Density SiAlONs

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... 

The bulk densities of all the materials were determined using Archimedes method (AS 1774.5, 1979). The Vickers indentation technique was used to measure the hardness in each case. The applied load in the Vickers hardness tests was 10 kg for silicon nitrides and sialons. However, using the same load produced severe lateral cracking in silicon carbides around indents, which prevented the accurate measurement of the diagonals of indents. Therefore the load was reduced to 0.3 kg for silicon carbide samples. 

Figure 15. Processing of SiAlON ceramics by nitridation of PAIC precursors evolution of the density and weight loss with the firing temperature.

When the a -SiAlON formation is completed, no more liquid exists for densification. This is the reason why pure a -SiAlON materials with low degrees of substitution n and m are difficult to densify to full density. Better densification can be reaUsed at higher n and m values (Fig. 14) [75-77] or in composite a /P -SiALON materials [78]. 

The lattice parameters of the hexagonal p-SiAlON phase were calculated from the XRD peaks ofthe products by employing the least-squares method. The lattice parameter a was calculated from (100), (110), (20 0), (2 10), (3 0 0), and (310) peaks of P-SiAlON, and the lattice parameter c was calculated from the (101) peak using the calculated a value. The bulk density of the spark-plasma-sintered (SPSed) specimens was measured according to the Archimedean principle, using distilled water as the medium. The detailed experimental procedure was published in paper [11]. 

Pure P-SiAlONs were obtained through SPS, though the CSed powders were not pure P-SiAlON products. The bulk density was measured by the Archimedes principle, while theoretical density values were obtained from literature. The relative densities of the SPSed P-SiAlON with z= 1-3 were more than 99% of the... 

TC-7000, ULVAC Sinku Riko Co., Yokohama, Japan) from room temperature to 800 °C. The thermal diffusivity was analyzed with the ty2 method. The bulk density was measured according to the Archimedean principle using distilled water as the medium. All the experiments were carried out under a flowing argon gas atmosphere. The thermal conductivity (K) of P-SiAlONs was determined by following equation ... 

Yield and absolute hardness, 72 Y-sialon glass density, 229 Knoop hardness, 229 Modulus, 229 Young s modulus of AljOj, 241, 259-261 anisotropy in /3-AI2O3, 281 of B4C, 228, 241 and bond type, 172 and crack depth, 155 and cracking, 147 of CrjCj, 302 of germanium, 252 of glass, 238 and hardness, 72 hardness ratio, 179 from Knoop indents, 180 mismatch stress, 273 of MgO, 241, 269 and penetration depth, 47, 240 and plasticity parameter, 241 and residual impression parameter, 240... 

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