Hot-pressed Si-Al-O-N Type Materials Made from “Shirasu” and Al Powder

Abstract

The Si-Al-O-N type materials made from the mixture of “Shirasu” and Al powder of 40, 50, 60wt% were fabricated using hot-pressing apparatus at the temperature of 1600°C to 1900°C under a pressure of 200kg/cm² for 1h.
Dense Si-Al-O-N type materials were obtained even at such the low temperature of 1600°C. With increasing hot-pressing temperature, apparent porosity of the hot-pressed specimens increased slightly and the bulk density decreased with increase of weight loss.
The phases observed in each specimen were β′-Si₃N₄, α-Al₂O₃ and 15R-AlN. The ratio of each phase varied with Al content in the specimen and hot-pressing temperature; β′-Si₃N₄ increased, α-Al₂O₃ and 15R-AlN decreased with increasing temperature in the specimen made from “Shirasu”+40wt% Al, 15R-AlN increased, α-Al₂O₃ and β′'-Si₃N₄ decreased with temperature in the specimen made from “Shirasu”+50wt% Al mixture and 15R-AlN was main phase in the specimen made from “Shirasu” +60wt% Al mixture.
The fractured surface of the specimens hot-pressed at 1600°C revealed the presence of glassy phase during hot pressing. Grain boundary of β′-Si₃N₄ and lath-like structure of 15R-AlN appeared in the specimen hot-pressed at 1800°C due to the disappearance of glass by thermal reduction.