SiAlONs properties

Five aspects of the preparation of solids can be distinguished (i) preparation of a series of compounds in order to investigate a specific property, as exemplified by a series of perovskite oxides to examine their electrical properties or by a series of spinel ferrites to screen their magnetic properties (ii) preparation of unknown members of a structurally related class of solids to extend (or extrapolate) structure-property relations, as exemplified by the synthesis of layered chalcogenides and their intercalates or derivatives of TTF-TCNQ to study their superconductivity (iii) synthesis of a new class of compounds (e.g. sialons, (Si, Al)3(0, N)4, or doped polyacetylenes), with novel structural properties (iv) preparation of known solids of prescribed specifications (crystallinity, shape, purity, etc.) as in the case of crystals of Si, III-V compounds and... 

Siaions consist of three-dimensional arrays of (Si—Al) (O.N)4 tetrahe-dra. These oxynitrides are traditionally fabricated with silicon nitride An example is beta-sialon, where the O and Si are partially replaced by N and Al, respectively. Advanced sialons are now being researched to enhance fracture toughness and iinpioved cieep properties,... 

Mandal H, Hoffmann MJ (2000) Novel Developments in a-SiAlON Ceramics. In Sajgalik P, Lences Z (eds) Engineering Ceramics Multifunctional Properties-New Perspectives. Trans Tech Publications Ltd, Switzerland, p 131... 

Lewis MH (1994) Crystallisation of Grain Boundary Phases in Silicon Nitride and SiAlON Ceramics. In Hoffmann MJ, Petzow G (eds) Tailoring of Mechanical Properties of Si3N4 Ceramics. NATO ASi Ser E 276, Kliiwer Academic Publishers, Dordrecht, p 217... 

Cao GZ, Melselaar R, Ziegler G (1992) Microstructure and properties of mixed o. +ff-Sialons. In Carlsson R, Johansson T, Kahlman L (eds) Ceramics Materials and Components for Engines. Elsevier, London, p 188... 

Since the macroscopic properties of a material are strongly dependent on its structure, studies of structure/property relationships are among the most important issues in material science. The properties of SiAlON ceramics are strongly influenced by their microstructure and chemical composition. 

Mizutani, T., Kusunose, T., Sando, M. et al, Fabrication and properties of nano-sized BN-particulate dispersed Sialon ceramics, Ceram. Eng. Sci. Proc., 1997, 18(4B) 669. 

Zhao, Z., Johnson, M., Shen, Z. (2002), Microstructure and mechanical properties of titanium carbonitride whisker reinforced P-sialon composites , Materials Research Bulletin, 37, 1175-1187. 

Sialon is the generic name for the large family of silicon nitride solid solutions containing the basic elements Si, Al, O and N. Over the last three decades, the matrix sialon phases (a-, P-, and 0-) have been developed and various excellent reviews are available (Cao and Metselaar, 1991 Ekstrom and Nygren, 1992 Izhevskiy et al., 2000). In the sialon family, a- and P-sialons offer most interest as engineering ceramics because of their excellent combination of mechanical and high-temperature properties. 

As with other ceramic composites, the combination of a- and/or P-sialon with reinforcement agents results in sialon composites. This simple and obvious statement encompasses many factors which must be taken into account for successfully fabricating composites with a designed microstructure and improved properties (Prewo, 1989). For sialon matrix composites, the most important factors are physical compatibility including Young s modulus, elastic strain (Kerans and Parthasarathy, 1991) and thermal expansion coefficient (Sambell etal., 1972a, b), and chemical compatibility between sialon matrix... 

Table 18.1 Effects of starting powder, composition on phase present, microstructure and mechanical properties of a-sialons...

As shown in Table 18.2, both the volume content of Cf and the sintering temperature affect the properties and fracture behaviour of Cf/a-sialon... 

Table 18.2 Effect of sintering temperature on the properties of Cf/sialon composites...

It is worth pointing out that carbon fibre itself has anisotropic thermal expansion properties, and therefore this mismatch between the carbon fibres and the a-sialon matrix should be considered in both the radial and axial directions when carbon fibres are unidirectionally aligned in the composite. The thermal stress caused by thermal expansion differences between the carbon fibres and the matrix in the radial (cr) and axial (oa) directions can be estimated from the formulae (Chawla, 1993 Kerans and Parthasarathy, 1991) ... 

Table 18.3 Properties of carbon fibre/a-sialon composites with and without added Zr02...

Table 18.4 Mechanical properties of as-received and heat-treated SiCf/ 5-sialon...

Ekstrom, T., (1992a), Preparation and properties of alpha-sialon ceramics , J. Hard. Mater., 3, 109-118. 

Thompson, D.R, (1994), a P Sialon transformation , in Hoffmann, M.J. and Petzow, G., Tailoring of Mechanical Properties ofSi3N4 Ceramics, Dordrecht, Kluwer Academic, 125-136. 

Hampshire, S. (2003b), SiAlON glasses, their properties and crystallisation , Key Eng. Mater., 237, 239 16. 

Pomeroy, M J., Nestor, E., Ramesh, R., Hampshires (2005), Properties and crystallisation of rare earth SiAlON glasses containing mixed trivalent modifiers J. Amer. Ceram. Soc., 88(4), 875-881. 

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