Intergranular amorphous phase

This approach has been applied for Si-Al-O-N ceramics. The results can explain the existence of the amorphous phase in the grain boundaries (Fig. 24), depending on the overall composition of the system ([equ% O] = 16, 12, 8 and [equ% Al] = 10.6) and on the strength of interaction (Ap). In a strict sense it must be concluded that the conventional phase diagrams of Si3N4 ceramics are incomplete representations of materials containing an amorphous intergranular phase. 

This class of materials was developed to combine the chemical stability of alumina and properties of Si3N4 with ease of sintering. A beta Sialon is formed by substitution of Al and O ions for Si and N in Si3N4 lattice, as Sie-zAlzOzNg-z- The resultant structure contains elongated beta-Sialon grains, typically with some intergranular phase, which could be amorphous or crystalline. Substitution of alumina adds to the chemical stability... 

J.-M. Greneche, Properties and Applications of Nanocrystalline Alloys from Amorphous Precursors, in Intergranular Phase in Nanocrystalline Alloys Structural and Magnetic Aspects, ed. by B. Idzikowski, P. Svec, M. Miglierini, D. Petridis (Kluwer Academic, Dordrecht, 2005), pp. 373-384... 

Knickerbocker, S. H., Zangvil, A. and Brown, S. D., High-temperature mechanical properties and microstructures for hot-pressed silicon nitrides with amorphous and crystalline intergranular phases. J. Am. Ceram. Soc., 1985, 68, pp. C-99-101. 

Fig. 5.23 Grain boundaries in SrTiOa (mpe = 9-5 10 cm" ) recorded by high-resolution electron microscopy a) atomically shaup, low-energy grain boundary (symmetrical E3 (111), without amorphous interfacial layer), b) triple point with sunorphous intergranular phase (thickness 1 nm) c) faceted grain boundary with amorphous interfaciaJ layer (thickness sa 1 nm). Fracture surface (d) with energetically favourable, step-shaped surfaces. From Refs. [139,140].

In this overview, we will first discuss how transmission electron microscopy (TEM) techniques can be used to determine the presence or absence of intergranular amorphous phases at interphase boundaries in structural... 

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