Grain boundary glass

Microcracks are also known to occur in the elevated temperature creep of alumina with little or no preexisting glass phase. For example, the development of microcracks during creep fracture of two hot-pressed aluminas, which were free of grain boundary glass films, was studied by Wilkinson et al.52 who employed tensile and four-point bend specimens. They found that the concentrations and morphology of the cavities and microcracks were strongly... 

Modification of grain boundary glass chemistry in silicon nitride has profound effects on properties. Summarising ... 

Fig. 3 shows a reinterpretation of the original curve and it is clear that the discontinuities in the curve can be associated with the transformations observed from y- to a-to p-Y2Si207 and the crystallisation of Si2N20. This may be problematic for silicon nitride ceramics where the temperature of operation may differ from that used to crystallise the grain boundary glass. 

Litde is known of the corrosion of polycrystalline aluminas, but in general it is considered to be very low, and even negligible (which explains why such little interest has been expressed in the study of the mechanism involved). However, the results of the few studies to be conducted have suggested that the corrosion of polycrystalline alumina is controlled by the corrosion resistance of the grain boundary glass. 

Keywords Silicon nitride, liquid phase sintering, SiAIONs, a-phase, P-phase, grain boundary glass, oxynitride glasses, microstructural engineering, microstructure-property relationships. 

The effects on viscosity of changes in grain boundary glass chemistry, as a result of changes in sintering additives, can be summarised as follows ... 

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