Society v.16 no.6 ,pp. 653 - 664 , 1996 , 0955-2219 ,

    초록

    Abstract Microstructural changes and the related strength degradation were investigated for SiCO Nicalon and SiNCO HPZ fibres during heat treatments in air and argon at 1000–1400 °C for 0.5 to 90 h. While the as-received Nicalon fibre contains β-SiC and carbon nanocrystals in an amorphous SiO 1.12 C 0.44 phase, the HPZ fibre is completely amorphous. It is also inhomogeneous in surface composition compared with that of the bulk. The time-dependent strength degradation of the Nicalon fibre in argon is related to the gradual decomposition of the SiO 1.12 C 0.44 phase from the surface which produces surface defects, β-SiC grain growth and intergranular porosity. The strength degradation of the HPZ fibre results from surface crystallization into α-SiO 2 , Si 2 N 2 O and β-SiC. On the other hand, the HPZ fibre core — which has composition close to SiN 1.02 C 0.23 — shows structural stability for all heat treatment conditions.

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  9. [해외논문]   The Influence of α- and β-Si3N4 precursors on formation of α-SiAlON ceramics  

    Haviar, Miroslav
    Journal of the European Ceramic Society v.16 no.6 ,pp. 665 - 670 , 1996 , 0955-2219 ,

    초록

    Abstract During the formation of α-SiAlON from a powder mixture wet-milled in isopropyl alcohol at a temperature of 1500–1600 °C there appears considerable amount of β-SiAlON. β-SiAlON is formed in high α- as well as in high β-Si 3 N 4 starting powders. The β-SiAlON is dissolved at higher temperatures. The rate of dissolution of α-Si 3 N 4 was observed to be higher than that of β-Si 3 N 4 and the densification and rate of α-SiAlON formation is higher in high α-Si 3 N 4 powder.

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  10. [해외논문]   Surface charge and viscosity of mixed Si3N4Y2O3 suspensions containing lignosulphonate  

    Fagerholm, Heidi ; Johansson, Leena-Sisko ; Graeffe, Mats ; Rosenholm, Jarl B.
    Journal of the European Ceramic Society v.16 no.6 ,pp. 671 - 678 , 1996 , 0955-2219 ,

    초록

    Abstract We have studied the surface charge and the dispersion behavior of silicon nitride-yttrium oxide-lignosulfonate powder dispersions, prior to sintering. In our previous study we reported on the effect of pH on the adsorption of yttria (Y 2 O 3 ) and lignosulfonate (LS) on the surface of silicon nitride (Si 3 N 4 ) powder. The adsorption was studied by particle size measurements, scanning electron microscopy, X-ray photoelectron spectroscopy (ESCA) and carbon analyses. In this study, we report the results from the electrophoretic mobility and surface charge determinations and viscosity measurements of the slip. The viscosity measurements were performed as a function of the LS concentration added in the dispersion. This was done in order to determine the optimum concentration of lignosulfonate added in the dispersion, i.e. the concentration which would result in the lowest viscosity for the highest possible dry content of the slip. The surface charge was determined via potentiometric titrations and by measuring the electrophoretic mobility.

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