The formation of single-phase Si-Al-O-N ceramics

Lewis, M. H.; Powell, Bob; Drew, P.K.P.; Lumby, R. J.; North, Brian C; Taylor, Adam

doi:10.1007/bf00738472

Cited by 116 publications

(27 citation statements)

References 7 publications

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“…1 to 3). Similarly, the creep strength of sialons has been found to depend not only on the impurity levels but also on the Si/Al ratio [12,22]. It is noteworthy, however, that the creep behaviour of the sialon sample tested in the present programme was similar to that for the RBSN examined, indicating that sialons can be produced having a creep resistance at least equal to that of reaction-bonded materials (Figs.…”

Section: Creep Characteristics Of Silicon Nitride Ceramicssupporting

confidence: 55%

“…No specific conclusions can be drawn from the exact differences in the creep resistance of these materials since the high temperature properties of each type of product are known to vary depending on the impurity levels [9,10,13,19,20] and the detailed fabrication procedures used [9,10,21,22], e.g. the decrease in creep strength associated with the presence of a higher MgO content is evident from the results obtained for the two samples of hot-pressed silicon nitride considered (Figs.…”

Section: Creep Characteristics Of Silicon Nitride Ceramicsmentioning

confidence: 99%

“…As a result, a number of deformation mechanisms dependent on the presence of grain boundaries have been considered in order to account for the observed creep behaviour. These include diffusional creep processes [29][30][31], grain boundary sliding controlled by the viscosity of the impurity phases at crystal boundaries [13], dissolution and redeposition of material [22]; and transfer of the viscous phases from boundaries under compression to those under tension [32]. Support for the view that viscous flow of impurity phases controls the creep behaviour of RBSN and HPSN [13] has been taken from the fact that the activation energy for flow of certain silicate glasses [33] can be of the order of the observed values for creep (~ 650kJmol-1).…”

Section: Deformation Processes During Creepmentioning

confidence: 99%

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The compression creep behaviour of silicon nitride ceramics

Birch

Wilshire

1978

J Mater Sci

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A comparison has been made of the compression creep characteristics of samples of reaction-bonded and hot-pressed silicon nitride, a sialon and silicon carbide. In addition, the effects of factors such as oxide additions and fabrication variables on the creep resistance of reaction-bonded material and the influence of dispersions of SiC particles on the creep properties of hot-pressed silicon nitride have been considered. For the entire range of materials examined, the creep behaviour appears to be determined primarily by the rate at which the development of grain boundary microcracks allows relative movement of the crystals to take place.

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Section: Creep Characteristics Of Silicon Nitride Ceramicssupporting

confidence: 55%

Section: Creep Characteristics Of Silicon Nitride Ceramicsmentioning

confidence: 99%

Section: Deformation Processes During Creepmentioning

confidence: 99%

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The compression creep behaviour of silicon nitride ceramics

Birch

Wilshire

1978

J Mater Sci

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“…Preparation techniques and the evolution of microstructure in these materials have been described previously by Lewis et al [5,6]. Hot-pressed materials are essentially single-phase/3' of composition Sis A1ON7 with grain size ~ 1/~m, containing impurity segregation at grain-boundaries (mainly Mg and Ca, within a multilayer oxygen-rich film, or Mn + Mg + Ca, depending on the presence of sintering aids MgO and Mn304).…”

Section: Experimental Techniquesmentioning

confidence: 99%

Oxidation mechanisms in Si-Al-O-N ceramics

Lewis

Barnard

1980

J Mater Sci

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Oxidation mechanisms in single-and two-phase Si-AI-O-N ceramics have been studied using scanning and transmission electron microscopy together with energy-dispersive X-ray microanalysis. Silicate layers formed on single-phase (/3') ceramics are non-crystalline, with viscosity and resulting oxidation kinetics controlled by outward diffusion of grainboundary segregated impurities. Aluminium substitution in/3' is important in compensating for the viscosity reduction imposed by the divalent ion impurities and inhibiting crystallization. Crystallization, induced only on slow furnace cooling, produces mullite and cristobalite phases. Two-phase (/3' and matrix) ceramics exhibit comparatively poor oxidation kinetics with formation of a porous crystalline silicate layer due to the continued availability of a high concentration of metallic ions in the matrix phase. 1, IntroductionThe successful application of Si3N4 and related Si-AI-O-N ceramics in a high-temperature oxidizing environment is dependent on the formation of a surface oxide film via a reaction of the type:Si3N4 + 302 ~ 3SIO2 + 2N2.Studies of film composition and structure, for 13-Si3 N4 ceramics have shown [1][2][3] that the film is a "silicate" containing a large concentration of ions derived from the impurity sintering "catalysts" (e.g. MgO) together with accidental impurities. The films are sometimes partially crystalline, containing phases such as enstatite (MgSiO3)in MgO-additive materials.Recently, it has been demonstrated [4] that the "protection" conferred by the oxide film is not due to the requirement for diffusion of the components of the oxidation reaction through the film, as normally interpreted from parabolic oxidation kinetics. Rather, the oxidation rate is limited by the rate of outward diffusion of metallic impurity ions into the SiO2 film, reducing its viscosity and hence its solubility for Si3Na. Si is transported through the silicate layer for reaction with atmospheric oxygen. While the exact oxidation mechanism is not proven experimentally, it has been shown that outward impurity diffusion is rate-limiting by demonstrating no increase in kinetics of further oxidation on removal of the initial silicate film.

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“…The final β-Si 3 N 4 grain size and shape distribution in the material are controlled by the Si 3 N 4 starting powder characteristics, the metal oxide sintering additives, and the processing conditions. Microstructural observations have shown that the β-Si3N4 grains grow as elongated hexagonal prisms in suitable liquid-phase environment 1 .…”

Section: Introductionmentioning

confidence: 99%

Development of the microstructure of the silicon nitride based ceramics

1999

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Basic regularities of silicon nitride based materials microstructure formation and development in interrelation with processing conditions, type of sintering additives, and starting powders properties are discussed. Models of abnormal or exaggerated grain growth are critically reassessed. Results of several model experiments conducted in order to determine the most important factors directing the microstructure formation processes in RE-fluxed Si3N4 ceramics are reviewed. Existing data on the mechanisms governing the microstructure development of Si3N4-based ceramics are analyzed and several principles of microstructure tailoring are formulated.

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The formation of single-phase Si-Al-O-N ceramics

Cited by 116 publications

References 7 publications

The compression creep behaviour of silicon nitride ceramics

The compression creep behaviour of silicon nitride ceramics

Oxidation mechanisms in Si-Al-O-N ceramics

Development of the microstructure of the silicon nitride based ceramics

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