Abstract
Four kinds of Si3N4-RE2Si2O7 (RE:Nd, Sm, Y, Yb) ceramics have been fabricated by hot pressing at 1725-1750°C for 2 h in N2 gas flow and post-annealing at 1450°C for 4 h. The effect of rare-earth oxide additions on the densification process was investigated by measuring the shrinkage of the compact. Results revealed that the rare-earth oxides affect the densification process of Si3N4-RE2Si2O7 ceramics in which the shrinkage temperature varies with the types of rare-earth additives. The Si-RE-O-N liquid phase formation temperature can be estimated from the onset temperature of final shrinkage stage, and the temperature is in the order of Sm < Nd < Y < Yb. Flexural strength was examined at temperature in a range of 25-1600°C in N2 gas flow. The high temperature strength of Si3N4-Yb2Si2O7 or Si3N4-Y2Si2O7 ceramics is better than that of Si3N4-Sm2Si2O7 or Si3N4-Nd2Si2O7 ceramics. There is a roughly linear relation between the strength retention and the liquid phase formation temperature. Present results indicate that Si3N4-RE2Si2O7 ceramics with high strength retention can be fabricated by adopting additives with small ionic radius and high ionic charge.
Original language | English |
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Pages (from-to) | 527-534 |
Number of pages | 8 |
Journal | Journal of the European Ceramic Society |
Volume | 22 |
Issue number | 4 |
DOIs | |
Publication status | Published - 2002 Apr |
Externally published | Yes |
Keywords
- Grain boundaries
- Hot-pressing
- Mechanical properties
- SiN
- Strength
ASJC Scopus subject areas
- Ceramics and Composites
- Materials Chemistry