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Abstracts (International Journals and Books)

[35]   K. Itatani, I. J. Davies, H. Kuwano, and M. Aizawa, “Sinterability of magnesium silicon nitride powder with yttrium oxide addition coated using the homogeneous precipitation method”, J. Maters. Sci., 37(4) pp. 737-744 (2002).

Abstract: Properties of MgSiN₂ powder with 0-4 mass% Y₂O₃ addition coated using the homogeneous precipitation method and their resulting hot-pressed compacts (31 MPa/1550 ^oC/N₂/90 min) were investigated. Mg/Si ratios for the MgSiN₂ compacts with Y₂O₃ addition were close to unity for all cases whilst the pure MgSiN₂ ceramic contained 3.0 mass% of oxygen and that of the MgSiN₂ ceramic with 1 mass% of Y₂O₃ addition contained 1.2 mass%. Relative densities of the pure MgSiN₂ ceramics with and without Y₂O₃ additions were ~99% apart for the compact with 4 mass% Y₂O₃ addition (~98%). Vickers hardness of the pure MgSiN₂ compact hot-pressed at 1550 ^oC for 90 min was 19.7 GPa whilst the thermal conductivity was as low as 20 W·m^-1·K^-1 and attributed to the presence of a secondary phase (Y₂Si₃O₃N₄) that surrounded the MgSiN₂ grains together with the small average grain size.

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[34]   S. Tanaka, K. Itatani, H. Uchida, M. Aizawa, I. Okada, I. J. Davies, H. Suemasu, and A. Nozue, “The effect of rare-earth oxide addition on the hot-pressing of magnesium silicon nitride”, J. Eur. Ceram. Soc., 22(5) pp. 777-783 (2002).

Abstract: The effect of rare-earth oxide addition (1-5 mass% of Ln₂O₃ addition; Ln=Y, La, Nd, Sm, Gd, Dy, Er, and Yb) on the properties of hot-pressed (1550 ^oC, 90 min, 31 MPa) magnesium silicon nitride (MgSiN₂) has been investigated. The role of rare-earth oxide addition on the relative density was classified as follows: (i) positive effect (Y₂O₃, La₂O₃, and Yb₂O₃ additions), (ii) no appreciable effect (Nd₂O₃ and Er₂O₃ additions), and (iii) negative effect (Sm₂O₃, Gd₂O₃, and Dy₂O₃ additions). The average grain size (0.3-0.9 mm) for hot-pressed MgSiN₂ compacts with rare-earth oxide addition was smaller compared to that of the pure MgSiN₂ compact (0.95 mm). The average Vickers hardness of the MgSiN₂ ceramic with 1 mass% of Y₂O₃ addition showed the highest value (21.5 GPa) amongst the MgSiN₂ ceramics with rare-earth oxide addition. The thermal conductivity of the MgSiN₂ ceramics was maximum for the case of 1 mass% of Yb₂O₃ addition (26.6 W·m^-1·K^-1) and is believed to be the highest value so far reported for MgSiN₂. Overall, it was concluded that the relative density and Vickers hardness were best enhanced through the use of Y₂O₃ addition whereas the addition of Yb₂O₃ was most suitable for enhancing the thermal conductivity.

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[33]   K. Itatani, F. Takahashi, M. Aizawa, I. Okada, I. J. Davies, H. Suemasu, and A. Nozue, “Densification and microstructural developments during the sintering of aluminium silicon carbide”, J. Maters. Sci., 37(2) pp. 335-342 (2002).

Abstract: Densification and microstructural developments during the sintering of aluminium silicon carbide (Al₄SiC₄) were examined. Two types of Al₄SiC₄ powders were prepared by the solid-state reactions between: (i) Al, Si, and C at 1600 ^oC for 10 h (designated as Al₄SiC₄(SSR)), and (ii) chemically-vapour deposited ultrafine Al 4C 3 and SiC powders at 1500 ^oC for 4 h (Al₄SiC₄(CVD/SSR)). The specific surface areas of the Al₄SiC₄(SSR) and Al₄SiC₄(CVD/SSR) powders were 2.7 and 15.5 m²·g^-1, respectively. Relative densities of the pressureless-sintered Al₄SiC₄(SSR) and Al₄SiC₄(CVD/SSR) compacts were as low as 60~70% for firing temperatures between 1700 ^oC and 2000 ^oC. The relative densities of Al₄SiC₄(SSR) and Al₄SiC₄(CVD/SSR) compacts could be enhanced using the hot-pressing technique with that of the Al₄SiC₄(SSR) compact hot-pressed at 1900 ^oC for 3 h being 97.0% whereas that of the Al₄SiC₄(CVD/SSR) compact hot-pressed at 1900 ^oC for 1 h attained 99.0%. The former microstructure was composed of plate-like grains of width 10~30 mm and thickness ~10 mm whilst the latter microstructure was comprised of equiaxed grains with a typical diameter of 10 mm. Densification of the Al₄SiC₄(CVD/SSR) compacts appeared to be promoted compared to the Al₄SiC₄(SSR) compact and this was attributed to the higher surface area, reduced agglomeration of the starting primary particles, and more homogeneous chemical composition.

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[32]   I. J. Davies, T. Ogasawara, and T. Ishikawa, “Scanning electron microscopy study of failure in glass-sealed SiC/SiC-based composite (NUSK-CMC) creep tested at 1100 and 1200 ^oC in air”, Adv. Composite Maters., 10(4) pp. 357-367 (2001).

Abstract: A scanning electron microscopy investigation was carried out for glass-sealed 3D woven SiC/SiC-based composite that had failed following creep testing at 1100 and 1200 ^oC in air. It was shown that most specimens failed due to oxygen ingression into the composite that initiated at the specimen corner. The main path for oxygen movement with specimens was found to be along z fibre bundles. A simple analysis of the glass evaporation rate showed higher evaporation rates to always exist at the specimen corners and this could help to explain initiation of long-term creep failure.

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[31]   I. J. Davies, T. Ogasawara, and T. Ishikawa, “Fibre/matrix interface shear strength estimated from fibre pullout length data for Tyranno^® Si-Zr-C-O fibre composites with different SiC-based matrices and interfaces”, J. Maters. Sci. Letts., 20(23) pp. 2127-2130 (2001).

Abstract: The present work has indicated that reasonable values for the fibre/matrix interface shear strength, τ, for Tyranno^® Si-Zr-C-O fiber composites with different silicon carbide-based matrices and interfaces may be qualitatively estimated using only fiber pullout length data together with a previously determined correction factor. The resulting values of τ were slightly below those noted for Tyranno^® Si-Ti-C-O fiber composites but generally within the range of 2–22 MPa noted by previous researchers.

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