Silicon nitride has been researched intensively, largely in response to the challenge to develop internal combustion engines with hot-zone components made entirely from ceramics. The ceramic engine programs have had only partial success, but this research effort has succeeded in generating a degree of understanding of silicon nitride and of its processing and properties, which in many respects is more advanced than of more widely used technical ceramics. This review examines from the historical standpoint the development of silicon nitride and of its processing into a range of high-grade ceramic materials. The development of understanding of microstructure–property relationships in the silicon nitride materials is also surveyed. Because silicon nitride has close relationships with the SiAlON group of materials, it is impossible to discuss the one without some reference to the other, and a brief mention of the development of the SiAlONs is included for completeness.

Silicon Nitride and Related Materials

Silicon-based oxynitride and nitride phosphors for white LEDs—A review

This letter reports a β-SiAlON:Eu2+ green phosphor with the composition of Eu0.00296Si0.41395Al0.01334O0.0044N0.56528. The phosphor powder exhibits a rod-like morphology with the length of ∼4μm and the diameter of ∼0.5μm. It can be excited efficiently over a broad spectral range between 280 and 480 nm, and has an emission peak at 535 nm with a full width at half maximum of 55 nm. It has a superior color chromaticity of x=0.32 and y=0.64. The internal and external quantum efficiencies of this phosphor is 70% and 61% at λex=303nm, respectively. This newly developed green phosphor has potential applications in phosphor-converted white LEDs.

Characterization and properties of green-emitting β-SiAlON:Eu2+ powder phosphors for white light-emitting diodes

Tempering of martensitic steels involves the segregation of carbon, the precipitation of carbides, the decomposition of retained austenite, and the recovery and recrystallization of the martensitic structure Because these several reactions overlap and occur on such a fine scale, it is only recently that our knowledge of the resulting structures has become reasonably complete Our present understanding of the processes involved in the tempering of iron-carbon martensites and how they are affected by alloying elements is reviewed

Tempering of steel

The theme of the review is the construction of a model embracing the mechanism of formation of reaction-bonded silicon nitride, the development of microstructure and mechanical properties. Possible nitridation reactions are discussed, with emphasis on kinetics and on phase composition and microstructure of the reaction product. The influence of Fe, a common impurity in silicon powders, and of H2, as an additive to the nitriding atmosphere, is considered in some detail. The optical, electrical and thermal properties are briefly discussed and areas for further research and development studies identified.

Reaction-bonded silicon nitride: its formation and properties

TSUGE et al.1 have shown that β -Si3N4 can accommodate up to about 60% by weight Al2O3 in solid solution without major change of crystal structure but with increasing a and c unit-cell dimensions as the Al2O3 concentration increases. The products, obtained by sintering the mixed powders at 1,700 and 1,770° C, are undoubtedly similar to a new phase observed by Oyama and Kamigaito2 in mixtures of Si3N4, Al2O3 and Li2CO3 hot-pressed at 1,750° C. We report here a variety of ceramic materials built up of (Si,Al)(N,O)4 tetrahedra joined by sharing corners just as the silicate structures are built up of SiO4 and (Si,Al)O4 units.

Ceramics based on the Si-Al-O-N and Related Systems

Nature of χ-Carbide and Its Possible Occurrence in Steels

Low-porosity ceramics with O′-sialon as the major crystalline phase have been successfully fabricated by pressureless sintering. Densification at 1400 to 1800° C is interpreted using Kingery's liquid-phase sintering model. Particle rearrangement accounts for a significant proportion of the overall densification and is closely related to the amount and viscosity of the liquid present. The oxidation resistance of fabricated samples is good but, at temperatures above 1300° C, decreases with increasing alumina content in the starting mix. Modulus of rupture values of about 420 MPa at room temperature are high enough to encourage further work.

The fabrication of O′-sialon ceramics by pressureless sintering

The nitriding of compacted silicon powder shapes to give reaction-bonded components (RBAN), their more recent densification by post-preparative methods (SRBSN), and the liquid-phase densification of silicon nitride powder by hot-pressing (HPSN) were all innovative at the time of their discovery but have since had only limited success. The goal from the earliest days of silicon nitride technology has been the ceramic gas turbine, and there is still no commercial process for producing complex shapes to engineering tolerances with the required combination of properties. One approach to the problem is by ceramic alloying and, to illustrate the nature of innovation through its various stages, the development of Sialons is described. Silicon nitrides have silicate structures to which simple principles of silicate chemistry can be applied. This has provided new vitreous and crystalline materials, some of which seem suitable for engine applications.

Silicon Nitride, Sialons, and Related Ceramics

Although silicon nitride is at present a leading contender for gas turbines and other hightemperature engineering applications, it is only the first of a wide field of nitrogen ceramics, other members of which offer better prospects for technological exploitation. “Sialons” are phases in the Si-Al-O-N and related systems and are comparable in variety and diversity with the mineral silicates. They are built up of one-, two-, and threedimensional arrangements of (Si, Al) (O, N)4 tetrahedra in the same way that the fundamental structural unit in the silicates is the SiO4 tetrahedron. These new oxynitrides include structure types based uponα andΒ silicon nitrides, silicon oxynitride, aluminium nitride and silicon carbide, eucryptite, spinel, melilite and apatite. They are being explored for their thermal, mechanical, chemical and electrical properties.

Sialons and related nitrogen ceramics

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