THERMODYNAMIC ANALYSIS AS A ROUTE FOR SELECTING OXIDE SINTERING AIDS FOR SiC-BASED STRUCTURAL CERAMICS

Thermodynamic analysis is a powerful tool in determination and evaluation of potential physicochemical processes in various reaction systems, which makes it possible to reduce experimental testing especially at high temperatures. The present paper discusses chemical interaction of silicon carbide with different oxides based on Gibbs energy calculation in temperature interval from 273 to 2300 K in order to select oxide sintering aids for producing SiC-based structural ceramics. The results suggest that the most suitable additives for SiC would be oxides with strong propensity for binding to oxygen. The higher this value, i.e. the stronger the bond between element and oxygen is, the less possible becomes any chemical interaction. This pattern becomes most obvious for oxides of metals in Group II of the Periodic table (Ca, Mg, Sr). On the contrary, elements with poor oxophilicity (Fe, Mn, Ti, Zr) which show high mobility of oxygen ions in crystal lattice, are prone to partial reduction and SiC oxidation in a wide temperature range. Therefore, candidate oxides for sintering aids synthesis in the energy-efficient SiC-based ceramics production would be CaO, MgO, SrO, Al2O3, Y2O3, Sc2O3 as well as Ln(2)O(3) oxides.