Influence of sintering additives on densification kinetics and high-temperature strength in γ-Y₂Si₂O₇ ceramics

Pressureless sintering of pure γ-Y₂Si₂O₇ powders that had been synthesized by a solid-liquid reaction method using Y₂O₃ and SiO₂ powders with Li₂O, MgO, and Al₂O₃ additives was reported. The sintering kinetics of γ-Y₂Si₂O₇ powders was analyzed to track details of densification evolution. Apparent activation energies of the densification of γ-Y₂Si₂O₇ powders were reported for the first time, which was 57.1, 96.6, and 100.2 kJ/mol for the powders with Li₂O, MgO, and Al₂O₃ additives, respectively, indicating that Li₂O could promote the densification behavior effectively. The flexural strengths as a function of temperature for the γ-Y₂Si₂O₇ ceramics with different additives were also investigated. The degradation of high-temperature flexural strength was mainly ascribed to the softening of grain-boundary glassy phase. γ-Y₂Si₂O₇ specimens fabricated using the powders with MgO or Al₂O₃ additives exhibited better high-temperature mechanical properties.