Sintering additives for SiC based on the reactivity: A review

Silicon carbide (SiC) is one of the most attractive materials for high temperature applications, being used in many areas, such as gas turbines, heat exchangers, and space shuttles, because of its excellent strength, oxidation resistance and chemical stability at high temperatures. Moreover, SiC and its composites are being considered as structural materials for advanced fission reactors and future fusion reactors owing to its additional low induced radioactivity under neutron irradiation conditions. On the other hand, pure SiC can only be densified by sintering at high temperatures and pressures because of its high covalent bonding nature and low self-diffusivity. Therefore, the addition of sintering additives is essential for enhancing the densification of SiC. This paper reviews the criteria for the selection of effective SiC sintering additives based on the Gibbs free energy to predict the reactivity between the sintering additive and SiC, particularly for liquid phase sintering at 1700-1900 °C. The thermodynamic simulation was verified by offering the experimental results for various types of sintering additives, such as main group metals, metal oxides, and rare earth elements. This review suggests a guideline for the selection of sintering additives for SiC.