Calculation of heterogeneous phase equilibria in the system Si-Mg-N-O

✍ Scribed by H.-J. Richter; M. Herrmann; W. Hermel

• Publisher: Elsevier Science
• Year: 1991
• Tongue: English
• Weight: 533 KB
• Volume: 7
• Category: Article
• ISSN: 0955-2219
• DOI: 10.1016/0955-2219(91)90046-3

✦ Synopsis

The thermodynamic calculations of phase equilibria especially refer to the pseudoternary system Si3N 4-SizN20-MgaSiO 4. With the model, the liquid phase is treated as a mixture of the quasicomponents 1/7 Si3N 4, 1/3 SiO 2 and 1/2 MgO, for which an eutectic point was calculated at 1510°C with the composition 0"153 Si3N 4 + 0"194 SizN20 + 0"653 Mg2SiO 4. For the equilibria Si3N4-1iquid phasegaseous phase the partial pressures of Mg and SiO were calculated in dependence on temperature, nitrogen partial pressure and composition of the liquid phase. The results of thermodynamic calculations and experimental studies of sintered Si3N 4 materials with MgO additives are used to interpret the development o1 microstructure and the mechanical behaviour at high temperatures.