Intergranular phase

W.C. Carter and A.M. Glaeser. The morphological stability of continuous intergranular phases—thermodynamics considerations. Am. Ceram. Soc. Bull., 63(8) 993-993, 1984. 

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. 

Krivanek, O.L., Shaw, T.M. and Thomas, G., (1979), Imaging of thin intergranular phases by high-resolution electron microscopy ,/. Appl. Phys., 50 (6), 4223—4227. 

The structure of the ceramic consists of ZnO grains of diameter 10-50 /mi with an intergranular phase varying in thickness between 1 nm and 1 /mi. The intergranular phase, which usually has a high bismuth content, is insulating with a resistivity of the order of 106 Qm. 

As the temperature increases defects and charge carriers become more responsive to applied fields, causing both permittivity and loss to increase. However their inertia prevents them from responding effectively at high frequencies so that the loss falls, particularly at higher temperatures. An intergranular phase will clearly have a considerable effect on both the resistivity and the dissipation factor. 

Above the threshold, deformation occurs as a consequence of direct particle interaction. Several mechanisms of interaction have been suggested solution-precipitation flow of fluid between particles and cavity formation at the particle matrix interface. These theories of creep suggest several rules to improve creep behavior (1) increase the viscosity of the matrix phase in multiphase materials (2) decrease the volume fraction of the intergranular phase (3) increase the grain size (4) use fiber or whisker reinforcement when possible. As the creep rupture life is inversely proportional to creep rate, lifetime can be improved by improving creep resistance. 

Fluids in HP and UHP metamorphic rocks are known to exist as intergranular phases, and, must... 

The sintering of sialon powders can be subject to the same difficulties as experienced with Si3N4, and similar sintering additives (MgO or Y2O3) have been found to assist. The nature of the intergranular phases formed by these oxides during sintering of 3-sialon has been studied by Si, Al, Mg and Y MAS NMR (MacKenzie and Meinhold 1996). 

Gruen and co-workers[90] and Fausett et al. [81] also discussed about manufacturing smoother diamond films by modifying the growth conditions, but these films usually contain nondiamond intergranular phases. They found that nanocrystalline diamond films produced from CgolAr gas mixtures demonstrated basic electrochemical properties that were similar to... 

As a general conclusion it may be stated that the main effect of the various additives mentioned above is to change the microstructure of the magnet body. This is true in particular with regard to the nature of the intergranular phase. In this connection it is important to note that many authors found that the effect of most of the additives was to decrease the anisotropy field of the main phase (Nd2Fe14B) while there is an increase in coercivity. 

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