Hot-pressed Si3N4 ceramics containing CaO-Al2O3-AlN modifying additives

We have studied the influence of SHS aluminum nitride content (5?C15%) and particle size on the fabrication conditions (hot pressing in a nitrogen atmosphere) of Si₃N₄-based ceramics containing CaO-Al₂O₃-AlN sintering aids. The results demonstrate that the reaction of Si₃N₄ with a eutectic calcium aluminate mixture during liquid-phase sintering leads to the formation of ??-sialon-based intergranular phases: Ca _m/z Si_{12 ? (m ? n)}Al_{(m + n)}O _n N_{16 ? n} . The addition of AlN to starting mixtures contributes to a more complete conversion of the calcium aluminate sintering aid to Ca-??-sialon and influences the relationship between ??-Si₃N₄ and ??-Si₃N₄ in the ceramics. We examine the influence of synthesis conditions and the percentages of added calcium aluminates and aluminum nitride on the density, porosity, and bending strength of the ceramics. Thermogravimetric analysis data demonstrates that the Si₃N₄ + Ca-??-sialon composites obtained are stable to oxidation in air up to 1300°C.