High-Temperature Interactions of Silicon-Aluminum Oxynitrides (Sialons) with Sodium Fluoride

The high-temperature interactions of β-SiAlONs with sodium fluoride NaF at 1650 °C under a nitrogen atmosphere are described in this paper. It was found that in case of Si5AlON7 the formation of phases enriched with aluminum occurred, including Si4Al2O2N6 at an NaF loading of 0.5 wt.% and Si4Al2O2N6 and Si3.1Al2.9O2.9N5.1 at an NaF loading of 2.0 wt.%, although Si5AlON7 still was a major phase. For Si4Al2O2N6, a kind of disproportionation was observed, and Si5AlON7 formed together with Si3Al3O3N5 and Si3.1Al2.9O2.9N5.1. Moreover, the initial phase Si4Al2O2N6 was not identified at all, while Si5AlON7 was found to be a major phase at an NaF loading of 0.5 wt.% and Si3.1Al2.9O2.9N5.1 prevailed at an NaF loading of 2.0 wt.%. All the samples showed a high degree of densification when studied with scanning electronic microscopy.