Chemistry and inherent viscosity of glasses segregated at grain boundariesof silicon nitride and silicon carbide ceramics

Electron microscopy/microanalysis and internal friction characterizations h ave been concurrently used to quantitatively assess both the morphology/che mistry and the inherent viscosity of residual high-SiO2 glasses segregated to grain boundaries of polycrystalline Si3N4 and SIC ceramics. The anelasti c relaxation peak of internal friction, arising from the viscous slip along grain boundaries wetted by glass, was collected in a plot of internal fric tion vs temperature. The peak was analyzed with respect to its shift upon c hanging the oscillation frequency, in order to assess the inherent viscosit y of the intergranular glass film. From the internal friction analysis and the precise information of both thickness and chemistry of the grain-bounda ry him obtained by electron microscopy, a quantitative determination of the intergranular viscosity and the activation energy for viscous flow was att empted. The viscosity of intergranular high-SiO2 glasses as a function of t emperature is compared to the literature data for bulk SiO2 glass and discu ssed in terms of the respective anion structure of the glass. (C) 2000 Else vier Science B.V. All rights reserved.