The spark plasma sintering (SPS) of SÍ3N4 powders plus AI2O3 and Y2O3 sintering additives, added in variable amounts from 2.5 to 7 wt%, is reported for the range of temperatures 1500 1675 °C. Same compositions hot pressed (HP) at higher temperatures (1600 1750 °C) only give dense materials for the composite with 7 wt% of additives. For lower additive contents, full densification is only possible by SPS. The comparison between the shrinkage rate curves of SPS specimens and published data for conventionally sintered SÍ3N4 of similar characteristics points out that an enhancement of the particle rearrangement stage by SPS occurs. A lack of homogeneity in the distribution of glassy phase is observed in the HP material with the lowest additive content, whereas the equivalent SPS material shows a completely wetting grain boundary phase. Based on these results, the role played by electrowetting in the first sintering stage of liquid phase sintering is signalled as responsible of the enhanced sintering rate.

Funding for this work was provided by Spanish Ministry of Science and Innovation (MICINN) and Spanish National Research Council (CSIC) under projects MAT2006 7118 and HA2007 0083. J. Gonzalez Julian acknowledges the financial support of the JAE (CSIC) fellowship Program.

7 paginas, 5 figuras, 2 tablas.-- Trabajo presentado al 8th Pacific Rim Conference on Ceramic and Glass Technology celebrado en canada del 31 de mayo al 5 de junio de 2009.

Peer reviewed