Sialons also

Materials made of siHcon nitride, siHcon oxynitride, or sialon-bonded siHcon carbide have high thermal shock and corrosion resistance and may be used for pump parts, acid spray nozzles, and in aluminum reduction ceUs (156—159). A very porous siHcon carbide foam has been considered for surface combustion burner plates and filter media. It can also be used as a substrate carrying materials such as boron nitride as planar diffusion source for semiconductor doping appHcations. 

Vapor—sohd reactions (13—17) are also commonly used ia the synthesis of specialty ceramic powders. Carbothermic reduction of oxides, ia which carbon (qv) black mixed with the appropriate reactant oxide is heated ia nitrogen or an iaert atmosphere, is a popular means of produciag commercial SiC, Si N, aluminum nitride [24304-00-3], AIN, and sialon, ie, siUcon aluminum oxynitride, powders. 

Shrink-resist science/technology development of, 26 391 Shrink-resist treatments, 26 391-393 additive, 26 393 chlorine-based, 26 392 chlorine-free, 26 392-393 Shuiskite, 6 471t Shutdown period, 29 494 Shutdown systems, 20 671-672 Shuttle vectors, 26 482-483 Sialon-bonded silicon carbide, 22 541 Siberian red lead, 6 468 S-iB-S block copolymers, 24 707 SiC-ceramic, 22 525. See also Silicon carbide... 

With increasing zvalue the density of P-SiAlON decreases linearly, similarly lowering Young s modulus, strength, thermal conductivity, hardness and fracture toughness.30 On the other hand, for low zvalues (z< 1) the hardness and fracture toughness increase and when z > 1 they decrease. It has been also depicted that glass-free microstructures could be obtained in P-SiAlON polycrystals with substitutional level z> 2.31... 

For B2-A1 laminate, there is a gradual transition from an a-rich region to P-rich one in XRD analyses. The transition zone is about 400 pm in thickness, and the P-SiAlON proportion in this zone changed from 20% to 70% as expected (Fig. 6.6). The gradual change in the amount of phases was also... 

For the powder bed method, a composition rich in P-SiAlON (named B2) was selected as a compact composition to observe compact-powder bed interaction. Two different powder bed compositions, a-SiA10N (100 wt%) and A1N BN mixture (50 50 wt%), were prepared. P-SiAlON-rich pellets were embedded into the powder bed compositions, as schematically shown in Fig. 6.21. Both green and sintered pellets were embedded into the same powder bed composition in order to compare the effect of presintering on the interaction. Sintering of the pellets was carried out under 22 bar nitrogen gas pressure at 1800°C for 1 hour. To understand the effect of pressure on the interaction zone, pressureless sintering was also carried out for comparison. 

Thermal mismatch between SiC fibres and a sialon matrix is also an issue which can cause poor mechanical performance, even though there may be excellent chemical and physical compatibility between the fibres and the... 

There is also scope for the development of new techniques such as chemical vapour infiltration (CVI) (Caputo and Lackey, 1984 Caputo et al., 1985), normal chemical reaction bonding processes, laminar sialon composites, etc. More recently, laminated composites in non-oxide and sialons have demonstrated very promising results for strengthening (Goto and Kato, 1998) and even achieved a non-brittle failure behaviour accompanied by high damage tolerance (Yu and Krstic, 2003 Yu et al., 2005). 

Y NMR has also been reported extensively from yttrium sialon ceramics. Yttria is an important sintering aid for densifying silicon nitride. The properties of the sialon produced are determined by the nature of the grain boundary phase, which is usually a crystalline or glassy yttrium sialon. The often disordered nature of such phases can mean that broader 89Y resonances are... 

The structure of these sialons is based on that of a-SisN4, but requires the presence of other metal ions (M) for stabilisation. The M ions are typically yttrium and rare-earths, but can also be Mg or Ca. The values of m and n in the formula depend on the metal ion present. The a-sialons, which have extremely good mechanical properties, also form technically useful solid solutions with P-sialons. The Si chemical shift of a-sialon (about - 48 ppm) is similar to that of Si3N4 and appears to be insensitive both to the sialon composition and the nature of the M ion (Leach et al. 1990). 

Carbothermal synthesis has been used to prepare yttrium a-sialon from mixtures of halloysite clay and Y2O3 with either Si02 or elemental Si. The reaction mechanism, particularly the role played by intermediate SiC phases, was monitored by Si NMR (Ekstrom et al. 1998). The preparation of fine-grained Ca a-sialon has also been studied by 2 Si NMR (Hewitt et al. 1994). 

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