The microstructures of silicon nitride ceramics during hot-pressing transformations

Drew, P.K.P.; Lewis, M. H.

doi:10.1007/bf00550950

Cited by 141 publications

(30 citation statements)

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“…By comparing'Figs 9 and 10 it is realized that adding 6 wt % yttria (with no alumina) accelerates the transformation kinetics with respect to that of the original powder by nearlY a factor of three (at 1750 ° C), clearly substantiating the influence of the liquid phase formed. This observation provides evidence for a solution-precipitation reaction of the form proposed by some authors [4,22,23]. The dependence of the percentage of/~ on the alumina concentration shown in Fig.…”

Section: Resultsmentioning

confidence: 60%

Sinter and sinter-HIP of silicon nitride ceramics with yttria and alumina additions

1989

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The sintering behaviour of silicon nitride ceramics has been investigated by preparing powder mixtures containing controlled amounts of yttria and alumina. The fired density of the compacts, having a fixed quantity of yttria, has been observed to increase with increasing amounts of alumina added to the powder. There exists, however, a maximum limit to the beneficial effect of AI203, because an excess of alumina in the powder mixture does not produce a further increase in density. Sintering of green compacts, obtained by uniaxial pressing, has been carried out at various temperatures and pressures in order to determine the relationship between fired density and the processing variables. The results obtained, after subjecting a selection of specimens to different sinter-HIP cycles, clearly show that the final density is very sensitive to the applied pressure and the time at which it is applied. The range of microstructures produced by different processing routes has also been followed by electron microscopy. From the results obtained by X-ray diffractometry it is shown that the additions of yttria and alumina not only produce denser specimens than pure silicon nitride, but also promote the ~-fl transformation.

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Section: Resultsmentioning

confidence: 60%

Sinter and sinter-HIP of silicon nitride ceramics with yttria and alumina additions

1989

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“…Wild et al (1972 c) showed, by detecting silicon oxynitride and enstatite (magnesium silicate) as devitrification products in silicon nitride hotpressed with magnesia, that this phase was a glass containing nitrogen. The glass was first observed directly by electron microscopy by Drew and Lewis (1974), who suggested that the mechanism of sintering involves solution and reprecipitation of silicon nitride crystals. Attempts were made to determine the glass composition (Powell and Drew, 1974), and it was found that impurity ions such as calcium could be accommodated in the glass.…”

Section: Formation Of Oxynitride Liquids In Silicon Nitride Ceramicsmentioning

confidence: 99%

Nitride Ceramics

Hampshire

2006

Materials Science and Technology

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“…Densification is achieved by liquid-phase sintering. Following the early identification of effective sintering additives [63] and a recognition of the microstructure development mechanism as a solution-reprecipitation process within a silicate-based liquid [64], the subsequent development of sintering additives has proceeded largely through empirical studies. Fig.…”

Section: Sintering Chemistry Of Additives In Bulk Nitride Ceramicsmentioning

confidence: 99%

Chemical research needed to improve high-temperature processing of advanced ceramic materials (Technical report)

Kolář

2000

Pure and Applied Chemistry

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Republication or reproduction of this report or its storage and/or dissemination by electronic means is permitted without the Chemical research needed to improve high-temperature processing of advanced ceramic materialsAbstract: Of the principal classes of engineering materials, ceramics are in many ways the most interesting and challenging. Many properties, or combination, of properties, not achievable with other classes of materials give ceramics enormous technical potential. The main obstacles that prevent the wider use of ceramics include insufficient reliability, reproducibility, and high cost. The physical basis of the processing steps is well established, however, the chemical reactions which occur during the high-temperature processing frequently influence the densification process and microstructure development of ceramics in an unpredictable way. Therefore, an ability to understand and control the chemical processes that occur during ceramic processing are necessary to advance and open up new uses for technical ceramics. The aim of this present report, resulting from discussions of an ad hoc group of ceramists and chemists, is to expose the areas of chemical research that can most benefit the processing, and further the use, of ceramic materials.

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The microstructures of silicon nitride ceramics during hot-pressing transformations

Cited by 141 publications

References 1 publication

Sinter and sinter-HIP of silicon nitride ceramics with yttria and alumina additions

Sinter and sinter-HIP of silicon nitride ceramics with yttria and alumina additions

Nitride Ceramics

Chemical research needed to improve high-temperature processing of advanced ceramic materials (Technical report)

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