2008 Volume 49 Issue 8 Pages 1926-1928
The pressure-assisted master sintering surface (PMSS) of silicon nitride has been constructed, in which the sintered density during hot pressing can be predicted as a function of the integral of a temperature function over time at a given pressure, irrespective of the heating path. High-purity α-Si3N4 powder with the additives of 6.25% Y2O3 and 1% Al2O3 was used for this research. Densifications of silicon nitride were continuously recorded during heating at two different ramping rates of 0.083°C/s and 0.167°C/s up to 1800°C at fixed pressures from 7 to 34 MPa. The activation energy was estimated as 698 kJ/mol. During the hot pressing, the microstructural evolution of α-Si3N4 to β-phase known as a solid/liquid/solid mechanism was also observed. Using the PMSS of silicon nitride, the final density can be predicted to about 1% accuracy for a fixed pressure and an arbitrary temperature-time path.
