The Experts below are selected from a list of 18 Experts worldwide ranked by ideXlab platform
Michael J. Pomeroy - One of the best experts on this subject based on the ideXlab platform.
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Silicon Nitride Grain boundary oxyNitride glass interfaces deductions from glass bulk properties
International Journal of Applied Ceramic Technology, 2013Co-Authors: Stuart Hampshire, Michael J. PomeroyAbstract:OxyNitride glasses exist as Grain boundary phases in Si3N4 ceramics. This paper provides an overview of oxyNitride glasses outlining effects of composition on properties. A review of the effects of Grain boundary glass chemistry on fracture resistance of Silicon Nitride is given. A knowledge of overall additive compositions and their quantities in Si3N4 combined with measured properties of bulk glasses allows residual stresses in the interfacial glasses to be calculated. Increase in Y:Al ratio leads to higher thermal expansion mismatch and higher residual stresses in intergranular glasses. Values are in good agreement with those obtained using micromechanical finite element analysis.
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sialon bulk glasses and their role in Silicon Nitride Grain boundaries composition structure property relationships
Journal of The Korean Ceramic Society, 2012Co-Authors: Stuart Hampshire, Michael J. PomeroyAbstract:SiAlON glasses are silicates or alumino-silicates, containing Mg, Ca, Y or rare earth (RE) ions as modifiers, in which nitrogen atoms substitute for oxygen atoms in the glass network. These glasses are found as intergranular films and at triple point junctions in Silicon Nitride ceramics and these Grain boundary phases affect their fracture behaviour. This paper provides an overview of the preparation of M-SiAlON glasses and outlines the effects of composition on properties. As nitrogen substitutes for oxygen in SiAlON glasses, increases are observed in glass transition temperatures, viscosities, elastic moduli and microhardness. These property changes are compared with known effects of Grain boundary glass chemistry in Silicon Nitride ceramics. Oxide sintering additives provide conditions for liquid phase sintering, reacting with surface silica on the Si₃N₄ particles and some of the Nitride to form SiAlON liquid phases which on cooling remain as intergranular glasses. Thermal expansion mismatch between the Grain boundary glass and the Silicon Nitride causes residual stresses in the material which can be determined from bulk SiAlON glass properties. The tensile residual stresses in the glass phase increase with increasing Y:Al ratio and this correlates with increasing fracture toughness as a result of easier debonding at the glass/β-Si₃N₄ interface.
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Grain boundary glasses in Silicon Nitride a review of chemistry properties and crystallisation
Journal of The European Ceramic Society, 2012Co-Authors: Stuart Hampshire, Michael J. PomeroyAbstract:Abstract Silicon Nitride for engineering applications is densified by liquid phase sintering using oxide additives such as yttria and alumina. The oxyNitride liquid remains as an intergranular glass. This paper provides a review of microstructural development in Silicon Nitride, Grain boundary oxyNitride glasses and effects of chemistry on properties. Nitrogen increases Tg, viscosities, elastic moduli and microhardness. These property changes are compared with known effects of Grain boundary glass chemistry in Silicon Nitride ceramics where significant improvements in fracture resistance of Silicon Nitride can be achieved by tailoring the intergranular glass chemistry. Crystallisation of the Grain boundary Y–Si–Al–O–N glass phase can improve properties. Nucleation and crystallisation of a Y–Si–Al–O–N glass, similar to that found in Grain boundaries of Silicon Nitride densified with yttria and alumina, can be optimised to form different Y-disilicate polymorphs at different temperatures. One solution to provide a single disilicate phase over a range of temperatures is discussed.
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Silicon Nitride Grain Boundary Glasses: Chemistry, Structure and Properties
Key Engineering Materials, 2011Co-Authors: Stuart Hampshire, Michael J. PomeroyAbstract:Silicon Nitride is recognised as a high performance material for both wear resistant and high temperature structural applications. Oxide sintering additives such as yttrium oxide and alumina are used to provide conditions for liquid phase sintering, during which the additives react with surface silica present on the Si3N4 particles and some of the Nitride to form an oxyNitride liquid which allows densification and transformation of - to -Si3N4 and on cooling remains as an intergranular oxyNitride glass. This paper provides an overview of liquid phase sintering of Silicon Nitride ceramics, Grain boundary oxyNitride glasses and the effects of chemistry and structure on properties. As nitrogen substitutes for oxygen in oxyNitride glasses, increases are observed in glass transition and softening temperatures, viscosities, elastic moduli and microhardness. These property changes are compared with known effects of Grain boundary glass chemistry in Silicon Nitride ceramics.
Stuart Hampshire - One of the best experts on this subject based on the ideXlab platform.
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Silicon Nitride Grain boundary oxyNitride glass interfaces deductions from glass bulk properties
International Journal of Applied Ceramic Technology, 2013Co-Authors: Stuart Hampshire, Michael J. PomeroyAbstract:OxyNitride glasses exist as Grain boundary phases in Si3N4 ceramics. This paper provides an overview of oxyNitride glasses outlining effects of composition on properties. A review of the effects of Grain boundary glass chemistry on fracture resistance of Silicon Nitride is given. A knowledge of overall additive compositions and their quantities in Si3N4 combined with measured properties of bulk glasses allows residual stresses in the interfacial glasses to be calculated. Increase in Y:Al ratio leads to higher thermal expansion mismatch and higher residual stresses in intergranular glasses. Values are in good agreement with those obtained using micromechanical finite element analysis.
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sialon bulk glasses and their role in Silicon Nitride Grain boundaries composition structure property relationships
Journal of The Korean Ceramic Society, 2012Co-Authors: Stuart Hampshire, Michael J. PomeroyAbstract:SiAlON glasses are silicates or alumino-silicates, containing Mg, Ca, Y or rare earth (RE) ions as modifiers, in which nitrogen atoms substitute for oxygen atoms in the glass network. These glasses are found as intergranular films and at triple point junctions in Silicon Nitride ceramics and these Grain boundary phases affect their fracture behaviour. This paper provides an overview of the preparation of M-SiAlON glasses and outlines the effects of composition on properties. As nitrogen substitutes for oxygen in SiAlON glasses, increases are observed in glass transition temperatures, viscosities, elastic moduli and microhardness. These property changes are compared with known effects of Grain boundary glass chemistry in Silicon Nitride ceramics. Oxide sintering additives provide conditions for liquid phase sintering, reacting with surface silica on the Si₃N₄ particles and some of the Nitride to form SiAlON liquid phases which on cooling remain as intergranular glasses. Thermal expansion mismatch between the Grain boundary glass and the Silicon Nitride causes residual stresses in the material which can be determined from bulk SiAlON glass properties. The tensile residual stresses in the glass phase increase with increasing Y:Al ratio and this correlates with increasing fracture toughness as a result of easier debonding at the glass/β-Si₃N₄ interface.
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Grain boundary glasses in Silicon Nitride a review of chemistry properties and crystallisation
Journal of The European Ceramic Society, 2012Co-Authors: Stuart Hampshire, Michael J. PomeroyAbstract:Abstract Silicon Nitride for engineering applications is densified by liquid phase sintering using oxide additives such as yttria and alumina. The oxyNitride liquid remains as an intergranular glass. This paper provides a review of microstructural development in Silicon Nitride, Grain boundary oxyNitride glasses and effects of chemistry on properties. Nitrogen increases Tg, viscosities, elastic moduli and microhardness. These property changes are compared with known effects of Grain boundary glass chemistry in Silicon Nitride ceramics where significant improvements in fracture resistance of Silicon Nitride can be achieved by tailoring the intergranular glass chemistry. Crystallisation of the Grain boundary Y–Si–Al–O–N glass phase can improve properties. Nucleation and crystallisation of a Y–Si–Al–O–N glass, similar to that found in Grain boundaries of Silicon Nitride densified with yttria and alumina, can be optimised to form different Y-disilicate polymorphs at different temperatures. One solution to provide a single disilicate phase over a range of temperatures is discussed.
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Silicon Nitride Grain Boundary Glasses: Chemistry, Structure and Properties
Key Engineering Materials, 2011Co-Authors: Stuart Hampshire, Michael J. PomeroyAbstract:Silicon Nitride is recognised as a high performance material for both wear resistant and high temperature structural applications. Oxide sintering additives such as yttrium oxide and alumina are used to provide conditions for liquid phase sintering, during which the additives react with surface silica present on the Si3N4 particles and some of the Nitride to form an oxyNitride liquid which allows densification and transformation of - to -Si3N4 and on cooling remains as an intergranular oxyNitride glass. This paper provides an overview of liquid phase sintering of Silicon Nitride ceramics, Grain boundary oxyNitride glasses and the effects of chemistry and structure on properties. As nitrogen substitutes for oxygen in oxyNitride glasses, increases are observed in glass transition and softening temperatures, viscosities, elastic moduli and microhardness. These property changes are compared with known effects of Grain boundary glass chemistry in Silicon Nitride ceramics.
Gabrielle G Long - One of the best experts on this subject based on the ideXlab platform.
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cavitation contributes substantially to tensile creep in Silicon Nitride
Journal of the American Ceramic Society, 1995Co-Authors: William E Luecke, Sheldon M Wiederhorn, Bernard J Hockey, Ralph F Krause, Gabrielle G LongAbstract:During tensile creep of a hot isostatically pressed (HIPed) Silicon Nitride, the volume fraction of cavities increases linearly with strain; these cavities produce nearly all of the measured strain. In contrast, compressive creep in the same stress and temperature range produces very little cavitation. A stress exponent that increases with stress ({dot {var_epsilon}} {proportional_to} {sigma}{sup n}, 2 < n < 7) characterizes the tensile creep response, while the compressive creep response exhibits a stress dependence of unity. Furthermore, under the same stress and temperature, the material creeps nearly 100 times faster in tension than in compression. Transmission electron microscopy (TEM) indicates that the cavities formed during tensile creep occur in pockets of residual crystalline silicate phase located at Silicon Nitride multiGrain junctions. Small-angle X-ray scattering (SAXS) from crept material quantifies the size distribution of cavities observed in TEM and demonstrates that cavity addition, rather than cavity growth, dominates the cavitation process. These observations are in accord with a model for creep based on the deformation of granular materials in which the microstructure must dilate for individual Grains t slide past one another. During tensile creep the Silicon Nitride Grains remain rigid; cavitation in the multiGrain junctions allows the silicate tomore » flow from cavities to surrounding silicate pockets, allowing the dilation of the microstructure and deformation of the material. Silicon Nitride Grain boundary sliding accommodates this expansion and leads to extension of the specimen. In compression, where cavitation is suppressed, deformation occurs by solution-reprecipitation of Silicon Nitride.« less
William E Luecke - One of the best experts on this subject based on the ideXlab platform.
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cavitation contributes substantially to tensile creep in Silicon Nitride
Journal of the American Ceramic Society, 1995Co-Authors: William E Luecke, Sheldon M Wiederhorn, Bernard J Hockey, Ralph F Krause, Gabrielle G LongAbstract:During tensile creep of a hot isostatically pressed (HIPed) Silicon Nitride, the volume fraction of cavities increases linearly with strain; these cavities produce nearly all of the measured strain. In contrast, compressive creep in the same stress and temperature range produces very little cavitation. A stress exponent that increases with stress ({dot {var_epsilon}} {proportional_to} {sigma}{sup n}, 2 < n < 7) characterizes the tensile creep response, while the compressive creep response exhibits a stress dependence of unity. Furthermore, under the same stress and temperature, the material creeps nearly 100 times faster in tension than in compression. Transmission electron microscopy (TEM) indicates that the cavities formed during tensile creep occur in pockets of residual crystalline silicate phase located at Silicon Nitride multiGrain junctions. Small-angle X-ray scattering (SAXS) from crept material quantifies the size distribution of cavities observed in TEM and demonstrates that cavity addition, rather than cavity growth, dominates the cavitation process. These observations are in accord with a model for creep based on the deformation of granular materials in which the microstructure must dilate for individual Grains t slide past one another. During tensile creep the Silicon Nitride Grains remain rigid; cavitation in the multiGrain junctions allows the silicate tomore » flow from cavities to surrounding silicate pockets, allowing the dilation of the microstructure and deformation of the material. Silicon Nitride Grain boundary sliding accommodates this expansion and leads to extension of the specimen. In compression, where cavitation is suppressed, deformation occurs by solution-reprecipitation of Silicon Nitride.« less
Kozo Ishizaki - One of the best experts on this subject based on the ideXlab platform.
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qualitative and quantitative evaluation of Silicon Nitride Grain boundary phase by cryogenic specific heat measurements
Journal of the American Ceramic Society, 1994Co-Authors: Toyohiro Hamasaki, Kozo IshizakiAbstract:Three types of Si[sub 3]N[sub 4] have been hot isostatically pressed at 1,700 C under 60 MPa for 1 h in a capsule. The quantity and quality (i.e., crystalline or glassy structure) of the Grain-boundary phase of the three types of Si[sub 3]N[sub 4] can be evaluated by measuring cryogenic specific heats. The specific heats of Si[sub 3]N[sub 4] ceramics with Al[sub 2]O[sub 3] and Y[sub 2]O[sub 3] additives have been measured at different temperatures between 10 and 40 K. The temperature dependency of measured cryogenic specific heat provides quantitative and qualitative information of the Grain-boundary phases. This method is very useful for evaluating small changes in the amount and crystalline structure of Grain-boundary phases and can clarify different heat histories of the sintering processes in Si[sub 3]N[sub 4] ceramics. This proposed method is nondestructive, and the sensitivity can be extremely high. This method eventually leads to a new quality control method of ceramics.