Impurity Oxygen-Triggered α- → β-Si3N4 Phase Transformation at 1900 °C
Open Access
Abstract
Oxide additive-free α- → β-Si3N4 phase transformation of a high-purity commercial α-Si3N4 powder was investigated at 1600 to 1900 °C under a nitrogen pressure of 980 kPa. The XRD analysis revealed that the α- → β-Si3N4 phase transformation proceeded mainly at 1900 °C, and was completed by the extensive 1900 °C heat treatment for 20 h. This phase transformation temperature was 33 °C lower than the theoretical α-Si3N4 dissociation temperature and was confirmed as completely different from that often discussed for the liquid-phase sintering of α-Si3N4 powder by direct comparison with the phase transformation behavior of a reference powder, α-Si3N4 powder doped with 1 mol% Y2O3. The unique α- → β-Si3N4 phase transformation was further studied by a set of characterization techniques including elemental analysis, HAADF-STEM and STEM-EDS analyses. The results strongly suggested that the oxide additive-free α- → β-Si3N4 phase transformation was governed by the formation of a metastable solid solution between α-Si3N4 and impurity oxygen of approximately 0.6 wt%, which promoted the dissociation below the theoretical α-Si3N4 dissociation temperature to afford thermodynamically favorable β-Si3N4. Along with the β-Si3N4 formation, the impurity oxygen concentrated at the grain boundaries was released from the sample via the grain boundary diffusion to afford high-purity β-Si3N4.Keywords
All Related Versions
This publication has 44 references indexed in Scilit:
- Local symmetry breaking of a thin crystal structure of -Si3N4 as revealed by spherical aberration corrected high-resolution transmission electron microscopy imagesJournal of Electron Microscopy, 2012
- Silicon nitride: Enthalpy of formation of the α- and β-polymorphs and the effect of C and O impuritiesJournal of Materials Research, 1999
- Phase transformation and microstructural changes of Si3N4 during sinteringJournal of Materials Science, 1995
- Effects of Free Silicon on the α to βPhase Transformation in Silicon NitrideJournal of the American Ceramic Society, 1987
- HIP Sintering of Silicon Nitride without AdditivesJournal of the Ceramic Association, Japan, 1987
- Calculation of heterogeneous phase equilibria in oxide-nitride systemsCalphad, 1981
- The ?/? silicon nitride phase transformationJournal of Materials Science, 1978
- Grain Boundary Phases in a Hot‐Pressed MgO Fluxed Silicon NitrideJournal of the American Ceramic Society, 1977
- Observations on the αβ‐3‐Si 3 N 4 TransformationJournal of the American Ceramic Society, 1977
- The reactivity and polymorphism of selected nitrides at high temperatures and high pressuresJournal of Inorganic and Nuclear Chemistry, 1966