THERMODYNAMIC CALCULATION OF THE SI-N-O SYSTEM

The experimental information on Si3N4 and Si2N2O is examined and their thermodynamic properties are critically reviewed. The properties of the liquid SiO2-Si3N4 phase are predicted by a thermodynamical model. The SiO2 - Si3N 4 phase diagram is then calculated with and without the gas phase. Isothermal sections of the Si - N - O phase diagram are calculated at a series of temperatures. Potential phase diagrams are also calculated at a series of temperatures for the Si - N - O - C system below the critical carbon activity where Si transforms to beta-SiC and at an activity of unity when beta-SiC is formed.